1. Snowball Earth History of Glaciation

2. Main Periods of Glaciation Huronian glaciations 2.5-2.2 billion years ago Late Proterozoic glaciations 900-545 million years ago Late Ordivician glaciations 446-440 million years ago Permo-carboniferous glaciations 310-270 million years ago Pleistocene glaciations 1.8 million – 10,000 years ago

3. Huronian Glaciations How do we get glaciers in a methane-rich atmosphere? - rise of O 2 atmosphere 2.3 bya - elimination of methane in atmosphere - decreased greeenhouse gases - Earth enters deep-freeze Evidence?

4. Huronian Glaciations: Evidence Kump, Kasting, and Crane (2004)

5. Huronian Glaciations: Recovery CO 2 outgassing

6. Snowball Earth Late Proterozoic Glaciation Glaciation on 6 of 7 continents - Antarctica: maybe was glaciated but too much ice today to tell Evidence: tillites, glacial striations, dropstones Continental reconstructions show land was centered around equator

7. http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html Carbonate cap above glacial dropstones in Namibia

8. Bagganjarga tillite and striated bedrock in Norway

9. How did Earth Cool? Less solar luminosity – about 6% less than today Removal of CO 2 from atmosphere continents at equator – silicate weathering even as Earth cools

10. http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

11. How did Earth Cool? Polar ice sheets form at poles and grow increased albedo decreased surface temperatures

12. http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

13. How did Earth warm? Earth completely frozen Silicate weathering ceases CO 2 outgassing continues Ice starts melting decreased albedo increased suface temperatures

14. Times, temps, and rates Glaciers freezing from 30 degrees to equator - decades Surface temperature = -40 or -50 degrees C CO2 buildup during Snowball Earth - 10 million years Entire disappearance of glaciers after CO2 buildup - thousands of years CO2 rich atmosphere, low albedo - surface temperature = 50 or 60 degrees C Silicate weathering increases, climate system restored