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Climate > Week 14 > Flashcards

Week 14 Flashcards

1
Q

Ice age =

A

Long period geological t with tendency for cold T and ice accumulation

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2
Q

Glaciation =

A

Shorter duration period within ice age

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3
Q

Phanerozoic eras

A

Cenozoic

Mesozoic

Palaeozoic

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4
Q

Cenozoic periods

A

Quaternary

Tertiary

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5
Q

Mesozoic periods

A

Cretaceous

Jurassic

Triassic

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6
Q

Palaeozoic periods

A

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

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7
Q

Precambrian

A

Proterozoic

Archaean

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8
Q

Cenozoic

A

65-present

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9
Q

Mesozoic

A

250-65

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10
Q

Palaeozoic

A

543-50ma

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11
Q

Cretaceous

A

145-65ma

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12
Q

Jurassic

A

199-145ma

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13
Q

Triassic

A

251-199ma

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14
Q

Permian

A

299-251ma

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15
Q

Carboniferous

A

359-299ma

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16
Q

Devonian

A

416-359ma

17
Q

Silurian

A

443-416ma

18
Q

Ordovician

A

488-433ma

19
Q

Cambrian

A

542-488ma

20
Q

Proterozoic

A

2.5-0.54ga

21
Q

Archaean

A

4-2.5ma

22
Q

Archaean overview

A

32% earth’s history

Erosion = -geochemical evidence

Hydrosphere present (Greenland rounded clasts)

Probably low continental land area (small and independent; end = joined)

Blue green algae = stromatolites precipitation

Likely reducing atmosphere (no free O, CH4/CO2 dominated) - outgassing of earth’s atmosphere = free stable O at end

Life (Cyanobacteria - photosynthesis = O, red beds) 3.6-3.8Ga

23
Q

Archaean atmosphere

A

During Hadean H released to space

‘Cold trap’/inversion/CH4 smog

—> water-rich air trapped and low UV

Global “haze”

24
Q

Faint young sun paradox

A

Luminosity varies due to molecular mass
- over t H —> He = increases

Early sun 70% modern brightness

SO WHY IS 1ST GLACIATION ~2.7Ga and LOTS OF EVIDENCE FOR LIQUID WATER?

25
Q

Explanations for faint young sun paradox

A
  1. Volcanic outgassing = more GHG
  2. Impact heat 4.2-3.9Ga
  3. Dust in atmosphere due to impacts
  4. Less heat loss to atmosphere
  5. Less weathering (less continents) = less CO2
  6. Lower T = less chemical weathering = less CO2
  7. Fewer plant species = C precipitation not forced
26
Q

Forms of chemical weathering

A

Hydrolysis (key for removing CO2)

Dissolution

27
Q

Requirements for chemical weathering

A

Silicate minerals (in CC)

Rainwater

CO2 from atmosphere

28
Q

What are weathering rates controlled by?

A

Temperature
- +10’C = x2

Vegetation
- 10x compared to bare

Soil microbiology

Rain/warm/humid = more vegetation/photosynthesis/orogenic

—> negative feedback = stability

29
Q

Proterozoic summary

A

No land plants/animals

Primitive sea life

Continents = barren rock

END- deglaciation, Cambrian explosion and rodinia splitting (W Gondwana, E Gondwana, Laurentia)

30
Q

Odd thing about Proterozoic glaciations

A

3 major low latitude glacial events

31
Q

What/when were the 3 major low latitude G events?

A

730-700Ma
Older cryogenian
Sturtian

665-635Ma
Younger cryogenian
Marinoan

635-542Ma
Ediacaran

32
Q

Explanations for low latitude glaciations

A

Snowball earth

Very high obliquity

Continental unzipping

Slushball earth

33
Q

Snowball earth, texts

A

Millions of years glaciations

Frozen seas

Runaway albedo positive feedback?

34
Q

Snowball earth freeze phase

A

Low latitude continents have higher albedo>tropical oceans
—> extreme tropical weathering (reduces CO2)

Once ice is present from 30’ onwards = +ve feedback = snowball earth

35
Q

Snowball earth thaw phase

A

Ice covered surfaces don’t react with volcanic CO2

Oceans frozen 5-30Ma

CO2 accumulation = super greenhouse = melt

Equator open ocean absorb more sunlight (lower albedo) = positive feedback

36
Q

Evidence for snowball earth

A

GLACIAL

PALAEOMAGNETISM

BIFS

CAP CARBONATES
N.B possible explanations:

  • rapid hothouse earth deposition
  • high atmospheric CO2 after snowball earth = rapid continental weathering
  • upwelling alkalinity-charged ocean deep waters
37
Q

Issues with snowball earth

A

Could be low latitude alpine style G

Could be local O-deprived basins

Large errorbars for dates

Recovery?!

No biological record gap
- Refugia?!

Palaeomagnetism sites ~reliable

38
Q

How the alternatives to snowball earth work:

A

V HIGH OBLIQUITY
>54’ —> strong equatorial seasonality
Lower mean T at equator than piles
But recovery?!

CONTINENTAL UNZIPPING
Rodinia break up
High plateaus = accumulate ice
Rift zone basins = BIFS

SLUSHBALL EARTH
Life can survive
Water around equator (for sedimentary rock deposition and G ice streams requiring space to increase velocity)

Climate (11 decks)

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