Snowball Part_part1.pdf

Breathe Deep and then… freeze… Present Phanerozoic Proterozoic Archean Textbook Figure 12-11 ¡ Currently, atmospheric methane concentration is ~ 1900 ppb ¡ Methane is a potent greenhouse gas. ¡ However, a higher concentrations (>1000 ppm), it has an anti-greenhouse effect http://upload...

Breathe Deep and then… freeze… Present Phanerozoic Proterozoic Archean Textbook Figure 12-11 ¡ Currently, atmospheric methane concentration is ~ 1900 ppb ¡ Methane is a potent greenhouse gas. ¡ However, a higher concentrations (>1000 ppm), it has an anti-greenhouse effect http://upload.wikimedia.org/wikipedia/commons/8/84/Titan_in_natural_color_Cassini.jpg Textbook Figure 12-5 Present Phanerozoic Proterozoic Paleo Proterozoic Archean Textbook Figure 12-11 Lake Huron, southern Canada ¡ Redbeds ¡ Sediments deposited under ice ¡ Detrital uraninite and pyrite 2.2 Ga 2.45 Ga http://www.humboldt.edu/~natmus/lifeThroughTime/PreCam.web/Conglom20.JPG Pyrite and uraninite are two minerals that weather rapidly when exposed to oxygen. But in 2.45 Ga old rocks: • they are common • http://www.humboldt.edu/~natmus/lifeThroughTime/PreCam.web/Conglom20.JPG show evidence of transport over long periods and distances Drop Stone, Gondwana Formation, Huronian Supergroup, Ontario Dropstone Huronian Supergroup, ON Melezhik (ed): Frontiers in Earth Science, 2013 Lake Huron, southern Canada 2.2 Ga ¡ Redbeds free O2 ¡ Sediments deposited under ice Glaciation ¡ Detrital uraninite and pyrite no O2 2.45 Ga These rock sequences were also observed elsewhere: Western Australia, South Africa, Fennoscandia These rock sequences were also observed elsewhere! Western Australia, South Africa, Fennoscandia. Onset of Mass-Dependent Sulfur Isotope Fractionation has been confirmed in rocks just below the glacial deposits! Warke et al. PNAS, 2020 2.2 Ga ¡ Redbeds free O2 ¡ Sediments deposited under ice Glaciation Onset of Mass dependent Sulfur Isotope Fractionation increasing O2 ¡ Detrital uraninite and pyrite no O2 2.45 Ga ¡ Increasing O2 concentrations poison methanogens ¡ Atmospheric CH4 concentrations fall ¡ Only CO2 and water vapor are now left as greenhouse gases ¡ Solar flux was lower at the time. ¡ The Earth System plunges into its first major glaciation: Huronian Glaciation Present Proterozoic Paleo Proterozoic Huronian Glaciation Archean likely warm, stable Textbook Figure 12-11