Deep Time Earth Quiz - lectures 7-12

Question 1

Dates: oxygenic photosynthesis evolution and the Great Oxidation?

Answer 1

~2.7 Ga and roughly 2.4 Ga

Question 2

Sources of evidence for the Great Oxidation?

Answer 2

Disappearance of BIFs
Disappearnace of MIF of sulphur isotopes
Appearance of red beds and oxidised iron in paleosols (ancient soils)

Question 3

What type of motabolism do most eukaryotes use?

Answer 3

Aerobic respiration

Question 4

When was there a second rise in atmospheric oxygen, what is it associated with?

Answer 4

600-400 Ma with the rise of plants

Question 5

To what latitude does sea-ice have to extend to rigger snowball Earth, and what could have triggered the Neoproterozoic snowball Earth?

Answer 5

30degrees N/S of equator
The continents were clustured around the equator, providing warm and moist conditions, so silicate weathering was greater, and/or basalt outpouring, and/or life accelerating weathering

Question 6

How does the Earth get out of a snowball state? What evidence even is there for such events?

Answer 6

Built-up of CO2 in the atmosphere as biological pump shuts down (and dark patches, increasing absorption)
Evidenced by cap carbonates, BIFs, striations and dropstones and their low paleo-latitudes

Question 7

When was the first life and how did it survive the snowball Earth’s?

Answer 7

Originated in Archean Eon (~3.8 or 3.5 or 3.25 Ga)

Supposedly survived snowball Earth’s in warm oases nearby hot springs or volcanic areas

Question 8

Give the dates and epoch names (within the Paleozoic Era, in the Phanerozoic Eon) associated with the evolution of:

1. Bryophyte plants
2. First vacular plants
3. First forests

Answer 8

1. Ordovician (~475-460Ma)
2. Silurian (425Ma)
3. Devonian (385-375Ma)

Question 9

How do plants cool the planet and by how much?

Answer 9

Plants accelerate silicate weathering, which increases C burial, which reduces greenhouse gas blanket, so less heat retained
Plats amplify this weathering by a factor of 2-10

Question 10

How did the evolution of plants increase O content of the atmosphere? Did a lack of O hold back the evolution of intelligent life?

Answer 10

Accelerating phosphorus weathering, increasing organic carbon burial (and producing high C/P material and thereby increasing organic carbon burial)

No, at least not for the last 400 Myrs because the charcoal record shows it can’t have gone below 15%

Question 11

What is the upper and lower limit on oxygen? Why?

Why do models predict a peak in atmospheric oxygen in the Carbonigerous?

Answer 11

Lower limit - 15% (fossil charcoal)
Upper limit - 25-30% (continuous forests in records)

Peak oxygen - lots of organic carbon buried at that time, which is a source for O, still as coal today

Question 12

What are the 2 main extinction events, which was largest and when did they occur?

Answer 12

End-Permian = 250 Ma, the largest
End-Cretaceous = 65 Ma

Question 13

What were the mass extinction triggers and what evidence is there?
What happened to life in the ocean at the end of the cretaceous?

Answer 13

End-Permian - Siberian traps eruption (increasing CO2, CH4); ocean anoxia, acidification, ozone damage, global warming
End-Cretaceous - Meteorite and Deccan traps eruption = most life died, productivity shut down, adding more CO2

Question 14

What and when was the PETM and what is a hypothesised trigger?

Answer 14

Paleocene-Eocene Thermal Maximum (in the Cenozoic Era, the last of the Phanerozoic), at 55 Ma
A period of unsually rapid warming and increased CO2 and CH4 - perhaps triggered by volcanic magma plumes in the North Atlantic that cooked organic material into such gases

Question 15

What amplified the PETM and roughly how much C was released? How long did it take the carbon cycle and climate to recover?

Answer 15

Warming triggered the release (and destabilisation) of Methane Hydrates in ocean sediments
Recovery period is about 100,000 years