Earth magma ocean

Crystallization of the magma ocean would have allowed fractionation of high-pressure silicate and oxide minerals that dominate the Earth s deep interior. The olivine-rich... 

However, the strong and uniform fractionation of some element ratios that would be expected from crystallization of a magma ocean is not apparent on Earth. Perhaps our planet s magma ocean was vigorously stirred by convection, obliterating such geochemical effects. 

Righter K. and Drake M. J. (1999) Effect of water on metal-silicate partitioning of siderophile elements a higji pressure and temperature magma ocean and core formation. Earth Planet Sci. Lett. 171, 383—399. 

The above models differ with respect to timing and therefore can be tested with isotopic techniques. However, not only are the models very different in terms of timescales, they also differ with respect to the environment that would be created on Earth. In the first two cases the Earth would form with a hot dense atmosphere of nebular gas that would provide a ready source of solar noble gases in the Earth. This atmosphere would have blanketed the Earth and could have caused a dramatic buildup of heat leading to magma oceans (Sasaki, 1990). Therefore, the evidence from dynamic models can also be tested with compositional data for the Earth, which provide information on the nature of early atmospheres and melting. 

Except for the small amount of evidence for early mantle melting we are in the dark about how and when Earth s continents first formed (Figure 13). We already have pointed out that in its early stages Earth may have had a magma ocean, sustained by heat from accretion and the blanketing effects of a dense early atmosphere. With the loss of the early atmosphere during planetary collisions, the Earth would have cooled quickly, the outer portions would have solidified and it would thereby have developed its first primitive crust. 

Earth accretion, core formation, and degassing over first 100 Myr i Possible hot dense atmosphere I Magma oceans. Little chance for life ... 

It may also be that a hotter Earth had a surface that was inherently unstable. Some argued that the earliest crust was like the lunar highlands—made from a welded mush of crystals that had previously floated on the magma ocean. Others have suggested that it was made of denser rocks more like those of the Earth s present oceanfloor (Galer and Goldstein, 1991). But firm evidence has so far been sparse. 

Matsui T. and Abe Y. (1986a) Evolution of an impact-induced atmosphere and magma ocean on the accreting Earth. Nature 319, 303 - 305. 

Ruble D. C., Melosh H. J., Reid J. E., Liebske C., and Righter K. (2003) Mechanisms of metal-sihcate equilibration in the terrestrial magma ocean. Earth Planet. Set Lett. 205, 239-255. 

Sasaki S. and Nakazawa K. (1986) Metal-silicate fractionation in the growing Earth energy source for the terrestrial magma ocean. J. Geophys. Res. 91, B9231-B9238. 

Tonks W. B. and Melosh H. J. (1990) The physics of crystal settling and suspension in a turbulent magma ocean. In Origin of the Earth (eds. H. E. Newsom and J. H. Jones). Oxford University Press, Oxford, pp. 17—174. 

If the fertile mantle protolith to oceanic and subcontinental mantle is nonchondritic in refractory elements, and if the bulk silicate Earth is chondritic in refractory elements, then a complimentary reservoir must exist elsewhere, presumably buried in the deep lower mantle and isolated from mantle convection (e.g., Anderson, 1989 Kellogg et al., 1999 Albarede and van der HUst, 1999). The primitive upper mantle could have acquired a superchondritic ratio as a consequence of crystal fractionation in a magma ocean, or perhaps by extraction of an early crust with low CaO/AbOs. 

Figure 1 Schematic cross-section through the Earth, showing (a) an early magma ocean stage and (b) a later cool...

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