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SCIENTIFIC DATA

https://www.sciencedirect.com/book/9780080158273/the-expanding-earth#book-description

https://www.sciencedirect.com/book/9780123852274/earth-as-an-evolving-planetary-system

https://www.sciencedirect.com/science/article/pii/B9780080250168500119

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   Astronomy in the Quran

     The Quran is full of reflections on the Heavens. In the preceding chapter on the Creation, we saw how the plurality of the Heavens and Earths was referred to, as well as what the Quran calls an intermediary creation 'between the Heavens and the Earth', modern science has verified the latter. The verses referring to the Creation already contain a broad idea of what is to be found in the heavens, i.e. of everything outside the earth.

       Apart from the verses that specifically describe the Creation, there are roughly another forty verses in the Quran which provide information on astronomy complementing what has already been given. Some of them are not much more than reflections on the glory of the Creator, the Organizer of all the stellar and planetary systems. These we know to be arranged according to balancing positions whose stability Newton explained in his law of the mutual attraction of bodies.

           The first verses to be quoted here hardly furnish much material for scientific analysis: the aim is simply to draw attention to God's Omnipotence. They must be mentioned however to give a realistic idea of the way the Quranic text described the organization of the Universe fourteen centuries ago.

            These references constitute a new fact of divine Revelation. The organization of the world is treated in neither the Gospels nor the Old Testament (except for a few notions whose general inaccuracy we have already seen in the Biblical description of the Creation). The Quran however deals with this subject in depth. What it describes is important, but so is what it does not contain. It does not in fact provide an account of the theories prevalent at the time of the Revelation that deal with the organization of the celestial world, theories that science was later to show were inaccurate. An example of this will be given later. This negative consideration must however be pointed out. [ I have often heard those who go to great lengths to find a human explanation-and no other-to all the problems raised by the Quran Bay the following: "if the Book contains surprising statements on astronomy, it is because the Arabs were very knowledgeable on this subject." In so doing they forget the fact that, in general, science in Islamic countries is very much post-Quran, and that the scientific knowledge of this great period would in any case not have been sufficient for a human being to write some of the verses to be found in the Quran. This will be shown in the following paragraphs.]

A. GENERAL REFLECTIONS CONCERNING THE SKY

--sura 50,verse 6.

The subject is man in general.

      "Do they not look at the sky above them, how We have built it and adorned it, and there are no rifts in it."

--sura 31, verse 10:

"(God) created the heavens without any pillars that you can see..."

--sura 13, verse 2:

       "God is the One Who raised the heavens without any pillars that you can see, then He firmly established Himself on the throne and He subjected the sun and moon . . ."

        These two verses refute the belief that the vault of the heavens was held up by pillars, the only things preventing the former from crushing the earth.

--sura 55, verse 7:

"the sky (God) raised it . . ."

--sura 22, verse 65:

"(God) holds back the sky from falling on the earth unless by His leave . . ."

         It is known how the remoteness of celestial masses at great distance and in proportion to the magnitude of their mass itself constitutes the foundation of their equilibrium. The more remote the masses are, the weaker the force is that attracts one to the other. The nearer they are, the stronger the attraction is that one has to the other: this is true for the Moon, which is near to the Earth (astronomically speaking) and exercises an influence by laws of attraction on the position occupied by the waters of the sea, hence the phenomenon of the tides. If two celestial bodies come too close to one another, collision is inevitable. The fact that they are subjected to an order is the sine qua non for the absence of disturbances.

The subjection of the Heavens to divine order is often referred to as well:

--sura 23, verse 86.

God is speaking to the Prophet.

"Say: Who is Lord of the seven heavens and Lord of the tremendous throne?"

We have already seen how by 'seven heavens' what is meant is not 7, but an indefinite number of Heavens.

--sura 45, verse 13:

"For you (God) subjected all that is in the heavens and on the earth, all from Him. Behold! In that are signs for people who reflect."

--sura 55, verse 5:

"The sun and moon (are subjected) to calculations"

--sura 6, verse 96:

"(God) appointed the night for rest and the sun and the moon for reckoning."

--sura 14, verse 33:

"For you (God) subjected the sun and the moon, both diligently pursuing their courses. And for you He subjected the night and the day."

Here one verse completes another: the calculations referred to result in the regularity of the course described by the heavenly bodies in question, this is expressed by the word da'ib, the present participle of a verb whose original meaning was 'to work eagerly and assiduously at something'. Here it is given the meaning of 'to apply oneself to something with care in a perseverant, invariable manner, in accordance with set habits'.

--sura 36, verse 39: God is speaking:

"And for the moon We have appointed mansions till she returns like an old shriveled palm branch."

This is a reference to the curled form of the palm branch which, as it shrivels up, takes on the moon's crescent. This commentary will be completed later.

--sura 16, verse 12:

"For you (God) subjected the night and the day, the sun and the moon; the stars are in subjection to His Command. Verily in this are signs for people who are wise."

The practical angle from which this perfect celestial order is seen is underlined on account of its value as an aid to man's travel on earth and by sea, and to his calculation of time. This comment becomes clear when one bears in mind the fact that the Quran was originally a preaching addressed to men who only understood the simple language of their everyday lives. This explains the presence of the following reflections.

--sura 6, verse 97:

"(God) is the One Who has set out for you the stars, that you may guide yourselves by them through the darkness of the land and of the sea. We have detailed the signs for people who know."

--sura 16, verse 16:

"(God sets on the earth) landmarks and by the stars (men) guide themselves."

--sura 10, verse 5:

"God is the One Who made the sun a shining glory and the moon a light and for her ordained mansions, so that you might know the number of years and the reckoning (of the time). God created this in truth. He explains the signs in detail for people who know."

This calls for some comment. Whereas the Bible calls the Sun and Moon 'lights', and merely adds to one the adjective 'greater' and to the other 'lesser', the Quran ascribes differences other than that of dimension to each respectively. Agreed, this is nothing more than a verbal distinction, but how was one to communicate to men at this time without confusing them, while at the same time expressing the notion that the Sun and Moon were not absolutely identical 'lights'?

B. NATURE OF HEAVENLY BODIES

The Sun and the Moon

The Sun is a shining glory (diya') and the Moon a light (nur). This translation would appear to be more correct than those given by others, where the two terms are inverted. In fact there is little difference in meaning since diya' belongs to a root (dw') which, according to Kazimirski's authoritative Arabic/French dictionary, means 'to be bright, to shine' (e.g. like a fire). The same author attributes to the substantive in question the meaning of 'light'.

The difference between Sun and Moon will be made clearer by further quotes from the Quran.

--sura 25, verse 61:

"Blessed is the One Who placed the constellations in heaven and placed therein a lamp and a moon giving light."

--sura 71, 15-16:

"Did you see how God created seven heavens one above an other and made the moon a light therein and made the sun a lamp?"

--sura 78, verses 12-13:

"We have built above you seven strong (heavens) and placed a blazing lamp."

The blazing lamp is quite obviously the sun.

Here the moon is defined as a body that gives light (munir) from the same root as nur (the light applied to the Moon). The Sun however is compared to a torch (siraj) or a blazing (wahhaj) lamp.

A man of Muhammad's time could easily distinguish between the Sun, a blazing heavenly body well known to the inhabitants of the desert, and the Moon, the body of the cool of the night. The comparisons found in the Quran on this subject are therefore quite normal. What is interesting to note here is the sober quality of the comparisons, and the absence in the text of the Quran of any elements of comparison that might have prevailed at the time and which in our day would appear as phantasmagorial.

It is known that the Sun is a star that generates intense heat and light by its internal combustions, and that the Moon, which does not give of flight itself, and is an inert body (on its external layers at least) merely reflects the light received from the Sun.

There is nothing in the text of the Quran that contradicts what we know today about these two celestial bodies.

 The Stars

As we know, the stars are heavenly bodies like the Sun. They are the scene of various physical phenomena of which the easiest to observe is their generation of light. They are heavenly bodies that produce their own light.

The word 'star' appears thirteen times in the Quran (najm, plural nujum); it comes from a root meaning to appear, to come into sight. The word designates a visible heavenly body without saying of what kind, i.e. either generator of light or mere reflector of light received. To make it clear that the object so designated is a star, a qualifying phrase is added as in the following sura:

--sura 86, verses 1-3:

"By the sky and the Night-Visitor, who will tell thee what the Night-Visitor is, the Star of piercing brightness." [ Here, the sky and a star are used to bear witness to the importance of what is to come in the text.]

The evening star is qualified in the Quran by the word takib meaning 'that which pierces through something' (here the night shadows) . The same word is moreover used to designate shooting stars (sura 37, verse 10): the latter are the result of combustion.

The Planets

It is difficult to say whether these are referred to in the Quran with the same exact meaning that is given to the heavenly bodies in the present day.

The planets do not have their own light. They revolve around the Sun, Earth being one of them. While one may presume that others exist elsewhere, the only ones known are those in the solar system.

Five planets other than Earth were known to the ancients: Mercury, Venus, Mars, Jupiter and Saturn. Three have been discovered in recent times: Uranus, Neptune and Pluto.

The Quran would seem to designate these by the word kaukab (plural kawakib) without stating their number. Joseph's dream (sum 12) refers to eleven of them, but the description is, by definition, an imaginary one.

A good definition of the meaning of the word kaukab in the Quran Seems to have been given in a very famous verse. The eminently spiritual nature of its deeper meaning stands forth, and is moreover the subject of much debate among experts in exegesis. It is nevertheless of great interest to offer an account of the comparison it contains on the subject of the word that would seem to designate a 'planet'.

Here is the text in question: (sura 24, verse 35)

"God is the light of the heavens and the earth. The similitude of His light is as if there were a niche and within it a luminary. The luminary is in a glass. The glass is as if it were a planet glittering like a pearl."

Here the subject is the projection of light onto a body that reflects it (glass) and gives it the glitter of a pearl, like a planet that is lit by the sun. This is the only explanatory detail referring to this word to be found in the Quran.

The word is quoted in other verses. In some of them it is difficult to distinguish which heavenly bodies are meant (sura 6, verse 76; sura 82, verses 1-2).

In one verse however, when seen in the light of modern science, it would seem very much that these can only be the heavenly bodies that we know to be planets. In sura 37, verse 6, we see the following:

"We have indeed adorned the lowest heaven with an ornament, the planets."

Is it possible that the expression in the Quran 'lowest heaven' means the 'solar system'? It is known that among the celestial elements nearest to us, there are no other permanent elements apart from the planets: the Sun is the only star in the system that bears its name. It is difficult to see what other heavenly bodies could be meant if not the planets. The translation given would therefore seem to be correct and the Quran to refer to the existence of the planets as defined in modern times.

The Lowest Heaven

The Quran mentions the lowest heaven several times along with the heavenly bodies of which it is composed. The first among these would seem to be the planets, as we have just seen. When however the Quran associates material notions intelligible to us, enlightened as we are today by modern science, with statements of a purely spiritual nature, their meaning becomes obscure.

