603-pp7 - www.snowbal earth.org 3 Why are snowball events...

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1 Snowball Earth Hypothesis February 4, 2008 Lucie Novoveska Late Neoproterozoic Glaciation 750-600 MA Paul F. Hoffman and Daniel P. Schrag The snowball Earth hypothesis: testing the limits of global change Terra Nova, 14, 129–155, 2002 1) Distribution of glacial deposits 2) Ice reaching equator 3) Occurrence of cap carbonates 4) δ 13 C anomalies before and after glacial event 5) Reoccurrence of iron formations Fig.1 Late Neoproterozoic Glacial Deposits (LNGD) Fig.2 Neoproterozoic glacial features Fig.3,4 Cap carbonate (Ice Brook Mackenzie Mountains, north-west Canada) Fig.5 Cap carbonate sequence of the Otavi platform, northwest Namibia
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2 Fig.6-7 The snowball Earth hypothesis Test 1: Representative δ 13 C profiles Fig.9 Otavi platform in northern Namibia Fig.10 Large inputs of alkalinity are required to maintain seawater saturation if atmospheric pCO 2 greatly increased in a snowball event Test 2: Cap carbonates Test 3: Iron formations Deposits of iron oxides occur strictly with LNGD Fig.12 Would eukaryotes survive?
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Unformatted text preview: www.snowbal earth.org 3 Why are snowball events rare? What triggers them? Continents in the tropics, where it is hot and wet Global rate of silicate weathering was high CO 2 concentrations in the atmosphere decreased Breakup of pre-Pangean supercontinent Rodinia Weathering rates increase Subglacial volcanoes in Iceland www.snowbal earth.org How did the glacial event end? Plate tectonics/volcanism delivers CO 2 Methane released from permafrost Green house gases Reverse albedo effect Alternative hypotheses 1. G. E. Williams- Large orbital obliquity 2. Sheldon- Shielding of sunlight 3. Reliable data? 4. Misinterpretation of data? www.snowbal earth.org Can this happen again? How reliable is the evidence? Is this possible scenario? Small icecap instability, possible switch to the ice-free branch (e.g. disappearance of Arctic sea ice) due to anthropogenic global warming. Discussion Questions www.snowbal earth.org 4 www.snowbal earth.org...
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603-pp7 - www.snowbal earth.org 3 Why are snowball events...

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