Evolution of the Earth and its Atmosphere 4.7 billion years ago: The proto-Earth was a loosely-packed ball of “dirt” (primarily silicon, iron, nickel and their oxides), surrounded by a thin primordial atmosphere of hydrogen and helium (with traces of argon, neon and krypton).
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4.7 billion years ago:
4.7 billion years ago – 4.3 billion years ago:
4.3 billion years ago – 4.0 billion years ago:
Disassociation ofNH3 2NH3 + uv N2 + 3H2
Conversion of someH2O and most CO H2O + CO + sunlight H2 + CO2
(As most H2O condensed to create the oceans, rain, erosion and tides began “weathering” the Earth’s surface.)
Carbonate rock formation CaO + CO2 CaCO3 (limestone)(CO2 absorption) MgO + CO2 MgCO3 (dolomite)
Summary: most H2 escaped; N2 kept accumulating (since it didn’t react with anything else); most H2O was condensed or converted; most CO was converted; CO2 accumulated, though a lot was absorbed in “weathering”; most NH3 disassociated; and CH4 accumulated (since it didn’t react with anything else at this point).
4.0 billion years ago – 3.8 billion years ago:
Life on Earth had begun, despite its inhospitable atmosphere!
3.8 billion years ago – 2.5 billion years ago:
Photosynthesis 6H2O + 6CO2 + sunlight C6H12O6 + 6O2(This provided food, in the form of glucose, to these primitive aquatic plants, and very importantly, began the release of oxygen into the atmosphere!)
2.5 billion years ago – 600 million years ago:
600 million years ago – 3 million years ago:
Conversion of most CH4 2CH4 + 3O2 4H2O + 2CO(This eliminated most of the atmospheric methane, which would have been toxic to surface-dwelling animals.)
Ozone production 3O2 + uv 2O3(This created the “ozone layer” high in the atmosphere, which blocked solar uv from reaching the ground and made it possible for plants and animals to survive above the ocean surface.)
3.0 million years ago - 200 years ago:
Section Components % by Wt Total %
Crust SiO2 & misc other 1 1
Mantle SiO2 30 MgO 20 FeO 6 Fe2O3 6 Al2O3 2 CaO 2 66
Core Fe 24 Ni 4 Si 4 32
Atmospheric Composition (excluding H2O)
Gas Formula % by Volume
Nitrogen N2 78.08
Oxygen O2 20.95
Argon Ar .93
Carbon DioxideCO2 .035
Hydrogen, Helium, H2, He Neon, Krypton, Ne, Kr Carbon Monoxide, CO Ammonia, NH3 .005 Sulphur Dioxide, SO2 Methane, Ozone CH4, O3 Nitrous Oxide, N2O CFC’s,etc_______
Gases in green are “greenhouse” gases!
Carbon Dioxide (CO2)
Nitrous Oxide (N2O)
Sulphur Dioxide (SO2)