Quiz on lectures 7-13 with answers

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When did oxygenic photosynthesis evolve?
Roughly 2.7 Ga
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When was the Great Oxidation?
Roughly 2.4 Ga (2.45-2.32 Ga)
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Name two sources of evidence for the Great Oxidation
Appearance of oxidised iron in paleosols (ancient soils), appearance of red beds, disappearance of mass independent fractionation (MIF) of sulphur isotopes
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What type of metabolism do most eukaryotes use?
Aerobic respiration
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When was there a second rise in atmospheric oxygen?
Roughly 600-400 Ma
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To what latitude does sea-ice have to extend to trigger snowball Earth?
About 30 degrees north/ south (the Tropics)
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How does the Earth get out of a snowball state?
By a build up of CO2 in the atmosphere (plus maybe dirt/mud collecting on the ice and making it darker)
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Name three sources of geological evidence for snowball Earth
Paleomagnetism showing low latitudes for glacial (striated/scratched) rocks, dropstones, appearance of banded iron formations, cap carbonates
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What could have made it cold enough to trigger the Neoproterozoic snowball Earths?
Increase of silicate weathering due to continents gathering at the equator, and/or basalt outpouring, and/or life accelerating weathering
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How did complex life survive snowball Earth?
In warm ‘oases’ e.g. around volcanic hot springs
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When did the first bryophyte plants evolve?
In the Ordovician Period, around 475-460 Ma
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When did the first vascular plants evolve?
In the Silurian Period, around 425 Ma
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When did the first forests appear?
In the Devonian Period, around 385-375 Ma
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How do plants cool the planet?
They accelerate silicate weathering
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By how much do plants amplify weathering rates?
A factor of 2 to 10
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Name one process by which the evolution of plants increased the oxygen content of the atmosphere.
Accelerating phosphorus weathering and thus increasing organic carbon burial (and producing high C/P material and thereby increasing organic carbon burial)
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What is the lower limit on oxygen (% of atmosphere) consistent with fossil charcoal?
15-17%
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What is the upper limit on oxygen (% of atmosphere) consistent with continuous forests?
25-30%
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Why do models predict a peak in atmospheric oxygen in the Carboniferous?
Because large amounts of organic carbon were deposited at that time (and are still with us as coal today)
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Has lack of oxygen been holding back the evolution of intelligent life?
No, not for the last 370 million years at least
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When was the largest mass extinction in the Phanerozoic?
251 Ma at the end Permian
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What was the trigger for the end Permian mass extinction?
Volcanism – eruption of the Siberian traps
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Name two changes in the Earth system that contributed to the end Permian extinction
Ocean anoxia, ocean acidification, extreme global warming, possible depletion of the ozone layer.
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What triggered the end Cretaceous extinction
An asteroid impact, plus volcanism – eruption of the Deccan traps
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What happened to life in the ocean at the end Cretaceous?
Most of it died / productivity shut down, thus adding CO2 to the atmosphere
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When was the Paleocene-Eocene Thermal Maximum (PETM)?
55ma
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What is a hypothesised trigger for the PETM?
Volcanic intrusion into fossil fuel reserves in the North Atlantic releasing methane (CH4) and CO2 to the atmosphere
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What is thought to have amplified the PETM?
Warming triggering release of CH4 from frozen hydrates/clathrates in ocean sediments
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Roughly how much carbon was released at the PETM?
1500-4500 GtC (billion tonnes of carbon) depending on what its isotopic composition was
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How long did it take the carbon cycle and climate to recover at the PETM?
Over 100,000 years
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In the Himalayan uplift hypothesis what causes Cenozoic climate cooling?
Mountain uplift increasing physical erosion and chemical (silicate) weathering, thus taking up CO2 from the atmosphere
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Note one problem with the hypothesis
No clear evidence for a global increase in erosion, timing of CO2 drawdown does not match well the timing of major phases of mountain building
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Name two sources of evidence for reconstructing past CO2 levels
Fossil leaves (stomata density), paleosols (carbon isotope composition), phytoplankton (carbon isotope composition)
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What has happened to CO2 levels over the last 24 million years?
They have been remarkably stable (around 250-300ppm)
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When did the first hominins diverge from other chimpanzees?
Around 6 Ma
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Other cards in this set

Card 2

Front

When was the Great Oxidation?

Back

Roughly 2.4 Ga (2.45-2.32 Ga)

Card 3

Front

Name two sources of evidence for the Great Oxidation

Back

Preview of the front of card 3

Card 4

Front

What type of metabolism do most eukaryotes use?

Back

Preview of the front of card 4

Card 5

Front

When was there a second rise in atmospheric oxygen?

Back

Preview of the front of card 5
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