It's generally agreed an asteroid impact 66 million years ago helped kill off the dinosaurs, but some researchers are suggesting it was just the first event in a two-part punch that eventually did them in.
They cite compelling geological evidence that the seismic shock of the asteroid smash kicked off or at least accelerated massive volcanic eruptions in India lasting hundreds of thousands of years.
The combination of the asteroid impact and the volcanism would have blanketed the Earth with dust and toxic fumes, leading to the disappearance of not just the dinosaurs but also many other land and marine animal species, they say.
Researchers dating lava flows in an area of India known as the Deccan Traps say there is evidence that slow eruptions going on at the time of the impact had their output doubled in the succeeding 50,000 years.
The amount of lava pouring forth "would correspond to something like half a million cubic kilometers," says Paul Renne, a geochronologist at the Berkeley Geochronology Center and lead author of a study appearing in the journal Science. "It's enough to cover the entire Earth to a depth of something like a meter or so. It's really big."
For decades, scientists have argued over the effects of the global events, with some researchers saying the volcanic eruptions played little or no part in the extinction of the dinosaurs, while others have argued the long-term die-off of species was mostly down to the volcanic events with the asteroid impact being just a "blip" in the process.
The new research cannot entirely settle the debate, researchers acknowledge, not that it matters that much.
"Based on our dating of the lavas, we can be pretty certain that the volcanism and the impact occurred within 50,000 years of the extinction, so it becomes somewhat artificial to distinguish between them as killing mechanisms: both phenomena were clearly at work at the same time," says Renne, who is also a professor of earth and planetary science at the University of California, Berkeley. "It is going to be basically impossible to ascribe actual atmospheric effects to one or the other. They both happened at the same time."
Ongoing research and dating is drawing the events — the extinctions, the impact and the major episode of volcanism — ever closer in time, making it harder to deny the likelihood of a connection among them, according to study co-author and UC Berkeley scientist Mark Richards, who originally proposed the theory that the asteroid impact reignited the volcanism in the Deccan Traps region.
"The scenario we are suggesting — that the impact triggered the volcanism — does in fact reconcile what had previously appeared to be an unimaginable coincidence," he explains.
