Lecture 3: Atmospheric Oxygen Flashcards
Oxygen reactions:
- organic carbon cycle (photosynthesis and respiration)
- pyrite formation produces oxygen, weathering takes it up into rock
oxygen release is associated with
low O2 environments= formation of pyrite
carbon and oxygens relationship
- when CO2 low, O2 is high
- seen post evolution of photosynthesis
effects of high O2
- fires
- effect on photosynthesis
- increased respiration?
high O2 and fires
- carboniferous and Permian
- easy to find in fossil record = charcoal
- increase in oxygen, increase in number of fires,
- clear when oxygen gets to 25%
- 30% oxygen = wetland fires
O2 effects on photosynthesis
= photorespiration
- carbon dioxide and oxygen both compete for rubisco
- for photosynthesis high O2 is NOT good
- currently 25% rubisco picks O2 not CO2, binds to CO2 at O
- rubisco evolved in really low O2 environments, easily tricked
- 40% O2, 30% decrease to crop plants
O2 effect on increased respiration
- main animals = invertebrates (mainly insects)
- GIANT INSECTS in fossil records
- dragon flies size of car tyres
- arthropleura 8ft long, 2ft wide
high O2 on plants and animals
-plants not ideal but survived, animals thrived
giant insects and high O2, why was there size limited?
- transfer air by tracheae
- as get bigger, so must tracheae system exponentially
- MAIN ISSUE = tracheae must pass through joints (i.e. leg joints)
- as they get bigger, they block leg joints, as they expand exponentially whereas joint doesn’t
- so for given O2 conc, the size of the insect is limited
- max size of beetle today = 16cm
experiment to show O2 conc effect on growth
Drosophila melanogaster across 5 generations at 35% O2 20% increase in females, and 12% in males
-ALSO shown in reptiles (increase in spine length)
oxygen toxicity in vertebrates:
- Key in vertebrates (not so much invertebrates)
- can end in death
- so O2’s increase in size is limited by O2 toxicity
Low oxygens effect on animals =
- Can be a huge problem
- alligator hatchlings at low O2 = effect development, more emphasis on yolk, creating bigger food store, comes at expense of hatchling mass
After the rise in O2 during the Carboniferous, there was a rapid drop in oxygen at the end of the
Permian
- This coincides with biggest mass extinction event in the history of the planet
- Also an increase in CO2 at this time
Post permian O2 drop: WHY
1) CO2 released: trees began to decompose due to appearance of lignin degrading fungi
2) break up Pangaea
3) Siberian Trap Eruption (volcanic activity) due to mantle plume during break up of Pangaea
carboniferous and plants =
major plant growth, but little decomposed so simply buried (burial of CO2), a lot of coal formation
