Hadean Earth and primordial continents：The cradle of prebiotic life

The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere.The Earth-Moon system had many features in common during the birth stage.Solidification of the dry magma ocean at 4.53 Ga generated primordial continents with komatiite.We...

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Bibliographic Details
Published in:Di xue qian yuan. 2017-03, Vol.8 (2), p.309-327
Main Authors: Santosh, M., Arai, T., Maruyama, S.
Format: Article
Language:English
Subjects:
ABEL bombardment
Anorthosite
Asteroids
Basalt
Bombardment
Carbon dioxide
Chemical evolution
Continents
Convection
Disintegration
Earth mantle
Earth surface
Earth-Moon system
Fractionation
Gallium
Hadean plate tectonics
Iron
Kreep
Kyanite
Magma
Magnesium
Manganese
Plate tectonics
Primordial continents
Solidification
Tectonic erosion
Volatile compounds
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Summary:The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere.The Earth-Moon system had many features in common during the birth stage.Solidification of the dry magma ocean at 4.53 Ga generated primordial continents with komatiite.We speculate that the upper crust was composed of fractionated gabbros and the middle felsic crust by anorthosite at ca.21 km depth boundary,underlain by meta-anorthosite（grossular ＋ kyanite 4 quartz）down to 50-60 km in depth.The thickness of the mafic KREEP basalt in the lower crust,separating it from the underlying upper mantle is not well-constrained and might have been up to ca.100-200 km depending on the degree of fractionation and gravitational stability versus surrounding mantle density.The primordial continents must have been composed of the final residue of dry magma ocean and enriched in several critical elements including Ca,Mg,Fe,Mn,P,K,and Cl which were exposed on the surface of the dry Earth.Around 190 million years after the solidification of the magma ocean, ＂ABEL bombardment＂ delivered volatiles including H_2O,CO_2,N_2 as well as silicate components through the addition of icy asteroids.This event continued for 200 Myr with subordinate bombardments until 3.9 Ga,preparing the Earth for the prebiotic chemical evolution and as the cradle of first life.Due to vigorous convection arising from high mantle potential temperatures,the primordial continents disintegrated and were dragged down to the deep mantle,marking the onset of Hadean plate tectonics.
ISSN:1674-9871
2588-9192
DOI:10.1016/j.gsf.2016.07.005