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ESSHP: Section 1 > Lecture 7: The Rise of Oxygen > Flashcards

Lecture 7: The Rise of Oxygen Flashcards

1
Q

When are the first forms of photosynthesis thought to have occurred?

A

~3.7Ga

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2
Q

Describe the first forms of photosynthesis

A

Anoxygenic - it did not use water or produce oxygen, instead it used hydrogen or hydrogen sulphide.

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3
Q

What colour are the organisms that carried out the earliest forms of photosynthesis thought to be?

A

Green or purple which would have caused the ocean to turn purple

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4
Q

What is the general equation for any form of photosynthesis?

A

Carbon dioxide + electronic donor + light energy = carbohydrates + water + oxygen

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5
Q

What are 3 possible electronic donor?

A

Hydrogen, Hydrogen Sulphide, Ferrell Iron

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6
Q

Why was anoxygenic photosynthesis not based on water?

A

because at the time of its conception it was not an abundant resource especially compared to the supply of other elements that could be used

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7
Q

What is the equation for the most common photosynthesis carried out today?

A

Carbon dioxide + water + light energy = carbohydrates + water + oxygen

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8
Q

How long did it take for the form of photosynthesis carried out by cyanobacteria to develop from the first forms of photosynthesis?

A

~1 billion years

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9
Q

Why was the development of cyanobacteria and their method of photosynthesis so important?

A

Because this form of photosynthesis was crucial for our development and they are technically our ancestors

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10
Q

What does “cyan” in cyanobacteria refer to?

A

Their colour - which caused the oceans to appear the colour they are today

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11
Q

When and what was the first oxygen rise?

A

~2.7Ga - oxygenic photosynthesis begins

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12
Q

How big was the first oxygen rise and why?

A

Small rise - because once the oxygen was released by the cyanobacteria it was rapidly combined with ferrous iron and other compounds that were stored within the oceans and atmosphere

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13
Q

What did the small amount of oxygen released in the first oxygen rise also react with?

A

Metal elements such as molybdenum in continental rocks that are sensitive to reactions where there are even low levels of oxygen

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14
Q

What was important about oxygen’s reaction with metal elements in continental rocks during the first oxygen rise?

A

It was preserved in the record which provided critical evidence of this event

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15
Q

What happened to the concentration of oxygen in the atmosphere, surface ocean and deep ocean following the first oxygen rise?

A

Atmosphere: Big increase
Surface Ocean: transformed from anoxic to partly oxygenated
Deep Ocean: Remained anoxic

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16
Q

How much did the concentration of oxygen in the atmosphere increase by following the first oxygen rise?

A

From 10^-12 atm to 10^-6 atm

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17
Q

What does atm stand for?

A

the standard atmosphere unit

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18
Q

What are the two main ways that oxygen is produced today in great masses for the long-term oxygen balance?

A

oxygenic photosynthesis and recombining the oxygen sugars and carbohydrates again through anaerobic respiration

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19
Q

How is methanogrophy involved in the long-term oxygen balance?

A

Dead organic matter sinks to the ocean to become methane, it then is recombined with oxygen by the bacteria that make up the carbon component of the methane molecule.

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20
Q

How is iron involved in the long-term oxygen balance?

A

It may react with ocean oxygen in the oceans

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21
Q

How do volcanoes contribute to the long-term oxygen balance?

A

They produce elements from below such as hydrogen and methane that react with the oxygen that sneaks in to the atmosphere from the oceans

22
Q

How does the decomposition of cyanobacteria link with other factors to contribute to the long-term oxygen balance?

A

Carbon enters cyanobacteria where it dies then falls to the ocean floor where its biomass is converted back in to methane where it bubbles out of the ocean to react rapidly with the oxygen produced.

23
Q

What will happen to oxygen concentration if methane becomes too abundant?

A

It will accumulate at the top of the atmosphere where it can then be split by ultraviolet radiation leaving hydrogen to be free and because it is so light it will escape to the strato. This means the oxygen cannot react with them and so its concentration as a sole molecule increases

24
Q

When was the Great Oxidation?

A

2.45-2.32Ga

25
Q

What was the concentration of oxygen in the atmosphere like before the Great Oxidation?

A

small and non-important

26
Q

What happened to the oxygen concentration of the atmosphere, surface and deep ocean as a result of the great oxidation?

