CONTINENTAL DRIFT

In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth’s crust slowly drift atop a liquid core . The fossil record supports and gives credence to the theories of continental drift and plate tectonics.

Wegener hypothesized that there was a gigantic supercontinent 200 million years ago, which he named Pangeae. meaning “All Earth”.

Pangeae started to break up into two smaller supercontinents, called laurasia and Gondwanaland, during the jurassic period. By the end of the cretaceous period, the continents were separating into land masses that look like our modern day continents.

FOSSIL EVIDENCE IN SUPPORT OF THE THEORY

Eduard Suess was an Austrian geologist who first realized that there had once been a land bridge connecting South America, Africa,India, Australia, and Antartica. He named this large land mass Gondawanaland (named after a district in india where the fossil plant Glossopteris was found). This was the southern supercontinent formed after pangeae broke up during the jurassic period. Suess based his deduction on the fossil plant Glossopteris, which is found throughout India, South America, Southern Africa, Australia and Antartica.

Fossils of Mesosaurus (one of the first marine reptiles, even older than the dinosaurs) were found in both South america and south africa. These finds, plus the study of sendimentation and the fossil plant Glossopteris in these southern continents led alexander duToit, a south african scientist, to bolster the idea of the past existence of a supercontinent in the southern hemisphere, Eduard Suess’s Gondwanaland. This lent further support to A. Wegener’s.

Continental drift The possible movement of the continents relative to one another in the geological past was first outlined at length by Alfred Wegener in 1912, and it became a matter of controversy for many years. During the 1960s, however, new evidence came to light which conclusively demonstrated that drifting had taken place;

The evidence came largely from the study of magnetism in the rocks of the Earth’s crust and from detailed surveys of the ocean floors. These demonstrated that the continents have not remained in their same ralative position and that the ocean floors are much younger than the continents they separate.

An extensive glaciation in carboniferous times affected what is now southern Africa, india, south Australia and parts of brazil and argentina, as evidenced by glacial deposits found in all those areas. This glaciation is readily explained if the glaciated lands were originally parts of Gondwanaland, the earth’s south pole at the time being situated at about the centre of the area.

When the continet broke up and its several parts began to separate When the continet broke up and its several parts began to separate., some 200 my ago, Africa and india moved northwards and eventually impinged upon marginthe soiuthern margin of the Eurasian continent, where great fold mountain systems –the Atlas, Alps and Himalayas –were ridged up in early Teritary times. It is estimated that Idian block moved nothwards at arate of some 20 cm per year to reach its present position.

It will be noticed that between the drifting continents lie the oceanic ridges. These, and tge ocean floor on the either side of them, provide evidence that explains the mechanism for continental drift.