Thus the verse quoted could easily be understood, except that the following verse (7) of the same sura 37 speaks of a 'guard against every rebellious evil spirit', 'guard' again being referred to in sura 21, verse 32 and sura 41, verse 12, so that we are confronted by statements of quite a different kind.

What meaning can one attach moreover to the 'projectiles for the stoning of demons' that according to verse 5, sura 67 are situated in the lowest heaven? Do the 'luminaries' referred to in the same verse have something to do with the shooting stars mentioned above? [ It is known that when a meteorite arrives at the upper layers of the atmosphere, it may produce the luminous phenomenon of a 'shooting star'.]

All these observations seem to lie outside the subject of this study. They have been mentioned here for the sake of completeness. At the present stage however, it would seem that scientific data are unable to cast any light on a subject that goes beyond human understanding.

C. CELESTIAL ORGANIZATION

The information the Quran provides on this subject mainly deals with the solar system. References are however made to phenomena that go beyond the solar system itself: they have been discovered in recent times.

There are two very important verses on the orbits of the Sun and Moon:

--sura 21, verse 33:

"(God is) the One Who created the night, the day, the sun and the moon. Each one is travelling in an orbit with its own motion."

--sura 36, verse 40:

"The sun must not catch up the moon, nor does the night outstrip the day. Each one is travelling in an orbit with its own motion."

Here an essential fact is clearly stated: the existence of the Sun's and Moon's orbits, plus a reference is made to the travelling of these bodies in space with their own motion.

A negative fact also emerges from a reading of these verses: it is shown that the Sun moves in an orbit, but no indication is given as to what this orbit might be in relation to the Earth. At the time of the Quranic Revelation, it was thought that the Sun moved while the Earth stood still. This was the system of geocentrism that had held sway since the time of ptolemy, Second century B.C., and was to continue to do so until Copernicus in the Sixteenth century A.D. Although people supported this concept at the time of Muhammad, it does not appear anywhere in the Quran, either here or elsewhere.

The Existence of the Moon's and the Sun's Orbits

The Arabic word falak has here been translated by the word 'orbit'. many French translators of the Quran attach to it the meaning of a 'sphere'. This is indeed its initial sense. Hamidullah translates it by the word 'orbit'.

The word caused concern to older translators of the Quran who were unable to imagine the circular course of the Moon and the Sun and therefore retained images of their course through space that were either more or less correct, or hopelessly wrong. Sir Hamza Boubekeur in his translation of the Quran cites the diversity of interpretations given to it: "A sort of axle, like an iron rod, that a mill turns around; a celestial sphere, orbit, sign of the zodiac, speed, wave . . .", but he adds the following observation made by Tabari, the famous Tenth century commentator: "It is our duty to keep silent when we do not know." (XVII, 15). This shows just how incapable men were of understanding this concept of the Sun's and Moon's orbit. It is obvious that if the word had expressed an astronomical concept common in Muhammad's day, it would not have been so difficult to interpret these verses. A Dew concept therefore existed in the Quran that was not to be explained until centuries later.

 1. The Moon's Orbit

Today, the concept is widely spread that the Moon is a satellite of the Earth around which it revolves in periods of twenty-nine days. A correction must however be made to the absolutely circular form of its orbit, since modern astronomy ascribes a certain eccentricity to this, so that the distance between the Earth and the Moon (240,000 miles) is only the average distance.

We have seen above how the Quran underlined the usefulness of observing the Moon's movements in calculating time (sura 10, verse 5, quoted at the beginning of this chapter.) This system has often been criticized for being archaic, impractical and unscientific in comparison to our system based on the Earth's rotation around the Sun, expressed today in the Julian calendar.

This criticism calls for the following two remarks:

a) Nearly fourteen centuries ago, the Quran was directed at the inhabitants of the Arabian Peninsula who were used to the lunar calculation of time. It was advisable to address them in the only language they could understand and not to upset the habits they had of locating spatial and temporal reference-marks which were nevertheless quite efficient. It is known how well-versed men living in the desert are in the observation of the sky. they navigated according to the stars and told the time according to the phases of the Moon. Those were the simplest and most reliable means available to them.

b) Apart from the specialists in this field, most people are unaware of the perfect correlation between the Julian and the lunar calendar: 235 lunar months correspond exactly to 19 Julian years of 365 1/4 days. Then length of our year of 365 days is not perfect because it has to be rectified every four years (with a leap year) .

With the lunar calendar, the same phenomena occur every 19 years (Julian). This is the Metonic cycle, named after the Greek astronomer Meton, who discovered this exact correlation between solar and lunar time in the Fifth century B.C.

2. The Sun

It is more difficult to conceive of the Sun's orbit because we are so used to seeing our solar system organized around it. To understand the verse from the Quran, the position of the Sun in our galaxy must be considered, and we must therefore call on modern scientific ideas.

Our galaxy includes a very large number of stars spaced so as to form a disc that is denser at the centre than at the rim. The Sun occupies a position in it which is far removed from the centre of the disc. The galaxy revolves on its own axis which is its centre with the result that the Sun revolves around the same centre in a circular orbit. Modern astronomy has worked out the details of this. In 1917, Shapley estimated the distance between the Sun and the centre of our galaxy at 10 kiloparsecs i.e., in miles, circa the figure 2 followed by 17 zeros. To complete one revolution on its own axis, the galaxy and Sun take roughly 250 million years. The Sun travels at roughly 150 miles per second in the completion of this.

The above is the orbital movement of the Sun that was already referred to by the Quran fourteen centuries ago. The demonstration of the existence and details of this is one of the achievements of modern astronomy.

 Reference to the Movement of the Moon and the Sun in Space With Their Own Motion

This concept does not appear in those translations of the Quran that have been made by men of letters. Since the latter know nothing about astronomy, they have translated the Arabic word that expresses this movement by one of the meanings the word has: 'to swim'. They have done this in both the French translations and the, otherwise remarkable, English translation by Yusuf Ali. [ Pub. Sh. Muhammad Ashraf, Lahore (Pakistan)]

The Arabic word referring to a movement with a self-propelled motion is the verb sabaha (yasbahuna in the text of the two verses). All the senses of the verb imply a movement that is associated with a motion that comes from the body in question. If the movement takes place in water, it is 'to swim'; it is 'to move by the action of one's own legs' if it takes place on land. For a movement that occurs in space, it is difficult to see how else this meaning implied in the word could be rendered other than by employing its original sense. Thus there seems to have been no mistranslation, for the following reasons.

-The Moon completes its rotating motion on its own axis at the same time as it revolves around the Earth, i.e. 291/2 days (approx.), so that it always has the same side facing us.

-The Sun takes roughly 25 days to revolve on its own axis. There are certain differences in its rotation at its equator and poles, (we shall not go into them here) but as a whole, the Sun is animated by a rotating motion.

It appears therefore that a verbal nuance in the Quran refers to the Sun and Moon's own motion. These motions of the two celestial bodies are confirmed by the data of modern science, and it is inconceivable that a man living in the Seventh century A.D.-however knowledgeable he might have been in his day (and this was certainly not true in Muhammad's case) -could have imagined them.

This view is sometimes contested by examples from great thinkers of antiquity who indisputably predicted certain data that modern science has verified. They could hardly have relied on scientific deduction however; their method of procedure was more one of philosophical reasoning. Thus the case of the pythagoreans is often advanced. In the Sixth century B.C., they defended the theory of the rotation of the Earth on its own axis and the movement of the planets around the Sun. This theory was to be confirmed by modern science. By comparing it with the case of the Pythagoreans, it is easy to put forward the hypothesis of Muhammad as being a brilliant thinker, who was supposed to have imagined all on his own what modern science was to discover centuries later. In so doing however, people quite simply forget to mention the other aspect of what these geniuses of philosophical reasoning produced, i.e. the colossal blunders that litter their work. It must be remembered for example, that the Pythagoreans also defended the theory whereby the Sun was fixed in space; they made it the centre of the world and only conceived of a celestial order that was centered on it. It is quite common in the works of the great philosophers of antiquity to find a mixture of valid and invalid ideas about the Universe. The brilliance of these human works comes from the advanced ideas they contain, but they should not make us overlook the mistaken concepts which have also been left to us. From a strictly scientific point of view, this is what distinguished them from the Quran. In the latter, many subjects are referred to that have a bearing on modern knowledge without one of them containing a statement that contradicts what has been established by present-day science.

The Sequence of Day and Night

At a time when it was held that the Earth was the centre of the world and that the Sun moved in relation to it, how could any one have failed to refer to the Sun's movement when talking of the sequence of night and day? This is not however referred to in the Quran and the subject is dealt with as follows:

--sura 7, verse 54:

"(God) covers the day with the night which is in haste to follow it . . ."

--sura 36, verse 37:

"And a sign for them (human beings) is the night. We strip it of the day and they are in darkness."

--sura 31, verse 29:

"Hast thou not seen how God merges the night into the day and merges the day into the night."

--sura 39, verse 5:

". . . He coils the night upon the day and He coils the day upon the night."

The first verse cited requires no comment. The second simply provides an image.

It is mainly the third and fourth verses quoted above that provide interesting material on the process of interpenetration and especially of winding the night upon the day and the day upon the night. (sura 39, verse 5)

'To coil' or 'to wind' seems, as in the French translation by R. Blachère, to be the best way of translating the Arabic verb kawwara. The original meaning of the verb is to 'coil' a turban around the head; the notion of coiling is preserved in all the other senses of the word.

What actually happens however in space? American astronauts have seen and photographed what happens from their spaceships, especially at a great distance from Earth, e.g. from the Moon. They saw how the Sun permanently lights up (except in the case of an eclipse) the half of the Earth's surface that is facing it, while the other half of the globe is in darkness. The Earth turns on its own axis and the lighting remains the same, so that an area in the form of a half-sphere makes one revolution around the Earth in twenty-four hours while the other half-sphere, that has remained in darkness, makes the same revolution in the same time. This perpetual rotation of night and day is quite clearly described in the Quran. It is easy for the human understanding to grasp this notion nowadays because we have the idea of the Sun's (relative) immobility and the Earth's rotation. This process of perpetual coiling, including the interpenetration of one sector by another is expressed in the Quran just as if the concept of the Earth's roundness had already been conceived at the time-which was obviously not the case.

Further to the above reflections on the sequence of day and night, one must also mention, with a quotation of some verses from the Quran, the idea that there is more than one Orient and one Occident. This is of purely descriptive interest because these phenomena rely on the most commonplace observations. The idea is mentioned here with the aim of reproducing as faithfully as possible all that the Quran has to say on this subject.

The following are examples:

--In sura 70 verse 40, the expression 'Lord of Orients and Occidents'.

--In sura 55, verse 17, the expression 'Lord of the two Orients and the two Occidents'.

--In sura 43, verse 38, a reference to the 'distance between the two Orients', an image intended to express the immense size of the distance separating the two points.

Anyone who carefully watches the sunrise and sunset knows that the Sun rises at different point of the Orient and sets at different points of the Occident, according to season. Bearings taken on each of the horizons define the extreme limits that mark the two Orients and Occidents, and between these there are points marked off throughout the year. The phenomenon described here is rather commonplace, but what mainly deserves attention in this chapter are the other. topics dealt with, where the description of astronomical phenomena referred to in the Quran is in keeping with modern data.

