Tectonics and Climate 1

Question 1

What is the biggest carbon reservoirs on Earth?

How much carbon are in fossil fuels?

Answer 1

• biggest carbon reservoirs are in the sedimentary rocks

- 4700 Gt(C) (gigatons)

Question 2

(Organic Carbon Cycles)

1. What are the organic carbon cycles?
2. How long does organic carbon stay in the atmosphere?
3. How long does the burial of organic materials into fossil fuel take?

Answer 2

1. Photosynthesis
   CO2 + H2O > CH2O + O2
   - land sources: plants
   - ocean sources: phytoplankton, diatom, cocolithophorids
2. Atmospheric CO2 = 760 Gt(c)
   Photosynthesis = 60 Gt(c)
   Residence time = 760 / 60 = ~10 years

3.
Carbon in sedimentary rocks = 10,000,000 Gt(c)
Sedimentation / Burial = 0.05 Gt(c)
Time taken = 10,000,000 / 0.05 = 200 million years

Question 3

(Inorganic Carbon Cycle)

1. What are the processes for carbonate weathering and calcium-silicate weathering on land and water?
2. How long does inorganic carbon stay in the atmosphere?
3. How long does the burial of inorganic carbon into fossil fuel take?

Answer 3

Carbonate Weathering
- CaCO3 + H2CO3 > Ca2+ + 2HCO3- (dissolution)
Calcium Silicate Weathering
- CaSiO3 + 2H2CO3 > Ca2+ + 2HCO3- + SiO2 + H2O (hydrolysis)

2. 
Atmospheric CO2 = 760 Gt(c)
Carbonate weathering = 0.17 Gt(c)
Calcium Silicate weathering = 0.03 Gt(c)
Residence time = 760 / 0.2 = 1000 years

3.
Carbonate sedimentary rocks = 40,000,000 Gt(c)
Sedimentation / burial = 0.2 Gt(c)
Time taken = 10,000,000 / 0.2 = 20 million years

Question 4

What is the Faint Young Sun Paradox?

Answer 4

• the contradictions between the observations of liquid water in early Earth, and the expectation that the sun’s radiative output was 25 - 30% dimmer when Earth was first formed about 4.6 b.y. ago
• Earth should have been frozen until 2 b.y.

Question 5

Why was the sun less luminous initially?

Answer 5

• Sun’s density increased over time, increasing luminosity (helium accumulates in the core, density of the sun increases, more favourable for nuclear fusion)
• the sun’s luminosity has increased linearly since

Question 6

What are the evidences that water was present in early Earth?

Answer 6

1. Pillowy Basalt, 3 b.y. (Canada, Australia)
   - formed when volcanoes erupt underwater
2. Sedimentary Rocks, 3.8 b.y.
   - require water to form
3. Stromatolites, 2.7 b.y.
   - implications: there was water, life and oxygen
4. Zircon
   - formed when magmatic source interacts with water
   - oldest element on Earth

Question 7

What are the possible solutions to the Faint Young Sun Paradox?

Answer 7

1. Lower albedo in the past (Not probable)
   - Earth’s albedo has to be 0 for this to be possible
2. Geothermal heat from Earth’s interior (not probable)
   - could be sufficient to prevent the oceans from freezing to the bottom
3. Greenhouse Effect (Most likely)
   - earth’s greenhouse effect was larger in the past

Question 8

What periods of time did Snowball Earth occur?

Answer 8

• about 10% of the Earth’s life
• Archean Eon (2.9 b.y.)
• Proterozoic Eon (850 - 550 m.y.)

Question 9

What are the geologic evidence for glaciers? (NOT FOR SNOWBALL EARTH)

Answer 9

1. Tillites
   - packed pebbles, sand and mud. remnants of moraines
2. Glacial Striations
   - scratches from rocks dragged by moving ice
3. Dropstones
   - rocks transported by icebergs and dropped into finely laminated sediment (IRD)
4. Glacial sediments having paleomagnetic orientations consistent with paleo-tropical latitudes

Question 10

What are the evidences for a Snowball Earth?

Answer 10

1. Dropstones within Banded Iron Formation (850 - 550 m.y.)
   - atmosphere during this time was nearly the same as today
   - hypothesised that global ocean was completely covered in ice
   - oceans became anoxic, reduced iron accumulates in the ocean
2. Glacial debris deposited at the tropics
3. Cap Carbonates forms after glacier recedes
4. Carbon Isotopic Signatures
   - Low C12/C13 values in cap carbonates