Geology and Continental Drift

During the past century, considerable advances have been made in the field of geology. The discovery of plate tectonics has provided researchers with a unifying theory that explains many fundamental earth processes. Of the various hypotheses that led to plate tectonic theory, the most important was proposed by Alfred Wegener. Wegener's ideas on continental drift were supported by much evidence. However, perhaps because of its overwhelming implications, the theory was met with considerable resistance. Only in recent decades has scientific investigation collected sufficient evidence to definitively establish the validity of the continental drift hypothesis.

The theory of plate tectonics describes a lithosphere consisting of approximately the Earth's outer 100 kilometers. This layer comprises the uppermost mantle and all of the crust. Moreover, the lithosphere is broken up into several rigid plates. These include seven major structural plates and roughly twenty adjoining smaller plates (2:172-187). These rigid structures act as distinct mechanical units. They slide over a partially molten, plastic mantle zone known as the asthenosphere. According to the relative motions of adjacent plates, three different types of plate boundaries have been defined. These include the following: (1) divergent boundaries; (2) transform faults; and (3) boundaries of convergence (6:498-500). For one, divergent boundaries occur where plates are

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ther continental margins. Besides the geometric evidence, Wegener also noted the remarkable similarity of rocks, geologic structures, and fossils on opposite sides of the Atlantic. For instance, the Precambrian basement rocks in a large area of Northwest Africa are approximately 2 billion years old. Further, this Precambrian province is bordered on the east by rocks which are only about 550 million years old. In Africa, the boundary between the two provinces heads out to sea. During the 1960s, a search for the same boundary in Brazil confirmed its existence in the exact location as had been predicted (2:172-187). In fact, if the continents could be brought together in the correct orientation, the blocks would "line up precisely (7:8-17)." Likewise, Permian glacial deposits in South America, Africa, India, and Australia can also be explained by continental drift. It would be unlikely that several glaciers would form separately--some of which might occur near the equator. In contrast, if the southern continents were united to form a single landmass, one large continental glacier might account for all of the known deposits. Fossil evidence was also used to support continental drift ideas. For instance, vertebrate an
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Approximate Word count = 2680
Approximate Pages = 11 (250 words per page)