Snowball Earth
Ice reaches nearly to the equator
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The evidence lies in glacial deposits laid down at tropical latitudes, found on every continent. The mechanism is a runaway feedback: more ice means higher albedo, which means more cooling, which means more ice. What finally broke the cycle was volcanic CO₂ accumulating in the atmosphere because weathering — the normal carbon sink — was frozen shut. The warming that followed was violent, and shortly afterwards the first large multicellular organisms appear in the fossil record.
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Earth became so cold that ice spread from the poles almost to the equator. From space the planet looked like a white snowball. Life barely survived, in water beneath the ice and near hot volcanic vents.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org