The Evolution of the Universe

Task. Scan the text and compare the “open” and “closed universe” theories.

Galaxies

Task. Scan the text. Choose the one best alternative to each question following it. Answer all questions on the basis of what is stated or implied in the text.

The Lunar Surface

The moon was hardly a mystery even before the voyages of Apollo 11 and of the other manned spacecraft that followed it there. Even a small telescope reveals the chief features of the lunar landscape: wide plains, jagged mountain ranges, and innumerable craters of all sizes. Each mountain stands out in vivid clarity, with no clouds or haze to hide the smallest detail. Mountain shadows are black and sharp-edged. When the moon passes before a star, the star remains bright and clear up to the moon’s very edge. From these observations we conclude that the moon has little or no atmosphere. Water is likewise absent, as indicated by the complete lack of lakes, oceans, and rivers.

But there is still no substitute for direct observation and laboratory analysis, and each spacecraft that has landed on the moon and returned to earth, manned or unmanned, has brought back information and samples of the greatest value. The lack of a protective atmosphere and of running water to erode away surface features means that there is much to be learned on the moon about our common environment in space, both past and present. And from the composition and internal structure of the moon hints can be gleaned of its origin and past history, which may well bear upon those of the earth as well. Thus the study of the moon is also a part of the study of the earth, doubly justifying the effort of its exploration.

With the help of no more than binoculars it is easy to distinguish the two main kinds of lunar landscape, the dark, relatively smooth maria and the lighter, ruggedly mountainous highlands. Mare means “sea” in Latin, but the term is still used even though it has been known for a long time that these regions are not covered with water.

The maria are large, dark, smooth regions on the lunar surface that consist of lava pulverized by meteorites.

They are not perfectly smooth, but are marked by small craters ranging up to 236 km in diameter. Most of the craters are circular with raised rims that are steeper on the inside than on the outside, and some have mountain peaks at their centers. Craters resembling those on the moon are produced on the earth both by volcanic activity and by meteoric impact. There is no question that some of the lunar craters are of meteoric origin. However, present evidence points to a volcanic origin far in the past for the majority of the craters.

The Planets

The planets seem to fall naturally into two categories. The inner planets of Mercury, Venus, Earth, and Mars are solid, relatively small, and rotate fairly slowly on their axes. The outer planets of Jupiter, Saturn, Uranus, and Neptune are gaseous, large, and rotate fairly rapidly. Although relatively little is known about Pluto, it seems to resemble the inner planets more than the outer ones despite its status as the outermost one of all.

Mercury

Mercury, smallest of the planets, has a crater-pocked surface much like that of the moon but lacking the extensive lava flows so prominent there. The Mariner 10 spacecraft detected a weak magnetic field around Mercury but no atmosphere. A bleak place, but an interesting one because the combination of a high density and little surface melting in the past suggests a quite different geologic history from that of the earth. Surface temperatures on the sunlit side are 300⁰ C or so, and because there is no atmosphere to transfer or retain heat, the temperature drops at night to about - 175⁰C.

Venus

In size and mass the planet Venus resemble s the earth more closely than any other member of the sun’s family. Apart from the sun and the moon, Venus is the brightest object in the sky, and is even visible in daylight. Venus has the distinction of spinning “backward” on its axis; that is, looking downward on its north pole, Venus rotates clockwise, whereas the earth and the other planets rotate counterclockwise. The rotation of Venus is extremely slow, so that a “day” on that planet represents 243 of our days.

The surface of Venus is obscured by thick layers of clouds. The dense atmosphere is mainly carbon dioxide, with a little nitrogen and a trace of water vapor also present. At the surface, atmospheric pressure is a hundred times that of the earth. On the earth carbon dioxide is an important absorber of radiation from the earth that prevents the rapid loss of heat from the ground after sunset. Venus, blanketed more effectively by far than the earth, retains more heat; estimates based on data radioed back by spacecraft suggest an average surface temperature of about 430⁰ C, enough to melt lead. Since the temperature is so high, the existence of life on Venus seems impossible.

Mars

The reddish planet Mars has long fascinated astronomers and laymen alike, for it is the only other known body on which surface conditions seemed suitable for life of some kind. Yet Martian climates are exceedingly severe by our standards, and the thin atmosphere does little to screen solar ultraviolet radiation. If life exists on Mars, it is adapted to an environment that would soon destroy most earthly organisms.

