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EAS 205 > Great Oxidation Event > Flashcards

Great Oxidation Event Flashcards

1
Q

Arrange the following from oldest to most recent:

hadean, archaean, proterozoic

A
  1. proterozoic
  2. archaean
  3. hadean
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2
Q

what are komatiites? under what conditions did these rocks first form on early earth?

A

ultramafic lava rocks; formed when temperatures dropped below 1000 degrees celcius

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3
Q

What is the oldest rock on Earth?

A

4.0 Gyr Acasta Gneiss from the Northwest Territories

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4
Q

Was there an ozone layer on early earth? Explain.

A

no ozone layer b/c no free atmospheric O2, only greenhouse gases like methane and CO2

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5
Q

Was the rain on early earth acidic or basic?

A

acidic

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6
Q

Explain the “Organic Soup” model.

A

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

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7
Q

What is Panspermia?

A

pre-formed life that were brought by extraterrestrial comets and meteorites

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8
Q

What is the major problem with the “Organic Soup” model?

A

“Late Heavy Bombardment” - giant impacts constrained the timing of life’s origin

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9
Q

What kind of environment offered the most favourable conditions for early life?

A

black smokers and mid-ocean ridge systems

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10
Q

What 2 chemical compounds did the earliest cells use? What is the evidence?

A

sulfur (H2S) - mats of H2S oxidizing bacteria forming elemental sulfur
methane (CH4) - deep-sea vent emit methane from methanogenic bacteria

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11
Q

What does evidence for ancient life come from? (4)

A
  1. microfossils
  2. biogenic structures (e.g. stromatolites)
  3. isotopes
  4. biomarkers
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12
Q

Which came first?

a) anoxygenic photosynthesis
b) oxygenic photosynthesis

A

a) anoxygenic photosynthesis

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13
Q

What does MISS stand for?

A

microbially induced sedimentary structures

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14
Q

In what kind of environment do MISS form?

A

energetic tidal flat settings

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15
Q

What makes biomarkers particularly useful?

A

they retain some resemblance to the original biological molecules even after decomposition

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16
Q

What are the primary producers of early earth? What kind of photosynthesis did they do?

A

cyanobacteria; oxygenic photosynthesis

17
Q

What occurred during the GOE? What year did it occur?

A
  • first time oxygen accumulated into the atmosphere
  • 2.5 Gyr
18
Q

What organism might have triggered the GOE? How did they do this?

A

cyanobacteria –> produce O2 that is released into the atmosphere

19
Q

What happened during the Lomagundi event?

A

lots of primary productivity and isotopic carbon

20
Q

What is the best GOE evidence? why?

A

sulfur bif –> when sulfur bif disappears, O2 increases in the atmosphere

21
Q

How can you tell if an iron band formed before the GOE?

A

not red

22
Q

Which type of iron is oxidized?

A

ferric (Fe3+)

23
Q

List some evidence for the GOE.

A
  1. banded iron formation (BIF)
  2. sulfur bif
  3. manganese ore
  4. pyrite
24
Q

Why was there a drop in nickel along with CH4 before the GOE?

A

methane-producing bacteria need nickel to survive

25
Q

Do cyanobacteria or methanogens thrive more in shallow water?

A

cyanobacteria

26
Q

During the GOE: (fill in blank with increased/decreased)

sulfate ___________
O2 ____________
CH4 ____________
Ni ___________
Cr ____________

A

sulfate increased
oxygen increased
methane decreased
nickel decreased
chromium increased

27
Q

Oxidation of what compound led to the release of Cr into the ocean?

A

pyrite

28
Q

Where did Cr accumulate during the GOE? open ocean or coast?

A

coast

29
Q

Do basic or acidic conditions mobilize Cr?

A

acidic

30
Q

Explain the process of Earth’s 1st acid rock drainage. (hint: chromium release during GOE)

A
  1. GOE occurs in 2.5 Gyr, increase in O2
  2. O2 oxidizes pyrite that built up (due to previous lack of O2)
  3. sulfate and sulfuric acid form
  4. Cr dissolves and washes into the ocean
  5. ocean becomes acidic
  6. now all the pyrite is gone, and the Cr burst ends (b/c there is no more pyrite to dissolve)
31
Q

What are the theories that address why oxygen took so long to accumulate in the atmosphere (GOE)? (4)

A
  1. cyanobacteria in the Archaean were nutrient starved and never produced enough O2
  2. high dissolved Fe(II) was toxic to cyanobacteria
  3. so many reductants, that it took atmospheric oxygen a long time to accumulate
  4. minimal exposed continental crust –> not enough landmass to be colonized by cyanobacteria mats
32
Q

How can we tell there were animals by observing a stromatolite?

A

no lamin –> animals present (and feeding/burrowing)
lamination –> no animals present

33
Q

What is another name for unlaminated stromatolites?

A

thrombolites

34
Q

What is a very famous area where BIF’s and fossils can be found?

A

Gunflint chert

35
Q

What are acritarchs?

A

organic-walled microfossils of unknown biological affinity, with eukaryotic features

36
Q

Do acritarchs still exist?

A

no

EAS 205 (16 decks)

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