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
What are glaciation events associated with?
A second increase in atmospheric oxygen to 21%
What were the causes and consequences of the neoproterozoic revolution?
- Rise in oxygen, glaciation events, tectonics and colonisation of the land by rock weathering organisms
- Resulted in animals!
Why is diversity believed to have increased hugely during the Cambrian explosion?
- High levels of oxygen?
- Origin of eyes allowed for predator prey relationships and the beginning of the modern food web
- Origin of shells, so possibly a conservation bias
What is GOBE?
Great Ordovician Biodiversification Event
Advent and diversification of marine invertebrates
How is tectonic forcing possibly linked to an increase in biodiversity?
- During Ordovician greatest continental dispersal of the Paleozoic
- Differences in latitude and changes in currents
- Cause massive geographical differentiation of faunas
When do the following begin to appear?
- Fish
- Insects
- Amphibians
- Reptiles (amneotic eggs)
- Plants and gynosperms
1 + 2. Denovian
- Mid paleozoic
- Mid-late paleozoic
- Late ordovician, late paleozoic
What are the 5 big mass extinction events?
- Late Ordovician
- Late Denovian
- Late Permian (Great Dying)
- Late Triassic
- Late Creataceous (KT)
Which mass extinction event was the most severe?
Late Permian, 95% of species disappear
What are the 3 proposed causes of the Late Permian extinction event?
- Widespread volcanism
- Oxygen depletion
- Sulfide build-up
Name 3 biological events of the Mesozoic era?
- Dinosaurs became dominant
- Both mammals diversify and birds evolve
- Advent and diversification of angiosperms in the cretaceous
What were the 4 inital hypothesese for the KT (Cretaceous-Tertiary) extinction event?
- Volcanism
- Disease
- Ozone destruction for nearby supernovae
- Climate change
What evidence is there for the KT extinction being caused by a comet impact?
- Iridium rains down at a constant rate as “cosmic dust” however at time of KT extinction levels 100* the normal
- Evidence for impact and massive wildfires seen worldwide in the few centimetres of stratigraphy that represent this time
