Continental drift

The concept of Continental drift was first proposed by Alfred Wegener in 1912 considering the apparent way that the shapes of continents on either side of the Atlantic Ocean seem to fit together (for example Africa and South America). The similarity of Southern continent fossil faunas and some geological formations had led a relatively small number of Southern hemisphere geologists to conjecture as early as 1900 that all the continents had once been joined into a supercontinent. The concept was initially ridiculed by most geologists, lacking an explanation as to how continents could in fact move. The idea of continental drift did not become widely accepted as theory until the 1950s in Europe. By the 1960s geological research conducted by Robert Dietz, Bruce Heezen, and Harry Hess led to acceptance among North American geologists.

The Theory of Continental Drift is a part of the concept of plate tectonics. Continents have been drifting for hundreds of millions of years. Through convection of the mantle, heat flows from Earth's core to its crust. As the asthenosphere is plastic, the brittle lithosphere floatss along these convection currents.

Various Data

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

Evidence for continental drift

Evidence for continental drift is now extensive, in the form of plant and animal fossils of the same age found around different continent shores, suggesting that these shores 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 rockss 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 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.




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