Did a global deep freeze turn Earth into a giant, ice-covered snowball?

Nature · Published 3 October 2026 Swipe more like this →

In short: Around 650 million years ago, Earth entered a period of extreme cooling known as the Marinoan glaciation. This event, part of the Snowball Earth hypothesis, suggests our planet was largely or entirely encased in ice, with glaciers reaching even the equator. How did life survive this frozen, hostile world?

The Marinoan glaciation occurred during the Cryogenian Period, roughly 650 to 635 million years ago. It stands as one of the most severe ice ages in geological history, characterized by ice sheets that may have reached as far as the equator. While the term is often linked to the broader Snowball Earth hypothesis—which posits the planet was covered in ice up to two kilometers thick—some researchers argue the hydrological cycle slowed down so drastically that the planet may not have been fully encased.

The origins of this deep freeze are tied to the breakup of the supercontinent Rodinia. Volcanic activity associated with this tectonic shift is believed to have increased weathering, which stripped carbon dioxide from the atmosphere and weakened the greenhouse effect. As the planet cooled, glaciers expanded, creating a feedback loop of extreme cold. Evidence for this period is found globally, from the Flinders Ranges in South Australia to China and the Svalbard archipelago, where glacial deposits like diamictites remain as markers of the icy past.

The end of this era was as dramatic as its onset. Massive volcanic eruptions are thought to have pumped enough carbon dioxide back into the atmosphere to trigger rapid warming. As the ice retreated, oxygen levels in the oceans and atmosphere rose, potentially paving the way for new biological developments. Despite the harsh conditions, life persisted; evidence suggests that benthic macroalgae survived in mid-latitude coastal habitats, while other organisms likely clung to existence in hydrothermal vents or meltwater ponds, waiting for the planet to thaw.

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