The relationship between dinosaurs and volcanoes has historically not always appeared so amiable.
For decades, scientists argued over whether volcanoes or an asteroid caused dinosaurs’ abrupt extinction some 65 million years ago. It wasn’t until 2010 that an international panel of experts formally declared that it was the space rock, and not giant eruptions, that was the primary cause of dino demise.
And now a team of researchers is presenting the most compelling evidence yet that massive volcanic events likely helped the dinosaurs take over the planet, at least in another era. Their results were published Monday in the Proceedings of the National Academy of Sciences.
The Triassic Period, which began roughly 250 million years ago, was a time of massive ecological change following the largest mass extinction event on record. While dinosaurs had emerged in this time period, they were different: skinnier, more reptilian-looking, less of the toothy box office hits we flock to movie theaters to see. But it was during this time period that dinosaurs diversified until they became wondrous beasts like Tyrannosaurus rex or the Triceratops that dominated ecosystems all over planet Earth through the end of the Cretaceous period.
To understand what drove this dinosaur transformation, scientists looked at a phase spanning two million years during the Triassic Period known as the Carnian Pluvial Episode, or CPE. During that episode, from 234 million to 232 million years ago, the planet experienced an increase in global temperature, humidity and rainfall — a climate often referred to as a “mega-monsoon.”
The researchers analyzed sediment and plant fossil evidence from a lake in Northern China and were able to match four intense phases of volcanic activity with the changes of the Carnian Pluvial Episode.
Previously, researchers had hypothesized that global carbon cycle changes during the episode were the result of major volcanic eruptions from what is now a mass of igneous rock found throughout western North America. The new study links the timing of the episode with four distinct peaks in mercury — a well-established indicator of volcanic activity — to carbon cycle shifts as well as rainfall, which led to local changes in the vegetation on land and in the lake.
“We’re often able to link volcanism to global warming, but our study is unusual in that we’ve also linked it to periods of intense rainfall,” said Jason Hilton, a paleobotanist at the University of Birmingham in England and a study co-author. “With each pulse of volcanism, we see an increase in plants adapted to wet and aquatic settings.”
Jing Lu, a researcher at the China University of Mining and Technology and also a co-author of the study, added that these eruptions “were powerful enough to drive evolutionary processes during the Triassic.”
During the episode, plant species that couldn’t adapt to the more humid environment went extinct, as did a number of animal species, from large reptilian herbivores on land to small gastropods in the water. “These changes freed up ecological space for other groups of organisms, like dinosaurs, to thrive,” Dr. Hilton said.
In addition to dinosaur diversification, researchers believe the Carnian Pluvial Episode laid the foundation for today’s ecosystems.
“During the CPE, we’re starting to see this perfect mix of prehistoric monsters as well as modern day mammals and reptiles,” said Emma Dunne, a researcher at the University of Birmingham who was not involved in the study but whose work is focused on the drivers of diversification of ancient tetrapods like dinosaurs. “You had turtles, but also pterosaurs.”
This new evidence has researchers reflecting more on our rapidly changing climate.
“The scale of these eruptions dwarfs every volcanic eruption in human history,” says Sarah Greene, a study co-author and paleoclimatologist at the University of Birmingham. “But the rate at which these eruptions emit carbon dioxide is tiny compared to human carbon dioxide emissions today.”
Dr. Dunne echoed that thought. “That two million years was the blink of an eye in geological time, so to think that we’re changing the planet at an even more rapid rate as humans, it’s a little scary,” she said. “Who knows what we’ll cause.”