Week 2 - Precambrain

Question 1

What are ratchet mechanisms?

Answer 1

Factors that favour being multicellular, and actively prevent successful reversion to single celled status.

Question 2

Why was the Archaean Earth able to sustain life?

Answer 2

• Its atmosphere is similar in thickness to today (Protection from UV)/
• Atmosphere was made up of primarily N2, CO2, and CH4 necessary for the first anaerobic organisms.
• Extensive ocean (water is essential for life)
• Archean earth had a greenhouse atmosphere that trapped heat (sustained habitable temperature range).

Question 3

What eons comprise the Precambrian super-eon

Answer 3

Hadean, Archaean, Proterozoic

Question 4

When was the Great Oxidation event? and what provides evidence for it?

Answer 4

2.5 billion years ago (took around 200 million years).
banded iron formations in the rock - iron oxide

Question 5

What was the evidence for photosynthetic organisms causing the great oxidation event?

Answer 5

• Fossil stromatolites
• organic carbon-rich shales (suggesting the fixation of carbon into tissue).
• Molecular clock