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, already suited to warm and oxygen-poor water, should have fared better than polar ones, and the fossil record agrees.

Why it matters

This is the closest life has come to ending. A loss on that scale means every ecosystem was 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. Beyond the warming and the oxygen loss, acidification, hydrogen sulfide and damage to the ozone layer have each been proposed, and none of them excludes 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