Starting around 234 million years ago, the Earth experienced four bursts of volcanic activity in the space of less than two million years. The warming these induced favored early dinosaurs compared to their competitors, helping to push them towards the planetary dominance that lasted more than 150 million years, researchers have concluded.
Sediments from the Jiyuan Basin provide a record of climate changes in what is now northern China halfway through the Triassic. An analysis in Proceedings of the National Academy of Sciences shows the rises in temperature were accompanied by increased levels of mercury. With no industrialization to spread the heavy metal around, the only source of such mercury was volcanoes.
"Within the space of two million years the world's animal and plant life underwent major changes including selective extinctions in the marine realm and diversification of plant and animal groups on land. These events coincide with a remarkable interval of intense rainfall known as the Carnian Pluvial Episode,” said study co-author Professor Jason Hilton of the University of Birmingham in a statement.
The Carnian Pluvial Episode has been well documented from sedimentation laid down on land and in the sea, but this work at Jiyuan has shown there was not one Episode but four; “Each one driven by discrete pulses of powerful volcanic activity associated with enormous releases of carbon dioxide into the atmosphere,” Hilton said. “These triggered an increase in global temperature and humidity."
Geological records from places as dispersed as Central Europe, Greenland, Morocco, and Argentina show the increased rainfall was a global rather than local phenomenon.
Dinosaurs had recently begun to diversify before the Carnian Pluvial Episode, but they took advantage of the newly warm and humid conditions to expand to an otherwise unlikely extent. Nor were they the only winners. “This remarkable period in Earth history was also important for the rise of modern conifer groups and had a major impact on the evolution of terrestrial ecosystems and animal and plant life – including ferns, crocodiles, turtles, insects and the first mammals." Hilton said.
The Wrangellia Large Igneous Province – off what is now western Canada – was laid down around the same time, and has been suspected of being the site of the volcanism. The paper cannot confirm this, but the authors agree it is probable.
It can seem like these changes to global temperatures were incredibly sudden, but temperatures probably took thousands or tens of thousands of years to rise by 4-8º C (7-15º F). The total rise today may be smaller, but the pace is much faster. Nevertheless, it still won't bring the dinosaurs back.