Formation and differentiation of the Earth Earth’s composition

An atom of the element carbon (C) The nucleus contains 6 protons and 6 neutrons Six electrons orbit the nucleus, confined to specific orbits called energy-levels The first shell can only contain 2 electrons The second shell can contain 8 electrons In the case of a carbon atom, the second shell is therefore half full and contains only 4 electrons

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

The growth of terrestrial planets from a disk of planetary embryos. Each panel shows the semi-major axis and eccentricity of the bodies in the system, the size of each dot being proportional to the mass. The color initially reflects the starting position of each embryo. When two (or more) embryos collide, the formed object assumes the color corresponding to the embryo population that has mostly contributed to its total mass. A system of four terrestrial planets, closely resembling our solar system, is formed in 200 Myr.

Formation of the solar system

Differenciation of planets

Meteorites Shooting stars

Falls Ensisheim, France (XVI th century)

Impacts

… on other planets Mercury Moon Mars

Meteorite types Stony Undiffere nciated ~ 80 %Chondrites Differenciated ~ 5 %Achondrites Numerous sub-types incl. « Martian » Stone-iron occasional Pallasites Iron ~15 %Siderites

Chondrites

Chondrite compositions

Achondrites (Eucrite)

Achondrites composition

Siderites

Pallasite

Continental crust Ca. 30 km

a b Figure Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton.

d c

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% CrustMantleCore ContinentalOceanicUpperLowerOuterInner O Si Al Fe Ca K Na Mg Ti C0.3 H0.2 Mn Ni 520 Cr 0.51