EXTINCTIONS

The Great Dying

~252 million years ago

Phanerozoic · Paleozoic · Permian

Volcanoes in Siberia burned through coal beds and vented carbon for perhaps a million years. The sea warmed, lost its oxygen and turned acid; on land the forests went. Something like nine marine species in ten died, and the whole crisis fits inside 200,000 years, which in geology is an instant. It killed unevenly: warming and oxygen loss together predict that tropical species should have fared better than polar ones, because they were already built for warm, thin water, and the fossil record agrees.

Why it matters

This is the closest life has come to ending. Ninety per cent gone means every ecosystem rebuilt out of whoever was left, and the survivors were not the animals that had been in charge. The Palaeozoic world went in and the Mesozoic world came out. The roads to the dinosaurs and to the mammals both start on the far side of it.

Dating & uncertainty

The date, 251.9 million years ago, and the duration, under 200,000 years, come from uranium-lead ages on volcanic ash beds in South China, and are among the most precise in deep time. What did the killing is less settled. Warming and oxygen loss taken together predict which animals died and where, and that prediction matches the rocks; acidification, hydrogen sulfide and ozone damage have each been proposed as well, and none of them exclude the others.

Sources

1. Shen et al. (2011), Science · Calibrating the end-Permian mass extinction
2. Burgess et al. (2014), PNAS · High-precision timeline for Earth's most severe extinction
3. Penn et al. (2018), Science · Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction
4. Dal Corso et al. (2022), Nature Reviews Earth & Environment · Environmental crises at the Permian-Triassic mass extinction

Earth history as one day

22:40:041 h 20 min before midnight

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