First 600 Ma, B4 first rocks, time of huge impacts
Oldest rocks
4.0 Ba
Oldest mineral?
Zircon (western australia) 4.2 Ba
Zircon?
A mineral in granite, i.e. the main rock in continents
The oldest rocks?
Ultra hot pillow lavas (1600 degrees c) Proves the was already an ocean and earth was hotter below the surface
Source of gas and water?
60 - 70% of the gas from volcanos is water vapour, rest is CO2 and N2
How did oceans form?
Condensation of water vapour
Composition of early atmosphere?
60% carbon dioxide, 30% Nitrogen, 10% argon
Composition of current atmosphere?
78% Nitrogen, 21% Oxygen, 1% others
Evidence for oxygen poor atmosphere?
Pyrite and uraninite pebbles in ancient conglomerates. Palaoisols are all grey (acient soils), and early oceans had dissolve oxgyen in them which is impossilbe with oxygen in the atm.
Where is oxygen produced?
Small amounts in upper atm as UV light splits water vapour up. (photodissociation. Also Photosynthesis.
Evidence for dissolved iron in oceans?
Banded Iron formations, formed in shallow marine environments bewteen 3.5 - 2.0 Ba
Progression of Oxygen?
3.8 Ba microbes producing O2 in the ocean and precipitiaing BIF's. BIF's stopped at 2.0 Ba and red beds were formed on land, indication oxygen in atm.
