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ESSHP: Section 1 > Early Earth Events up to Extinctions (4.6-0.5Ga) > Flashcards

Early Earth Events up to Extinctions (4.6-0.5Ga) Flashcards

1
Q

What was dated to 4.4Ga and what is it?

A

Oldest zircon found which is a small weathering-resistant mineral

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2
Q

What are the two important characteristics of zircons for reconstructions?

A

Uranium Isotopes = cross-examined to date their age

Oxygen isotopes = indication of whether or not oceans are present

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3
Q

What do zircons indicate the presence of and why?

A

The high oxygen 18 content suggested that it had formed within the oceans, possibly during an interglacial period, and the fact that these zircons are found in sedimentary rocks, which form under high pressure marine conditions, suggested the presence of oceans at the time of its dating

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4
Q

When were the first Zircons dated to?

A

4.4Ga

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5
Q

Where was the first rock that was thought to have contained the oldest zircon thought to have formed?

A

Western Australia

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6
Q

What is the oldest rock that remains in the same state today and where is it found?

A

4.28Ga in Quebec Canada

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7
Q

What type of rock is the oldest rock that has been found? What is the significance of this?

A

Igneous Rock - suggests that it has undergone major continental, geological and climatological processes that may contain information on really important characteristics

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8
Q

What evidence is there for the earth’s oceans forming as a result of an extra-terrestrial impact?

A

Water rich carbonate-chondrites found in a known extra-terrestrial meteorite that landed on earth have a similar deuterium to hydrogen ratio as the earth’s ocean floors

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9
Q

When is the LHB thought to have happened, which date is probably most accurate?

A

4.1-3.9Ga, however the estimation is that it is closes to 3.9ga

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10
Q

What evidence is there for the LHB on the moon?

A

Craters and rocks taken from them during the Apollo missions are found to date back to 3.9Ga

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11
Q

What is thought to have caused meteorites to bombard the moon and earth during the LHB?

A

Deflection of meteorites or asteroids etc. as a result of resonance between Saturn and Jupiter orbits

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12
Q

What was dated to 3.85Ga

A

oldest sedimentary rocks

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13
Q

What was interesting about the oldest sedimentary rocks?

A

They appear to have featured striping of oxidised and non-oxidised rock

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14
Q

What was the significance of the striping in the oldest sedimentary rocks?

A

It suggested that organisms were present that were carrying out oxygenic photosynthesis.

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15
Q

What was the counter-argument to the striping of oxidised sedimentary rocks being caused by organisms?

A

There did not appear to be any micro structures present in the rock so it was suggested that they were not biologically derived.

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16
Q

When was the oldest sedimentary rocks dated to ?

A

3.85Ga

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17
Q

What was dated to 3.8Ga?

A

In Greenland they found an outcrop of rock (shale) that was banded by carbon

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18
Q

What state was the organic carbon found in the Greenland outcrop?

A

Graphite that was rich in 12C and depleted in 13C.

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19
Q

What was the significance of the state the carbon found within the Greenland shale/rock?

A

Very high 12C content is an indication that organism communities were maybe present because this isotope is much preferred by organisms carrying out photosynthesis

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20
Q

What type of photosynthesis is thought to have been occurring if it was at all in the organic carbon found within the Greenland shale banding?

A

Anoxygenic

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21
Q

What happened 3.7Ga?

A

Anoxygenic photosynthesis is thought to have started

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22
Q

What were the early forms of anoxygenic photosynthesis like and why?

A

Electron donor was probably hydrogen and hydrogen sulphide because water was not very abundant at this time

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23
Q

When did anoxygenic photosynthesis begin?

A

3.7ga

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24
Q

What were dated to 3.5ga?

A

first stromatolites and the first fossils of cells

25
Q

What are stromatolites?

A

Microstructures thought to have been created as a result of organism communities trapping and excreting sediment

26
Q

When are stromatolites dated to?

A

3.5Ga

27
Q

Who were the two scholars that argued over the first fossils of cells discovered and what did they argue over?

A

Schopf argued that the first fossils were biologically derived whereas Brasier et al. argued that they were not biologically derived

28
Q

When were the first fossils of cells dated to?

A

3.5Ga

29
Q

What was dated to 3.26Ga?

A

The first fossilised capturing of cell division

30
Q

When were the first fossilised capturing of cell division dated to?

A

3.26Ga

31
Q

Where was the first fossilised capturing of cell division found?

