Crust - Thinnest & Lightest Layer
Crust is differentiated into Continental Crust and Oceanic Crust
|No||Oceanic Crust||Continental Crust|
|2||Denser & Heavier (3 - 3.5 )||Less Dense & Lighter (2- 2.5)|
|3||Felsic, Predominance of NFMS, High Silica content|
|4||Thinner (1-3)Km||Thicker (80)Km|
|5||Fundamental||Formed from Oceans|
Origin and evolution of the earth's crust
- First crust - the first crust was formed was probably because of cooling off the planet from the ancient nebula.
- Meteorite impacts - In the absence of atmosphere, the earth surface must have been overwhelmed by meteorite impacts that must have cracked the earth's crust at numerous places resulting in pressure release of the mantle, mantle turbulence, first convection cells and numerous volcanic eruptions on the surface.
- Mafic eruptions - The eruptions must have been extremely mafic even after partial melting of the mantle rocks.
- First oceanic crust / Basalt - These mafic eruptions must have subducted many times and recycled before the first oceanic crust. Basalt was formed.
- First microcontinent - The subduction of these 1st ocean basalts must have created the first continental andesite. These were the first microcontinents and once formed can float and move on the surface but resist subduction.
- Protocontinent - the microcontinents must have collided with one another fused forming a larger continent and first fold mountains must have been formed the protocontinent.
Peninsular India has numerous such micro continent which has been fused. The three major micro or proto continents are are 1. Singhbum proto continent 2. Dharwad proto continent 3. Aravali proto continent These proto continents fused along Narmada-Son-Godavari river lineaments.
- Ancient fold mountains - every time the continents collide there must have formed ancient fold mountains.
The Aravalis are the remnants of such ancient fold mountains.
- Earth is Unique - This process of tectonic dynamism is found on no other planet and may to some extent in Venus. Hence no other planet as the type of crust earth has and the fold mountains our earth has.
The processes in the origin and evolution of earth is not the same as the theories and processes in the origin of a earth crust.