Our Earth is Two Billion Years Old

By Thomas Elway

New tidal theory explains how planets sprang from the sun.

ONE DAY, EONS AGO, AS THE lonely planetless sun, a rotating ball of white-hot gases, was drifting through space, it was partly disrupted by the close approach and gravitation of another large, swift-moving star.

The terrific attraction of the new star raised two enormous tides of gas on the sun, one on each side. As the bulging sun continued to revolve, two great waves of gaseous fire, thousands of miles high, rolled around its surface during each rotation.

These hot tides became too vast for the sun’s own gravitation to hold back. Bit by bit, gas was sprayed out from the tidal crusts as though the summit of an ocean tide erupted a giant geyser. So immense were these outbursts, so speedy the jets of white-hot gas as they escaped, that at last one long, sausage-shaped projection of gaseous solar matter stretched itself out on the side toward the passing star. Perhaps a similar cosmic blimp shot out from the other side, on the opposite side of the sun.

Some of this solar gas condensed, forming eight planets and some of their moons. One of these planets, as small beside its parent sun as a pea beside a volley ball, was the Earth.

The mighty celestial upheaval that created the Earth and the planets Mercury, Venus, Mars, Jupiter, Neptune, Saturn, and Uranus took place not more than 3,000,000,000 years ago and probably not less than 1,300,000,000. In round figures, then, it may be said that the birthday of the Earth occurred 2,000,000,000 years ago. Such, in substance, are science’s latest answers to the perennial questions: How old is the Earth? And how did it originate?

The new hypothesis regarding the Earth’s beginning, known as the tidal theory, was worked out principally by two distinguished British scholars, Sir James Jeans and Dr. Harold Jeffreys, both of whom have published books upon the subject within the last few weeks.

Among the happenings on the Earth’s birthday was the creation of a gaseous dusty veil behind which the sun is believed to have disappeared until the series of planets was fully formed. Dr. Jeffreys calls this veil the “resisting medium.” And it is from this that he derives his best hints about the latest date at which the Earth’s birthday can be placed.

Not all of the gas that spurted out of the sun during its encounter with the passing star collected into the globes of the planets. Much of this solar gas must have remained in space as gas or perhaps as myriads of tiny globules cooled to particles of solid dust. Dr. Jeffreys says that this vast cloud of dust and gas probably revolved around the sun, together with the newly created planets, like drapery on an Oriental dancer. The sun’s veil whirled with its owner, a cosmic dust-dress spangled with cooling worlds.

Thus spinning with the sun, this dust cloud would not slow up the motion of the planets in their orbits to make them fall ultimately into the sun, as a dust cloud at rest in space would do. But even the spinning cloud would have one planetary effect. lt would make the orbit of each planet as nearly a circle as possible. For only by moving in an exact circle around the sun could a planet reduce to a minimum the friction encountered from the dust cloud.

The orbits of the planets certainly were not all perfect circles in the solar system’s beginning, or even as near to circles as most of these orbits are today. Instead, the orbits of the inner planets, in particular, were probably stretched out into lengthened ellipses, like cross sections of footballs. For the planet Mercury, smallest of the solar system and closest to the sun, for example. Dr. Jeffreys has calculated what this elongation of the original orbit was just after the Earth’s birthday. Astronomers know what the orbit is now—very nearly a circle. The difference gives a measure of how potently the dust cloud of the sun’s veil must have worked on this orbit to make it a circle between that remote birthday and today.

It is possible, too, to calculate about how thick the original veil was and about how fast it would operate to convert the lengthened orbit of Mercury into a circle.

With the preceding data, that permits calculation of the orbit’s age—in other words, of the birthday of Mercury. And because Mercury and the Earth were born at the same time, this same date must have been the birthday of the Earth. It is safe to say, Dr. Jeffreys concludes, that this date cannot have been later than 1,000,000,000 years ago.

In searching for the earliest date that may mark the terrestrial birthday, help comes from the Earth’s crust. In some of the rocks are minerals containing uranium, a chemical element which turns very slowly into lead—about one half of it in five million years. Analyzing these minerals to discover how much uranium and how much lead they now contain, geochemists compute the number of years since each was formed in the Earth’s crust. Such age estimates, made from uranium and lead minerals in many parts of the Earth’s crust indicate, says Dr. Jeffreys, that the Earth’s crust cannot be younger than about 1,300,000,000 years, and probably is not older than 3,000,000,000 years. These are the limits between which must lie the missing date.

The 1,000,000,000 year minimum calculated from the orbit of Mercury is confirmatory. A midway date of about 2,000,000,000 years ago fits everything, including another limiting date which can be calculated from the time probably necessary for the former veil of dust and gases to be absorbed completely into the sun except for its small present remnant, probably a thin disk in the plane of the Earth’s orbit. This memento of the Earth’s creation is believed to be responsible for the dim, conical glow in the sky, pointing upward from the horizon like a thick finger, which may be observed on spring nights and which astronomers call the zodiacal light. Thus the Earth’s birth date ls written in the heavens and also stamped upon minerals which are buried deep beneath its own crust.

