Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents nev...Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents never existed during Hadean Earth,and the continental volume has kept increasing.On the other hand,recent studies reported the importance of the primordial continents on the origin of life,implying their existence.In this paper,we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean.Although depending on the timing of the initiation of plate tectonics and its convection style,subduction erosion,which is observed on the present-day Earth,might have carried the primordial continents into the deep mantle.展开更多
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 ...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.展开更多
基金supported by JSPS KAKENHI(Grand-in-Aid for Scientific Research(S)) Grant No.23224012(Growth of the second continent and mantle)
文摘Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth.From these facts,many scientists believe that the primordial continents never existed during Hadean Earth,and the continental volume has kept increasing.On the other hand,recent studies reported the importance of the primordial continents on the origin of life,implying their existence.In this paper,we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean.Although depending on the timing of the initiation of plate tectonics and its convection style,subduction erosion,which is observed on the present-day Earth,might have carried the primordial continents into the deep mantle.
基金supported by Foreign Expert Funding from China University of Geosciences Beijing
文摘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.
