Red Earth, Green Earth Flashcards
How does life affect the environment?
Creates an entropy/free energy gradient which causes a thermodynamic desiquilibrium
How does Lovelock propose thermodynamic desiquilibrium could be a bioindicator?
Earth’s atmosphere is a lot further from equilibrium that non-living planets
What are the main eons?
Hadean, Archean, Proterozoic, Phanoic
What was the earth’s atmospheric composition before life?
- Mostly composed of volcanic gases (H2, H2O, CO2, N2, SO2, H2S)
- 0.8 bar of moderatley inert N2
- Higher CO2 and H2 (interior is more radioactive)
- Extremely trace levels of O2
How do methanogens metabolise and how might this solve the ‘faint young sun’ problem?
4H2 + CO2 –> CH4 + 2H2O
Produced methane which is a more powerful greenhouse gas than CO2
How did anoxygenic photosynthesis also contribute to methane production?
2H2 + CO2 + hv –> CH2O + H2O
fermentation: 2CH2O –> CH4 + CO2
How would Earths surface have looked during high methane atmosphere concentrations?
Hazy
How does the water splitting centre work?
Uses 4 Mn and 1 Ca atom as well as the energy from 4 photons to release 4 e- from H2O
When is oxygenic photosynthesis believed to have evolved?
2.7 Ga, no convincing evidence past 3 Ga
Name 3 points of evidence for an environment lacking in oxygen
- Rounded sidenite/uranite/pyrite suggest long term transport, would usually have been dissolved in oxygenated water
- Dissolved O2 would have converted Fe2+ to Fe+3. Ancient soils have little Fe and modern soils have a lot of Fe3+
- Banded iron formations 3-1.8 Ga require Fe2+ in the oceans + a local oxidant
What is the “smoking gun” for the great oxidation event?
Farquhar (2000)
- A isotope 33S only forms in an oxygen free atmosphere and was discovered to be ubiquitous in sulfur bearing sediments
- No 33S after 2.3 Ga
How are eukaryotes different to prokaryotes?
- Larger, more complicated cells (have a nucleus containing DNA)
- Require O2
- Much more information can be passed to the next generation of eukaryotes
What are achritarchs and when did they begin to appear?
- Small non acid-soluble organism that cannot otherwise be accounted for
- Usually spherical with some surface markings
- 2 Ga
What are tappania and bengiamorpha pubescens believed to be?
- Tappania (1.5 Ga) has an cytoskeleton, believed to be a fungus
- Bengiamorpha pubescens (1 Ga) is a sexually reproducing multicellular algae
When are the 3 snowball earth and glaciation events?
What evidence is there for this?
700 Ma, 640 Ma, 580 Ma
- Glacial tills indicate ice flow
- Dropstones dropped in ocean sediment possibly transported by ice