D. EVOLUTION OF THE HEAVENS

Having called modern concepts on the formation of the Universe to mind, reference was made to the evolution that took place, starting with primary nebula through to the formation of galaxies, stars and (for the solar system) the appearance of planets beginning with the Sun at a certain stage of its evolution. Modern data lead us to believe that in the solar system, and more generally in the Universe itself, this evolution is still continuing.

How can anybody who is aware of these ideas fail to make a comparison with certain statements found in the Quran in which the manifestations of divine Omnipotence are referred to.

The Quran reminds us several times that: "(God) subjected the sun and the moon: each one runs its course to an appointed term."

This sentence is to be found in sura 13, verse 2. sura 31, verse 29; sura 35, verse 13 and sura 39, verse 5.

In addition to this, the idea of a settled place is associated with the concept of a destination place in sura 36, verse 38: "The Sun runs its course to a settled place. This is the decree of the All Mighty, the Full of Knowledge."

'Settled place' is the translation of the word mustaqarr and there can be no doubt that the idea of an exact place is attached to it.

How do these statements fare when compared with data established by modern science?

The Quran gives an end to the Sun for its evolution and a destination place. It also provides the Moon with a settled place. To understand the possible meanings of these statements, we must remember what modern knowledge has to say about the evolution of the stars in general and the Sun in particular, and (by extension) the celestial bodies that automatically followed its movement through space, among them the Moon.

The Sun is a star that is roughly 4½ billion years old, according to experts in astrophysics. It is possible to distinguish a stage in its evolution, as one can for all the stars. At present, the Sun is at an early stage, characterized by the transformation of hydrogen atoms into helium atoms. Theoretically, this present stage should last another 5½ billion years according to calculations that allow a total of 10 billion years for the duration of the primary stage in a star of this kind. It has already been shown, in the case of these other stars, that this stage gives way to a second period characterized by the completion of the transformation of hydrogen into helium, with the resulting expansion of its external layers and the cooling of the Sun. In the final stage, its light is greatly diminished and density considerably increased; this is to be observed in the type of star known as a 'white dwarf'.

The above dates are only of interest in as far as they give a rough estimate of the time factor involved, what is worth remembering and is really the main point of the above, is the notion of an evolution. Modern data allow us to predict that, in a few billion years, the conditions prevailing in the solar system will not be the same as they are today. Like other stars whose transformations have been recorded until they reached their final stage, it is possible to predict an end to the Sun.

The second verse quoted above (sur'a 36, verse 38) referred to the Sun running its course towards a place of its own.

Modern astronomy has been able to locate it exactly and has even given it a name, the Solar. Apex: the solar. system is indeed evolving in space towards a point situated in the Constellation of Hercules (alpha lyrae) whose exact location is firmly established; it is moving at a speed already ascertained at something in the region of 12 miles per. second.

All these astronomical data deserve to be mentioned in relation to the two verses from the Quran, since it is possible to state that they appear to agree perfectly with modern scientific data.

The Expansion of the Universe

The expansion of the Universe is the most imposing discovery of modern science. Today it is a firmly established concept and the only debate centres around the way this is taking place.

It was first suggested by the general theory of relativity and is backed up by physics in the examination of the galactic spectrum; the regular movement towards the red section of their spectrum may be explained by the distancing of one galaxy from another. Thus the size of the Universe is probably constantly increasing and this increase will become bigger the further away the galaxies are from us. The speeds at which these celestial bodies are moving may, in the course of this perpetual expansion, go from fractions of the speed of light to speeds faster than this.

The following verse of the Qur' an (sura 51, verse 47) where God is speaking, may perhaps be compared with modern ideas:

"The heaven, We have built it with power. Verily. We are expanding it."

'Heaven' is the translation of the word sama' and this is exactly the extra-terrestrial world that is meant.

'We are expanding it' is the translation of the plural present participle musi'una of the verb ausa'a meaning 'to make wider, more spacious, to extend, to expand'.

Some translators who were unable to grasp the meaning of the latter provide translations that appear to me to be mistaken, e.g. "we give generously" (R. Blachère). Others sense the meaning, but are afraid to commit themselves: Hamidullah in his translation of the Quran talks of the widening of the heavens and space, but he includes a question mark. Finally, there are those who arm themselves with authorized scientific opinion in their commentaries and give the meaning stated here. This is true in the case of the Muntakab, a book of commentaries edited by the Supreme Council for Islamic Affairs, Cairo. It refers to the expansion of the Universe in totally unambiguous terms.

E. THE CONQUEST OF SPACE

From this point of view, three verses of the Quran should command our full attention. One expresses, without any trace of ambiguity, what man should and will achieve in this field. In the other two, God refers for the sake of the unbelievers in Makka to the surprise they would have if they were able to raise themselves up to the Heavens; He alludes to a hypothesis which will not be realized for the latter.

1) The first of these verses is sura 55, verse 33: "O assembly of Jinns and Men, if you can penetrate regions of the heavens and the earth, then penetrate them! You will not penetrate them save with a Power." [ This verse is followed by an invitation to recognize God's blessings. It forms the subject of the whole of the sura that bears the title 'The Beneficent'.]

The translation given here needs some explanatory comment:

a) The word 'if' expresses in English a condition that is dependant upon a possibility and either an achievable or an unachievable hypothesis. Arabic is a language which is able to introduce a nuance into the condition which is much more explicit. There is one word to express the possibility (ida), another for the achievable hypothesis (in) and a third for the unachievable hypothesis expressed by the word (lau). The verse in question has it as an achievable hypothesis expressed by the word (in). The Quran therefore suggests the material possibility of a concrete realization. This subtle linguistic distinction formally rules out the purely mystic interpretation that some people have (quite wrongly) put on this verse.

b) God is addressing the spirits (jinn) and human beings (ins), and not essentially allegorical figures.

c) 'To penetrate' is the translation of the verb nafada followed by the preposition min. According to Kazimirski's dictionary, the phrase means 'to pass right through and come out on the other side of a body' (e.g. an arrow that comes out on the other side). It therefore suggests a deep penetration and emergence at the other end into the regions in question.

d) The Power (sultan) these men will have to achieve this enterprise would seem to come from the All-Mighty.

There can be no doubt that this verse indicates the possibility men will one day achieve what we today call (perhaps rather improperly) 'the conquest of space'. One must note that the text of the Quran predicts not only penetration through the regions of the Heavens, but also the Earth, i.e. the exploration of its depths.

2) The other two verses are taken from sura 15, (verses14 and 15). God is speaking of the unbelievers in Makka, as the context of this passage in the sura shows:

"Even if We opened unto them a gate to Heaven and they were to continue ascending therein, they would say. our sight is confused as in drunkenness. Nay, we are people bewitched."

The above expresses astonishment at a remarkable spectacle, different from anything man could imagine.

The conditional sentence is introduced here by the word lau which expresses a hypothesis that could never be realized as far as it concerned the people mentioned in these verses.

When talking of the conquest of space therefore, we have two passages in the text of the Quran: one of them refers to what will one day become a reality thanks to the powers of intelligence and ingenuity God will give to man, and the other describes an event that the unbelievers in Makka will never witness, hence its character of a condition never to be realized. The event will however be seen by others, as intimated in the first verse quoted above. It describes the human reactions to the unexpected spectacle that travellers in space will see. their confused sight, as in drunkenness, the feeling of being bewitched . . .

This is exactly how astronauts have experienced this remarkable adventure since the first human spaceflight around the world in 1961. It is known in actual fact how once one is above the Earth's atmosphere, the Heavens no longer have the azure appearance we see from Earth, which results from phenomena of absorption of the Sun's light into the layers of the atmosphere. The human observer in space above the Earth's atmosphere sees a black sky and the Earth seems to be surrounded by a halo of bluish colour due to the same phenomena of absorption of light by the Earth's atmosphere. The Moon has no atmosphere, however, and therefore appears in its true colors against the black background of the sky. It is a completely new spectacle therefore that presents itself to men in space, and the photographs of this spectacle are well known to present-day man.

Here again, it is difficult not to be impressed, when comparing the text of the Quran to the data of modern science, by statements that simply cannot be ascribed to the thought of a man who lived more than fourteen centuries ago.

LINK: https://www.islam-guide.com/bqs/17astronomy.htm

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SOME OF THE CREATION OF ALLAH

Our Solar System

A solar system is a star and all of the objects that travel around it—planets, moons, asteroids, comets and meteoroids. Most stars host their own planets, so there are likely tens of billions of other solar systems in the Milky Way galaxy alone. Solar systems can also have more than one star. These are called binary star systems if there are two stars, or multi-star systems if there are three or more stars.

The solar system we call home is located in an outer spiral arm of the vast Milky Way galaxy. It consists of the Sun (our star) and everything that orbits around it. This includes the eight planets and their natural satellites (such as our moon), dwarf planets and their satellites, as well as asteroids, comets and countless particles of smaller debris.

Size and Distance

Our solar system extends much farther than the eight planets that orbit the Sun. The solar system also includes the Kuiper Belt that lies past Neptune's orbit. This is a sparsely occupied ring of icy bodies, almost all smaller than the most popular Kuiper Belt Object, dwarf planet Pluto.

Pluto nearly fills the frame in this image from the Long Range Reconnaissance Imager (LORRI) aboard NASA's New Horizons spacecraft, taken on July 13, 2015, when the spacecraft was 476,000 miles (768,000 kilometers) from the surface. Image Credit: NASA/JHUAPL/SWRI

And beyond the fringes of the Kuiper belt is the Oort Cloud. This giant spherical shell surrounds our solar system. It has never been directly observed, but its existence is predicted based on mathematical models and observations of comets that likely originate there.

The Oort Cloud is made of icy pieces of space debris the sizes of mountains and sometimes larger, orbiting our Sun as far as 1.6 light years away. This shell of material is thick, extending from 5,000 astronomical units to 100,000 astronomical units. One astronomical unit (or AU) is the distance from the Sun to Earth, or about 93 million miles (150 million kilometers). The Oort Cloud is the boundary of the Sun's gravitational influence, where orbiting objects can turn around and return closer to our Sun.

The Sun's heliosphere doesn't extend quite as far. The heliosphere is the bubble created by the solar wind—a stream of electrically charged gas blowing outward from the Sun in all directions. The boundary where the solar wind is abruptly slowed by pressure from interstellar gases is called the termination shock. This edge occurs between 80-100 astronomical units.

Two NASA spacecraft, launched in 1977, have crossed the termination shock: Voyager 1 in 2004 and Voyager 2 in 2007. But it will be many thousands of years before the two Voyagers exit the Oort Cloud.​

Formation

Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby exploding star, called a supernova. When this dust cloud collapsed, it formed a solar nebula—a spinning, swirling disk of material.

At the center, gravity pulled more and more material in. Eventually the pressure in the core was so great that hydrogen atoms began to combine and form helium, releasing a tremendous amount of energy. With that, our Sun was born, and it eventually amassed more than 99 percent of the available matter.

