Continental drift (plate tectonics)
The theory of continental drift was proposed at the beginning of the last century by German scientist Alfred Wegener.
Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and, as it cooled down, it To decrease in size or volume.. This process formed wrinkles, or mountains, on the Earth’s crust.
If this was the case, then mountains would be spread evenly over the Earth’s surface. We know that this is not the case.
Wegener’s theory
Wegener suggested that mountains formed when the edge of a drifting continent collided with another, causing it to crumple and fold. For example, the Himalayas formed when India came into contact with Asia.
It took more than 50 years for Wegener’s theory to be accepted. One of the reasons was that it was difficult to work out how whole continents could move. It was not until the 1960s that evidence of convection currents within the mantle was discovered to support the theory fully.
This slideshow explains Wegener’s theory.
Image caption, Wegener’s theory
Earth around 200 million years ago – all the continents are merged into one supercontinent
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Evidence for continental drift
What was the evidence for Wegener’s theory?
- The match in shape between the east coast of South America and the west coast of Africa suggests both were once part of a single continent (meaning that the outlines of the continents fit together like a jigsaw).
- There are similar patterns of rocks on both sides of the Atlantic.
- There are similar fossils on both sides of the Atlantic – including the fossil remains of land animals that would have been unable to swim across from one side to the other.
