Question

why is the continental crust called Sial

Answer 1

The top layer of the earth is called the crust. Now, it’s important to know that there is two different kind of crusts: sial, and sima. Sima is the oceanic crust. Sial is the continental crust. The continental crust is a busy place, we all live on it! Sial is primarily made of the mineral silica as well as aluminum ore. In fact, the word sial is a word derived from the names silica and aluminum.

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Sial vs. Sima
How is sial different from sima? Besides the obvious that one is under the ocean and the other is not, there are lots of differences! It is much lighter than the sima beneath it. It is also thicker, 22 miles thick on average and not as dense as sima.

Because it is less dense, the sial “floats” on top of the sima. We call this floating ‘isostasy‘. You can see it when you notice that all the continents can fit together in a certain place. Before they started drifting around, they once all formed together to create Pangaea. But that is another story.

Sial is more complex in its structure than sima. It is made at subduction zones. New sial also occurs around continental margins. There, sediment from a nearby trench adds to the continent. These margins are marked by volcanoes.

Answer 2

This layer is sometimes called sial because its bulk composition is more felsic compared to the oceanic crust, called sima which has a more mafic bulk composition. ... About 40% of Earth's surface is currently occupied by continental crust.

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