[Right, enormous tidal waves of fiery gas were formed on each side of the sun by the close approach of another star. At least one of these projections was pulled away.]

The tidal theory of the Earth’s origin really is a modification and elaboration of two earlier hypotheses. One, advanced in France in 1796 by Pierre Simon, Marquis de Laplace, is called the nebular hypothesis. Stating that all the planets of the solar system might have been formed out of matter left behind in the slow contraction of a great gas ball or nebula, the condensed mass of which is the present sun, this nebular hypothesis was taught universally in the schoolbooks until less than thirty years ago.

About a century after its promulgation, mathematicians found that the theory was impossible and it was abandoned. That left the Earth, so far as science knew, without a beginning, but other theorists hastened to bridge the gap.

Two professors then at the University of Chicago, the late Dr. T. C. Chamberlin and Dr. F. R. Moulton, who has since left the field of education for that of business, elaborated a new idea—the so-called planetesimal hypothesis. According to this idea, the Earth and the other planets, like the goddess Minerva who, in Roman mythology, sprang full-fledged from the head of Jupiter, were born from the body of their father, the sun. It was this theory which first pictured the great solar adventure as having resulted from the close approach of another star, whose proximity and gravitation disrupted the sun.

As has been seen, the part of the hypothesis was taken over by Sir James Jeans and Dr. Jeffreys. But another part, involving the so-called planetesimals, which gave the theory its name, has been rejected. These planetesimals, as their name implies, were considered to be very small, very numerous bodies like minute planets, pulled out of the sun by the near approach of the other star, soon chilled to solidity by the cold of space, and then gathered up one by one to form the mass of greater planets like the Earth, just as the globe continually encounters meteorites at present.

In the Chamberlin-Moulton interpretation, the Earth scarcely had a definite birthday. Like Topsy, it just grew, little by little and millennium by millennium as it gathered up the planetesimals in its path. Like the earlier nebular hypothesis, this portion ol the planetesimal hypothesis has proved to possess fatal mathematical flaws.

First of all, it implies that the Earth was never molten but merely grew together bit by bit out of ice-cold planetesimals. Certain geological facts, however, indicate that the Earth once was molten.

Secondly, mathematicians compute that such a cloud of planetesimals never could have combined into a solid planet but, if it changed into anything at all, would have produced a cloud of hot gas generated by mutual friction and collision.

Another defect of the hypothesis lies in the calculation that the planetesimals never could have produced the changes now believed actually to have taken place in the shapes of the planets’ orbits. Starting from the same idea of the near-coming star, the tidal theory assumes that the matter drawn out of the sun was gas instead of solid planetesimals.

The tidal theory of what happened on the Earth’s birthday explains many things about the solar svstem. It accounts for the fact that all the planets revolve around the sun in the same direction and very nearly in the same plane, like runners circling a central pillar in a stadium. Direction and plane, of course, are those in which the visiting star went by. The theory explains, too, why the outer planets are less dense than the inner ones, for the less dense chemical elements were probably more plentiful in the outer layers of the primitive sun and went farther when the gases jetted out during the encounter.

This suggests that the outer planets Uranus and Neptune, perhaps even Jupiter, may be worlds with atmospheres of light gases such as hydrogen or helium, instead of the denser gases of the Earthly air.

Sometime in the early youth of the Earth, before its crust could have much more than cooled, the adolescent planet suffered a similar convulsion to that which gave the planets birth, astronomers believe, but one more violent in proportion. This was the birth of the moon, a body believed to have been formed by the tidal disruption of an Earth still hot and liquid in its interior. The cause was the gravitation of the sun.

Some geologists hold that the deep basin of the Pacific Ocean is the scar left when the moon was torn away. It has not been possible, as yet, to calculate the ages of the Earth and the moon from their present mutual relations. But there are indications that this may be possible some day, when it will provide a check on the calculations from the orbit of Mercury.

In the moons of other planets, too, and in the orbits and characters of those mysterious small planets called asteroids circulating between Mars and Jupiter—objects still quite unexplained by any theory of solar system origin—it is probable that future astronomical mathematicians will find other possible measures of the Earth’s age; other celestial horse-teeth which may be examined to see how far time and circumstances have worn them down. Meanwhile, a date about two billion years ago is the experts’ best estimate for our planet’s birthday. Until some more exact figure is proved by further discoveries, this approximate date is likely to be accepted. 

Thomas Elway was a frequent contributor to “Popular Science.” This article is reprinted from the January, 1930, issue. Elway also authored the reprint of “Do Beavers Rule Mars?” that appeared in the July, 2013 issue of “Perihelion.”