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eas > Lecture 26: Proterozoic Biosphere > Flashcards

Lecture 26: Proterozoic Biosphere Flashcards

1
Q

What years did the Proterozoic era span?

A

Between 2.5 billion and 540 million

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2
Q

How long ago did the Great Oxidation event occur?

A

2.5 Billion years ago

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3
Q

What was the Great Oxidation event?

A

A period in time when the atmosphere accumulated oxygen

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4
Q

What was the composition of the atmosphere before the great oxidation?

A

N2, CO2 and Methane

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5
Q

What gives evidence for early life?

A
  • Stromatolites
  • Microfossils
  • Isotopes
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6
Q

Why are sulfur isotopes able to tell us about the atmosphere?

A

Because organisms tend to fractionate these isotopes which are measurable and then tell us about the atmosphere

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7
Q

How is Pyrite affected by the presence of oxygen?

A

It forms sulfuric acid

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8
Q

How does sulfur evidence of the great oxidation event?

A

Fractionation of sulfur in by bacteria tells us that there was oxygen from pyrite that went into the ocean which tells us there was oxygen in the atmosphere

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9
Q

How is 33 sulfur produced?

A

The lack of oxygen in the atmosphere causes a lack of Ozone which is affected by fluxes in UV

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10
Q

How is 33 Sulfur evidence for the great oxidation event?

A

The levels of 33 sulfur dropped after the great oxidation event meaning that ozone existed due to the lack of UV rays

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11
Q

What is a Red Bed?

A

Iron oxide that precipitated onto other things

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12
Q

How do Red Beds tell us there is oxygen in the atmosphere?

A

Because the iron in the ocean would not precipitate out unless there is oxygen in the atmosphere

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13
Q

How do Red breds provide evidence of the Great Oxygenation Event?

A

When iron precipitates out of oceans, atmospheric oxygen is needed, telling us that oxygen was available in the atmosphere

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14
Q

What does increase roundness of a rock mean?

A

The more its been transported

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15
Q

How do rounded pyrite grains tell us about the Great Oxidation event?

A

Rounded pyrite grains mean that there was no oxygen in the atmosphere because if there was oxygen in the atmosphere it would have oxidized the pyrite

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16
Q

How does Manganese tell us about the great oxidation event?

A

Finding layers of manganese oxide tells us that there was oxygen in the atmosphere

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17
Q

How many years does it take to fully oxidate the planet?

A

About 200 million years

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18
Q

Through what period did the great oxidation event occur?

A

2.5 - 2.3 billion years

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19
Q

How many years ago did banded iron formations form?

A

3.8 billion years ago to 1.8 billion years ago

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20
Q

What kind of sediments are Banded Iron Formations?

A

Chemical sediments with no sand, silt or clay just iron oxide

21
Q

What metal is rust?

A

Ferrihydrite Fe(OH)3

22
Q

What are the two ways that BIFs are proposed to develop?

A

One method is through oxygenic photosynthesis of plankton and the other is through oxygen photosynthesis producing ferrihydrite

23
Q

What is the process of ferrihydrite development driven by?

A

Biological processes

24
Q

What are the two oxidation states of Chromium?

A

The reduced phase and the oxidized phase

25
Q

Which phase of chromium is insoluble?

A

The reduced phase

26
Q

How does chromium tell us about the great oxidation event?

A

Sediments in the ocean accumulating chromium tells us that there is either oxygen or a lot of acid from pyrite

27
Q

Why does the level of chromium drop?

A

Because the chromium reserves are all depleted after being reacted with acid

28
Q

What are the various indicators for life in the Archaea?

A
  • Stromatolites
  • Microfossils
  • Isotopes
  • Biomarkers
  • Microbial mats
29
Q

Why aren’t stromatolites abundant today?

A

Animals eat them today

30
Q

What is a Thrombolite?

A

A messed up stromatolite that has been eaten by organisms

31
Q

How long ago did Gunflint Cherts exist?

A

1.9 billion years ago

32
Q

Why are Gunflint cherts the best example of life in the precambrian?

A

They contain many microfossils that are well preserved

33
Q

What kind of bacteria are preserved in Gunflint Chert?

A

Microfossils of cyanobacteria

34
Q

What is Gyrpanis?

A

A large algae that formed 1.9 years

35
Q

How long ago did Red Algae form?

A

1.2 billion years ago

36
Q

What is Acritarchs?

A

A fossil with a complex structure that was probably biological but aren’t sure what they are

37
Q

What is Rodinia associated with?

A

Snowball earth

38
Q

How do we know there was Global Galciation?

A

Because we find rocks at the equator which tell us there was a glacier

39
Q

Why were snoball events shortlived?

A

Chemical weather by geothermal energy forms CO2 into the atmosphere which caused things to weather and melt

40
Q

How many times did snowball earth occur?

A

Twice

41
Q

How did life exist during the snowball events?

A

There were pockets of open water

42
Q

What is the rise of animals associated with?

A

Deglaciation

43
Q

How does glaciation cause the rise of animals?

A

Deglaciation increases the amount of nutrients available increasing primary productivity allowing for evolution

44
Q

What are Ediacaran Fauna?

A

Fossils found after deglaciation that are visible to the naked eye that disappeared after the proterozoic era

45
Q

Why are Fauna significant?

A

Because they are the very first organism to form shells

46
Q

What is seen at the end at the precambrian?

A

Pediatric Fauna and worm burrows but still small in general

47
Q

What is seen at the beginning of the Precambrian?

A

Bacteria

48
Q

What is seen in the Phanerozoic?

A

Animals and Plants

eas (33 decks)

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