The Inaccessible Earth pp 76-102 | Cite as
The accretion and layering of the terrestrial planets
Abstract
Our attention now focuses on the processes that determined the present compositions and internal structures of the Earth and its near neighbours. We have seen that the wide diversity of chemical elements found in the Solar System was produced by nucleosynthesis processes, mostly inside stars. Moreover, the chemical composition of the small, dense terrestrial planets is dominated by heavy elements that comprised just 2% of the Solar Nebula. So what processes were responsible for selectively concentrating these elements into the terrestrial planets, how did they operate and at what stage during the progressive accumulation of dust grains into planetesimals, planetary embryos and finally planets? Meteorites provide us with a good starting point (Section 4.5) for they show that similar chemical selection, and in some cases internal differentiation processes, operated as far out from the Sun as the asteroid belt. But beyond the asteroids, planetary densities are much lower (Table 4.1) implying compositions much closer to the Solar Nebula. Moreover, there are variations in density among even the terrestrial planets, and this may be due to chemical differences between them (Section 5.2.2). So there must have been a primary differentiation of the elements across the nebula.
Keywords
Solar System Terrestrial Planet Solar Nebula Condensation Temperature Volatile ElementPreview
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Further Reading
General books
- Cattermole (1989): volcanic processes on all planets, including satellites.Google Scholar
- Cole (1984): review of the physical properties of planets.Google Scholar
- Rothery (1992): planetary satellites; surface and internal processes.Google Scholar
Advanced journals
- Head et al. (1991) and Solomon et al. (1991): volcanism and tectonics on Venus.Google Scholar
- Kaula (1990): good account of contrasts between Earth and Venus.Google Scholar
- Liu (1988): water in the terrestrial planets and their atmospheres.Google Scholar
- Newsom and Sims (1991): account of core formation during accretion.Google Scholar
- Newsom and Taylor (1989): the giant impact model for Moon formation, and consequences for Earth-Moon geochemistry.Google Scholar
- Rama Murthy (1991): review of the chemical differentiation of the Earth.Google Scholar
- Russell et al. (1991): pre-solar grains in meteorites.Google Scholar
Advanced books
- Heiken et al. (1991): useful reviews of various aspects of the Moon’s geochemistry and formation.Google Scholar
- Kerridge and Matthews (1988): wide range of topics covering meteorites, planets, etc.Google Scholar
- Newsom and Jones (1990): compilation of modern papers covering most aspects of the Earth’s accretion.Google Scholar
- Weaver and Danly (1989): review papers on early Solar Nebula processes and planetary embryo formation.Google Scholar