CLIMATE × EARTH

The Long Ice Age

~360 to 260 million years ago

Phanerozoic · Paleozoic · Devonian

Ice covered much of the southern supercontinent for a hundred million years, the longest and hardest cold that complex life has been through. What held it there was a shortage of carbon dioxide without precedent in the whole record: boron in fossil shells traces eighty million years of it. Then, about 294 million years ago, the level rose fourfold in short order and the ice let go.

Why it matters

Every other long ice age is known from rock alone. This one comes with the animals and plants that lived through it, so the link between carbon dioxide and cold can be read against a biosphere rather than a model. The coal that started the industrial revolution formed while it lasted, which is a loop worth noticing: we are burning the ice age's own carbon.

Dating & uncertainty

Not one glaciation but a run of them, separated by ice-free spells shorter than a million years, which is why its start and end are quoted differently by different records. High-latitude basins in Gondwana peak in the Carboniferous; tropical records suggest an Early Permian peak instead. Boron isotopes date the main deglaciation to a fourfold rise in carbon dioxide around 294 Ma, though scattered ice held on for tens of millions of years after that.

Sources

1. Jurikova et al. (2025), Nature Geoscience · Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age
2. Griffis et al. (2023), Geological Society, London, Special Publications · A Carboniferous apex for the late Paleozoic icehouse
3. Kent & Muttoni (2020), Palaeogeography, Palaeoclimatology, Palaeoecology · Pangea B and the Late Paleozoic Ice Age

Earth history as one day

22:05:481 h 54 min before midnight

if Earth’s 4.54 billion years were compressed into a single day