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Lecture 3: The Great Oxidation Event Flashcards

1
Q

What do we start to see as the precambrian period goes on…?

A

New types of sediment being deposited.

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2
Q

When did banded iron formations (BIFs) begin?

A

~3.8 Ga

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3
Q

How did banded iron formations (BIFs) form?

A

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.

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4
Q

How were organisms protected from UV bombarding Earth’s shallow waters?

A

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.

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5
Q

What became abundant in shallow water by 3.5 Ga?

A

Cyanobacteria
Anoygenic -> oxygenic photosynthesis
H2O + CO2 + light -> CH2O + O2

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6
Q

What is toxic to cell metabolism?

A

O2

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7
Q

What did cyanobacteria evolve to deal with toxic oxygen producing free O2?

A

Enzymes

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8
Q

What was the first wave of massive global extinctions>

A

The Great Oxidation Event.
Free O2 is a deadly toxin to anaerobic prokaryotes.
This radically changed oceans and atmosphere

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9
Q

Younger (& shallower water) BIFs were produced in a different way as oceans become oxygenated…

A

~3.0 Ga cyanobacteria O2 begins to oxidise ocean waters.

Fe2+ from hydrothermal vents is oxidised into insoluble Fe3+ oxides.

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10
Q

What happened when O2 began to diffuse into the atmosphere?

A

The land (Fe2+) began to then oxidise into Fe3+

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11
Q

What did…

H2O + UV -> Free O2

Lead to…?

A

New supply of microbial O2

= Ozone layer formation which protects from UV bombardment…

This made the planet MUCH MORE habitable.

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12
Q

What did the ozone layer formation lead to?

A

More habitable conditions for eukaryotic cells to evolve from prokaryotic cells.

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13
Q

What was the evidence for the 1st eukrayotes?

A

Chemical fossils

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14
Q

When did sexual reproduction occur?

A

~1.2 Ga
Red algae
Gene exchange accelerates evolution
Single cells -> multicellular

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15
Q

Cells need to:

A

Adhere (collagen)
Communicate
Specialise

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16
Q

What were the first plants?

A

Red algae and seaweeds

17
Q

What were the first animals?

A

Sponges

18
Q

Dropstones/tillites are…

A

Cold water deposits

19
Q

Evaporites/ limestones are…

A

Warm water deposits

20
Q

What are banded iron formations (BIFs)?

A

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)

21
Q

Explain the potential importance of clay minerals in the early evolution of life.

A

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

22
Q

What was the ice albedo feedback effect?

A

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.

23
Q

Evidence for 1st eukaryotes:

A

eukaryotic chemical fossils (biomarkers): sterols
1.89 Ga Barney Creek Formation, Oz
eukaryotic cells are larger
eukaryotic body fossils by 1.4 Ga (China)

24
Q

The ‘Boring Billion’

A

Earth’s climate stabilized
oxygen levels steadied
not much change for around a billion years?
not entirely true…

25
Q

One becomes two…

A

Bitter Springs Chert, Australia – 1 Ga 850 Ma
preserve nuclei eukaryotes
vegetative reproductive stages

26
Q

SEX (two become one…)

A

Hunting Formation, Canada, 1.2 Ga
red algae: sexual reproduction arrives
gene exchange / recombination: evolution accelerates

27
Q

Was the glaciation global?

Palaeomagnetic evidence

A

Measure palaeomagentic inclination angle recorded by magnetic minerals in the rocks.
Work out latitude where rocks were originally deposited

28
Q

Global climate models

Albedo

A

oceans – low albedo
land – medium albedo
snow – high albedo

29
Q

Snowball Earth?

A 
if ice-sheets >30N/S
 ice-albedo feedback
runaway icehouse
planet freezes over
…permanently 
but not ice-bound today…thus surely couldn’t have happened – was the data faulty?
30
Q

Approximately when did the Great Oxygenation Event begin?

A

End of the Archean/Beginning of the Proterozoic 2.5 BY ago

31
Q

When, approximately, do we find the first evidence of extensive glaciation on the Earth (transition from a hothouse to an icehouse state)?

A

The Late Archean/Beginning of the Proterozoic 2.7-2.4 BY ago.

32
Q

Which statement best describes the “Great Oxygenation Event”?

A

A geologically slow event (hundreds of millions of years) where atmospheric oxygen built from nearly 0 to about 1% of its current value

33
Q

What process/event do most scientists think primarily led to the Snowball Earth events?

A

The breakup of Rodinia—proliferation of photosynthetic algae followed by organic carbon burial

34
Q

Approximately when did multicellular life develop?

A

During the Snowball Earth episodes (between 850 and 580 MY ago)

35
Q

What permanent change did the Snowball Earth episodes make in Earth’s systems that allowed the development of multicellular life?

A

It led to the permanent buildup of oxygen in Earth’s atmosphere

36
Q

What happened during the great oxygenation event?

A

Oxygen build up in atmosphere - from photosynthetic bacteria in coastline - algae

37
Q

What do rocks older than 2.5 billion years lack?

A

iron banding from lack of oxygen

38
Q

What do rocks 2.5 billions old or newer have?

A

iron banding from oxygen

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