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ESSHP: Section 1 > Lecture 11: Extinction Events > Flashcards

Lecture 11: Extinction Events Flashcards

1
Q

Why is evidence of extinction events mostly confined to the Phanerozoic eon?

A

There is less evidence for them

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2
Q

What are the two main extinction events in the Phanerozoic eon? Which was biggest

A

End Permian Extinction
End Cretaceous/Mesozoic extinction.
End Permian biggest

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3
Q

What extinction event is known for the extinction of dinosaurs?

A

End Mesozoic/Cretaceous

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4
Q

What happened to the biodiversity during the Phanerozoic?

A

Increase in biodiversity - most present on land compared to oceans

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5
Q

Where are the mass extinction events inferred from? Why is this strange?

A

Most are identified from the MARINE sedimentary record, even though there were more mammals on the land.

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6
Q

Why is the marine sedimentary record used instead of the continental sedimentary record?

A

Because it preserved better

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7
Q

Describe the state of biodiversity between the Ordovician and Permian (Phanaerozoic) eras

A

Steady state with occurrences of extinction events

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8
Q

What collective term is used to describe the biggest extinction events during the Phanerozoic?

A

‘big five’

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9
Q

What are the ‘big five’ extinction events?

A 
End Ordovician 
Late Devonian
End Permian
End Triassic 
End Cretaceous
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10
Q

How is the magnitude of an extinction event calculated?

A

The percentage loss of biodiversity

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11
Q

What is the most commonly believed reason for extinction events?

A

Extra-terrestrial impacts

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12
Q

What is the catch with extra-terrestrial impacts possibly causing extinction events?

A

Some are thought to cause extinction events where as others have not

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13
Q

What are the two categories of causes for mass extinction events and what do the include?

A

External: meteorites and massive volcanism
Internal: feedbacks within the earth system

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14
Q

What was the state of the Pangea supercontinent at the start of the end Permian extinction?

A

It was starting to break up but was largely still together in places

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15
Q

What was the impact of the end Permian extinction on marine, continental and total biological families?

A

Continental: 63%
Marine: 49%
Total: 61%

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16
Q

What is mutagenesis?

A

An alteration of the ozone layer permits greater penetration of UV light that morphs and mutated different plant types

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17
Q

What happened to forests during the end Permian extinction?

A

they were eradicated

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18
Q

What were the forests replaced with and how long did it take for forests to recover?

A

Forests were replaced with different fern types. It tool ~5myr for forests to recover

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19
Q

What impact did the replacement of forests with fern types have on soils?

A

Reduction in strength and increased erosion

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20
Q

What was the only remaining animal on land after the end Permian extinction?

A

Lystrosaurus - lizard

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21
Q

What evidence is there that suggests the end Permian extinction was caused by a massive external impact event from an asteroid?

A

Quartz structures, massive crater on Australian coast, fullerenes present with trapped Argon and Helium representing apparently an isotopic signature from an extra-terrestrial source

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22
Q

What was the Achilles heal in the evidence for an extra-terrestrial impact event causing the end Permian extinction?

A

There was no Iridium present in the craters or signatures that were apparently caused by an asteroid. This is regarded as the key piece of evidence when determining whether something is caused by extra-terrestrial impacts

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23
Q

What was another fault in the evidence for an extra-terrestrial impact event causing the end Permian extinction?

A

Fullerene results that were presented initially were not replicable through sophisticated models

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24
Q

Was the extra-terrestrial cause for the end Permian extinction rejected?

A

yes

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25
Q

Describe the volcanic situation at the end of the Permian era?

A

Massive volcanic eruptions of Siberian traps (known today) that are large igneous provinces.

26
Q

What is the volcanic theory for how the end Permian extinction event happened?

A

the eruptions in the Siberian Traps were enormous and happened in the space of 1 million years, possibly even tens of thousands of years. the release of gases in to the atmosphere could have depleted the ozone layer which would have led to the mutagenesis and extinction of plants

27
Q

What area did the eruptions of the Siberian Traps cover and what depth and volume were the lava flows?

A

Area covered: 1.6m KM squared
Flow Size: 2m km squared
Depth: 3000m

28
Q

How did the volcanic theory for the end Permian extinction also alter the carbon cycle, further contributing to the extinction event’s occurrence?

A

As the eruptions work their way up through the crust, they cook the various carbon gases that are preserved in the sedimentary rock layers. They are then released to the atmosphere which leads to the increased concentration of carbon

29
Q

What record is there for how the carbon cycle changed as a result of volcanic eruptions?

A

12C is preferred by 13C by plants because of efficiency in photosynthesis. During the end Permian extinction, the sedimentary rock layer identified an injection of 13C depleted/12C rich material. This is because the plants within the sedimentary rock (rich in the preferred 12C) are cooked, as lava rises the carbon stored is then released to atmosphere which causes an enrichment of it in the atmosphere as found in the record.

30
Q

How much is the temperature estimated to have increased as a result of the increased carbon released from sedimentary cooking?

A

~10 degrees Celsius

31
Q

What happens to the carbon after it has entered the atmosphere? and how does it lead to extinction of some ocean species?

A

the carbon dissolves at the ocean’s surface which causes it to acidify. this inhibits formation of calcium carbonate shells which is bad for calcifying organisms in the oceans and so they suffer extinction.

32
Q

What did Lenton discover about the carbon acidification of oceans leading to extinction process?

A

It would have been rapid

33
Q

What happened to the oceans before they became acidified during the end Permian?

