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Geochemical Evolution of the Earth


We all Are aware about different internal layers of the Earth such as Crust, Mantle and Core.


But do you know that how these layers formed?

Why they have different mineral composition?


In this article, we will try to understand the answer of these questions.


Meaning of Differentiation of Earth


The process of flow and accumulation of heavy element in inward direction (Core) and lighter element towards outward is known as Differentiation of Earth.


During Differentiation, the heavier elements, such as iron and nickel, sunk to the center, and the lighter elements floated to the top. This led to a layered structure of the Earth


CAUSES OF DIFFERENTIATION


HEAT or High temperature act as a driving force for differentiation of earth.

The earth heated up by a combination of three processes of Radioactive decay of U. Th

and K, Gravitational compression and Meteorite impacts.


Process: how it happened.?


The Planet earth formed about 4.6 billion years ago in a fully molten state. Initially, Earth has Mixture of heavy and lighter element. Then as time passage, Similar elements stick together and creating a solid mass. The heat generated in this process melts the particles. The heavier elements sink to the centre because of gravity, creating the Earth's solid core.


Description-Early earth heats up due to radioactive decay and compression. Over time the temperature of the planet interior rises towards the Fe-melting. The iron “drops” follows gravity and accumulates towards the core. Lighter materials, such as silicate minerals, migrate upwards in exchange. These silicate-rich materials may well have risen to the surface in molten form, giving rise to an initial magma ocean.


After the initial segregation into a central iron and nickel dominated core and an outer silicate shell, further differentiation occurred into an inner solid and outer liquid core due to pressure effect as solid iron is more densely packed than liquid iron.


Differentiation also occuered between the mantle which is dominated by Fe &Mg silicates and the crust which is dominated by K &Na silicates.


Initially large portions of the crust might have been molten the so called magma ocean. later it would have cooled to form a layer of basaltic crust which is present beneath the oceans today. Continental crust would have formed later.


In this way, we find present day layered structure of earth


Inner Core:About 1200 km thick, consists of mainly iron and nickel in a molten state due to the intense heat and pressure.


Outer Core: The outer core is about 2300 km thick, and consists also mainly of nickel

and iron, but in a solid form. It represent Liquid state.


Mantle: The mantle, about 2900 km thick, is rich in

elements such as oxygen,

silicon, magnesium, and iron.Olivine is a dominant mineral here.


Crust: The crust is composed of the lightest elements of the earth, and varies in thickness from about 10 km beneath the oceans to about 70 km thick beneath the

continents.


And here The story of differentiation of earth end..


By,

Sneh Kumar Maurya

JRF at University of Lucknow

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