Great Oxidation Event Flashcards
Arrange the following from oldest to most recent:
hadean, archaean, proterozoic
- proterozoic
- archaean
- hadean
what are komatiites? under what conditions did these rocks first form on early earth?
ultramafic lava rocks; formed when temperatures dropped below 1000 degrees celcius
What is the oldest rock on Earth?
4.0 Gyr Acasta Gneiss from the Northwest Territories
Was there an ozone layer on early earth? Explain.
no ozone layer b/c no free atmospheric O2, only greenhouse gases like methane and CO2
Was the rain on early earth acidic or basic?
acidic
Explain the “Organic Soup” model.
key prebiotic monomers were formed when reduced atmospheric gases were subjected to UV irradiation and electrical discharges –> gases condensed to form more complex compounds, like amino acids –> complex compounds accumulate in sea water –> life evolved from here
What is Panspermia?
pre-formed life that were brought by extraterrestrial comets and meteorites
What is the major problem with the “Organic Soup” model?
“Late Heavy Bombardment” - giant impacts constrained the timing of life’s origin
What kind of environment offered the most favourable conditions for early life?
black smokers and mid-ocean ridge systems
What 2 chemical compounds did the earliest cells use? What is the evidence?
sulfur (H2S) - mats of H2S oxidizing bacteria forming elemental sulfur
methane (CH4) - deep-sea vent emit methane from methanogenic bacteria
What does evidence for ancient life come from? (4)
- microfossils
- biogenic structures (e.g. stromatolites)
- isotopes
- biomarkers
Which came first?
a) anoxygenic photosynthesis
b) oxygenic photosynthesis
a) anoxygenic photosynthesis
What does MISS stand for?
microbially induced sedimentary structures
In what kind of environment do MISS form?
energetic tidal flat settings
What makes biomarkers particularly useful?
they retain some resemblance to the original biological molecules even after decomposition
What are the primary producers of early earth? What kind of photosynthesis did they do?
cyanobacteria; oxygenic photosynthesis
What occurred during the GOE? What year did it occur?
- first time oxygen accumulated into the atmosphere
- 2.5 Gyr
What organism might have triggered the GOE? How did they do this?
cyanobacteria –> produce O2 that is released into the atmosphere
What happened during the Lomagundi event?
lots of primary productivity and isotopic carbon
What is the best GOE evidence? why?
sulfur bif –> when sulfur bif disappears, O2 increases in the atmosphere
How can you tell if an iron band formed before the GOE?
not red
Which type of iron is oxidized?
ferric (Fe3+)
List some evidence for the GOE.
- banded iron formation (BIF)
- sulfur bif
- manganese ore
- pyrite
Why was there a drop in nickel along with CH4 before the GOE?
methane-producing bacteria need nickel to survive
