Deep TimeCosmos & Earth

Carnian Pluvial Episode

234 million years agoNotableContested

A million-year burst of heavy rain and warming turns parts of arid Pangaea green, reshuffling life on land and in the sea just as the dinosaurs diversify.

Longest chain: The Big Bang → First atomic nuclei form → First stars ignite → First galaxies assemble → Milky Way takes shape → The Sun forms → Earth forms → Plate tectonics begins → Supercontinent Rodinia → Gondwana assembles → Supercontinent Pangaea → Carnian Pluvial Episode

The story

Around 234 to 232 million years ago, in the Late Triassic, the dry, monsoon-ruled interior of Pangaea becomes much wetter for about a million years. Geologists see it as lake deposits in places that were once desert, shifts in carbon isotopes in Italy's Dolomites and Alpine rocks, and a change in fossil plants and pollen. Fossil resin from the Dolomites, about 230 million years old, holds the oldest known amber-trapped insect and mite fauna.

The likely trigger is volcanism: the Wrangellia flood basalts, now spread across Alaska and British Columbia, released large amounts of carbon dioxide and warmed the planet. The warming and the rain coincide with extinctions of some marine and land groups, and with the rise of conifers and new reptiles. Dinosaurs, which had been rare, begin spreading and diversifying soon afterwards, and many researchers see the episode as an opening for them, though the link is still being tested.

Why it mattered

The rain episode reshuffled Triassic ecosystems and is a candidate cause of the dinosaurs' rise.
It shows that climate swings in Pangaea happened long before the end-Triassic extinction.
The Dolomites amber lets scientists see small Triassic insects that otherwise vanished without a trace.