Download Formation and differentiation of the Earth

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