C-The Rise of Oxygen

Question 1

What are the 3 other names for the Great Oxidation Event (GOE)?

Answer 1

Oxygen Catastrophe
Oxygen Crisis
Oxygen Holocaust

Question 2

What was the GOE related to?

Answer 2

Evolution in an anaerobic world

Question 3

When did the GOE occur?

Answer 3

2.4-2.1 Ga (2400-2100mya)

Question 4

What happened in the GOE?

Answer 4

Biologically induced appearance of O2 in Earth’s atmosphere (know when it happened but controversial as to why)

Question 5

What are proxies?

Answer 5

Indirect evidence

Question 6

How did we arrive at the GOE Model? (2)

Answer 6

Proxies preserved physical characteristics that track changes in variables of interest (eg. oxygen levels)
Many proxies available to examine ancient-ocean atmosphere system

Question 7

What 4 ways illustrate the GOE?

Answer 7

1) Distribution through time of detrital pyrite
2) First occurrence of terrestrial red beds
3) Fossil record of cyanobacteria and stromatolites
4) Banded iron formations

Question 8

What is the importance of the presence of detrital pyrite?

Answer 8

Pyrite altered in presence of oxygen
Generates Ferrous Iron (Fe2+) (Iron Sulphide)
Ferrous Iron is soluble in water and reacts in presence of water and oxygen to form iron hydroxides (rust) insoluble residues (Fe3+)
Colour turns to reds, yellows and oranges
Chemically stable

Question 9

What is the chemical formula for oxidation (ferrous iron to ferric iron (rust))?

Answer 9

4FeO + O2 = 2Fe2O3 (Fe2+ to Fe3+)

Question 10

How can we track atmospheric oxygen?

Answer 10

Based on 1st appearance of continental/terrestrial red beds

Question 11

When did red beds first appear?

Answer 11

Approx 2.3 Ga

Question 12

What was the only significant source of free oxygen on Earth’s Surface?

Answer 12

Cyanobacteria (oxygenic photosynthesis)

Question 13

What is the geological evidence of cyanobacteria (and therefore oxygen?)?

Answer 13

Fossilised?
They build distinctive biosedimentary structures (stromatolites)
Laminated sediments = good preservation potential

Question 14

What is the problem with using cyanobacteria as a source of info for GOE?

Answer 14

Cyanobacteria not the only microbes that form stromatolites

Some stromatolites may be abiogenic (purely physical processes) which means no oxygenic photosynthesis

Question 15

What is the estimated time frame for the origin of oxygenic photosynthesis?

Answer 15

3.8 to 2.35 Ga

Question 16

What if you assume older ages for oxygenic photosynthesis are correct? Why is oxygenation delayed until 2.4/2.1 Ga?

Answer 16

Banded Iron Formations

Question 17

What are Banded Iron Formations?

Answer 17

Alternating laminae of chert (type of quartz: silicon dioxide) and iron oxides

Question 18

How are Banded Iron Formations formed?

Answer 18

Episodic reaction between ferrous iron (Fe2+ soluble in water)(sourced from hydrothermal systems and released to water) and O2 forms iron oxides that precipitate out onto sea floor. Chert forms at other times.

Question 19

Why are Banded Iron Formations the answer to the delay in oxygenation?

Answer 19

Can only release O2 into atmosphere when Ferric iron Fe2+ reservoir is used up (or production of O2 exceeds rate it’s being used up at)

Question 20

In what conditions do red beds form?

Answer 20

When oxygen is available

Question 21

What should happen to Banded Iron Formations when more O2 is available?

Answer 21

They should stop and red beds should begin to form

Question 22

Where can red beds be found?

Answer 22

Huronian Group, Canada

Question 23

What are red beds?

Answer 23

Strata of reddish sedimentary rocks that were deposited in hot climates under oxidising conditions

Question 24

What is the key point about lithology and biology?

Answer 24

Lithology/ lithosphere is linked to biology/biosphere and it creates a non-uniformitarian geological record