Proterozoic

1
Proterozoic

• Snowball Earth Theory

2
Snowball earth theory

• From 750-600 Million years, lots of glaciers
• Sea ice 0.5 mile thick, temp -40 everywhere
• Most organisms die

3
How to warm up to form limestone?

• No photosynthesis
• Build up of CO2
• Switch to hothouse
• Ready for explosion of life after Proterozoic

4
Snowball Earth Theory

• Global glacial deposits younger than 600 Ma
• On top, limestone

5
Snowball Earth Theory

• Limestone only forms in warm water
• Limestone dissolves in cold water