Earth's crustal evolution
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Crustal evolution regards the formation, existence, destruction and eventual renewal of the rocky crust found on the surface of the Earth.
Evolution on this scale can take place through the unique composition of Earth's crust in comparison to other terrestrial planets. Mars, Venus, Mercury and other planetary bodies possess compositionally uniform crusts unlike that of the Earth where both oceanic and continental plates make up the overall outermost shell.
In particular, crustal evolution represents the growth and destruction rates of both types of crust.
Early crust
Mechanism
The Proto-Earth was entirely molten due to high temperatures created and maintained by compression of the early atmosphere, rapid axial rotation and regular impacts with neighbouring planetesimals.[1] However, over time the Earth began to cool as the frequency of planetary accretion slowed and heat stored within the magma ocean is lost to space through radiation. Once cool enough, the magma crystallises, starting from the base of the ocean, as this would cool more rapidly due to the lowering of the solidus nearer the surface where pressures are less than 25GPa.[2] The formation of a thin 'chill-crust' at the extreme surface would provide thermal insulation to the shallow sub surface, reinforcing a mechanism of deep magma ocean crystallisation.
The composition of early magma ocean crystallisation varies with depth. Experiments involving the melting of peridotite magma show that deep in the ocean (>700m), the main mineral present would be Mg-perovskite. Whereas olivine would dominate in the shallower areas along with it's high pressure polymorphs e.g. garnet and majorite.[3]
Types of crust
Crustal dichotomy
Impact cratering
Lifespan
Relative ages
Destruction
References
- ^ Erickson, Jon (2014-05-14). Historical Geology: Understanding Our Planet's Past. Infobase Publishing. ISBN 9781438109640.
- ^ "Early Earth differentiation". Earth and Planetary Science Letters. 225 (3–4): 253–269. 2004-09-15. doi:10.1016/j.epsl.2004.07.008. ISSN 0012-821X.
- ^ "Melting experiments of mantle materials under lower mantle conditions with implications for magma ocean differentiation". Physics of the Earth and Planetary Interiors. 143–144: 397–406. 2004-06-15. doi:10.1016/j.pepi.2003.09.016. ISSN 0031-9201.