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TollFreeHorse2475

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snowball earth geology paleo-proterozoic earth science

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This document provides an overview of the snowball Earth (part 1), discussing the atmospheric methane concentration, temperature and precipitation. It describes feedback loops and rock associations. The content features figures, diagrams, and illustrations supporting the discussion on geological timeline.

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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

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