Snowball Earth History of Glaciation Main Periods of Glaciation Huronian glaciations billion years ago Late Proterozoic glaciations million years ago Late Ordivician glaciations million years ago Permo-carboniferous glaciations 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 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 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 How did Earth Cool? Polar ice sheets form at poles and grow increased albedo decreased surface temperatures 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 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