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LEC.171 > Lecture 1: A brief history of the Earth > Flashcards

Lecture 1: A brief history of the Earth Flashcards

1
Q

What does ‘a’ stand for in Geological time?

A

Annum

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2
Q

How long is an annum?

A

1 Year

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3
Q

What does ‘ka’ stand for in Geological time?

A

Kilo-annum

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4
Q

How long is a kilo-annum

A

1000 Years

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5
Q

What does ‘Ma’ stand for in Geological time?

A

Mega-annum

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6
Q

How long is a mega-annum

A

1 million years (1000 ka)

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7
Q

What does ‘Ga’ stand for in Geological time?

A

Giga-annum

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8
Q

How long is a giga-annum

A

1 billion years (1000 Ma)

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9
Q

What were the four eons?

A

Phanerozoic
Proterozoic
Archean
Hadean

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10
Q

How long was the Hadean eon and how long ago?

A
  1. 7 Ga in length

4. 6 Ga from present

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11
Q

How long was the Archean eon and how long ago?

A
  1. 4 Ga in length

3. 9 Ga from present

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12
Q

How long was the Proterozoic eon and how long ago?

A
  1. 96 Ga in length

2. 5 Ga from present

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13
Q

How long was the Phanerozoic eon and how long ago?

A

0.54 Ga in length

We’re currently in this eon

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14
Q

What eons were in the precambrian eon?

A

Proterozoic
Archean
Hadean

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15
Q

How long ago was the big bang?

A

Approx 13.8 Ga ago

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16
Q

How long ago was the solar system created?

A

Approx 4.5 Ga ago

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17
Q

What theory describes the creation of the solar system?

A

Nebula Hypothesis

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18
Q

What does the nebula hypothesis suggest?

A

the origin of the solar system can be traced to a rotating cloud of gases and fine dust

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19
Q

What is the process of the nebula hypothesis?

A

rotating cloud of gases and fine dust - stars form with the coalescence(joining) of molecular hydrogen → gravitationally unstable GMCs (giant molecular clouds) → stars

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20
Q

What does GMC stand for?

A

Giant molecular clouds

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21
Q

How can GMCs form solar systems?

A

coalesce further (after forming a star) → matter → gravitationally attracted to these stars → solar systems

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22
Q

How can planetary accretion create a planet?

A

little rocks condensing out of the solar nebula as it cools forming bigger rocks. Process continues building up over time eventually coalesces into a planet

23
Q

How is energy created via planetary accretion?

A

kinetic energy → thermal energy

Radioactive decay creates additional thermal energy

24
Q

What different layers in planets did gravitational differentiation form?

A

High density core: mainly iron (Fe)
Medium density mantle: ultramafic silicate rock
Low density crust: felsic silicate rock

25
Q

When was differentiation of the lithosphere complete?

A

4.4 Ga ago

26
Q

What was the crust like 4.4 Ga ago and why?

A

Entirely igneous (because it solidified from a molten state)

27
Q

Lithosphere could have been recycled in an early form of plate tectonics - true or false?

A

True

28
Q

What was the primitive atmosphere composed of and how were these gases released?

A

Mainly Nitrogen, Water vapour and Carbon Dioxide

released via volcanic outgassing

29
Q

What compensated for the weak sun in the primitive atmosphere?

A

High concentrations of greenhouse gases

30
Q

How much dimmer was the sun compared to now in the primitive atmosphere?

A

30% dimmer

31
Q

How long ago did oceans form?

A

Between 4.5-3.8 Ga ago

32
Q

How were oceans formed?

A

water outgassed by volcanoes and brought to earth by comets

33
Q

What could have been the earliest organisms and where would they have been?

A

Hyperthemophilic chemoautotrophs at hot springs or deep hydrothermal vents

34
Q

hyperthemophilic definition

A

can tolerate very hot environments (more than 80 degrees)

35
Q

chemoautotrophs definition

A

primary producers of their energy from chemical reactions (don’t have to eat another animal/thing)

36
Q

Microfossil definition

A

a fossil or fossil fragment that can only be seen with a microscope

37
Q

Stromatolite definition

A

a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment, found in Precambrian rocks as the earliest known fossils

38
Q

What is the oldest evidence for photosynthesis?

A

Oldest chemofossils (organic residue) provide evidence of photosynthesis by 2.7 Ga

39
Q

Chemofossil definition

A

A fossil that consists only of chemicals remaining from the decomposition of a living organism.

40
Q

What was oxygen initially produced by?

A

Photosynthetic cyanobacteria

41
Q

Cyanobacteria definition

A

a division of microorganisms that are related to the bacteria but are capable of photosynthesis

42
Q

How were iron bands formed in the ocean?

A

Iron is soluble in water when oxygen concentrations are low (early oceans)
As oxygen levels rose – iron oxide minerals precipitated from seawater forming bands

43
Q

What factor in the oceans alternated and what was the atmosphere like then?

A

Oceans alternately oxic (O2 rich)/anoxic (O2 deprived), atmosphere anoxic at this time (doesn’t contain ‘free’ oxygen, not in the form O2 or O3)

44
Q

When did oxygen accumulate in the atmosphere?

A

Approx 2.4 Ga ago

45
Q

What evidence is there for O2 levels plateauing at 1% of the atmosphere?

A

rocks that were laid down as sediment in rivers 2 Ga ago, suggesting the atmosphere had enough oxygen to oxidise Fe2+ into Fe3+

46
Q

When did oxygen rise significantly to normal levels and why was this?

A

580 Ma ago
Probably due to mountain building, sediment production, burial of organic Carbon (preventing reactions with O2, causing a build up)

47
Q

What did the cambrian explosion (and the increase in oxygen) cause?

A

First multicellular animals (circa 575 Ma)
Rapid evol. of shells/skeletons → first fossils
542 Ma marks start of the Cambrian period of Phanerozoic eon
All major animal groups appeared within 10 Ma (arthropoda, chordata, mollusca, etc.)

48
Q

How many mass extinctions have there been in the Phanerozoic fossil record?

A

5, and several smaller ones

49
Q

What is the current mass extinction caused by?

A

Humans

50
Q

What are mass extinctions followed by?

A

evolutionary radiations - life evolves to fill the gaps left by dead creatures

51
Q

What causes Mass extinctions?

A

rapid environmental change (meteorite impact, volcanic eruptions, climate change)

52
Q

When’s the earliest plants on land?

A

850 Ma ago

53
Q

When’s the earliest hominids?

A

6 Ma ago

54
Q

When did the first homo sapiens evolve?

A

0.3 Ma ago (300 ka)

LEC.171 (8 decks)

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