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Continental drift

Continental drift was a theory proposed in 1912 by Alfred Wegener which postulated the movement of continents. This theory is a part of the concept of plate tectonics. Continents have been drifting for hundreds of millions of years.

Cause of Continental Drift

Through convection, heat flows from the Earth's core to its crust. As the asthenosphere is plastic, the lithosphere floats along the convection currents.

Initially ridiculed in North America the idea was widely accepted in Europe by the 1950s. In the 1960s geological research conducted by Robert Dietz[?], Bruce Heezen, and Harry Hess[?] led to acceptance in North America. The similarity of Southern continent fossil faunas and some geological formations led the relatively small number of Southern hemisphere geologists to conjecture as early as 1900 that all the continents had once been joined into a supercontinent. Various Data

South America and Africa are moving apart at 3cm per year, due to the Mid-Atlantic Ridge.

Evidence for continental drift

Nowadays there exists lots of evidence for continental drift. The most obvious is the way in which the continents seem to fit jigsaw-like (for example Africa and South America) together when looked at on a map. More scientific evidence comes in the form of plant and animal fossils of the same age found around different continent shores, suggesting that they were once joined. For example the fossils of the freshwater crocodile found in Brazil and South Africa. Another illustrative example is the discovery of fossils of the aquatic reptile Lystrosaurus[?] from rocks of the same age from locations in South America, Africa, and Antarctica. There is also living evidence - the same animals being found on two continents. An example of this is a particular earthworm found in South America and South Africa.

There exist two main forms of more geological evidence evident: rock sequences and magnetic stripes. When the rock strata of the tips of separate continents are very similar it suggests that these rocks were formed in the same way implying that they were joined initially. For instance, some parts of Scotland contain rocks very similar to those found in eastern North America. The second piece of evidence arises when the rocks were formed from magma erupting out of a volcano. When this happens the iron particles align with the earth's magnetic field and set in this position. As the earth's magnetic field flips every half-million years, strips of land of alternating magnetic orientation are formed - symmetrical from the volcano. This showed how some plates are moving away from each other.

See also: seafloor spreading



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