Science News looks at a case of climate change from millions of years before humans existed – a series of volcanic eruptions that caused 2 million years of rainstorms, which paved the way for dinosaurs to rule the planet:
Clues found in sediments buried deep beneath an ancient lake basin in China link the volcanic eruptions with climate swings and environmental changes that created a globe-spanning hot and humid oasis in the middle of the hot and dry Triassic Period, researchers report in the Oct. 5 Proceedings of the National Academy of Sciences. During this geologically brief rainy period 234 million to 232 million years ago, called the Carnian Pluvial Episode, dinosaurs started evolving into the hulking and diverse creatures that would dominate the landscape for the next 166 million years.
Previous research has noted the jump in global temperatures, humidity and rainfall during this time period, as well as a changeover in land and sea life. But these studies lacked detail on what caused these changes, says Jason Hilton, a paleobotanist at the University of Birmingham in England.
So Hilton and his colleagues turned to a several-hundred-meter-long core of lake-bottom sediments drawn from the Jiyuan Basin for answers. The core contained four distinct layers of sediments that included volcanic ash that the team dated to between 234 million and 232 million years ago, matching the timing of the Carnian Pluvial Episode. Within those layers, the team also found mercury, a proxy for volcanic eruptions. “Mercury entered the lake from a mix of atmospheric pollution, volcanic ash and also being washed in from surrounding land that had elevated levels of mercury from volcanism,” Hilton says.
The reconstructed history suggests that the volcanic pulses injected huge amounts of CO₂ into the atmosphere, says coauthor Jacopo Dal Corso, a geologist at the University of Leeds in England. That boosted temperatures and intensified the hydrologic cycle, enhancing rainfall and increasing runoff into lakes, he says. At the same time, terrestrial plants evolved, with humidity-loving flora becoming predominant. As the rains created wet environments, turtles, large amphibians called metoposaurids — and dinosaurs — began to thrive.
Together, these diverse lines of evidence reveal that the Carnian Pluvial Episode was actually four distinct pulses of significant environmental change — each triggered by massive volcanic eruptions, Dal Corso says.
You can read more about the four “pulses” of volcanic eruptions here, in the Proceedings of the National Academy of Sciences.