Lecture 3: The Great Oxidation Event Flashcards
What do we start to see as the precambrian period goes on…?
New types of sediment being deposited.
When did banded iron formations (BIFs) begin?
~3.8 Ga
How did banded iron formations (BIFs) form?
Early oceans still anoxic but full of iron in its reduced state (Fe2+) which is soluble in water.
No protection from UV bombarding Earth’s shallow waters.
How were organisms protected from UV bombarding Earth’s shallow waters?
Anoxygenic photosynthetic Fe2+ oxidising bacteria secreted insoluble ferric (Fe3+) oxides which protected from UV.
Once these bacteria died, they sank to the sea floor in a seasonal deposition of biogenic iron minerals.
What became abundant in shallow water by 3.5 Ga?
Cyanobacteria
Anoygenic -> oxygenic photosynthesis
H2O + CO2 + light -> CH2O + O2
What is toxic to cell metabolism?
O2
What did cyanobacteria evolve to deal with toxic oxygen producing free O2?
Enzymes
What was the first wave of massive global extinctions>
The Great Oxidation Event.
Free O2 is a deadly toxin to anaerobic prokaryotes.
This radically changed oceans and atmosphere
Younger (& shallower water) BIFs were produced in a different way as oceans become oxygenated…
~3.0 Ga cyanobacteria O2 begins to oxidise ocean waters.
Fe2+ from hydrothermal vents is oxidised into insoluble Fe3+ oxides.
What happened when O2 began to diffuse into the atmosphere?
The land (Fe2+) began to then oxidise into Fe3+
What did…
H2O + UV -> Free O2
Lead to…?
New supply of microbial O2
= Ozone layer formation which protects from UV bombardment…
This made the planet MUCH MORE habitable.
What did the ozone layer formation lead to?
More habitable conditions for eukaryotic cells to evolve from prokaryotic cells.
What was the evidence for the 1st eukrayotes?
Chemical fossils
When did sexual reproduction occur?
~1.2 Ga
Red algae
Gene exchange accelerates evolution
Single cells -> multicellular
Cells need to:
Adhere (collagen)
Communicate
Specialise
What were the first plants?
Red algae and seaweeds
What were the first animals?
Sponges
Dropstones/tillites are…
Cold water deposits
Evaporites/ limestones are…
Warm water deposits
What are banded iron formations (BIFs)?
640 billion tonnes deposited in early Proterozoic
Make up most abundant iron ore reserves
Alternate layers of iron oxide/silica have different compositions (often only mm thick)
Explain the potential importance of clay minerals in the early evolution of life.
Clay minerals played a key role in chemical evolution and the origins of life because of their ability to take up, protect (against ultraviolet radiation), concentrate, and catalyze the polymerization of, organic molecules
What was the ice albedo feedback effect?
Over millions of years weathering removes CO2 from the atmosphere to hydrosphere and lithosphere.
Less atmospheric greenhouse gases reduces global warming.
Cooling at the poles results in expansion of surface ice.
Positive ice albedo feedback kicks in.
More cooling -> more ice surface.
Evidence for 1st eukaryotes:
eukaryotic chemical fossils (biomarkers): sterols
1.89 Ga Barney Creek Formation, Oz
eukaryotic cells are larger
eukaryotic body fossils by 1.4 Ga (China)
The ‘Boring Billion’
Earth’s climate stabilized
oxygen levels steadied
not much change for around a billion years?
not entirely true…
