CLIMATE × LIFE

The Carnian Pluvial Episode

~234 to 232 million years ago

Phanerozoic · Mesozoic · Triassic

The Carnian pluvial episode was an interval of about two million years, between 234 and 232 million years ago, in which the world's dry climate turned humid and a third of marine genera, groups of closely related species, disappeared.

The Carnian pluvial episode is an interval of about two million years in which the world's dry climate turned humid. Pluvial means rainy, and the Carnian is a part of the Late Triassic. The climate changed at the same time as four pulses of volcanism from the Wrangellia province, a volcanic region. Its basalts, rocks of cooled lava, are now scattered across western North America. A third of marine genera disappeared. After the episode, the conifers, the crocodile lineage, the turtles, the lizards, the mammals and the dinosaurs are all more diverse than before. The episode is therefore one of the clearer cases of a turnover, in which groups that disappear are replaced by others, rather than a simple loss.

Why it matters

Researchers date the expansion of almost every group that now occupies the continents to the Carnian pluvial episode. This expansion coincides with the humid climate, and a causal link is not established. In the Argentine basins, the areas of accumulated sediment where the best early dinosaurs are found, the rocks clearly record the episode. They show no clear causal chain between the rainfall and the animals. The episode shows the scale of transformation that a biosphere, all the living things of a planet, can undergo when the climate remains humid for two million years.

Dating & uncertainty

Lu and colleagues (2021) dated a sequence of lake sediments in China by the uranium-lead method, which reads an age from the decay of uranium into lead. They place the episode between about 234.0 and 232.4 million years ago, with four distinct volcanic pulses. Outside the Tethys, an ancient ocean, the dating is less clear. Most Carnian sections, successions of rock layers, have few absolute ages, which are ages in years. The dating of several biological changes attributed to the episode is uncertain, so their coincidence with it is harder to establish.

Earth history as one day

22:45:461 h 14 min before midnight

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