Mars rotates on its axis in a little over 24 h; its revolution about the sun requires nearly 2 years; and its axis is inclined to the plane of its orbit at nearly the same angle as the earth’s. These facts mean that the Martian day and night have about the same lengths as ours and that Martian seasons are 6 months long and at least as pronounced as ours. Over half again farther from the sun than the earth, Mars receives considerably less light and heat. Its atmosphere, largely carbon dioxide, is extremely thin, so little of the sun’s heat is retained after nightfall. Daytime temperatures in summer rise to perhaps 30⁰ C, but at nightfall drop to perhaps – 75⁰C.

Another difficulty that life must face on Mars is the scarcity of water. A trifle is certainly there, as water vapor in the atmosphere and possibly in the white polar caps as well, but apparently not a great deal. The polar caps, which increase in area in winter and decrease in area in summer, are believed to be almost entirely frozen carbon dioxide (“dry ice”). However, water may well have once been more abundant on mars than it is today. Some surface features photographed by the Mariner 9 spacecraft early in 1972 strongly suggest erosion by running water within the past million years or so. The earth’s surface water probably was vented from volcanoes early in its history, and there seems no reason why the same process should not have occurred on Mars, whose surface is dotted with extinct volcanoes.

The fact that most terrestrial life requires liquid water and oxygen plus protection from solar ultraviolet radiation does not necessarily mean that life of some kind could not develop in their absence. Certain bacteria on the earth are known whose life processes require carbon dioxide, not oxygen, so an oxygen-containing atmosphere is not indispensable, at least for primitive forms of life. Conceivably organisms could exist which can thrive on water gleaned from traces of it in the minerals of surface rocks. And shells of some sort might protect Martian creatures from ultraviolet radiation. The absence of indications of life in photographs taken thousands of miles away from the Martian surface is in itself not significant; at such distances terrestrial life would probably not be apparent to a visitor from elsewhere. (And a closer look might suggest that the car is the most conspicuous form of life on earth.)

The pictures radioed back by Mariner 9 as it orbited Mars showed a host of intriguing geologic structures, many apparently of recent origin. The Martian landscape is extremely varied: there are regions pocked with huge craters, regions broken up into irregular short ridges and depressions, vast lava flows, channels that look as though they were carved by running water, even peculiar areas that seem to indicate glacial activity. Though rainstorms are absent – at least these days - violent winds periodically drive great clouds of dust around the planet. The surface markings so obvious through the telescope do not seem to coincide with the topographical features found by Mariner 9, and some of these markings are known to change color with the Martian seasons. Perhaps the dust storms also follow the seasons and are responsible for the color changes; perhaps some form of vegetation is the cause; perhaps the true explanation lies elsewhere.

Early in this century the Italian astronomer Giovanni Schiaparelli and the American Percival Lowell reported that the surface of Mars was covered with networks of fine lines, popularly called canals (a poor English translation of the Italian canali, meaning “cannels”). The apparent straightness and geometric patterns of these canals were considered evidence of the work of intelligent beings. But the pictures radioed back by the various spacecraft to pass near Mars show no signs of canals, though there do seem to be several regions where a number of craters are approximately in line. Probably the canals are optical illusions; certainly the existence of Martian creatures advanced enough to be capable of digging actual canals is highly unlikely.

Jupiter

The giant planet Jupiter, like Venus, is shrouded in clouds. The clouds occur in bands of changing color – yellow, red, brown, blue, purple, gray – and there are some semipermanent markings, such as the Red Sport some tens of thousands of kilometers across. The latter make possible a determination of the planet’s period of rotation. This turns out to be less than 10 h, which means that points on Jupiter’s equator travel at the enormous speed of 45,000 km/h; the earth’s equatorial speed is only 1,670 km/h. Because of its rapid rotation, Jupiter bulges much more at the equator than the earth does.

The four satellites of Jupiter that Galileo discovered over 3 centuries ago are conspicuous objects in a small telescope. The largest is as big as Mercury, and the smallest is about the size of the moon. The other eight satellites are very small (25 to 250 km in diameter), and one of them escaped detection until 1951.

Jupiter’s volume is about 1,300 times that of the earth, but its mass is only 300 times as great. The resulting low density – only a third more than that of water – means that Jupiter cannot be composed of a mixture of rock, iron, and nickel as is the earth. Like the other giant planets (Saturn, Uranus, and Neptune), Jupiter must consist chiefly of hydrogen and helium, the two lightest elements. Probably Jupiter does not have an actual surface; instead, its atmosphere gradually becomes thicker and thicker with increasing depth until it becomes a liquid. A terrestrial analogy might be the slushy surface of a snowbank on a warm winter day.

Jupiter’s interior is believed to be very hot, about 500,000⁰ C according to some estimates, but not hot enough for nuclear reactions to occur in its hydrogen content whose release of energy would turn Jupiter into a star. But if Jupiter’s mass were 30 times greater, the increased internal pressure would push the temperature to 20 million⁰ C, and the result would be a miniature star.

