The events of which I write must have occurred somewhat more than 2 billion years ago. As nearly as science can tell, that is the approximate age of the earth, and the ocean must be very nearly as old. It is possible now to discover the age of the rocks that compose the crust of the earth by measuring the rate of decay of the radioactive materials they contain. The oldest rocks found anywhere on earth—in Manitoba—are about 2.3 billion years old. Allowing 100 million years or so for the cooling of the earth’s materials to form a rocky crust, we arrive at the supposition that the tempestuous and violent events connected with our planet’s birth occurred nearly 2½ billion years ago. But this is only a minimum estimate, for rocks indicating an even greater age may be found at any time.[2]
The new earth, freshly torn from its parent sun, was a ball of whirling gases, intensely hot, rushing through the black spaces of the universe on a path and at a speed controlled by immense forces. Gradually the ball of flaming gases cooled. The gases began to liquefy, and Earth became a molten mass. The materials of this mass eventually became sorted out in a definite pattern: the heaviest in the center, the less heavy surrounding them, and the least heavy forming the outer rim. This is the pattern which persists today—a central sphere of molten iron, very nearly as hot as it was 2 billion years ago, an intermediate sphere of semiplastic basalt, and a hard outer shell, relatively quite thin and composed of solid basalt and granite.
The outer shell of the young earth must have been a good many millions of years changing from the liquid to the solid state, and it is believed that, before this change was completed, an event of the greatest importance took place—the formation of the moon. The next time you stand on a beach at night, watching the moon’s bright path across the water, and conscious of the moon-drawn tides, remember that the moon itself may have been born of a great tidal wave of earthly substance, torn off into space. And remember that if the moon was formed in this fashion, the event may have had much to do with shaping the ocean basins and the continents as we know them.
There were tides in the new earth, long before there was an ocean. In response to the pull of the sun the molten liquids of the earth’s whole surface rose in tides that rolled unhindered around the globe and only gradually slackened and diminished as the earthly shell cooled, congealed, and hardened. Those who believe that the moon is a child of Earth say that during an early stage of the earth’s development something happened that caused this rolling, viscid tide to gather speed and momentum and to rise to unimaginable heights. Apparently the force that created these greatest tides the earth has ever known was the force of resonance, for at this time the period of the solar tides had come to approach, then equal, the period of the free oscillation of the liquid earth. And so every sun tide was given increased momentum by the push of the earth’s oscillation, and each of the twice-daily tides was larger than the one before it. Physicists have calculated that, after 500 years of such monstrous, steadily increasing tides, those on the side toward the sun became too high for stability, and a great wave was torn away and hurled into space. But immediately, of course, the newly created satellite became subject to physical laws that sent it spinning in an orbit of its own about the earth. This is what we call the moon.
There are reasons for believing that this event took place after the earth’s crust had become slightly hardened, instead of during its partly liquid state. There is to this day a great scar on the surface of the globe. This scar or depression holds the Pacific Ocean. According to some geophysicists, the floor of the Pacific is composed of basalt, the substance of the earth’s middle layer, while all other oceans are floored with a thin layer of granite, which makes up most of the earth’s outer layer. We immediately wonder what became of the Pacific’s granite covering and the most convenient assumption is that it was torn away when the moon was formed. There is supporting evidence. The mean density of the moon is much less than that of the earth (3.3 compared with 5.5), suggesting that the moon took away none of the earth’s heavy iron ore, but that it is composed only of the granite and some of the basalt of the outer layers.
The birth of the moon probably helped shape other regions of the world’s oceans besides the Pacific. When part of the crust was torn away, strains must have been set up in the remaining granite envelope. Perhaps the granite mass cracked open on the side opposite the moon scar. Perhaps, as the earth spun on its axis and rushed on its orbit through space, the cracks widened and the masses of granite began to drift apart, moving over a tarry, slowly hardening layer of basalt. Gradually the outer portions of the basalt layer became solid and the wandering continents came to rest, frozen into place with oceans between them. In spite of theories to the contrary, the weight of geologic evidence seems to be that the locations of the major ocean basins and the major continental land masses are today much the same as they have been since a very early period of the earth’s history.
