Theories regarding evolution of Earth's crust - Jankari store

Theories regarding evolution of Earth's crust

Introduction:

Earth crust is the thinnest and the most basic layer that makes up the Earth. The crust is referred to as a chemical layer that has varying chemical composition. It is one of the five recognised Physical layers of the earth and is differentiated to show distinct chemical properties occuring at each layer. The earth's Crust along with the upper mantle has neccessary role in the creation and destruction of the crustal surface on which living organism exists. 

Fig: Structure of the Earth and it's Chemical

and physical compositions

# Types of Crust : 

There are two types of crust. 

i) Oceanic crust 

ii) Continental crust

Fig: Types of Earth's crust 

i) Oceanic Crust 

-Composed of different types of basalt rocks.

- dense (2gm/cm³)

ii) Continental Crust 

-Composed of different types of granite rocks. 

-Slightly less dense (2-7 gm/cm³)

#Origin / formation of Crust : 

There are three main theory regarding the Origin of the earth's crust.

(i)The Inhomogeneous model or the accretion. model:

→It explains that the earth's crust was formed during the accretion of planet, with lighter and volatile elements (like Nitrogen, Hydrogen, Carbon dioxide) forming thin layes on the primitive planet which became the crust.

→This model suggests that non-volatile elements Can only be found in the mantle; however this theory is rejected on the basis that non-volatile elements Such as uranium amd thorium are found on the earth's crust.

(ii) Impact model: 

→The Impact model suggests that asteroids and the other objects that impacted on earth resulted into melting of the earth and formation of earth's crust.

→The Oceanic crust which is mainly composed of basalt, Could have been formed by a basalt astroids that impacted the Earth. However, from the observation of the moon, basalts found on the lunar Surface were not due to collision of asteroids. Furthermore, the number of basalts produced from an impact event was too insignificant to form crusts.

→ In addition, a majority of the impact events on Earth happened after oceanic curst were formed. Therefore, this theory is unlikely to accept.

(iii) The terrestial model:

→The terrestial is the most likely explanation on the formation of the Earth's crust.

→This model explains that the crustal origin of the Earth was due to its internal processes.

→After the late accretion of the Earth, heat retained by the earth resulted in the complete melting of the upper mantle, Which formed a magma ocean that covered the surface of the earth. As the Earth cooled, the magma ocean crystallised to form a widespread crust.

→Another possible explanation was that the melted upper mantle rose up the surface to form a crust..

→The terrestrial model is most accepted explanation, as the magma ocean could explain some properties of Earth's crust. The uniform composition of the crust could be formed by a homogeneous magma ocean. The layered composition of Earth's crust may be due to the cooling of magma ocean over time, thus, the terrestrial model most likely to explains the formation of the Earth's Crust.

# Conclusion: 

The cuust is the superficial layer of the Earth which has a truly dynamic and fascinating features. from its early Origin as the hot lifeless covering shell of the earth to the home of all life on Earth, it has changed over the geological time span of the earth's history and continues to evolve till date. Thus it truly an amazing and astonishing thing to be learn and behold (observe).