Jupiter’s atmosphere apparently contains such gases as ammonia, methane, and water vapor as well as hydrogen and helium. As mentioned earlier, laboratory experiments show that when a mixture of these gases is exposed to energy sources such as are usually present in a planetary atmosphere (for instance lightning, ultraviolet light, streams of fast ions), the various organic compounds characteristic of life are formed. It seems entirely possible – some biologists think probable – that some form of life has evolved in the dense lower atmosphere of Jupiter. It is interesting that simple microorganisms such as bacteria and yeasts are able to survive when exposed to gas mixtures that simulate the Jovian atmosphere at temperatures and pressures comparable to those on Jupiter.

The American spacecraft Pioneer 10 passed close to Jupiter late in 1973 after a journey that lasted 20 months and covered over a billion kilometers. Of the wealth of information radioed back, a few items are especially notable. For example, Jupiter has a complex magnetic field about 8 times stronger than the earth’s, and this field traps high-energy protons and electrons from the sun in belts that extend many Jovian radii outward, (The Van Allen belts around the earth are similar, but 10,000 times weaker). Another important finding confirmed that Jupiter radiates over twice as much energy as it receives from the sun, which means that it has powerful internal sources of energy; by contrast, the atmospheres of Venus, Earth, and Mars are in balance, and radiate only as much energy as they get from the sun. It has been suggested that Jupiter is still contracting gravitationally, and in this contraction potential energy is turned into heat just as compressing air in a tire pump warms up the air.

Saturn

In its setting of brilliant rings, Saturn is the most beautiful of the earth’s kindred. The planet itself is much like Jupiter: similarly flattened at the poles by rapid rotation, similarly possessing a dense atmosphere, its surface similarly hidden by banded clouds. Farther from the sun than Jupiter, Saturn is considerably colder; ammonia is largely frozen out of its atmosphere, and its clouds consist mostly of methane.

The famous rings, two bright ones and a fainter inner one, surround the planet in the plane of its equator. This plane is somewhat inclined to Saturn’s orbit. Hence, as Saturn moves in its leisurely 29-year journey around the sun, we see the rings from different angles. Twice in the 29-year period the rings are edgewise to the earth; in this position they are practically invisible, which suggests that their thickness is small, perhaps 20 km as compared with the 270,000-km diameter of the outer ring.

The rings are not the solid sheets they appear to be but instead consist of myriad small bodies ranging in size from boulders a meter or more across to dust particles, each of which revolves about Saturn like a miniature satellite. No satellite of substantial size can exist close to its parent planet because of the disruptive effect of tide-producing forces, which are proportionately less the farther distant the satellite. The Roche limit is the minimum radius that a satellite orbit must have if the satellite is to remain intact; the limit is named in honor of E.A.Roche, who investigated the origin of Saturn’s rings a century ago. For Saturn the Roche limit is calculated to be 2,4 times the planet’s radius, and in fact the outer rim of the outer ring is 2,3 radii from the center of Saturn and the closest satellite never approaches closer that 3,1 radii from the center. Saturn has 10 ordinary satellites outside the rings; the innermost of these was discovered in 1966.

Uranus and Neptune

The two outermost planets, Uranus and Neptune, owe their discovery to the telescope. Uranus was found quite by accident in 1781, during a systematic search of the sky by the great English astronomer William Herschel. It is just barely visible to the naked eye, and in fact had been identified as a faint star on a number of sky maps prepared during the preceding hundred years. Herschel suspected Uranus to be a planet because, through the telescope, it appeared as a disk rather than as a point of light. Observations made over a period of time showed its position to be changing relative to the stars, and its orbit was determined from these data. The discovery of Neptune in 1846 was made as the result of predictions based on it gravitational effect on other planets.

Uranus and Neptune are large bodies, each with a diameter about 3 ½ times that of the earth. In most of their properties Uranus and Neptune resemble Jupiter and Saturn. Their atmospheres are largely methane, which accounts for their greenish color, with some hydrogen present as well. Because these planets are so far from the sun, their surface temperatures are below – 200⁰ C, and any ammonia present would be frozen out of their atmospheres.

Stellar Evolution

A star shines because it is a large, compact aggregate of matter that contains abundant hydrogen. A body of this sort cannot avoid being luminous because of the energy liberated in the conversion of its hydrogen into helium. We may imagine as the starting point in a star’s history a stage when its matter was an irregular mass of cool, diffuse gas and small, solid particles. Gravitation in such a mass would concentrate it into a smaller space. The gradual contraction would heat the gas, much as the gas in a tire pump is heated by compression. At length the temperature would grow high enough for hydrogen to be converted into helium, and the mass would begin to glow brightly. From this time on the tendency to contract would be counterbalanced by the pressure of radiation from the hot interior, so shrinking would stop and the star would maintain a nearly constant size. The diameter of a star is thus determined by equilibrium between gravitational forces pulling its material inward and forces due to radiation pushing its material outward.

