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Formation and differentiation of the Earth Earth’s composition Nucleosynthesis « Bethe’s cycle » Elements stability Elements abundance • Lights > Heavies • Even > Odd • Abundance peak close to Fe (n=56) Solar system abundance The Orion complex. Left: image of the Orion nebula M42 in the visible domain ( Anglo-Australian Telescope). Background: far-IR image (100 microns) of the Orion complex, by the IRAS satellite (1986), covering a very wide area (the angular scale is given). Note the widespread filamentary structure of the ‘‘giant molecular cloud’’. The bright spots are several star-forming regions belonging to the same complex, the most active one being M42 (box). Numerical three-dimensional simulation of star formation in a 10,000 Msun cloud, ~600,000 yrs after the initial collapse. The figure is 5 pc on a side. Note the similarity of the cloud structure with that of the Orion complex shown in the previous figure. The simulation eventually leads to the formation of ~500 stars. Formation of a planetary nebula - Planetary nebulas Temperature gradients in the planetary nebula A simulation of the runaway growth process for planetary embryos. In a disk of equal mass planetesimals, two ‘‘seeds’’ (planetesimals of slightly larger size) are embedded. As time passes, the two seeds grow in mass much faster than the other planetesimals,, becoming planetary embryos (the size of each dot is proportional to its mass). While the growing planetary embryos keep quasi-circular orbits, the remaining planetesimals have their eccentricities (and inclinations) excited by the close encounters with the embryos. Notice also that the separation between the embryos slowly grows in time Differenciation of planets Meteorites Shooting stars Falls Ensisheim, France (XVIth century) Impacts … on other planets Moon Mercury Mars Meteorite types Undiffere nciated ~ 80 % Chondrites Stony ~5% Iron Differenciated Stone-iron Achondrites occasional Pallasites ~15 % Siderites Numerous sub-types incl. « Martian » Chondrites Chondrite compositions Achondrites (Eucrite) Achondrites composition Siderites Pallasite Continental crust Ca. 30 km a b Figure 23-15. Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton. c d Figure 23-15. Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton. Orthogneiss NB- KSpar is spectacular but not ubiquitous. Plagioclase is more common Oceanic crust Gabbro NB- Oceanic crust gabbro normally has Cpx rather than Opx Mantle peridotite Mantle mineralogy • Continental crust = Bt + Pg + Qz ± KSpar • Oceanic crust = Pg + Cpx ± Opx ± Amp • Mantle = Ol + Opx ± Cpx ± Pg/Sp/Grt Composition of Earth shells Elements wt% Crust Mantle Core Continental Oceanic Upper Lower O 41.2 43.7 44.7 43.7 Si 28 22 21.1 22.5 Al 14.3 7.5 1.9 1.6 Fe 4.7 8.5 5.6 9.8 Ca 3.9 7.1 1.4 1.7 K 2.3 0.33 0.08 0.11 Na 2.2 1.6 0.15 0.84 Mg 1.9 7.6 24.7 18.8 Ti 0.4 1.1 0.12 0.08 C 0.3 H 0.2 Mn 0.07 0.15 0.07 0.33 Ni Cr 0.51 Outer Inner 10--15 80--85 80 5 20