Physics
Scientific paper
Aug 1974
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974natur.250..556h&link_type=abstract
Nature, Volume 250, Issue 5467, pp. 556-558 (1974).
Physics
2
Scientific paper
THREE recent hypotheses for the origin of the inner planets are based on chemical data obtained from meteorites or from solar observation1-5. The chondritic earth model of Ringwood1 or the cold accretion model (see summary in ref. 2) require partial melting of meteorite material and segregation of metal and sulphide to form a core, but the fractionation must have been a rapid, disequilibrium process to leave 2,000 p.p.m. Ni in the silicate mantle. The heterogeneous accretion model 3,4 overcomes the problem of high Ni in the mantle by having accretion of the metal core first, followed by silicate mantle and finally by volatile-bearing material which formed the crust, no two fractions having been in equilibrium. Lewis5 maintains that condensation from a homogeneous nebula under differing physical conditions can account for the density variation between the inner planets without invoking the metal-silicate fractionation suggested by Urey6. Compared to the above hypotheses based on meteorite composition, the following approach is more direct as it is based on a reliable estimate of modern upper mantle composition.
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