Historical Geology - Proterozoic Eon

Question 1

Where does the understanding of ancient atmosphere comes from?

Answer 1

• geochemistry of rocks and minerals
  • Certain minerals are stable in anaerobic conditions, but
  not in the presence of O2

Question 2

What was the atmosphere like during the early proterozoic period?

Answer 2

• No O2 (relative to modern)
• weathering was taking place so there must have been some sort of atmosphere

– Pyrite (FeS2) common
• Weathers to SO42-in aerobic environment
– Acid conditions

Question 3

How do scientist think Banded iron formation were formed?

Answer 3

They were formed in sea water as the result of oxygen released by photosynthetic cyanobacteria.

• first deposits coincide with origination of photosynthesis
• last deposits coincide with exhaustion of Fe ion supply in ocean

Question 4

How are red beds formed?

Answer 4

Formed when iron oxide minerals are exposed to O2

- rusting of rocks

Question 5

Describe the Precambrian atmosphere.

Answer 5

• anoxic - low in oxygen

- Presence of free oxygen in the atmosphere is a game changer

Question 6

List the geologic and biologic events of the Proterozoic Period.

Answer 6

-modern style of tectonics
- first evidence of O2 build-up in the atmospere
- first abundant fossils
oldest major glaciation

Question 7

What is special about the Bitter Springs formation? Where is it?

Answer 7

Located in Australia

- contains some of the best and most diverse Proterozoic fossils

Question 8

Describe the Bitter Springs Fossils.

Answer 8

Cynobacteria diversified early and spread globally

Question 9

When did Eukaryotes first appear?

Answer 9

First appearance ~1.8 Ga (green algae)

Question 10

What do Eukaryotes require for metabolism?

Answer 10

O2

Question 11

What was life in the proterozoic period dominated by?

Answer 11

prokaryotes and simple eukaryotes

Question 12

is there any environmental change that could explain the

sudden appearance of multicellular animals near the end of the Precambrian?

Answer 12

Neoproterozoic glacial deposits distributed across the entire planet

Question 13

What is the Snowball Earth hypothesis?

Answer 13

• worldwide distribution of Neoproterozoic glacial tillites and dropstones indicates that earth was completely covered in ice.

Question 14

How to create a snowball earth.

Answer 14

• the sun - had lower energy output in the past than it does now
• the continents - high latitudes, clustered in a supercontinent

Question 15

What is albedo?

Answer 15

reflection coefficient

Question 16

How does albedo contribute to the snowball effect?

Answer 16

Snow and ice have a high albedo and seawater, forests, grasslands and soil have a lower albedo so as earth”s climate cooled and ice formed at lower and lower altitudes the ice albedo feedback would speed up and result in lower temperatures.

Question 17

What reverses a snowball earth?

Answer 17

plate tectonics
-If the Earth was so cold that there was NO liquid water on continents, chemical weathering would cease, allowing atmospheric CO2 to build up to very high levels.
-Even in an Icehouse world, CO2 would continue to build up in the atmosphere due to volcanism caused by plate tectonics (at subduction zones).
-What happens when CO2 builds up to frighteningly high
levels in the atmosphere? We get a Greenhouse!

Question 18

When did the breakup of Rodinia take place?

Answer 18

Start of the Phanerozoic Eon. between 560 and 600 Ma