The age of the dinosaurs ended 66 million years ago with the ultimate bad day, not a prolonged period of climate change wrought by volcanic activity, according to new research.
The city-size asteroid that slammed into Earth would have plunged the planet into a drastic winter, which would have lasted for years, thereby creating a world largely unsuitable for dinosaurs to live in. The new study has poured more cold water on the theory that massive volcanic eruptions in the Deccan Traps, an area that now sits in modern-day India, played a significant role in their demise.
"The relative roles of these two potential kill mechanisms on the timing and magnitude of the extinction have been fiercely debated for decades," said the study.
"We show that only the asteroid impact, particularly with its prolonged consequences, was the real driver of the extinction," said Alessandro Chiarenza, who conducted the research while studying for his doctorate in the department of earth science and engineering at Imperial College London.
"Could it (the volcanic activity) have played a smaller role by making it harder for dinosaurs to thrive prior to the asteroid impact? No, we show that Deccan Traps activity, if anything, might have buffered the 'negative effects' of the impact on climate, potentially boosting the recovery after the extinction event."
To determine whether it was the asteroid that hit off the coast of Mexico or the volcanic activity that unleashed the climate-changing gases, the team combined geological markers of climate and powerful mathematical models with information about what kinds of environmental factors, such as rainfall and temperature, each species of dinosaur needed to thrive.
The scientists were then able to map where these conditions would still exist after either an asteroid strike or a period of massive volcanism. They found that the asteroid strike alone wiped out all potential dinosaur habitats, while volcanism left some viable regions around the equator.
"Instead of only using the geologic record to model the effect on climate that the asteroid or volcanism might have caused worldwide, we pushed this approach a step forward, adding an ecological dimension to the study to reveal how these climatic fluctuations severely affected ecosystems," said Alex Farnsworth, a paleoclimatologist at the University of Bristol and the co-lead author of the study, in a statement.
"The asteroid impact would have created a climate just too difficult for dinosaurs to survive, with globally freezing temperatures over many years not allowing vegetation to grow destabilizing the base of the food webs that the dinosaurs sat on top of," he explained.
The asteroid strike would have released particles and gases high into the atmosphere, blocking out the sun for years and causing extremely cold winters that made it impossible for nearly all dinosaur species, except those that evolved into birds, to survive, the study said.
"In one day, in a blink of a geologic eye, everything ended for them," said Chiarenza.
There have been five mass extinction events on Earth and volcanic activity is thought to have played a role in most of them.
The Deccan Traps eruptions occurred over the course of tens of thousands of years, beginning about 400,000 years before the mass extinction and continuing for about 500,000 years after, but the team said they were unlikely the cause of extinction.
In fact, the research team's models suggested that the volcanic activity could have played a role helping life bounce back from the asteroid strike, restoring habitats and helping the new species that evolved after the asteroid strike survive.
Although volcanoes release gases and particles that can block the sun, they also release carbon dioxide, a greenhouse gas. In the longer term these particles and gases drop out of the atmosphere, while carbon dioxide stays around and builds up, warming the planet and boosting the survival and recovery of animals and plants that made it through the extinction.
"What surprised us most was that contrary to popular theory, Deccan volcanism may well have been the benevolent hero of the time, attempting to ameliorate the effects of the so called 'nuclear winter' caused by the asteroid impact," said Farnsworth.
"Unfortunately for the dinosaurs it couldn't offset enough of the cooling, but perhaps fortunately for us it might have been enough to allow mammals to inherit and eventually dominate the Earth."