A

Atmosphere: increased
Surface ocean: partly oxygenated to oxygenated
Deep Ocean: remains anoxic

27
Q

What allowed the surface ocean to become more oxygenated and thus why the deep ocean was not able to?

A

the surface ocean equilibrates with the atmosphere because it is in contact with it. The tides also help to cause and even spread of oxygen across the surface ocean.

28
Q

What did the concentration of oxygen in the atmosphere increase to following the Great Oxidation?

A

from 10^-5 atm to 10^-3 atm

29
Q

What impact did the Great Oxidation have on the iron content?

A

The iron appears to have been secured as rusted bands which indicated that the oxygen concentration was high enough to secure the iron against vigorous erosion

30
Q

What evidence is there for the effect of the GO on the Iron?

A

red beds of sediment (hematites) found in areas of Canada and South Africa date back to 2.32Ga

31
Q

What evidence that iron was rusted before the GO is there?

A

Banded iron formations which are similar in appearance.

32
Q

How were the BIFs thought to be created?

A

Organisms that carried out anoxygenic photosynthesis used Ferrell iron as the electronic donor. As these organisms precipitated they produced banded lines

33
Q

What did Mass Independent Fractionation tell us about the great oxidation?

A

An ozone layer was established which suggests that oxygen concentration increased dramatically and a lot

34
Q

Why would it be difficult or near impossible for the oxygen concentration to go down after an oxygen rise?

A

because of the feedback between oxygen concentration and the incoming radiation

35
Q

what is the feedback between oxygen concentration and incoming radiation?

A

When there is no ozone layer radiation can enter earths atmosphere freely which fuels the methane and oxygen reaction. If oxygen increases to form and ozone layer it reduces the incoming radiation and rate of the reaction with methane. this allows oxygen to increase more as it is not reacting with methane. Eventually this makes it difficult for the oxygen concentration to ever decrease

36
Q

What is the reason for this sudden increase in the concentration of oxygen during the GO?

A

Unknown

37
Q

What is thought to have happened to the methane concentration as a result of the GO? and what would this mean for climate?

A

Decreased which likely reduced the GHG and cooled the planet to a snowball earth

38
Q

What benefit did the GO have for life on earth?

A

The rise of oxygen permitted more energy productive and efficient aerobic respiration, permitting a greater environmental metabolism, permitting the rise of complex eukaryote cells. This marked the dawn of complex multicellular life

39
Q

How old are the first believed to be eukaryote cells dated to?

A

Definitely before 1.8Ga and possibly ~2Ga

40
Q

What alternative idea is there for the occurrence of the first eukaryote cells?

A

That they developed in a niche environment where the oxygen concentration was much higher before it had evened out across the world

41
Q

What was holding back the evolutionary process during the Proterozoic eon and why?

A

The anoxic ocean that contained more volatile and anti-life compounds that were toxic and thus did not permit evolution of more complex organisms

42
Q

When did the third oxygen rise happen and what was it called?

A

Lesser oxygenation (0.6-0.4Ga)

43
Q

What happened to the oxygen concentration of the atmosphere, surface ocean and deep ocean after the third oxygen rise?

A

Atmosphere: increased
Surface ocean: well oxygenated
Deep Ocean: Oxygenated

44
Q

What did the third oxygen rise allow to happen?

A

the next evolutionary process

45
Q

What evidence was there for the evolutionary process that followed the third oxygen rise? When were they dated to?

A

Fossils that displayed much more complex and larger animals - dated to 0.58Ga

46
Q

When were the first animals discovered?

A

During the Ediacarans between 0.58-0.54Ga.

47
Q

What was the Cambrian exchange? and when?

A

Between 0.54-0.5Ga, animals had harder bodies and preserved better as fossils. They started to burrow in to the sea floor which also meant they preserved well

48
Q

What was the crucial step that allowed the third oxygen rise?

A

There needed to be an increase in the number of plants beforehand which could cause oxygen to reach a sufficient level

49
Q

Explain how the third oxygen rise happened?

A

Early plants (lichens and algae) weathered the rocks in search for nutrients which would have facilitated their growth. More biomass would have meant they release more oxygen and organic carbon to the atmosphere and ground. Once they decompose, they assist with the next plants growth and so on. So there is a feedback between the biological weathering of rocks and oxygen production.

50
Q

What was a key indication that oxygen had risen by looking at the fossils of animals after the third oxygen rise?

A

they had eyes and brains which need lots of oxygen to develop

ESSHP: Section 1 (18 decks)

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