Snowball Earth History of Glaciation Main Periods of

Snowball Earth History of Glaciation

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

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?

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

Huronian Glaciations: Recovery CO 2 outgassing

Snowball Earth Late Proterozoic 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

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

• Bagganjarga tillite and striated bedrock in Norway

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

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

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

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

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

Times, temps, and rates Glaciers freezing from 30 degrees to equator - decades Surface temperature = -40 or -50 degrees C CO 2 buildup during Snowball Earth - 10 million years Entire disappearance of glaciers after CO 2 buildup - thousands of years CO 2 rich atmosphere, low albedo - surface temperature = 50 or 60 degrees C Silicate weathering increases, climate system restored