Geological History Is Beneath: In the past they were almost entirely concerned with studying the rocky crust of the continents. They tended to ignore, therefore, the 71% of the earth's surface that is covered by water. Discoveries about the sea Floor have, over the past few years, forced earth scientists to change their viewpoint. The key to the earth's geological history is beneath the sea. The rocks of the continents are ancient in places, as old as three billion years, whereas the oldest rocks of the ocean floors, mere striplings, are younger than 200 million years. Thus, the earth is a dynamic place on which the crust beneath the oceans appears to be continuously created and destroyed. (See BREAKTHROUGH, p. 324.)
Although scientists can gain much information about the composition and history of the earth from laboratory and seismic methods, they are particularly interested in examining real samples of its internal material. Geologists have recently gained a view of thousands of years of polar history in a National Science Foundation (NSF) project in which drillings are being made through one and a half miles (2.4 km) of the Antarctic ice cap to the rock beneath.
As living organisms have always undergone continuous evolution, their fossil remains can be used to identify rocks of comparatively similar geological time. The fossil litter within sedimentary rocks enables palaeontologists to recognize different strata of the same age. And it can be logically deduced from the law of superposition that the remains of primitive life forms occur in rocks lying beneath those containing more advanced forms.
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