Matter farther out in the disk was also clumping together. These clumps smashed into one another, forming larger and larger objects. Some of them grew big enough for their gravity to shape them into spheres, becoming planets, dwarf planets and large moons. In other cases, planets did not form: the asteroid belt is made of bits and pieces of the early solar system that could never quite come together into a planet. Other smaller leftover pieces became asteroids, comets, meteoroids, and small, irregular moons.

Structure

The order and arrangement of the planets and other bodies in our solar system is due to the way the solar system formed. Nearest the Sun, only rocky material could withstand the heat when the solar system was young. For this reason, the first four planets—Mercury, Venus, Earth and Mars—are terrestrial planets. They're small with solid, rocky surfaces.

Meanwhile, materials we are used to seeing as ice, liquid or gas settled in the outer regions of the young solar system. Gravity pulled these materials together, and that is where we find gas giants Jupiter and Saturn and ice giants Uranus and Neptune.

Potential for Life

Our solar system is the only place we know of that harbors life, but the farther we explore the more we find potential for life in other places. Both Jupiter’s moon Europa and Saturn’s moon Enceladus have global saltwater oceans under thick, icy shells.

Moons

There are more than 150 known moons in our solar system and several more awaiting confirmation of discovery. Of the eight planets, Mercury and Venus are the only ones with no moons. The giant planets grab the most moons. Jupiter and Saturn have long lead our solar system’s moon counts. In some ways, the swarms of moons around these worlds resemble mini versions of our solar system. Pluto, smaller than our own moon, has five moons in its orbit, including the Charon, a moon so large it makes Pluto wobble. Even tiny asteroids can have moons. In 2017, scientists found asteroid 3122 Florence had two tiny moons.

These six narrow-angle color images were made from the first ever 'portrait' of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. Image Credit: NASA Planetary Photojournal

Our Sun

The Sun is a yellow dwarf star, a hot ball of glowing gases at the heart of our solar system. Its gravity holds the solar system together, keeping everything – from the biggest planets to the smallest particles of debris – in its orbit. The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts and auroras. Though it is special to us, there are billions of stars like our Sun scattered across the Milky Way galaxy.

The Sun has many names in many cultures. The Latin word for Sun is “sol,” which is the main adjective for all things Sun-related: solar.

Size and Distance

With a radius of 432,168.6 miles (695,508 kilometers), our Sun is not an especially large star—many are several times bigger—but it is still far more massive than our home planet: 332,946 Earths match the mass of the Sun. The Sun’s volume would need 1.3 million Earths to fill it.

This illustration shows the approximate size of Earth compared to the Sun. Image Credit: ESA & NASA

The Sun is 93 million miles (150 million kilometers) from Earth. Its nearest stellar neighbor is the Alpha Centauri triple star system: Proxima Centauri is 4.24 light years away, and Alpha Centauri A and B—two stars orbiting each other—are 4.37 light years away. A light year is the distance light travels in one year, which is equal to 5,878,499,810,000 miles or 9,460,528,400,000 kilometers.

Orbit and Rotation

The Sun, and everything that orbits it, is located in the Milky Way galaxy. More specifically, our Sun is in a spiral arm called the Orion Spur that extends outward from the Sagittarius arm. From there, the Sun orbits the center of the Milky Way Galaxy, bringing the planets, asteroids, comets and other objects along with it. Our solar system is moving with an average velocity of 450,000 miles per hour (720,000 kilometers per hour). But even at this speed, it takes us about 230 million years to make one complete orbit around the Milky Way.

The Sun rotates as it orbits the center of the Milky Way. Its spin has an axial tilt of 7.25 degrees with respect to the plane of the planets’ orbits. Since the Sun is not a solid body, different parts of the Sun rotate at different rates. At the equator, the Sun spins around once about every 25 days, but at its poles the Sun rotates once on its axis every 36 Earth days.

Formation

The Sun and the rest of the solar system formed from a giant, rotating cloud of gas and dust called a solar nebula about 4.5 billion years ago. As the nebula collapsed because of its overwhelming gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form our Sun, which accounts for 99.8% of the mass of the entire solar system.

Like all stars, the Sun will someday run out of energy. When the Sun starts to die, it will swell so big that it will engulf Mercury and Venus and maybe even Earth. Scientists predict the Sun is a little less than halfway through its lifetime and will last another 6.5 billion years before it shrinks down to be a white dwarf.

Structure

The Sun, like others stars, is a ball of gas. In terms of the number of atoms, it is made of 91.0% hydrogen and 8.9% helium. By mass, the Sun is about 70.6% hydrogen and 27.4% helium.

The Sun's enormous mass is held together by gravitational attraction, producing immense pressure and temperature at its core. The Sun has six regions: the core, the radiative zone, and the convective zone in the interior; the visible surface, called the photosphere; the chromosphere; and the outermost region, the corona.

At the core, the temperature is about 27 million degrees Fahrenheit (15 million degrees Celsius), which is sufficient to sustain thermonuclear fusion. This is a process in which atoms combine to form larger atoms and in the process release staggering amounts of energy. Specifically, in the Sun’s core, hydrogen atoms fuse to make helium.

The energy produced in the core powers the Sun and produces all the heat and light the Sun emits. Energy from the core is carried outward by radiation, which bounces around the radiative zone, taking about 170,000 years to get from the core to the top of the convective zone. The temperature drops below 3.5 million degrees Fahrenheit (2 million degrees Celsius) in the convective zone, where large bubbles of hot plasma (a soup of ionized atoms) move upwards. The surface of the Sun—the part we can see—is about 10,000 degrees Fahrenheit (5,500 degrees Celsius). That's much cooler than the blazing core, but it's still hot enough to make carbon, like diamonds and graphite, not just melt, but boil.

Surface

The surface of the Sun, the photosphere, is a 300-mile-thick (500-kilometer-thick) region, from which most of the Sun's radiation escapes outward. This is not a solid surface like the surfaces of planets. Instead, this is the outer layer of the gassy star.

We see radiation from the photosphere as sunlight when it reaches Earth about eight minutes after it leaves the Sun. The temperature of the photosphere is about 10,000 degrees Fahrenheit (5,500 degrees Celsius).

Atmosphere

Above the photosphere lie the tenuous chromosphere and the corona (crown), which make up the thin solar atmosphere. This is where we see features such as sunspots and solar flares.

Visible light from these top regions is usually too weak to be seen against the brighter photosphere, but during total solar eclipses, when the moon covers the photosphere, the chromosphere looks like a red rim around the Sun, while the corona forms a beautiful white crown with plasma streamers narrowing outward, forming shapes that look like flower petals.

Strangely, the temperature in the Sun's atmosphere increases with altitude, reaching as high as 3.5 million degrees Fahrenheit (2 million degrees Celsius). The source of coronal heating has been a scientific mystery for more than 50 years.

Potential for Life

The Sun itself is not a good place for living things, with its hot, energetic mix of gases and plasma. But the Sun has made life on Earth possible, providing warmth as well as energy that organisms like plants use to form the basis of many food chains.

Moons

The Sun and other stars don't have moons; instead, they have planets and their moons, along with asteroids, comets, and other objects.

Rings

The Sun does not have rings.

Magnetosphere

The electric currents in the Sun generate a complex magnetic field that extends out into space to form the interplanetary magnetic field. The volume of space controlled by the Sun's magnetic field is called the heliosphere.

The Sun's magnetic field is carried out through the solar system by the solar wind—a stream of electrically charged gas blowing outward from the Sun in all directions. Since the Sun rotates, the magnetic field spins out into a large rotating spiral, known as the Parker spiral.

This is an artist's concept of our Heliosphere as it travels through our galaxy with the major features labeled. Image Credit: NASA/Goddard/Walt Feimer

The Sun doesn't behave the same way all the time. It goes through phases of its own solar cycle. Approximately every 11 years, the Sun’s geographic poles change their magnetic polarity. When this happens, the Sun's photosphere, chromosphere and corona undergo changes from quiet and calm to violently active. The height of the Sun’s activity, known as solar maximum, is a time of solar storms: sunspots, solar flares and coronal mass ejections. These are caused by irregularities in the Sun's magnetic field and can release huge amounts of energy and particles, some of which reach us here on Earth. This space weather can damage satellites, corrode pipelines and affect power grids.

Quick Facts

Radius

432,168.6 miles | 695,508 kilometers

Star Type

Yellow dwarf

Distance from Earth

92.92 million miles | 149.60 million kilometers | 1 astronomical

Earth's Moon

Earth's Moon is the only place beyond Earth where humans have set foot, so far. The brightest and largest object in our night sky, the Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate. It also causes tides, creating a rhythm that has guided humans for thousands of years. The Moon was likely formed after a Mars-sized body collided with Earth several billion years ago.

Earth's only natural satellite is simply called "the Moon" because people didn't know other moons existed until Galileo Galilei discovered four moons orbiting Jupiter in 1610. In Latin, the Moon was called Luna, which is the main adjective for all things Moon-related: lunar

Size and Distance

With a radius of 1,079.6 miles (1,737.5 kilometers), the moon is less than a third the width of Earth. If Earth were the size of a nickel, the moon would be about as big as a coffee bean.

The moon is farther away from Earth than most people realize. The moon is an average of 238,855 miles (384,400 kilometers) away. That means 30 Earth-sized planets could fit in between Earth and the moon.

The moon is slowly moving away from Earth, getting about an inch farther away each year.

Orbit and Rotation

The moon is rotating at the same rate that it revolves around Earth (called synchronous rotation), so the same hemisphere faces Earth all the time. Some people call the far side — the hemisphere we never see from Earth — the "dark side," but that's misleading. As the moon orbits Earth, different parts are in sunlight or darkness at different times. The changing illumination is why, from our perspective, the moon goes through phases. During a "full moon," the hemisphere of the moon we can see from Earth is fully illuminated by the sun. And a "new moon" occurs when the far side of the moon has full sunlight, and the side facing us is having its night.

The moon makes a complete orbit around Earth in 27 Earth days and rotates or spins at that same rate, or in that same amount of time. Because Earth is moving as well — rotating on its axis as it orbits the sun — from our perspective, the moon appears to orbit us every 29 days.

Formation

The leading theory of the moon's origin is that a Mars-sized body collided with Earth about 4.5 billion years ago. The resulting debris from both Earth and the impactor accumulated to form our natural satellite 239,000 miles (384,000 kilometers) away. The newly formed moon was in a molten state, but within about 100 million years, most of the global "magma ocean" had crystallized, with less-dense rocks floating upward and eventually forming the lunar crust.

Structure

Earth's moon has a core, mantle and crust.

The moon’s core is proportionally smaller than other terrestrial bodies' cores. The solid, iron-rich inner core is 149 miles (240 kilometers) in radius. It is surrounded by a liquid iron shell 56 miles (90 kilometers) thick. A partially molten layer with a thickness of 93 miles (150 kilometers) surrounds the iron core.

The mantle extends from the top of the partially molten layer to the bottom of the moon’s crust. It is most likely made of minerals like olivine and pyroxene, which are made up of magnesium, iron, silicon and oxygen atoms.

