The most important feature of the crust is that it is not stable. It is a constantly changing stage upon which this drama will be unfolded, and the scene-shifter in this great theatre is called continental drift.
At some stages in history, the continents have been assembled into huge “supercontinents” which over millions of years are then broken apart into smaller fragments. These drift around until they are once more re-assembled but into a different configuration. Each cycle takes between 300 to 600 million years.
We are not sure when this process began. Continental drift squashes and changes the continents so much that it is very hard to work out their early history. Continental drift is still happening today and is important because it causes volcanic eruptions, earthquakes and tsunamis. Some people also think that it is one .
Today the theory of plate tectonics, which includes continental drift, forms a framework for the study of geology and the Earth. For the evidence that continental drift is happening, .
It is the heat generated by decay inside the Earth which drives this process. The center of the Earth contains uranium and other heavy atoms which decay, releasing energy. That is why the Earth’s core is hot.
Hot rock in the core turns to a viscous liquid (magma) which can rise up through the cooler rocks above. Magma rises up through the and spreads out on the surface to form the ocean floor. As the ocean floor spreads it pushes the continents ahead. They move one or two centimeters each year.
As the continents move around they sometimes hit each other, creating mountains. This is how the Alps and the Himalayas were created. Mountains like this are on the inside of continents.
Sometimes continents do not hit head on, but rub past each other. Since they do not have smooth edges, the rubbing is jerky and uneven. Pressure builds up and is then suddenly released. This creates earthquakes. The San Andreas Fault in California is an example of this.
On the Earth today, volcanoes are mainly formed by continental drift. As lighter continental rocks are pushed over heavier oceanic ones, friction melts the rock which rises and produces a volcano.
Volcanoes formed by continental drift
Such volcanoes are often found near the edges of continents. As it sinks it melts and hot rock rises up, creating volcanoes along the coast. The Andes are being created in this way. Sometimes the volcanoes lie in an arc just off the coast of a continent. The islands of Japan are being formed like this.
Vaalbara Supercontinent 3.6 to 2.1 bya
We have little idea what the continents looked like during the Archaean Era, but it seems that parts of what is now Africa and Australia were once assembled into a supercontinent called Vaalbara. It seems to have been assembled by continental drift between about 3.6 bya and 3.1 bya, during the Archaean Era.
It was then broken apart between about 2.7 and 2.1 bya.
Various theories exist about the climate during the Archaean. Some claim it was hot, others say warm and some think it was cold. The warm theory is partly based on the fact that, for the molecules of life to be formed, a source of energy would be necessary.
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