Before we can get to life as we know it today, we have to go through a very long period of, well, dinosaurs. Oxygen may have made the rise of diverse life possible, but just how did dinosaurs evolve into the hulking beasts they once were? It turns out that volcanoes may hold the answer.

Dinosaurs weren’t always gigantic monsters. They started out cat-sized. And then came two million years of rain caused by four major pulses of volcanic activity, and almost overnight, dinosaurs were huge and dominating the planet.

Scientists have now analyzed sediment found deep under an ancient lake bed in China that shows the link between the volcanic eruptions and the massive amounts of rainfall, which turned the Earth into a “hot and humid oasis” during the very hot and dry Triassic Period. The period lasted from 234 million to 232 million years ago and is called the Carnian Pluvial Episode, and that’s around the same time we see dinosaur fossils go from small to huge.

The results of the analysis of the core samples were published in PNAS, and they show that mercury entered the lake. Mercury is a sign of volcanic ash, and it gets washed into the lakes from the land near the eruptions. Additionally, the team found different types of carbon, and those correspond to four different eruption events, which would have released massive amounts of carbon dioxide. And then there were microfossils and pollens, which showed a change from species inclined toward dry climates to species that prefer it warm and humid.

All that rain and humidity caused plants to thrive and become huge first, which in turn, made space (and food) for the domination of the dinosaurs to start. It’s impressive what we can learn from sedimentary rocks.

More Information

A volcano-induced rainy period made Earth’s climate dinosaur-friendly (Science News)

“Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late Triassic),” Jing Lu et al., 2-21 October 5, PNAS