The crust has a thickness of about 43 miles (70 kilometers) on the moon’s near-side hemisphere and 93 miles (150 kilometers) on the far-side. It is made of oxygen, silicon, magnesium, iron, calcium and aluminum, with small amounts of titanium, uranium, thorium, potassium and hydrogen.

Long ago the moon had active volcanoes, but today they are all dormant and have not erupted for millions of years.

Surface

With too sparse an atmosphere to impede impacts, a steady rain of asteroids, meteoroids and comets strikes the surface of the moon, leaving numerous craters behind. Tycho Crater is more than 52 miles (85 kilometers) wide.

Over billions of years, these impacts have ground up the surface of the moon into fragments ranging from huge boulders to powder. Nearly the entire moon is covered by a rubble pile of charcoal-gray, powdery dust and rocky debris called the lunar regolith. Beneath is a region of fractured bedrock referred to as the megaregolith.

The light areas of the moon are known as the highlands. The dark features, called maria (Latin for seas), are impact basins that were filled with lava between 4.2 and 1.2 billion years ago. These light and dark areas represent rocks of different composition and ages, which provide evidence for how the early crust may have crystallized from a lunar magma ocean. The craters themselves, which have been preserved for billions of years, provide an impact history for the moon and other bodies in the inner solar system.

If you looked in the right places on the moon, you would find pieces of equipment, American flags, and even a camera left behind by astronauts. While you were there, you'd notice that the gravity on the surface of the moon is one-sixth of Earth's, which is why in footage of moonwalks, astronauts appear to almost bounce across the surface.

The temperature reaches about 260 degrees Fahrenheit (127 degrees Celsius) when in full sun, but in darkness, the temperatures plummets to about -280 degrees Fahrenheit (-173 degrees Celsius).

Atmosphere

The moon has a very thin and weak atmosphere, called an exosphere. It does not provide any protection from the sun's radiation or impacts from meteoroids.

Potential for Life

The many missions that have explored the moon have found no evidence to suggest it has its own living things. However, the moon could be the site of future colonization by humans, though there are no immediate plans to do so.

Moons

Earth's moon has no moons of its own.

Rings

The moon has no rings.

Magnetosphere

The early moon may have developed an internal dynamo, the mechanism for generating global magnetic fields for terrestrial planets, but today, the moon has a very weak magnetic field. The magnetic field here on Earth is many thousands of times stronger than the moon's magnetic field

MISCONCEPION OF SCIENCE ON CREATION

Science and Creationism

A View from the National Academy of Sciences

SECOND EDITION

THE NATIONAL ACADEMIES

National Academy of sciences • National Academy of Engineering • Institute of Medicine • National Research Council

NATIONAL ACADEMY PRESS
Washington, DC
1999

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NATIONAL ACADEMY PRESS
2101 Constitution Avenue, NWWashington, DC20418

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters.

Library of Congress Cataloging-in-Publication Data

Science and creationism: a view from the National Academy of Sciences

p. cm.

Includes bibliographical references (p. ).

ISBN 0-309-06406-6 (paperbound)

1. Evolution (Biology). 2. Creationism. 3. Cosmology. I. National Academy of Sciences (U.S.)

QH366.2 .S425 1999 99-6259

576.8—dc21

Printed in the United States of America

Copyright 1999 by the National Academy of Sciences. All rights reserved.

Science and Creationism: A View from the National Academy of Sciences, Second Edition, is available for sale from the
National Academy Press,
2101 Constitution Avenue, NW, Box 285, Washington, DC20055. Call 1-800-624-6242 or 202-334-3313 (in the Washington Metropolitan Area). The report also is available online atwww.nap.edu

Introduction

Science is a particular way of knowing about the world. In science, explanations are limited to those based on observations and experiments that can be substantiated by other scientists. Explanations that cannot be based on empirical evidence are not a part of science.

In the quest for understanding, science involves a great deal of careful observation that eventually produces an elaborate written description of the natural world. Scientists communicate their findings and conclusions to other scientists through publications, talks at conferences, hallway conversations, and many other means. Other scientists then test those ideas and build on preexisting work. In this way, the accuracy and sophistication of descriptions of the natural world tend to increase with time, as subsequent generations of scientists correct and extend the work done by their predecessors.

Progress in science consists of the development of better explanations for the causes of natural phenomena. Scientists never can be sure that a given explanation is complete and final. Some of the hypotheses advanced by scientists turn out to be incorrect when tested by further observations or experiments. Yet many scientific explanations have been so thoroughly tested and confirmed that they are held with great confidence.

The theory of evolution is one of these well-established explanations. An enormous amount of scientific investigation since the mid-19th century has converted early ideas about evolution proposed by Darwin and others into a strong and well-supported theory. Today, evolution is an extremely active field of research, with an abundance of new discoveries that are continually increasing our understanding of how evolution occurs.

This booklet considers the science that supports the theory of evolution, focusing on three categories of scientific evidence:

•                     Evidence for the origins of the universe, Earth, and life

•                     Evidence for biological evolution, including findings from paleontology, comparative anatomy, biogeography, embryology, and molecular biology

•                     Evidence for human evolution

At the end of each of these sections, the positions held by advocates of "creation science" are briefly presented and analyzed as well.

The theory of evolution has become the central unifying concept of biology and is a critical component of many related scientific disciplines. In contrast, the claims

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of creation science lack empirical support and cannot be meaningfully tested. These observations lead to two fundamental conclusions: the teaching of evolution should be an integral part of science instruction, and creation science is in fact not science and should not be presented as such in science classes.

Terms Used in Describing the Nature of Science*

Fact: In science, an observation that has been repeatedly confirmed and for all practical purposes is accepted as "true." Truth in science, however, is never final, and what is accepted as a fact today may be modified or even discarded tomorrow.

Hypothesis: A tentative statement about the natural world leading to deductions that can be tested. If the deductions are verified, it becomes more probable that the hypothesis is correct. If the deductions are incorrect, the original hypothesis can be abandoned or modified. Hypotheses can be used to build more complex inferences and explanations.

Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

The contention that evolution should be taught as a "theory, not as a fact" confuses the common use of these words with the scientific use. In science, theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In this sense, evolution is one of the strongest and most useful scientific theories we have.

The Origin of the Universe, Earth, and Life

The term "evolution" usually refers to the biological evolution of living things. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." In all of these cases there is change over time, although the processes involved are quite different.

In the late 1920s the American astronomer Edwin Hubble made a very interesting and important discovery. Hubble made observations that he interpreted as showing that distant stars and galaxies are receding from Earth in every direction. Moreover, the velocities of recession increase in proportion with distance, a discovery that has been confirmed by numerous and repeated measurements since Hubble's time. The implication of these findings is that the universe is expanding.

Hubble's hypothesis of an expanding universe leads to certain deductions. One is that the universe was more condensed at a previous time. From this deduction came the suggestion that all the currently observed matter and energy in the universe were initially condensed in a very small and infinitely hot mass. A huge explosion, known as the Big Bang, then sent matter and energy expanding in all directions.

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This Big Bang hypothesis led to more testable deductions. One such deduction was that the temperature in deep space today should be several degrees above absolute zero. Observations showed this deduction to be correct. In fact, the Cosmic Microwave Background Explorer (COBE) satellite launched in 1991 confirmed that the background radiation field has exactly the spectrum predicted by a Big Bang origin for the universe.

As the universe expanded, according to current scientific understanding, matter collected into clouds that began to condense and rotate, forming the forerunners of galaxies. Within galaxies, including our own Milky Way galaxy, changes in pressure caused gas and dust to form distinct clouds. In some of these clouds, where there was sufficient mass and the right forces, gravitational attraction caused the cloud to collapse. If the mass of material in the cloud was sufficiently compressed, nuclear reactions began and a star was born.

Some proportion of stars, including our sun, formed in the middle of a flattened spinning disk of material. In the case of our sun, the gas and dust within this disk collided and aggregated into small grains, and the grains formed into larger bodies called planetesimals ("very small planets"), some of which reached diameters of several hundred kilometers. In successive stages these planetesimals coalesced into the nine planets and their numerous satellites. The rocky planets, including Earth, were near the sun, and the gaseous planets were in more distant orbits.

The ages of the universe, our galaxy, the solar system, and Earth can be estimated using modem scientific methods. The age of the universe can be derived from the observed relationship between the velocities of and the distances separating the galaxies. The velocities of distant galaxies can be measured very accurately, but the measurement of distances is more uncertain. Over the past few decades, measurements of the Hubble expansion have led to estimated ages for the universe of between 7 billion and 20 billion years, with the most recent and best measurements within the range of 10 billion to 15 billion years.

A disk of dust and gas, appearing as a dark band in this Hubble Space Telescope photograph, bisects a glowing nebula around a very young star in the constellation Taurus. Similar disks can be seen around other nearby stars and are thought to provide the raw material for planets.

The age of the Milky Way galaxy has been calculated in two ways. One involves studying the observed stages of evolution of different-sized stars in globular clusters. Globular clusters occur in a faint halo surrounding the center of the Galaxy, with each cluster containing from a hundred thousand to a million stars. The very low amounts of elements heavier than hydrogen and helium in these stars indicate that they must have formed early in the history of the Galaxy, before large amounts of heavy elements were created inside the initial generations of stars and later distributed into the interstellar medium through supernova explosions (the Big Bang itself created primarily hydrogen and helium atoms). Estimates of the ages of the stars in globular clusters fall within the range of 11 billion to 16 billion years.

A second method for estimating the age of our galaxy is based on the present abundances of several long-lived radioactive elements in the solar system. Their abundances are set by their rates of production and distribution through exploding

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supernovas. According to these calculations, the age of our galaxy is between 9 billion and 16 billion years. Thus, both ways of estimating the age of the Milky Way galaxy agree with each other, and they also are consistent with the independently derived estimate for the age of the universe.

Radioactive elements occurring naturally in rocks and minerals also provide a means of estimating the age of the solar system and Earth. Several of these elements decay with half lives between 700 million and more than 100 billion years (the half life of an element is the time it takes for half of the element to decay radioactively into another element). Using these time-keepers, it is calculated that meteorites, which are fragments of asteroids, formed between 4.53 billion and 4.58 billion years ago (asteroids are small "planetoids" that revolve around the sun and are remnants of the solar nebula that gave rise to the sun and planets). The same radioactive time-keepers applied to the three oldest lunar samples returned to Earth by the Apollo astronauts yield ages between 4.4 billion and 4.5 billion years, providing minimum estimates for the time since the formation of the moon.

The oldest known rocks on Earth occur in northwestern Canada (3.96 billion years), but well-studied rocks nearly as old are also found in other parts of the world. In Western Australia, zircon crystals encased within younger rocks have ages as old as 4.3 billion years, making these tiny crystals the oldest materials so far found on Earth.

The best estimates of Earth's age are obtained by calculating the time required for development of the observed lead isotopes in Earth's oldest lead ores. These estimates yield 4.54 billion years as the age of Earth and of meteorites, and hence of the solar system.

