The Structure of Earth

Chemical Composition And Layering System Of The Earth

           E.Suess has thrown light on the chemical composition of the earth's interior. The earth is made up of several concentric layers. The outer layer is the earth's crust-the lithosphere. The crust is covered by a thin layer of sedimentary  rocks of very low density. This layer is composed of crystalline rocks, mostly silicate matter. The dominant minerals are feldspar and mica. The upper part of this layer is composed light silicate matter while heavy silicate matter dominates in the lower part. Suess identified three zones of different matter below the outer thin sedimentary cover.

1. SIAL -is located just below the outer sedimentary cover is composed of granites. this layer rich in silicates and aluminium minerals. it is sometimes equated with the continental crust because it is absent in the wide oceanic basin. But sial is a geochemical term rather than a plate tectonic term. Geologists often refers to the rocks in this layer as felsic, because they contains high levels of feldspar, an aluminium silicate mineral series. It's main mineral constituents are silica and alumina so it is collectively referred to as sial. It has an average density of 2.7-28 (kg/m3) which is lower than sima because presence of large amount of aluminium and decreased amounts of iron and magnesium. The base of the sial is not a strict boundary, it penetrates into the denser rocks of sima.The sial runs between 5 and 70 km deep.The conrad discontinuity has been proposed as the boundary but little known about it.

2.SIMA- It is just beneath the sialic layer. It is continuous zone of denser basaltic rocks forming the ocean floors, comprising mainly silica, iron and magnesium. It is therefore called sima and has an average density of 3. The sial and sima together form the earth crust. Since sial is lighter than sima, the continents is said to be floating on a sea of denser sima.

3.NIFE is located just below the sima layer.This layer is composed of nickel(NI) and iron (Fe). these metals are responsible for the high density of (11kg/m3) of this layer. The diameter of this layer is 6880 km

 references.

1.certificate physical and human geography by gc leong

2.physical geography by savindra singh

3.https://en.wikipedia.org/wiki/Sial

4.http://www.earthonlinemedia.com/