continental drift

CONTINENTAL DRIFTCONTINENTAL DRIFT

Movement of the Earth’s continents relative to each other.

Abraham Ortelius (1596)

first put forward the hypothesis that continents ‘drift’

In his work Thesaurus Geographicus suggested that the Americas were “torn away from Europe and Africa by earthquakes and floods”

Alfred Wegener (1596)

Continents had once formed a single landmass before breaking apart and drifting to their present locations

First use the phrase “continental drift”

Evidence that continents ‘drift’

Similar plant and animal fossils are found around different continents shores, suggesting that they were once joined.

Examples:Fossils of Mesosaurus, a fresh water

reptile rather like a small crocodile, found both in Brazil and South Africa

Fossils of the land reptile Lystrosaurus from rocks of the same age from South America, Africa and Antartica

fossils of the Glossopteris, an ancient fern, are found in South America, Africa, Antarctica, India, and Australia.

It was hypothesized that such a distribution could only come about if the continents were all part of the one super-continent.

The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence.

Wegener noted that the rock sequences in South America, Africa, India, and Australia are very similar. Wegener showed that the same three bottoms layers occurred on each of the continents.

The bottom layer, called tillite, was thought to be of glacial origin.

The middle layer composed of coal beds, shale and sandstone contained Glossopteris fossils, as did the bottom tillite layer.

The top most and youngest layer is lava flows. Such a strong similarity in the rock record of these localities, now separated by great geographic distance, lent credence to Wegener's notion of continental drift.

The occurrence of glacial features in the geologic record of South America, Africa, India ,and Australia provides further evidence for the notion of continental drift. Glaciers affected all or part of these continents at the same time in Earth history.

Rejection of Wegener’s theory

One problem was that the a plausible driving force was missing.

As late as 1953, Carey introduced the theory of plate tectonics thus the theory of continental drift was rejected by the physicist Scheiddiger