A star does not shine because some occult force has started I shining; it shines because it has a certain mass and a certain composition. If we could somehow build a star by heaping together sufficient matter of the right composition, it would start to shine of its own accord.

A star consumes its hydrogen rapidly if it is large, slowly if it is small. A fairly small star like our sun makes its supply of hydrogen last for a period of the order of 10 billion years; probably the sun is now about halfway through this part of its career. When the hydrogen supply at last begins to run low in a star like the sun, the life of the star is by no means ended but enters its most spectacular phase. Further gravitational contraction makes the interior still hotter and other nuclear reactions become possible - particularly reactions in which atoms of heavier elements are made by a combination of helium atoms. These reactions, once started, give out so much energy that the star expands to become a giant. Energy is now being poured out at a prodigious rate, so the star’s life as a giant is much shorter that the earlier part of its existence.

Eventually the new energy-producing reactions run out of fuel, and again the star shrinks – although probably not without a few last brief flare-ups, which we see from the earth as novae (“new stars”) that shine brilliantly for a week or two and then subside into insignificance. The shrinking ultimately reduces the star to the white dwarf state. As a slowly contracting dwarf the star may remain luminous for billions of years more with its energy now coming from the contraction, from nuclear reactions involving elements heavier than helium, and from proton-proton reactions in a very thin outer atmosphere of hydrogen.

Stars much more massive than the sun have somewhat different histories. Eventually they become unstable and explode violently, emitting enormous amounts of material. Such explosions we observe as supernovae, flare-ups 10,000 or more times as luminous as ordinary novae. Having lost perhaps half its mass, a star of this kind can then subside like its smaller brethren into a dwarf star.

Today astronomers believe that the residual dwarfs of supernovae are different from ordinary white dwarfs because of the large mass of their parent stars. These hypothetical dwarfs are calculated to have densities far in excess of ordinary dwarfs, with masses comparable to that of the sun packed into spheres perhaps 15 km (9 mi) in diameter. The matter of such a star would weigh billions of tons per cubic inch. (If the earth were this dense, it would fit into a large apartment house). Under the pressures that would be present the most stable form of matter is the neutron. Pulsars, which emit brief, intense bursts of radio waves at regular intervals, are believed to be rotating neutron stars with magnetic fields that lead to radio emission in narrow beams; as a pulsar rotates, its beams swing with it to produce the observed fluctuations. A notable pulsar is located at the center of the Crab nebula, which is the remnant of a supernova that was seen in A.D. 1054 and has been expanding and glowing brightly ever since.

This Earth of Ours

Earth is a minute fragment of a universe that is believed to have come into existence¹ as a result of a cataclysmic explosion of a single mass of highly concentrated matter some ten billion years ago. Out of this explosion evolved the galaxies, such as our Milky Way, that are made up of the many billions of stars that are known to exist in the heavens.

All of these stars, of which Sun is one, have been rushing farther and farther out into space at an extremely rapid rate ever since. But this rate is now believed to be slowing down². If so, eventually this expanding movement may come to a halt and its direction may then be reversed. In that event all the separate units of the universe might be pulled back together with a resulting new explosion that would repeat the sequence.

Where Earth had its origin and how it came to be have long been subjects of much speculation among mathematicians and astronomers, geologists and biologists, physicists and chemists, and philosophers and theologians. Some of the more modern concepts of highly capable scientists especially concerned with this subject appear sufficiently conclusive to make it possible to accept them as working hypotheses. But they still leave many points to be more fully explained.

Earth, located some 93 million miles out in space from Sun and revolving around it once every 365 days at a speed of about twenty-two miles a second, is believed to be³ an offshoot from Sun. It came into existence largely as a gaseous mass that began to solidify into its present form some four and one-half billion years ago. It is the third of a series of eight planetary satellites of Sun, of which Mercury and Venus are nearer to Sun, and Mars, Jupiter, Saturn, Uranus and Neptune are increasingly farther away from it.

Our solar system is not unique, and neither is Earth. Many millions of such systems are believed to exist⁴ in the universe. The number of stars, among the largest of which our sun is a mere midget, has been estimate at 10²⁰ , which means 10 multiplied by itself 20 times. And of these millions of millions of millions of stars, some 10⁸ have been estimated to have⁵ planetary systems similar to the one of which Earth is a part. From this, one may speculate that there are millions of planets that are so located with reference to the stars round which they revolve as to have conditions that are favorable for life. The living forms on these Earthlike planets may be very different from those with which we are familiar. Conceivably, the highest forms of life on some of these plants may be superior to man.