A

Swaziland

32
Q

What happened 2.7Ga and why?

A

1 billion years after the first anoxygenic photosynthesis is thought to have occurred, oxygenic photosynthesis begins and the production of oxygen led to the first significant rise of oxygen in the atmosphere so far.

33
Q

What prevented the oxygen concentration of the atmosphere reaching a significantly noticeable level as a result of the 2.7Ga event?

A

The oxygen that was produced was rapidly reacted with by Iron in the oceans and molybdenum in the continental rocks.

34
Q

When is oxygenic photosynthesis thought to have begun?

A

2.7Ga

35
Q

List the possible first pieces of evidence in chronological order with dates and what they are an specific indication of?

A
  1. 4Ga - Zircons (when the earth is possibly first inhabitable)
  2. 85Ga - Oldest sedimentary rocks (BIFs that suggested organisms caused rock striping)
  3. 8Ga - Greenland Shale Rock Outcrop (12C-rich graphite suggested that photosynthesising organisms existed)
  4. 5Ga - Stromatolites (micro structures possibly created by microorganisms)
  5. 26Ga - Cell Division (Fossilised in Swaziland)
36
Q

What is the earliest form of evidence for photosynthesis taking place why is it not the earlier thing?

A

3.85Ga sedimentary rocks had a lot of controversy around whether they are produced by microorganisms so they are not evidence. However, the 3.8Ga organic carbon in Greenland is thought to have been strong evidence due to high 12C and graphite form

37
Q

What is the most strongly agreed and latest possible evidence for life?

A

3.26Ga cell division

38
Q

When is the earliest and likeliest forms of evidence for when the earth was habitable?

A

Earliest (4.4Ga) [zircons suggested oceans] and the likeliest (3.85Ga) [after the late heavy bombardment]

39
Q

When is the transpermia idea dated to?

A

4.5Ga

40
Q

What evidence is there for the transpermia idea?

A

meteorite in Antarctica is known to be extra-terrestrial in nature but it contains evidence for fossilised cells that may have been transported here.

41
Q

What is the evidence for the deep hot biosphere idea today?

A

Bacteria found 3km deep in the earths core

42
Q

When did the Great Oxidation event happen?

A

2.45-2.32Ga

43
Q

What evidence is there for the Great Oxidation?

A

Hematites dated back to 2.32Ga

44
Q

Where were the hematites that were found and recognised as the first evidence of the great oxidation found?

A

Canada and South Africa

45
Q

What did the Great Oxidation event cause and what formed

A

The next evolutionary process of more complex life forms

46
Q

What happened 1.8 or possibly 2Ga in terms of life evolution?

A

The first complex life forms (eukaryote cells)

47
Q

When happened between 0.6-0.4Ga in terms of life evolution?

A

The 3rd oxygen rise known as the lesser oxygenation

48
Q

What allowed the 3rd oxygenation rise to happen?

A

the emergence of plants on the land that were much better at carrying out photosynthesis and so more oxygen was produced by them

49
Q

What happened between 0.58Ga and 0.54Ga?

A

Ediacarans evolution process

50
Q

What happened between 0.54-0.5Ga?

A

Cambrian Exchange

51
Q

What was so important about the Ediacarans?

A

The first animals emerged in this period

52
Q

What happened in the Cambrian Exchange?

A

Animals with harder bones which also started to burrow

53
Q

What was crucial for our understanding of what took place during the Ediacarans and Cambrian exchange?

A

organisms started to burrow and preserve much better in the ground which was important for our understanding of how evolution had developed

54
Q

When was the Ediacarans?

A

0.58-0.54Ga

55
Q

When was the Cambrian Exchange?

A

0.54-0.5Ga

56
Q

When did the first animals emerge?

A

0.58 - during the ediacarans

57
Q

What allowed forms of photosynthesis that caused the third oxygen rise to happen, to develop to a substantial level that they could actually cause oxygen rise?

A

Lichens and algae weathered the rocks and then the recycling of nutrients and biomass improved the biosphere in the next generation which meant more oxygen produced more effectively then they were recycled… this formed a positive feedback between plant growth and oxygen production

58
Q

When were all three oxygen rises and what were they characterised by?

A

1st: oxygenic photosynthesis begins
2nd: great oxidation
3rd: plants colonise the land which leads to more oxygenic photosynthesis which is more effective

ESSHP: Section 1 (18 decks)

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