The lithosphere is made up of the crust and the top part of the mantle. It is relatively cold and rigid.
The lithosphere is then broken into large pieces called tectonic plates.
The lithosphere is less dense than the mantle, so floats on top of it.
The tectonic plates move about 2.5 cm each year. This called continental drift.
The theory of continental drift was proposed by Wegner. However he was not a geologist, so he could not prove this. He was disbelived by other scientists until the 1960s, when new sea floor spreading evidence was found. Subsequent research led to Wegner's theory slowly becoming accepted.
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