The origins of life cannot be dated as precisely, but there is evidence that bacteria-like organisms lived on Earth 3.5 billion years ago, and they may have existed even earlier, when the first solid crust formed, almost 4 billion years ago. These early organisms must have been simpler than the organisms living today. Furthermore, before the earliest organisms there must have been structures that one would not call "alive" but that are now components of living things. Today, all living organisms store and transmit hereditary information using two kinds of molecules: DNA and RNA. Each of these molecules is in turn composed of four kinds of subunits known as nucleotides. The sequences of nucleotides in particular lengths of DNA or RNA, known as genes, direct the construction of molecules known as proteins, which in turn catalyze biochemical reactions, provide structural components for organisms, and perform many of the other functions on which life depends. Proteins consist of chains of subunits known as amino acids. The sequence of nucleotides in DNA and RNA therefore determines the sequence of amino acids in proteins; this is a central mechanism in all of biology.

Experiments conducted under conditions intended to resemble those present on primitive Earth have resulted in the production of some of the chemical components of proteins, DNA, and RNA. Some of these molecules also have been detected in meteorites from outer space and in interstellar space by astronomers using radio-telescopes. Scientists have concluded that the "building blocks of life" could have been available early in Earth's history.

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An important new research avenue has opened with the discovery that certain molecules made of RNA, called ribozymes, can act as catalysts in modem cells. It previously had been thought that only proteins could serve as the catalysts required to carry out specific biochemical functions. Thus, in the early prebiotic world, RNA molecules could have been "autocatalytic"—that is, they could have replicated themselves well before there were any protein catalysts (called enzymes).

Laboratory experiments demonstrate that replicating autocatalytic RNA molecules undergo spontaneous changes and that the variants of RNA molecules with the greatest autocatalytic activity come to prevail in their environments. Some scientists favor the hypothesis that there was an early "RNA world," and they are testing models that lead from RNA to the synthesis of simple DNA and protein molecules. These assemblages of molecules eventually could have become packaged within membranes, thus making up "protocells"—early versions of very simple cells.

For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells.

Will we ever be able to identify the path of chemical evolution that succeeded in initiating life on Earth? Scientists are designing experiments and speculating about how early Earth could have provided a hospitable site for the segregation of

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molecules in units that might have been the first living systems. The recent speculation includes the possibility that the first living cells might have arisen on Mars, seeding Earth via the many meteorites that are known to travel from Mars to our planet.

Of course, even if a living cell were to be made in the laboratory, it would not prove that nature followed the same pathway billions of years ago. But it is the job of science to provide plausible natural explanations for natural phenomena. The study of the origin of life is a very active research area in which important progress is being made, although the consensus among scientists is that none of the current hypotheses has thus far been confirmed. The history of science shows that seemingly intractable problems like this one may become amenable to solution later, as a result of advances in theory, instrumentation, or the discovery of new facts.

Creationist Views of the Origin of the Universe, Earth, and Life

Many religious persons, including many scientists, hold that God created the universe and the various processes driving physical and biological evolution and that these processes then resulted in the creation of galaxies, our solar system, and life on Earth. This belief, which sometimes is termed "theistic evolution," is not in disagreement with scientific explanations of evolution. Indeed, it reflects the remarkable and inspiring character of the physical universe revealed by cosmology, paleontology, molecular biology, and many other scientific disciplines.

The advocates of "creation science" hold a variety of viewpoints. Some claim that Earth and the universe are relatively young, perhaps only 6,000 to 10,000 years old. These individuals often believe that the present physical form of Earth can be explained by "catastrophism," including a worldwide flood, and that all living things (including humans) were created miraculously, essentially in the forms we now find them.

Other advocates of creation science are willing to accept that Earth, the planets, and the stars may have existed for millions of years. But they argue that the various types of organisms, and especially humans, could only have come about with supernatural intervention, because they show "intelligent design."

In this booklet, both these "Young Earth" and "Old Earth" views are referred to as "creationism" or "special creation."

There are no valid scientific data or calculations to substantiate the belief that Earth was created just a few thousand years ago. This document has summarized the vast amount of evidence for the great age of the universe, our galaxy, the solar system, and Earth from astronomy, astrophysics, nuclear physics, geology, geochemistry, and geophysics. Independent scientific methods consistently give an age for Earth and the solar system of about 5 billion years, and an age for our galaxy and the universe that is two to three times greater. These conclusions make the origin of the universe as a whole intelligible, lend coherence to many different branches of science, and form the core conclusions of a remarkable body of knowledge about the origins and behavior of the physical world.

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Nor is there any evidence that the entire geological record, with its orderly succession of fossils, is the product of a single universal flood that occurred a few thousand years ago, lasted a little longer than a year, and covered the highest mountains to a depth of several meters. On the contrary, intertidal and terrestrial deposits demonstrate that at no recorded time in the past has the entire planet been under water. Moreover, a universal flood of sufficient magnitude to form the sedimentary rocks seen today, which together are many kilometers thick, would require a volume of water far greater than has ever existed on and in Earth, at least since the formation of the first known solid crust about 4 billion years ago. The belief that Earth's sediments, with their fossils, were deposited in an orderly sequence in a year's time defies all geological observations and physical principles concerning sedimentation rates and possible quantities of suspended solid matter.

Geologists have constructed a detailed history of sediment deposition that links particular bodies of rock in the crust of Earth to particular environments and processes. If petroleum geologists could find more oil and gas by interpreting the record of sedimentary rocks as having resulted from a single flood, they would certainly favor the idea of such a flood, but they do not. Instead, these practical workers agree with academic geologists about the nature of depositional environments and geological time. Petroleum geologists have been pioneers in the recognition of fossil deposits that were formed over millions of years in such environments as meandering rivers, deltas, sandy barrier beaches, and coral reefs.

The example of petroleum geology demonstrates one of the great strengths of science. By using knowledge of the natural world to predict the consequences of our actions, science makes it possible to solve problems and create opportunities using technology. The detailed knowledge required to sustain our civilization could only have been derived through scientific investigation.

The arguments of creationists are not driven by evidence that can be observed in the natural world. Special creation or supernatural intervention is not subjectable to meaningful tests, which require predicting plausible results and then checking these results through observation and experimentation. Indeed, claims of "special creation" reverse the scientific process. The explanation is seen as unalterable, and evidence is sought only to support a particular conclusion by whatever means possible.

Evidence Supporting Biological Evolution

Along path leads from the origins of primitive "life," which existed at least 3.5 billion years ago, to the profusion and diversity of life that exists today. This path is best understood as a product of evolution.

Contrary to popular opinion, neither the term nor the idea of biological evolution began with Charles Darwin and his foremost work, On the Origin of Species by Means of Natural Selection (1859). Many scholars from the ancient Greek philosophers on had inferred that similar species were descended from a common ancestor. The word "evolution" first appeared in the English language in 1647 in a nonbiological connection, and it became widely used in English for all sorts of progressions from simpler beginnings. The term Darwin most often used to refer to biological evolution was "descent with modification," which remains a good brief definition of the process today.

Darwin proposed that evolution could be explained by the differential survival of organisms following their naturally occurring variation—a process he termed "natural selection." According to this view, the offspring of organisms differ from one another and from their parents in ways that are heritable—that is, they can pass on the differences genetically to their own offspring. Furthermore, organisms in nature typically produce more offspring than can survive and reproduce given the constraints of food, space, and other environmental resources. If a particular off-

Charles Darwin arrived at many of his insights into evolution by studying the variations among species on the Galápagos Islands off the coast of Ecuador.

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spring has traits that give it an advantage in a particular environment, that organism will be more likely to survive and pass on those traits. As differences accumulate over generations, populations of organisms diverge from their ancestors.

Darwin's original hypothesis has undergone extensive modification and expansion, but the central concepts stand firm. Studies in genetics and molecular biology—fields unknown in Darwin's time—have explained the occurrence of the hereditary variations that are essential to natural selection. Genetic variations result from changes, or mutations, in the nucleotide sequence of DNA, the molecule that genes are made from. Such changes in DNA now can be detected and described with great precision.

Genetic mutations arise by chance. They may or may not equip the organism with better means for surviving in its environment. But if a gene variant improves adaptation to the environment (for example, by allowing an organism to make better use of an available nutrient, or to escape predators more effectively—such as through stronger legs or disguising coloration), the organisms carrying that gene are more likely to survive and reproduce than those without it. Over time, their descendants will tend to increase, changing the average characteristics of the population. Although the genetic variation on which natural selection works is based on random or chance elements, natural selection itself produces "adaptive" change—the very opposite of chance.

Scientists also have gained an understanding of the processes by which new species originate. A new species is one in which the individuals cannot mate and produce viable descendants with individuals of a preexisting species. The split of one species into two often starts because a group of individuals becomes geographically separated from the rest. This is particularly apparent in distant remote islands, such as the Galápagos and the Hawaiian archipelago, whose great distance from the Americas and Asia means that arriving colonizers will have little or no opportunity to mate with individuals remaining on those continents. Mountains, rivers, lakes, and other natural barriers also account for geographic separation between populations that once belonged to the same species.

Once isolated, geographically separated groups of individuals become genetically differentiated as a consequence of mutation and other processes, including natural selection. The origin of a species is often a gradual process, so that at first the reproductive isolation between separated groups of organisms is only partial, but it eventually becomes complete. Scientists pay special attention to these intermediate situations, because they help to reconstruct the details of the process and to identify particular genes or sets of genes that account for the reproductive isolation between species.

A particularly compelling example of speciation involves the 13 species of finches studied by Darwin on the Galápagos Islands, now known as Darwin's finches. The ancestors of these finches appear to have immigrated from the South American mainland to the Galápagos. Today the different species of finches on the island have distinct habitats, diets, and behaviors, but the mechanisms involved in speciation continue to operate. A research group led by Peter and Rosemary Grant of Princeton University has shown that a single year of drought on the islands can drive evolutionary changes in the finches. Drought diminishes supplies of easily

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The different species of finches on the Galápagos Islands, now known as Darwin's finches, have different-sized beaks that have evolved to take advantage of distinct food sources.

cracked nuts but permits the survival of plants that produce larger, tougher nuts. Droughts thus favor birds with strong, wide beaks that can break these tougher seeds, producing populations of birds with these traits. The Grants have estimated that if droughts occur about once every 10 years on the islands, a new species of finch might arise in only about 200 years.

The following sections consider several aspects of biological evolution in greater detail, looking at paleontology, comparative anatomy, biogeography, embryology, and molecular biology for further evidence supporting evolution.

The Fossil Record

Although it was Darwin, above all others, who first marshaled convincing evidence for biological evolution, earlier scholars had recognized that organisms on Earth had changed systematically over long periods of time. For example, in 1799 an engineer named William Smith reported that, in undisrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top. Because bottom layers of rock logically were laid down earlier and thus are older than top layers, the sequence of fossils also could be given a chronology from oldest to youngest. His findings were confirmed and extended in the 1830s by the paleontologist William Lonsdale, who recognized that fossil remains of organisms from lower strata were more primitive than the ones above. Today, many thousands of ancient rock deposits have been identified that show corresponding successions of fossil organisms.

