Chemical Composition and Layering of Earth

E. Suess has thrown light on the chemical composition of the earth’s interior. The crust is covered by a thin layer of sedimentary rocks of very low density. There are three major and almost concentric layers in the earth. E. Suess explains these, and they are SIAL, SIMA and NIFE.

SIAL

It is the topmost layer of the earth found just below the sedimentary thin cover of the crust. Silicon (Si) and Aluminum (Al) are two very important elements found in abundance in this layer. They are named SIAL.

The average density of this layer is 2.75 to 2.90 g/cm3, and its average depth is 40 km. It is very thin below oceanic water (5 to 10 km), but below the mountains, it is very thick (up to 70 km). The main rock in this zone is granite.

SIMA

It is the second layer after SIAL from the surface towards the interior. It is named after Silicon (SI) and Magnesium (MA), as both elements are abundant in this layer. It is a very thick layer which goes almost up to a depth of 2900 km. It starts from a depth of 70 km below continents, while below the oceans, it is 5 to 10 km deep.

Its average density varies from 2.90 g/cm³ to 4.75 g/cm³. The main rocks in this layer are silicates of magnesium and iron. This layer is largely composed of basalt.

NIFE

It is the innermost layer of the earth. This layer is made up of Nickle (NI) and Ferrous (FE), and so it is named NIFE. It is just below the SIMA from a depth of 2900 km to the earth’s centre encircling from all directions.

Nickle and Ferrous are found here. They are very heavy and denser elements. Therefore, this layer has a higher density. Its density is about 11 to 12 g/cm3. It is believed that the existence of nickel and iron in the NIFE is the main cause of the earth’s magnetic properties.

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