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History of OXYGEN

Timeline of Oxygen in the Atmosphere

    Major Events Air / Climate Life More
A - oceans in the air
- no life yet
- 80% H2O
- 10% CO2
- 5-7% H2S

- Very Hot (Lava)
- no life yet - tumultuous lava flows steam off any water
B - early life
- oxygen can't accumulate yet
Intermittant Oxidation

- Snowball Earth
- microscopic life, including algae - except during Ice Ages, surface metals are oxidized and absorb all available oxygen
C - multicellular life - O2 up
- CO2 up

- Warm and Humid
- strange plants and animals different from modern life - surface metals fully oxidized, so oxygen can now accumulate in atmosphere
D - plants spread on land - O2 stable
- CO2 stable

- Warm, Wet and Mild
- Trilobites, Snails, Fish
- Moss and Early Plants on land
- plants and animals reach equilibrium, plants oxygen output is consumed by animal life
E - early trees and ferns - O2 up
- CO2 down

- Arid to Warm Temperate
- Trees and Ferns
- Insects, Amphibians
- plants colonize land, increase oxygen and deposit carbon
F - plants evolve bark
- much oxygen produced
- O2 up a lot
- CO2 down a lot

- Cool and Wet
- Plants evolve bark (8 bark to 1 wood!), nothing can eat it yet
- Giant Insects + Amphibians
- plants evolve lignin (lotsa bark), thus temporary plant supremacy, even more oxygen, more carbon deposit
- industrial age coal comes from here
G - (pangea) single continent
- hostile climate
- O2 drops a lot
- CO2 low

- (Pangea) Single Continent
- Cool, Very Dry
- Seasonal Rain
- Conifers
- Cockroaches, Reptiles
- desert too dry for many plants, so oxygen drops, carbon gap (very little deposit)
H - dinosaurs - O2 up
- CO2 up

- Warm and Humid
- Cycads and Ferns
- Dinosaurs
- warm humid climate favorable to plants, so oxygen rises again
I - no polar ice caps
- hothouse climate lets plants produce more oxygen
- O2 up
- CO2 down

- Max Oceans (2/3 as much land)
- Hot and Wet
- even at the poles
- Grass and flowers evolve
- Dinosaurs
- early Birds and Mammals
- no polar ice caps
- hothouse climate lets plants make more oxygen, deposit more carbon
- shelled plankton deposit chalk on ocean bottom, reducing CO2
J - birds and mammals
- a few ice ages
- O2 down
- CO2 down

- Cooling
- some Ice Ages
- Savannah
- Mammals and Birds
- ice caps return, and several ice ages
- lower oceans
- grasses dominate
- fewer plants, so oxygen goes down
K - humans
- terraforming
- CO2 up
- methane up a lot

- most stable climate ever, suitable for agriculture
- Humans! - Humans dig up and burn fossil fuels, depleting atmospheric oxygen and increasing CO2

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