1. Chemical Formation of the Earth
Cloud of elements condenses into planets
As they do so, they react to form compounds
They differentiate chemically and by density

2. Chemical Makeup of the Earth

4. Primary Differentiation of the Earth
The biggest redox reaction in the world
metals + nonmetals  compounds
Focus on “metals” and “nonmetals”
Metal here = elements that loses electrons
Nonmetals here = elements that gain electrons

5. Chemical Makeup of the Earth
Bulk Earth
Fe 35.4%
O 27.8%
Mg 17.0%
Si 12.6%
S 2.7%
Ni 2.7%
Ca 0.6%
Al 0.44%
All others: 3.5%
See Formation of … xlsl

6. Primary Differentiation of the Earth
1. So, we end up with excess iron. 2. It stays in the metallic state and is dense, so it sinks to the center of the earth, forming the metallic core. 3. Next question: what other elements go with Fe to the core? Which do not?

8. If Fe can reduce a cation of the other element
Reaction potential = Eoreaction = Eo(reduction) + Eo(oxidation)
If Eoreaction is positive, the reaction is favored.
If Fe can reduce a cation of the other element
to its neutral state, that element goes to the core.

9. Example: Nickel

11. Deficient Elements: log(cosmic/crust)
H 6.58 He
C 3.22
N 5.25 Ne
Compare to O: 0.79