Word: land
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Dates: during 1940-1949
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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...
...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...
...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...
...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...