But this is to anticipate the story, for when the moon was born there was no ocean. The gradually cooling earth was enveloped in heavy layers of cloud, which contained much of the water of the new planet. For a long time its surface was so hot that no moisture could fall without immediately being reconverted to steam. This dense, perpetually renewed cloud covering must have been thick enough that no rays of sunlight could penetrate it. And so the rough outlines of the continents and the empty ocean basins were sculptured out of the surface of the earth in darkness, in a Stygian world of heated rock and swirling clouds and gloom.
As soon as the earth’s crust cooled enough, the rains began to fall. Never have there been such rains since that time. They fell continuously, day and night, days passing into months, into years, into centuries. They poured into the waiting ocean basins, or, falling upon the continental masses, drained away to become sea.
That primeval ocean, growing in bulk as the rains slowly filled its basins, must have been only faintly salt. But the falling rains were the symbol of the dissolution of the continents. From the moment the rain began to fall, the lands began to be worn away and carried to the sea. It is an endless, inexorable process that has never stopped—the dissolving of the rocks, the leaching out of their contained minerals, the carrying of the rock fragments and dissolved minerals to the ocean. And over the eons of time, the sea has grown ever more bitter with the salt of the continents.
In what manner the sea produced the mysterious and wonderful stuff called protoplasm we cannot say. In its warm, dimly lit waters the unknown conditions of temperature and pressure and saltiness must have been the critical ones for the creation of life from non-life. At any rate they produced the result that neither the alchemists with their crucibles nor modern scientists in their laboratories have been able to achieve.
Before the first living cell was created, there may have been many trials and failures. It seems probable that, within the warm saltiness of the primeval sea, certain organic substances were fashioned from carbon dioxide, sulphur, nitrogen, phosphorus, potassium, and calcium. Perhaps these were transition steps from which the complex molecules of protoplasm arose—molecules that somehow acquired the ability to reproduce themselves and begin the endless stream of life. But at present no one is wise enough to be sure.
2
Our concept of the age of the earth is constantly undergoing revision as older and older rocks are discovered and as methods of study are refined. The oldest rocks now known in North America are in the Canadian Shield area. Their precise age has not been determined, but some from Manitoba and Ontario are believed to have been formed about 3 billion years ago. Even older rocks have been discovered in the Karelia Peninsula in the U.S.S.R., and in South Africa. Geologists are generally of the opinion that present concepts of geologic time will be considerably lengthened in the future. Tentative adjustments of the length of the various periods have already been made (see chart above) and the age of the Cambrian has been pushed back 100 million years compared with the dating assigned to it a decade ago. It is in that immense and shadowy time that preceded the Cambrian, however, that the greatest uncertainty exists. This is the time of the pre-fossiliferous rocks. Whatever life may have inhabited the earth during that time has left few traces, although by indirect evidence we may infer that life existed in some abundance before its record was written in the rocks.
By studies of the rocks themselves geologists have established a few good benchmarks standing out in those vast stretches of time indicated on the chart as the Proterozoic and Archeozoic Eras. These indicate a billion-year age for the ancient Grenville Mountains of eastern North America. Where these rocks are exposed at the surface, as in Ontario, they contain large amounts of graphite, giving silent testimony to the abundance of plant life when these rocks were forming, for plants are a common source of carbon. An age-reading of 1,700,000,000 years has been obtained in the Penokean Mountains of Minnesota and Ontario, formerly known to geologists as the Killarney Mountains. The remains of these once lofty mountains are still to be seen as low, rolling hills. The discovery of even older rocks in Canada, Russia, and Africa, dating back more than 3 billion years, suggests that the earth itself may have been formed about 4½ billion years ago.