The history of Earth is recorded on part in the rocks that are exposed to view and that have been reached by quarrying and boring. For convenience, this history is divided into five eras, of which the most recent, the Cenozoic era, covers the last 60n million years, since the folding that formed the Rocky Mountains. The next earlier Mesozoic era, extending back 130 million years farther, began with the folding that formed the Appalachian Mountains. Prior to that were the Paleozoic era of 360 million years following an extended period of widespread overflows of molten lava, the Proterozoic era of 900 million years after the Laurentian revolution, and the Archeozoic era that began in obscurity. These five eras total 2,000 million years, leaving 2,500 million more years to get us back to the beginning of time on Earth.

During the pre-Archeozoic era, Earth was a molten mass, the surface of which was cooling down to form a solid crust of rock. The moist vapor that originally surrounded Earth gradually condensed to form water. This existed mostly as such, but some of it joined to the minerals that formed as the molten rock cooled, and now exists in combined solid form. But the interior of Earth has remained hot down to the present time, the temperature of its central core being estimated to be⁶, at least 1, 500º C.

Volcanic Eruptions

Terrifying and highly destructive volcanic eruptions frequently follow earthquakes, the volcanoes belching forth great masses of molten rock, large volumes of flaming gases, and such vast quantities of ashes that often the Sun is blotted out for many miles around. Some 2,500 volcanic eruptions have been recorded, of which over 2,000 have taken place in the Pacific Ocean region. More than 450 of these eruptions have occurred within historic times. The most famous volcanic eruption was that of Mount Vesuvius in A.D.79, which completely buried the cities of Pompeii and Herculaneum near Naples, Italy, killing thousands of people and destroying all the living things about the nearby countryside. In 1908 the city of Messina, Italy, was totally destroyed by such an eruption, some 85,000 people being killed. As recently as 1943 a mountain of molten rock and ashes was piled up to a height of two thousand feet within a few days in the center of what had been a prosperous farming community near Paricutin, Mexico. About 80 per cent of the known active volcanoes on Earth are of the submarine type, such as the one that shoved up a new island among the Azores in 1957. The Hawaiian Islands are of volcanic origin, having been built up at some points to a height of fourteen thousand feet above sea level from a starting base that was at least that far below it.

Associated with the high temperature that result in the volcanic eruptions that continue to occur from time and from place to place are the large amounts of steam and boiling water that come to the surface in many parts of Earth. Old Faithful Geyser in Yellowstone National Park, which erupts quite regularly about once an hour the year round and has been doing so for many years, is a good example. At Hot Springs, Arkansas, forty-seven such hot-water springs, with reputed curative values, attract many thousands of visitors every year. The most extensive and long-continued hot springs known are located in New Zealand and in Iceland, where they are of great importance because of their heat value during the cold and extended winter periods.

Earthquakes are often closely followed by what have long been termed tidal waves that have been known to travel across¹ the ocean at speeds up to 450 miles an hour with disastrous effects when they reach a shore. This term is a misnomer in that these waves have no connection with tides. A better word, coined by the Japanese, who have great deal of experience with them, is tsunami. Japan has been hit by more than a dozen tsunamis within the last half-dozen years, eight of them highly destructive. One of these, on June 15, 1960, is estimated to have destroyed² ten thousand homes and to have killed 27,000 people. In 1883 a tsunami, originating as a result of an eruption of Mount Krakatoa in the South Pacific, had a height of well over one hundred feet as it rolled in on the adjacent islands of Sumatra and Java, drowning many thousands of people. This wave was recorded on tidal gauges as far away as the English Channel.

Earthquakes, volcanoes, and tsunamis have had far-reaching effects on the topography of the land and on the floor of the sea. But they have not had as much effect on the whole as the continuously operating cold, heat, wind, and rain. These forces break the surface rocks down into smaller and smaller pieces and have marked dissolving and transporting effects. Some idea of the rate of movement of rock and soil debris by the water that falls as rain is provided by the estimated two million tons of sediment that is being carried down to the mouth of the Mississippi River and dumped into the Gulf of Mexico every year. Thus the mountains and hills tend to be worn away and the ocean floor to be built up with the material that is carried off them. The Appalachian Mountains, which came into existence as a result of a strong upward thrust from deep beneath the surface of Earth some 200 million years ago, are believed originally to have rivaled³ the European Alps in height.