CLIMATE × LIFE

The Two Million Year Rain

~234 to 232 million years ago

Phanerozoic · Mesozoic · Triassic

A dry world turned humid for about two million years, in step with four pulses of volcanism from a province now scattered across western North America. A third of marine genera went. On the other side of it, the conifers, the crocodile line, the turtles, the lizards, the mammals and the dinosaurs are all more diverse than they were before.

Why it matters

Nearly every group now living on the continents has its expansion dated to this window. That is a striking coincidence, and it is still a coincidence: the Argentine basins with the best early dinosaurs record the wet interval clearly, and show no clean causal thread from the rain to the animals. What the episode does establish is how much can change in a biosphere while the climate stays wet for two million years.

Dating & uncertainty

Uranium-lead dates on a Chinese lake sequence place the episode between about 234.0 and 232.4 Ma, in four discrete volcanic pulses. Outside the Tethys the picture is looser: most Carnian sections carry few absolute ages, and the dates of several biological changes credited to the episode are uncertain, which makes the coincidence itself harder to pin down.

Sources

1. Dal Corso et al. (2020), Science Advances · Extinction and dawn of the modern world in the Carnian (Late Triassic)
2. Lu et al. (2021), PNAS · Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late Triassic)
3. Mancuso et al. (2020), Gondwana Research · Evidence for the Carnian Pluvial Episode in Gondwana: new multiproxy climate records and their bearing on early dinosaur diversification

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