Thus, the general sequence of fossils had already been recognized before Darwin conceived of descent with modification. But the paleontologists and geologists before Darwin used the sequence of fossils in rocks not as proof of biological evolution, but as a basis for working out the original sequence of rock strata that had been structurally disturbed by earthquakes and other forces.

In Darwin's time, paleontology was still a rudimentary science. Large parts of the geological succession of stratified rocks were unknown or inadequately studied.

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A geological cross section of the Grand Staircase-Escalante National Monument in Utah shows layers of sedimentary rock. These layers reveal deposits laid down over millions of years. Older fossils are found in the lower layers, revealing the succession of organisms over time

Weathering has exposed layers of sedimentary rock near the Paria River in Utah

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Darwin, therefore, worried about the rarity of intermediate forms between some major groups of organisms.

Today, many of the gaps in the paleontological record have been filled by the research of paleontologists. Hundreds of thousands of fossil organisms, found in well-dated rock sequences, represent successions of forms through time and manifest many evolutionary transitions. As mentioned earlier, microbial life of the simplest type was already in existence 3.5 billion years ago. The oldest evidence of more complex organisms (that is, eucaryotic cells, which are more complex than bacteria) has been discovered in fossils sealed in rocks approximately 2 billion years old. Multicellular organisms, which are the familiar fungi, plants, and animals, have been found only in younger geological strata. The following list presents the order in which increasingly complex forms of life appeared:

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So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. Actually, nearly all fossils can be regarded as intermediates in some sense; they are life forms that come between the forms that preceded them and those that followed.

The fossil record thus provides consistent evidence of systematic change through time—of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eucaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found.

Common Structures

Inferences about common descent derived from paleontology are reinforced by comparative anatomy. For example, the skeletons of humans, mice, and bats are strikingly similar, despite the different ways of life of these animals and the diversity of environments in which they flourish. The correspondence of these animals, bone by bone, can be observed in every part of the body, including the limbs; yet a person writes, a mouse runs, and a bat flies with structures built of bones that are different in detail but similar in general structure and relation to each other.

Scientists call such structures homologies and have concluded that they are best explained by common descent. Comparative anatomists investigate such homologies, not only in bone structure but also in other parts of the body, working out relationships from degrees of similarity. Their conclusions provide important inferences about the details of evolutionary history, inferences that can be tested by comparisons with the sequence of ancestral forms in the paleontological record.

A bat wing, a mouse forelimb, and a human arm serve very different purposes, but they have the same basic components The similarities arise because all three species share a common four-limbed vertebrate ancestor

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The mammalian ear and jaw are instances in which paleontology and comparative anatomy combine to show common ancestry through transitional stages. The lower jaws of mammals contain only one bone, whereas those of reptiles have several. The other bones in the reptile jaw are homologous with bones now found in the mammalian ear. Paleontologists have discovered intermediate forms of mammal-like reptiles (Therapsida) with a double jaw joint—one composed of the bones that persist in mammalian jaws, the other consisting of bones that eventually became the hammer and anvil of the mammalian ear.

The Distribution of Species

Biogeography also has contributed evidence for descent from common ancestors. The diversity of life is stupendous. Approximately 250,000 species of living plants, 100,000 species of fungi, and one million species of animals have been described and named, each occupying its own peculiar ecological setting or niche; and the census is far from complete. Some species, such as human beings and our companion the dog, can live under a wide range of environments. Others are amazingly specialized. One species of a fungus (Laboulbenia) grows exclusively on the rear portion of the covering wings of a single species of beetle (Aphaenops cronei) found only in some caves of southern France. The larvae of the fly Drosophila carcinophila can develop only in specialized grooves beneath the flaps of the third pair of oral appendages of a land crab that is found only on certain Caribbean islands.

How can we make intelligible the colossal diversity of living beings and the existence of such extraordinary, seemingly whimsical creatures as the fungus, beetle, and fly described above? And why are island groups like the Galápagos so often inhabited by forms similar to those on the nearest mainland but belonging to different species? Evolutionary theory explains that biological diversity results from the descendants of local or migrant predecessors becoming adapted to their diverse environments. This explanation can be tested by examining present species and local fossils to see whether they have similar structures, which would indicate how one is derived from the other. Also, there should be evidence that species without an established local ancestry had migrated into the locality.

Wherever such tests have been carried out, these conditions have been confirmed. A good example is provided by the mammalian populations of North and South America, where strikingly different native organisms evolved in isolation until the emergence of the isthmus of Panama approximately 3 million years ago. Thereafter, the armadillo, porcupine, and opossum—mammals of South American origin—migrated north, along with many other species of plants and animals, while the mountain lion and other North American species made their way across the isthmus to the south.

The evidence that Darwin found for the influence of geographical distribution on the evolution of organisms has become stronger with advancing knowledge. For example, approximately 2,000 species of flies belonging to the genus Drosophila are now found throughout the world. About one-quarter of them live only in Hawaii.

Until about 3 million years ago, North and South America were separated by a wide expanse of water, so mammals on the two continents evolved separately. After the isthmus of Panama formed, armadillos and opossums migrated north, and mountain lions migrated south. These movements are documented in the fossil record.

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More than a thousand species of snails and other land mollusks also are found only in Hawaii. The biological explanation for the multiplicity of related species in remote localities is that such great diversity is a consequence of their evolution from a few common ancestors that colonized an isolated environment. The Hawaiian Islands are far from any mainland or other islands, and on the basis of geological evidence they never have been attached to other lands. Thus, the few colonizers that reached the Hawaiian Islands found many available ecological niches, where they could, over numerous generations, undergo evolutionary change and diversification. No mammals other than one bat species lived in the Hawaiian Islands when the first human settlers arrived; similarly, many other kinds of plants and animals were absent.

The Hawaiian Islands are not less hospitable than other parts of the world for the absent species. For example, pigs and goats have multiplied in the wild in Hawaii, and other domestic animals also thrive there. The scientific explanation for the absence of many kinds of organisms, and the great multiplication of a few kinds, is that many sorts of organisms never reached the islands, because of their geographic isolation. Those that did reach the islands diversified over time because of the absence of related organisms that would compete for resources.

Similarities During Development

Embryology, the study of biological development from the time of conception, is another source of independent evidence for common descent. Barnacles, for instance, are sedentary crustaceans with little apparent similarity to such other crustaceans as lobsters, shrimps, or copepods. Yet barnacles pass through a free-swimming larval stage in which they look like other crustacean larvae. The similarity of larval stages supports the conclusion that all crustaceans have homologous parts and a common ancestry.

Similarly, a wide variety of organisms from fruit flies to worms to mice to humans have very similar sequences of genes that are active early in development. These genes influence body segmentation or orientation in all these diverse groups. The presence of such similar genes doing similar things across such a wide range of organisms is best explained by their having been present in a very early common ancestor of all of these groups.

New Evidence from Molecular Biology

The unifying principle of common descent that emerges from all the foregoing lines of evidence is being reinforced by the discoveries of modern biochemistry and molecular biology.

The code used to translate nucleotide sequences into amino acid sequences is essentially the same in all organisms. Moreover, proteins in all organisms are invariably composed of the same set of 20 amino acids. This unity of composition

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and function is a powerful argument in favor of the common descent of the most diverse organisms.

In 1959, scientists at Cambridge University in the United Kingdom determined the three-dimensional structures of two proteins that are found in almost every multicelled animal: hemoglobin and myoglobin. Hemoglobin is the protein that carries oxygen in the blood. Myoglobin receives oxygen from hemoglobin and stores it in the tissues until needed. These were the first three-dimensional protein structures to be solved, and they yielded some key insights. Myoglobin has a single chain of 153 amino acids wrapped around a group of iron and other atoms (called "heme") to which oxygen binds. Hemoglobin, in contrast, is made of up four chains: two identical chains consisting of 141 amino acids, and two other identical chains consisting of 146 amino acids. However, each chain has a heme exactly like that of myoglobin, and each of the four chains in the hemoglobin molecule is folded exactly like myoglobin. It was immediately obvious in 1959 that the two molecules are very closely related.

During the next two decades, myoglobin and hemoglobin sequences were determined for dozens of mammals, birds, reptiles, amphibians, fish, worms, and molluscs. All of these sequences were so obviously related that they could be compared with confidence with the three-dimensional structures of two selected standards—whale myoglobin and horse hemoglobin. Even more significantly, the differences between sequences from different organisms could be used to construct a family tree of hemoglobin and myoglobin variation among organisms. This tree agreed completely with observations derived from paleontology and anatomy about the common descent of the corresponding organisms.

Myoglobin, which stores oxygen in muscles, consists of a chain of 153 amino acids wrapped around an oxygen-binding molecule. The sequence of amino acids in myoglobin vanes from species to species, revealing the evolutionary relationships among organisms.

Similar family histories have been obtained from the three-dimensional structures and amino acid sequences of other proteins, such as cytochrome c (a protein engaged in energy transfer) and the digestive proteins trypsin and chymotrypsin. The examination of molecular structure offers a new and extremely powerful tool for studying evolutionary relationships. The quantity of information is potentially huge—as large as the thousands of different proteins contained in living organisms, and limited only by the time and resources of molecular biologists.

As the ability to sequence the nucleotides making up DNA has improved, it also has become possible to use genes to reconstruct the evolutionary history of organisms. Because of mutations, the sequence of nucleotides in a gene gradually changes over time. The more closely related two organisms are, the less different their DNA will be. Because there are tens of thousands of genes in humans and other organisms, DNA contains a tremendous amount of information about the evolutionary history of each organism.

Genes evolve at different rates because, although mutation is a random event, some proteins are much more tolerant of changes in their amino acid sequence than

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are other proteins. For this reason, the genes that encode these more tolerant, less constrained proteins evolve faster The average rate at which a particular kind of gene or protein evolves gives rise to the concept of a "molecular clock." Molecular clocks run rapidly for less constrained proteins and slowly for more constrained proteins, though they all time the same evolutionary events.

The figure on this page compares three molecular clocks: for cytochrome c proteins, which interact intimately with other macromolecules and are quite constrained in their amino acid sequences; for the less rigidly constrained hemoglobins, which interact mainly with oxygen and other small molecules; and for fibrinopeptides, which are protein fragments that are cut from larger proteins (fibrinogens) when blood clots. The clock for fibrinopeptides runs rapidly; 1 percent of the amino acids change in a little longer than 1 million years. At the other extreme, the molecular clock runs slowly for cytochrome c; a 1 percent change in amino acid sequence requires 20 million years. The hemoglobin clock is intermediate.

The concept of a molecular clock is useful for two purposes. It determines evolutionary relationships among organisms, and it indicates the time in the past when species started to diverge from one another. Once the clock for a particular gene or protein has been calibrated by reference to some event whose time is known, the actual chronological time when all other events occurred can be determined by examining the protein or gene tree.

Species that diverged longer ago have more differences in their corresponding proteins, reflecting changes in the amino acids over time. Proteins evolve at different rates depending on the constraints imposed by their functions. Cytochrome c, a protein involved in energy transfer, is tightly constrained and changes slowly. Fibrinopeptides, which are involved in blood clotting, are much less constrained, with hemoglobin an intermediate case. The estimates for times of divergence shown here are based on 1971 data and have changed slightly since then (see table on page 13).

