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 that runs the land today 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 prove is that a climate shift lasting two million years is long enough to redraw a biosphere.

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. Records outside the Tethys are thin, and the Argentine basins that hold the best early dinosaurs show the humid interval clearly but not a clean causal link to the dinosaurs themselves.

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