Snowball Earth Hypothesis
The snowball Earth hypothesis: testing the limits of global change
Late Neoproterozoic Glaciation
Paul F. Hoffman and Daniel P. Schrag
750-600 MA
Terra Nova, 14, 129–155, 2002
1) Distribution of glacial deposits
2) Ice reaching equator
3) Occurrence of cap carbonates
4) δ 13C anomalies before and after glacial event
5) Reoccurrence of iron formations
February 4, 2008
Lucie Novoveska
Neoproterozoic glacial features
Late Neoproterozoic Glacial Deposits (LNGD)
Fig.1
Fig.2
Cap carbonate (Ice Brook Mackenzie Mountains, north-west Canada)
Fig.3,4
Cap carbonate sequence of the Otavi platform, northwest Namibia
Fig.5
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The snowball Earth hypothesis
Test 1: Representative δ13C profiles
Fig.6-7
Otavi platform in northern Namibia
Test 2: Cap carbonates
Large inputs of alkalinity are required to maintain seawater
saturation if atmospheric pCO2 greatly increased in a snowball
event
Fig.10
Test 3: Iron formations
Deposits of iron oxides occur strictly with LNGD
Fig.9
Would eukaryotes survive?
Fig.12
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How did the glacial event end?
Why are snowball events rare?
What triggers them?
Continents in the tropics, where it is hot and wet
Plate tectonics/volcanism delivers CO2
Methane released from permafrost
Green house gases
Reverse albedo effect
Global rate of silicate weathering was high
CO2 concentrations in the atmosphere decreased
Breakup of pre-Pangean supercontinent Rodinia
Weathering rates increase
Subglacial volcanoes in Iceland
Alternative hypotheses
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4.
G. E. Williams- Large orbital obliquity
Sheldon- Shielding of sunlight
Reliable data?
Misinterpretation of data?
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Discussion Questions
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.
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