Precambrian Glaciations

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Precambrian Glaciations

• 2.4 Ga Huronian Glaciation immediately preceded
  the rise of oxygen
• 750-575 various glaciations, following the
  Varanger glaciation we have the first
  appearance of putative metazoans

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How do we know there were glaciations in the
Precambrian?

• Tillites and dropstones worldwide (Glacial
  depsoits)
• Carbon and oxygen isotopes indicate cool
  conditions

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Shallow ocean, warm water
Deep ocean, glacial rocks
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But, these were extraordinary glaciations because

• The tillites and dropstones were found at all
  latitudes, including the tropics
• The glacial rocks are immediately overlain by
  warm water, tropical limestones
• Metazoan (multicellular) life rose immediately
  thereafter

How do we account for all of these different
factors? Could they all be due to a single cause?
What if there was a Snowball Earth?
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