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An interesting additional line of evidence supporting evolution involves sequences of DNA known as "pseudogenes." Pseudogenes are remnants of genes that no longer function but continue to be carried along in DNA as excess baggage. Pseudogenes also change through time, as they are passed on from ancestors to descendants, and they offer an especially useful way of reconstructing evolutionary relationships.

With functioning genes, one possible explanation for the relative similarity between genes from different organisms is that their ways of life are similar—for example, the genes from a horse and a zebra could be more similar because of their similar habitats and behaviors than the genes from a horse and a tiger. But this possible explanation does not work for pseudogenes, since they perform no function. Rather, the degree of similarity between pseudogenes must simply reflect their evolutionary relatedness. The more remote the last common ancestor of two organisms, the more dissimilar their pseudogenes will be.

The evidence for evolution from molecular biology is overwhelming and is growing quickly. In some cases, this molecular evidence makes it possible to go beyond the paleontological evidence. For example, it has long been postulated that whales descended from land mammals that had returned to the sea. From anatomical and paleontological evidence, the whales' closest living land relatives seemed to be the even-toed hoofed mammals (modem cattle, sheep, camels, goats, etc.).

Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and have suggested that the closest land-bound living relative of whales may be the hippopotamus. In this case, molecular biology has augmented the fossil record.

Creationism and the Evidence for Evolution

Some creationists cite what they say is an incomplete fossil record as evidence for the failure of evolutionary theory. The fossil record was incomplete in Darwin's time, but many of the important gaps that existed then have been filled by subsequent paleontological research. Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on

Mammakian land ancestor

Ambulocetus

Modern whales trace their ancestry to land mammals that evolved into species progressively more adapted to the water.

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Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains. Undisturbed strata with simple unicellular organisms predate those with multicellular organisms, and invertebrates precede vertebrates; nowhere has this sequence been found inverted. Fossils from adjacent strata are more similar than fossils from temporally distant strata. The most reasonable scientific conclusion that can be drawn from the fossil record is that descent with modification has taken place as stated in evolutionary theory.

Special creationists argue that "no one has seen evolution occur." This misses the point about how science tests hypotheses. We don't see Earth going around the sun or the atoms that make up matter. We "see" their consequences. Scientists infer that atoms exist and Earth revolves because they have tested predictions derived from these concepts by extensive observation and experimentation.

Furthermore, on a minor scale, we "experience" evolution occurring every day. The annual changes in influenza viruses and the emergence of antibiotic-resistant bacteria are both products of evolutionary forces. Indeed, the rapidity with which organisms with short generation times, such as bacteria and viruses, can evolve under the influence of their environments is of great medical significance. Many laboratory experiments have shown that, because of mutation and natural selection, such microorganisms can change in specific ways from those of immediately preceding generations.

On a larger scale, the evolution of mosquitoes resistant to insecticides is another example of the tenacity and adaptability of organisms under environmental stress. Similarly, malaria parasites have become resistant to the drugs that were used extensively to combat them for many years. As a consequence, malaria is on the increase, with more than 300 million clinical cases of malaria occurring every year.

Molecular evolutionary data counter a recent proposition called "intelligent design theory." Proponents of this idea argue that structural complexity is proof of the direct hand of God in specially creating organisms as they are today. These arguments echo those of the 18th century cleric William Paley who held that the vertebrate eye, because of its intricate organization, had been specially designed in its present form by an omnipotent Creator. Modem-day intelligent design proponents argue that molecular structures such as DNA, or molecular processes such as

Rodhocetus

Balaenoptera (modern Blue whale)

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the many steps that blood goes through when it clots, are so irreducibly complex that they can function only if all the components are operative at once. Thus, proponents of intelligent design say that these structures and processes could not have evolved in the stepwise mode characteristic of natural selection.

However, structures and processes that are claimed to be "irreducibly" complex typically are not on closer inspection. For example, it is incorrect to assume that a complex structure or biochemical process can function only if all its components are present and functioning as we see them today. Complex biochemical systems can be built up from simpler systems through natural selection. Thus, the "history" of a protein can be traced through simpler organisms. Jawless fish have a simpler hemoglobin than do jawed fish, which in turn have a simpler hemoglobin than mammals.

The evolution of complex molecular systems can occur in several ways. Natural selection can bring together parts of a system for one function at one time and then, at a later time, recombine those parts with other systems of components to produce a system that has a different function. Genes can be duplicated, altered, and then amplified through natural selection. The complex biochemical cascade resulting in blood clotting has been explained in this fashion.

Similarly, evolutionary mechanisms are capable of explaining the origin of highly complex anatomical structures. For example, eyes may have evolved independently many times during the history of life on Earth. The steps proceed from a simple eye spot made up of light-sensitive retinula cells (as is now found in the flatworm), to formation of individual photosensitive units (ommatidia) in insects with light focusing lenses, to the eventual formation of an eye with a single lens focusing images onto a retina. In humans and other vertebrates, the retina consists not only of photoreceptor cells but also of several types of neurons that begin to analyze the visual image. Through such gradual steps, very different kinds of eyes have evolved, from simple light-sensing organs to highly complex systems for vision.

Eyes evolved over many millions of years from simple organs that can detect light.

Human Evolution

Studies in evolutionary biology have led to the conclusion that human beings arose from ancestral primates. This association was hotly debated among scientists in Darwin's day. But today there is no significant scientific doubt about the close evolutionary relationships among all primates, including humans.

Many of the most important advances in paleontology over the past century relate to the evolutionary history of humans. Not one but many connecting links—intermediate between and along various branches of the human family tree—have been found as fossils. These linking fossils occur in geological deposits of intermediate age. They document the time and rate at which primate and human evolution occurred.

Scientists have unearthed thousands of fossil specimens representing members of the human family. A great number of these cannot be assigned to the modem human species, Homo sapiens. Most of these specimens have been well dated, often by means of radiometric techniques. They reveal a well-branched tree, parts of which trace a general evolutionary sequence leading from ape-like forms to modem humans.

Paleontologists have discovered numerous species of extinct apes in rock strata that are older than four million years, but never a member of the human family at that great age. Australopithecus, whose earliest known fossils are about four million years old, is a genus with some features closer to apes and some closer to modem humans. In brain size, Australopithecuswas barely more advanced than apes. A number of features, including long arms, short legs, intermediate toe structure, and features of the upper limb, indicate that the members of this species spent part of the time in trees. But they also walked upright on the ground, like humans. Bipedal tracks of Australopithecus have been discovered, beautifully preserved with those of other extinct animals, in hardened volcanic ash. Most of our Australopithecus ancestors died out close to two-and-a-half million years ago, while other Australopithecus species, which were on side branches of the human tree, survived alongside more advanced hominids for another million years.

Distinctive bones of the oldest species of the human genus, Homo, date back to rock strata about 2.4 million years old. Physical anthropologists agree that Homo evolved from one of the species of Australopithecus. By two million years ago, early members of Homo had an average brain size one-and-a-half times larger than that of Australopithecus, though still substantially smaller than that of modem humans. The shapes of the pelvic and leg bones suggest that these early Homo were not part-time climbers like Australopithecus but walked and ran on long legs, as modem humans do. Just as Australopithecus showed a complex of ape-like, human-like, and intermediate features, so was early Homo intermediate between Australopithecus and modem humans in some features, and dose to modem humans in other respects. The earliest

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Early hominids, such as members of the Australopithecus afarensis species that lived about 3 million years ago, had smaller brains and larger faces than species belonging to the genus Homo, which first appeared about 2.4 million years ago. White parts of the skulls are reconstructions, and the skulls are not all on the same scale.

stone tools are of virtually the same age as the earliest fossils of Homo.Early Homo, with its larger brain than Australopithecus, was a maker of stone tools.

The fossil record for the interval between 2.4 million years ago and the present includes the skeletal remains of several species assigned to the genus Homo. The more recent species had larger brains than the older ones. This fossil record is complete enough to show that the human genus first spread from its place of origin in Africa to Europe and Asia a little less than two million years ago. Distinctive types of stone tools are associated with various populations. More recent species with larger brains generally used more sophisticated tools than more ancient species.

Molecular biology also has provided strong evidence of the close relationship between humans and apes. Analysis of many proteins and genes has shown that humans are genetically similar to chimpanzees and gorillas and less similar to orangutans and other primates.

DNA has even been extracted from a well-preserved skeleton of the extinct human creature known as Neanderthal, a member of the genus Homo and often considered either as a subspecies of Homo sapiens or as a separate species. Application of the molecular clock, which makes use of known rates of genetic mutation, suggests that Neanderthal's lineage diverged from that of modem Homo sapiens less than half a million years ago, which is entirely compatible with evidence from the fossil record.

Based on molecular and genetic data, evolutionists favor the hypothesis that modem Homo sapiens, individuals very much like us, evolved from more archaic humans about 100,000 to 150,000 years ago. They also believe that this transition occurred in Africa, with modem humans then dispersing to Asia, Europe, and eventually Australasia and the Americas.

Discoveries of hominid remains during the past three decades in East and South Africa, the Middle East, and elsewhere have combined with advances in molecular biology to initiate a new discipline—molecular paleoanthropology. This field of inquiry is providing an ever-growing inventory of evidence for a genetic affinity between human beings and the African apes.

Opinion polls show that many people believe that divine intervention actively guided the evolution of human beings. Science cannot comment on the role that supernatural forces might play in human affairs. But scientific investigations have concluded that the same forces responsible for the evolution of all other life forms on Earth can account for the evolution of human beings.

Conclusion

Science is not the only way of acquiring knowledge about ourselves and the world around us. Humans gain understanding in many other ways, such as through literature, the arts, philosophical reflection, and religious experience. Scientific knowledge may enrich aesthetic and moral perceptions, but these subjects extend beyond science's realm, which is to obtain a better understanding of the natural world.

The claim that equity demands balanced treatment of evolutionary theory and special creation in science classrooms reflects a misunderstanding of what science is and how it is conducted. Scientific investigators seek to understand natural phenomena by observation and experimentation. Scientific interpretations of facts and the explanations that account for them therefore must be testable by observation and experimentation.

Creationism, intelligent design, and other claims of supernatural intervention in the origin of life or of species are not science because they are not testable by the methods of science. These claims subordinate observed data to statements based on authority, revelation, or religious belief. Documentation offered in support of these claims is typically limited to the special publications of their advocates. These publications do not offer hypotheses subject to change in light of new data, new interpretations, or demonstration of error. This contrasts with science, where any hypothesis or theory always remains subject to the possibility of rejection or modification in the light of new knowledge.

No body of beliefs that has its origin in doctrinal material rather than scientific observation, interpretation, and experimentation should be admissible as science in any science course. Incorporating the teaching of such doctrines into a science curriculum compromises the objectives of public education. Science has been greatly successful at explaining natural processes, and this has led not only to increased understanding of the universe but also to major improvements in technology and public health and welfare. The growing role that science plays in modem life requires that science, and not religion, be taught in science classes.

LINK: https://www.nap.edu/read/6024/chapter/6