Habitable Planet Flashcards
What did Hadean and Archean Earth look like?
There was no differentiation in crust like oceanic vs continental until the Archaean, and no plate tectonics until 2.5Ga. Before 4Ga, the crust was much thinner and metal rich.
There were high greenhouse gas levels, so weaker insolation. High radioactivity. Sun weaker, no oxygen.
What is the Huronian event?
First global snowball event, when oxygen increased and so methane decreased, letting heat escape.
What is the Late Heavy Bombardment?
Period between 4.1Ga and 3.8Ga where there were major impacts every 100y on average
What is the Giant Impact Hypothesis?
At 4.5Ga, it was the imapct that created our moon. It was initially 4x closer with 30x stronger tides.
What three things are vital for living organisms
Carbon for biomass, a source of energy, and electrons for reducing power
What are 4 things present in every cell?
- Limited range of elements and molecules - H2O, C, N etc.
- Cell membrane - from hydrophobic and hydrophilic ends of fatty acids.
- Chiral molecules: sinistral amino acids and dextral nucleic acids - one catalyses itself
- Replication of information through generations
Replication is the most difficult to come by through natural processes - defines life
What is the Oparin-Haldane hypothesis
The synthesis of complex organic molecules comes from simpler precursors from the atmosphere.
The Miller-Urey experiment tried to simulate this atmosphere, and managed to form amino acids with lightning. However fewer proteins would form in the now-understood composition of the atmosphere compared to the one they used, since nitrates preferentially form.
What is the panspermia hypothesis?
Predicts the delivery of prebiotic materials from space.
Meteorites have been shown to yield nucleobases of RNA and comets have had organic compounds like amino acids.
What is the Hydrothermal hypothesis?
Localises synthesis to around alkaline black smokers.
There are favourable conditions and there are even bacteria that photosynthesise with IR.
What do you need to make sure something is biotic?
Viable context from geology, biological processing from geochemistry and biological morphology from palaeobiology.
E.g. in the Gunflint Chert, it is geologically plausible, has the same carbon isotope ratio and there are 12 bacteria species
Why are banded iron formations significant?
They show seasonal rusting of ocean sediments, which may insinuate photosynthesis. These date from 3.4bya
What are some impacts of the Great Oxygenation event (2.3bya)
Huronian glacial event
Mitochondrial and chloroplast symbiosis ~1.5bya
sexual reproduction ~1bya
Why did the Boring Billion occur?
The reduction of tectonic activity as the supercontinent Rodinia formed - less nutrients and shallow water.
What was the Ediacaran biota?
A separate biota before the Cambrian explosion when a second oxygenation event introduced oxygen to deep marine environments. They are likely the first multicellular organisms and have a range of morphologies, from quill-shaped rangeomorphs and shell-shaped dickinsoniomorphs.
4 causes of the Cambrian explosion?
- Bioturbations become much more complex and deeper burrowing into the sediment begins - infaunal. This allowed oxygen to get into the substrate, further developing diversity.
- It was also the start of predator-prey dynamics, with more muti-tiered food chains. Previous organisms were mostly filter-feeders. Predatory and protective evolution occurred at similar times.
- The through gut was also a key evolutionary innovation as more food can be processed with separate mouth and anus. The musculature for peristalsis is crucial for burrowing too.
- Biomineralization becomes much more prevalent, with calcium carbonate, calcium phosphate and silica. Many different phyla began independent of each other at this time.
When did terrestrialisation occur
microbes - Archean
Plants - Ordovician
Invertebrates - Silurian or earlier
Vertebrates - Devonian
Initially around water sources only.
What evolutionary modifications are needed for land?
Deeper roots and supports to overcome gravity in plants, or reduced reliance of water controlled by kidneys in animals.
How did geology change after terrestrialisation
Coal seams, resulting in decreased co2 and increased o2, stimulating more biodiversity, forest fires and decreasing T.
More meandering rivers as soils are developed and held together by roots.
What caused the start and end of the global snowball events 716-635mya?
Start
- Weathering increased with breakup of Rodinia as basalts produced near the equator can easily capture CO2. This offsets the CO2 pumped back to the atmosphere by volcanoes
- Sun 7% dimmer
- Franklin Large Igneous Province produced lots of sulfur.
- Albedo positive feedback
End
- Volcanoes kept releasing CO2, but rocks cannot take it in while under ice.
What is Gunflint Chert?
1.9Ga
- The gold standard
Biological morphology: 12 bacteria species
Biological processing: carbon isotope ratios are consistent with life as light is preferred
Geologically: banded iron formations
What is Strelley Pool?
3.4Ga
- Stromatolite morphology
- Potential fossils with carbon chains and clusters
- Strongly negative carbon isotope
- Pyrite indicating anoxia and having variations in sulphur over short distances indicating alteration by life through metabolism
What is Isua Formation?
3.8Ga
- Putative stromatolites, more consistent with deformation
- Some carbon rings within banded iron formations
- carbon isotope ratios are not consistent - perhaps as a result of metamorphism instead
Evidence for Snowball Earth?
Dropstones from glaciers, appearing in marine sediments and recording poles.
No carbonates present.
