wegener's theory

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Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years.

Diagram showing phase 1 of continental drift Diagram showing phase 2 of continental drift Diagram showing phase 3 of continental drift Diagram showing phase 4 of continental drift
1. About 200 million years ago the Earth is thought to have consisted of one super-continent called Pangaea 2. The single land mass began to crack and divide, due to the slow currents of magma beneath it 3. The new continents continued to drift apart 4. This is the current position of the continents

Wegener's evidence for continental drift was:

  • The same types of fossilised animals and plants are found in South America and Africa.
  • The shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle.
  • Matching rock formations and mountain chains are found in South America and Africa.
  Photo of a mountain in the Himalayas
 
Mount Cho Oyu in the Himalayas

Before Wegener developed his theory, it was thought mountains formed because the Earth was cooling down, and in doing so contracted. This was believed to form wrinkles, or mountains, in the Earth's crust. If the idea was correct, however, mountains would be spread evenly over the Earth's surface. We know this is not the case.

Wegener suggested mountains are formed when the edge of a drifting continent collides with another, causing it to crumple and fold. For example, the Himalayas were formed when India came into contact with Asia.

Criticisms of Wegener's Theory

Wegener's theory of continental drift was rejected by many geologists. Some of the reasons for this were:

  Photo of Alfred Wegener
  Alfred Wegener
(1880 - 1930)
  • The movement of continents could not be detected (because they only move by a few centimetres per year).
  • No-one could provide a good explanation of how whole continents could move apart.
  • Wegener was not a geologist (he trained as an astronomer and meteorologist).
  • There were other, simpler, explanations for the same evidence.
  • It was felt his idea was too big for the evidence at hand.

It was only in the 1960s, long after Wegener's death, that the theory of continental drift was accepted by scientists. The current theory is that the Earth's crust and uppermost mantle is made up of seven or eight giant slabs (called tectonic plates), with several smaller ones.

 

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