Around 66 million years ago, something catastrophic happened that killed off all but the avian dinosaurs. The purveyor of such destruction may have been an asteroid or comet more than six miles across, but it didn’t work alone. Massive lava flows from volcanoes in present-day India helped, reports Ian Sample for The Guardian.

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In 1980, scientists discovered traces of iridium—an element found in asteroids and comets, in rock layers around the world. Later work outlined the giant impact crater off the coast of Yucatán, but debates still raged about whether the impact was enough to set off a mass extinction. Now, researchers analyzing lava flows in India have found that the impact triggered a catastrophic series of eruptions, Sample reports.

He writes:

​The shockwaves produced when the space rock thumped into Earth likely shook up volcanic plumbing systems around the world, creating larger magma chambers that spewed out more material when they erupted.

The impact and the eruptions together would have filled Earth’s atmosphere with debris and toxic gases. Initially, the dusty skies would have blocked sunlight, chilling the planet and killing plants worldwide. But as the dust settled, the greenhouse gases would have forced temperatures toward a sweltering extreme.

The worst eruptions were from huge volcanoes in India. Ancient basalt lava flows from this activity still remain, covering an area nearly 200,000 square miles called the Deccan Traps. Before the asteroid or comet hit, the volcanoes would have been "bubbling along happily, continuously and relatively slowly," Renne says. Afterward, the size, volume and even chemistry of the eruptions changed.

Both the volcanism and impact happened within 50,000 years of the mass extinction, so distinguishing between them as "killing mechanisms" isn't possible, says lead researcher Paul Renne, a planetary scientist at UC Berkeley, in a press release. "Both phenomena were clearly at work at the same time." The team published their findings last week in Science.