O2 Flashcards
when was the first evidence of photosynthesis?
3.7 Ga
what type of photosynthesis happened 3.7Ga?
anoxygenic (no water, O2 as waste)
what is a redox reaction?
the transfer of electrons between 2 species
equation for photosynthesis with many donors
CO2 + 4Fe2+ + 11H2O + hv-> (CH2O)n + 4Fe(OH)3 + 8H+
what performs oxygenic photosynthesis?
cyanobacteria
what happens in the first stage of oxygen rise?
- O2 released by cyanobacteria was rapidly used up
- O2 reacted with ferrous Fe dissolved in the ocean and reduced gases in the atm
- began to react with metal elements in continental rocks that are sensitive to low levels of O2
what happens in the second stage of O2 rise?
- H loss to space steadily oxidised the crust and surface of the earth pushing it toward a tipping point
- once an alt high O2 state was stable, a small biological perturbation could have triggered the transition into it
- deep ocean remained anoxic
what was the oxygen catastrophe?
- O2 was toxic to most microbial life at the time
- anaerobic habitats on land and in the surface disappeared
- the formation of the ozone offered new protection form UV
- methane was removed from the atm contributing tp glaciations including the snowball earth 2.2 Ga
benefits of O2
- anti-oxidant molecules evolved
- aerobic respiration became common
- it yields more energy than anaerobic
- most eukaryotes use it
- made complex multicellular life possible
what happens in the third stage of O2 rise?
- parts of deep ocean show signs of oxygenation 580 Ma
- but there is evidence for deoxygenation of the ocean in the Cambrian period
when was the Cambrian period?
542-488 ma
when was the first evidence for O2 >17% of atm?
in charcoal 420 Ma
whent is the first evidence for complete oxygenation of the deep ocean?
Devonian period 400 Ma
when were there large deposits of phosphorous?
600-400 Ma