A

They became anoxic - demonstrated by loss of larger and more complex species from record and rise of hydrogen sulphide which only happens when oxygen decreases.

34
Q

How did the rise of hydrogen sulphide in the light of increasingly anoxic oceans affect life?

A

It is a compound dangerous for life

35
Q

What was the volcanic-related cause of increasing anoxia in oceans?

A

Lava flows are rich in phosphorus and when cooled to basalt they are easily weathered. meaning more phosphorus is washed to oceans which fuels production of oxygen. However, once the oxygen sinks to bottom of the oceans, it gets respired by organisms that do not have as much access to it thereby using it up. If this oxygen is not replenished then it will become anoxic.

36
Q

What is the temperature-related cause of increasing anoxia in oceans?

A

Temperature increase of world mean carbon dioxide will not dissolve as well as in to the oceans. This means there is a reduced supply of the oxygen component of CO2, but continued consumption of it will mean it becomes more anoxic

37
Q

What is the positive feedback that amplifies how increased phosphorus in to the oceans leads to anoxia?

A

When oceans receive phosphorus, biosphere becomes stronger and more productive meaning that more oxygen is used up. Phosphorus is recycled better, while more oxygen is used up leading to intense anoxia of oceans.

38
Q

What is the long-term negative feedback that will resupply the oxygen concentration back to the oceans?

A

Improved productivity will increase organic carbon burial which over a longer term will improve the marine biosphere leading to the resupply of oxygen

39
Q

What does the combination of the short-term positive feedback and long-term negative feedback mean for the oxygen concentration of the oceans?

A

The positive feedback will be counteracted by the long-term negative feedback to form a steady-state equilibrium

40
Q

What impact is the end Permian extinction thought to have had on the carbon cycle and ocean anoxia?

A

Oscillated for ~5myr

41
Q

How long was it estimated that the complex ecosystems took to recover from the end Permian extinction? How long did it take for global biodiversity to recover?

A 
Ecosystems = 10myr
Biodiversity = 100myr
42
Q

What transition occurred in the ecological state of the earth, especially in the oceans after the end Permian extinction?

A

Increase in the proportion of mobile animals to non-mobile animals, as well as proportion of predators to prey

43
Q

What appeared after the end Permian extinction?

A

Dinosaurs as well as gymnosperm plants

44
Q

What was the state of Pangea at the start of the end cretaceous extinction?

A

Started to break up across the world and was close to the current state of the world.

45
Q

What percentage of genera became extinct during the cretaceous extinction?

A

60%.

46
Q

What types of species were extinct during the end cretaceous extinction and what ones survived?

A

Dinosaurs were unable to survive whereas animals that could shelter or burrow (e.g. crocodiles) survived.

47
Q

What happened to vegetation during the end Permian extinction?

A

Evergreen vegetation suffered more than high-attitude deciduous vegetation

48
Q

What evidence was there for the end cretaceous extinction event being caused by an extra-terrestrial impact?

A

Alvarez & Alvarez (1980s) found a strong Iridium concentration in the ground that was supported by the work by Hilderbrand who produced evidence of a 10km wide crater caused by an asteroid.

49
Q

What other theory has been put forward for the cause of the end cretaceous extinction event?

A

Increase in volcanic activity in the Deccan Traps (smaller than Siberian Traps).

50
Q

How much lava outpoured from the Deccan Traps over what period just before the end cretaceous extinction?

A

365,000 km cubed over 800kyr

51
Q

What was the effect of the Deccan Traps eruptions on the end Cretaceous extinction but what uncertainty is there?

A

Warming the planet through release of GHG, however it is not certain whether this or the extra-terrestrial impact event happened first

52
Q

What happened to ocean photosynthesis during the end cretaceous extinction?

A

Wiped out/partially shut down

53
Q

What happened to calcerous nanoplankton during the end cretaceous extinction?

A

90% species loss - only 12% remaining

54
Q

What causes are put forward for the reduction in ocean photosynthesis?

A
  1. Annoxia of the oceans (another question)

2. Displacement of material from an asteroid that blocked sunlight

55
Q

What was the main consequence of the reduction in ocean photosynthesis during the end cretaceous extinction?

A

Shutting down of the biological pump

56
Q

What is the biological pump?

A

Photosynthesis activity at the ocean surface prefers 12C over 13C which means that as the organisms decompose and sink the 12C is transported/pumped down, leaving the 13C at the surface.

57
Q

What is created as a result of the biological pump related to the carbon isotopes?

A

Gradient of more 12C at the bottom and then as you reach the ocean surface the 13C concentration increases

58
Q

What appears to have happened to the biological pump gradient during the end cretaceous extinction?

A

Gradient appears to have disappeared

59
Q

What happens as a result of the shutting off of the biological pump during the end cretaceous? why?

A

Dying off of nanoplankton and other types of plankton means that they do not decompose and so less carbon is transported down to the bottom of the oceans. This would have been used to form carbonate shells but there is evidence of them decreasing in occurrence as a result.

60
Q

What does the shutting off of the biological pump mean for the carbon cycle and climate?

A

More carbon at surface ocean means it is more able to come out of the ocean leading to a 2-3x increase in the atmospheric CO2 as the carbon reacts with oxygen, leading to warming.

61
Q

What are general consequences of extinction events?

A

Origination rates increase - loss of life forms existed before extinction means new types of life can occur. This is how mammals arrived after the end cretaceous which allowed eventually humans to develop

ESSHP: Section 1 (18 decks)

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