GEO 330 Lecture Notes - Lecture 4: Planetary Differentiation, Planetesimal, Goldschmidt Classification
1 Feb 2018
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Document Summary
Collapse of molecular cloud of dust and gas into rotating disc over a period of about 10,000 years - solar nebula. Dust particles collide and stick ultimately achieving km-scale within about 100,000 years - planetesimals. Collision of planetesimals give rise to planetary embryos. Sun "ignition" results in solar winds that sweep out dust, ice, and gas beyond "snow line" where giants planets form. Current consensus theory of planet formation is planetesimal hypothesis. During accretion, planetary embryos form and sweep up smaller planetesimals - perhaps a few hundred embryos at most. Example of current controversy is degree to which accreting planetesimals were themselves differentiated into core-mantle-crust. Elements have differing geochemical affinity which governs their "partitioning" behavior when solids crystallize from melts or condense from very high temperature gas: Lithophile - form minerals found in rocky material (e. g. , oxides, silicates) and concentrate in mantle and crust. Siderophile - tend to form metallic phases (e. g. , fe-ni) and concentrate in metal cores.
