Formation and differentiation of the Earth Earth’s composition

Formation and differentiation Formation and differentiation of the Earthof the Earth

Earth’s compositionEarth’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 severalstar-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 thesimilarity 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 ofequal mass planetesimals, two ‘‘seeds’’ (planetesimals of slightly larger size) are embedded. Astime passes, the two seeds grow in mass much faster than the other planetesimals,, becomingplanetary embryos (the size of each dot is proportional to its mass). While the growingplanetary embryos keep quasi-circular orbits, the remaining planetesimals have their eccentricities(and inclinations) excited by the close encounters with the embryos. Notice also thatthe separation between the embryos slowly grows in time

Differenciation of planets

Meteorites

Shooting stars

Falls

Ensisheim, France (XVIth century)

Impacts

… on other planets

Mercury

Moon

Mars

Meteorite types

Stony

Un

differen

ciate

d

~ 80 % Chondrites

Diffe

ren

ciated

~ 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

aa

bb

Figure 23-15. Progressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy © John Shelton.

dd

cc

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 shellsElements wt%

  Crust Mantle Core

  Continental Oceanic Upper Lower Outer Inner

O 41.2 43.7 44.7 43.710--15

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 80--85 80

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         5 20

Cr       0.51