Science: Land from the Depths

Little drops of water, little grains of sand, Make the mighty ocean and the pleasant land.

Until recently scientists knew little more than the nursery rhyme about why the earth has oceans and land, or why most of its high land masses are concentrated on one side, opposite the Pacific Ocean. If the earth condensed from gases or from meteorlike particles, as many theories have held, it should be smooth and symmetrical with a deep layer of water covering the whole surface.

Within the last few years a wealth of new information—from seismology, astronomy and nuclear physics—has been brought to bear on the problem. Scientists are beginning to explain why the earth is not too smooth for such land animals as man to live on.

All Water. Nobel Prizewinner Harold C. Urey of the University of Chicago is one of the scientists who has arrived at a new theory of the earth’s birth and development. According to Urey, the earth and the moon were formed at the same time out of the primeval dust cloud around the sun. First materials to “precipitate” from the cloud were light stony silicates, which formed the cores of the earth and moon. But the earth’s core was bigger than the moon’s, and it attracted much more of the heavy iron which precipitated later from the dust cloud. For this reason, says Urey, the moon is lighter, volume for volume, than the earth.

After the iron had precipitated, the earth was a solid, fairly cool but basically unstable object. In its center was a ball of comparatively light rock. Around the rock was a thick layer of mixed iron and stone. Then came a very thin layer of stone. The whole great ball was smooth and symmetrical, with no land. Deep ocean covered the whole surface.

In this round-the-world ocean, Urey thinks, life evolved a billion and a half years ago. There is no record of these ancient creatures because they were all “pelagic,” living at or near the surface of the water. They did not develop heavy, easily preserved shells or skeletons because there was no land or shallow bottom for non-floating forms to live on.

Divided Land. But while life was evolving, the earth was heating up because of the radioactivity of its stony ingredients. The stony core got hotter and so did the stone-iron mixture. Eventually the outer mixture got soft enough for the iron to trickle down toward the center. Its “fall” of several thousand miles made the earth’s middle layers even hotter.

Then, says Urey, the light stone core began to float up through the iron like a tennis ball through molasses. As it approached the surface, land appeared for the first time; the oceans were crowded to one side, as on the third day of biblical creation.* For a while the earth had only a single continent (Pangea), but the continuing rise of the core material and its spreading out near the surface broke Pangea into chunks and carried them apart. His theory, says Urey, accounts for the remarkable fact, first pointed out by Alfred Wegener in his theory of continental drift, that the eastern coast of the Americas looks as if it had been split away from the western coast of the Old World.

* “And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear: and it was so.”—Genesis 1:9.