Week 14

Question 1

Ice age =

Answer 1

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

Question 2

Glaciation =

Answer 2

Shorter duration period within ice age

Question 3

Phanerozoic eras

Answer 3

Cenozoic

Mesozoic

Palaeozoic

Question 4

Cenozoic periods

Answer 4

Quaternary

Tertiary

Question 5

Mesozoic periods

Answer 5

Cretaceous

Jurassic

Triassic

Question 6

Palaeozoic periods

Answer 6

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Question 7

Precambrian

Answer 7

Proterozoic

Archaean

Question 8

Cenozoic

Answer 8

65-present

Question 9

Mesozoic

Answer 9

250-65

Question 10

Palaeozoic

Answer 10

543-50ma

Question 11

Cretaceous

Answer 11

145-65ma

Question 12

Jurassic

Answer 12

199-145ma

Question 13

Triassic

Answer 13

251-199ma

Question 14

Permian

Answer 14

299-251ma

Question 15

Carboniferous

Answer 15

359-299ma

Question 16

Devonian

Answer 16

416-359ma

Question 17

Silurian

Answer 17

443-416ma

Question 18

Ordovician

Answer 18

488-433ma

Question 19

Cambrian

Answer 19

542-488ma

Question 20

Proterozoic

Answer 20

2.5-0.54ga

Question 21

Archaean

Answer 21

4-2.5ma

Question 22

Archaean overview

Answer 22

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

Question 23

Archaean atmosphere

Answer 23

During Hadean H released to space

‘Cold trap’/inversion/CH4 smog

—> water-rich air trapped and low UV

Global “haze”

Question 24

Faint young sun paradox

Answer 24

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?

Question 25

Explanations for faint young sun paradox

Answer 25

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

Question 26

Forms of chemical weathering

Answer 26

Hydrolysis (key for removing CO2) Dissolution

Question 27

Requirements for chemical weathering

Answer 27

Silicate minerals (in CC) Rainwater CO2 from atmosphere

Question 28

What are weathering rates controlled by?

Answer 28

Temperature - +10’C = x2 Vegetation - 10x compared to bare Soil microbiology Rain/warm/humid = more vegetation/photosynthesis/orogenic —> negative feedback = stability

Question 29

Proterozoic summary

Answer 29

No land plants/animals Primitive sea life Continents = barren rock END- deglaciation, Cambrian explosion and rodinia splitting (W Gondwana, E Gondwana, Laurentia)

Question 30

Odd thing about Proterozoic glaciations

Answer 30

3 major low latitude glacial events

Question 31

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

Answer 31

730-700Ma Older cryogenian Sturtian 665-635Ma Younger cryogenian Marinoan 635-542Ma Ediacaran

Question 32

Explanations for low latitude glaciations

Answer 32

Snowball earth Very high obliquity Continental unzipping Slushball earth

Question 33

Snowball earth, texts

Answer 33

Millions of years glaciations Frozen seas Runaway albedo positive feedback?

Question 34

Snowball earth freeze phase

Answer 34

Low latitude continents have higher albedo>tropical oceans —> extreme tropical weathering (reduces CO2) Once ice is present from 30’ onwards = +ve feedback = snowball earth

Question 35

Snowball earth thaw phase

Answer 35

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

Question 36

Evidence for snowball earth

Answer 36

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

Question 37

Issues with snowball earth

Answer 37

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

Question 38

How the alternatives to snowball earth work:

Answer 38

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)