Triassic rocks in the Italian Dolomites bear evidence of a surprisingly wet episode in Earth’s history.Credit: Arterra/Universal Images Group via Getty
Nature has an interesting post about a spell of wet weather in the middle Triassic that may have spurred the evolution of the dinosaurs. This wet spell occurred for about a million years about 232 million years ago. The evidence for the very wet period (pluvial episode) is contained in Triassic rocks from the Carnian age. These rocks have been found in Germany, the United States, the Himalayas, and other places. The origins of the dinosaurs coincided with this wet period and may have helped them to rise to the dominance they enjoyed in the Jurassic and Cretaceous periods.
Alastair Ruffell could see there was something odd about the rocks near his childhood home in Somerset, UK. The deposits hail from the Triassic period, more than 200 million years ago, and most are a dull orange-red, signifying that they formed when the region was a parched landscape, baked by the sun. Nothing strange there. But outcrops on Somerset’s Lipe Hill have a thin stripe of grey running through the heart of the red stone. That band signals a time when arid desert disappeared and the region transformed into a swampy wetland. For some reason, an incredibly dry climate had turned wet, and stayed that way for more than a million years.
The change intrigued Ruffell when he first found the outcrops in the mid-1980s, but the young geologist had a PhD project to finish. So he put the Triassic puzzle to one side, until a chance encounter in 1987 with another young scientist, palaeontologist Michael Simms. During his postdoctoral studies, Simms had discovered evidence of extinctions in the Late Triassic, during Ruffell’s mysterious wet period. In the late 1980s, the pair pushed the idea that the two findings were connected, but for years, their results were dismissed.
Three decades later, there is a growing consensus that they were right, after all. Something strange happened in the Late Triassic — and not just in Somerset. About 232 million years ago, during a span known as the Carnian age, it rained almost everywhere. After millions of years of dry climates, Earth entered a wet period lasting one million to two million years. Nearly any place where geologists find rocks of that age, there are signs of wet weather. This so-called Carnian pluvial episode coincides with some massive evolutionary shifts.
