The hothouse after the ice
From snowball to bathwater in a few thousand years
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Cap carbonates are among the strangest rocks that exist: tens of metres of dolomite or limestone deposited directly on glacial sediment, with strongly negative carbon isotope values and structures that form nowhere else. The Otavi Group in Namibia is the reference locality. The interpretation is that CO₂ had built to perhaps several hundred times today's level because weathering — the normal carbon sink — was frozen shut. When the ice collapsed, the planet went from extreme cold to extreme heat faster than in any other climate change we know of. The first large animals appear in the aftermath.
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What finally melted the ice was volcanoes. They exhaled CO₂ for millions of years while weathering lay frozen shut. When the ice gave way at last, the planet was left with an enormous greenhouse effect and turned scorching almost overnight. Directly on top of the glacial deposits sits a layer of limestone laid down in that boiling sea.
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Part of Terra Saga — the story of Earth on a timeline. terrasaga.org