Layers of the Earth

In a bid to find out what lies beneath the surface of the Earth, scientists have left no stone unturned. After years of research, scientists have finally concluded that there are four layers of the Earth. These four layers, namely the crust, mantle, outer core and the inner core, were formed in the process of cooling of the Earth during its formation.

Interior Structure: Main Layers of the Earth

Our understanding about the interior structure of the Earth is based on various geographical studies, including analysis of the seismic waves, experiments with crystalline solids at high pressure, etc. Given below are details of each of these layers as shown in the diagram of the Earth layers.

Crust: The crust is the outermost layer of the Earth, with a depth ranging between 3 - 40 miles. It is basically divided into two portions - the continental crust, with an average depth of 22 - 25 miles, and the oceanic crust, with an average depth of 3 - 6 miles. The continental crust is composed of sodium potassium aluminum silicate rocks, which are a lot like granite, whereas the oceanic crust is composed of dense iron magnesium silicate rocks, which are a lot like basalt. These rocks which make up the crust of the Earth are broadly categorized into two types - sial (silica + alumina) and sima (silica + magnesium).

Mantle: The second layer of the Earth is the mantle, which is also the thickest layer of the planet with its depth extending for about 1,800 miles. The mantle is composed of silicate rocks, relatively rich in terms of iron and magnesium content. Though solid, this layer of the Earth is also ductile to some extent - a property which can be attributed to the high temperature of the inner Earth. The ductility goes on increasing as you travel deeper, owing to the fact that the pressure increases with depth. The viscosity is highest at the point where mantle and core adjoin.

Core: It is virtually impossible to reach the core, which is the innermost layer of the Earth, to determine its condition, and thus, whatever information we have about the Earth's core is mainly based on seismic measurements. The core is basically divided into two portions - the solid inner core and the liquid outer core.

• Inner Core: The solid inner core is believed to be composed of iron and nickel. This is based on the belief that during the formation of the Earth, melting caused the denser substances to settle at the center, while lighter substances floated to the surface in a process called the planetary differentiation. According to the dynamo theory, the liquid outer core spins around the inner core, which is believed to be the trigger factor for the Earth's magnetic field.
• Outer Core: The liquid outer core is believed to be composed of iron mixed with nickel, along with some traces of other lighter elements. This part of the interior of the Earth is typically characterized by intense pressure and high temperature. In fact, scientists believe that the temperature of the inner core is more than the temperature of the surface of the Sun. The solid state of the inner core can be attributed to the intense pressure in this region which makes sure that the entire matter doesn't move.

This was a brief information about the four main layers of the Earth - the crust, mantle, inner, outer core and the inner core. Similarly, the Earth's atmosphere is also divided into five layers - the troposphere, stratosphere, mesosphere, thermosphere and the exosphere. These atmospheric layers of the planet are as important as the inner layers when it comes to making the Earth the only planet with life.