Life on Earth probably wouldn't be extinguished by a comet strike alone. Mass extinctions require at least two kinds of mega-events, one of which is often a volcano that erupts for thousands of years.
Over at Discovery News, io9 pal Michael Reilly reports on a study about the exact ingredients required to whip up a mass extinction event like the one in the Permian-Triassic, which destroyed 90 percent of life on the planet. Researchers Nan Arens and Ian West argue that a mass extinction is caused by a combination of "pulse" events - short, sharp shocks like meteor strikes - and "press" events like millennia-long climate change from constantly-erupting volcanoes. Arens and West base their assertions on intensive study of mass extinction events in Earth's past.
Can researchers come up with a "Grand Unified Theory" of ancient apocalypse?
West and Arens think so. They combed the last 300 million years of geologic record, noting impact craters, massive eruptions, periods of ancient climate change, and then comparing them to extinctions. The rate at which species die off spiked dramatically, they found, when a "pulse"-type event occurred within a million years or so of a "press."
The theory fits well for the dinosaurs. Around the time of their demise 65 million years ago, a comet slammed into the Yucatan Peninsula and a huge volcano, the Deccan Traps, was erupting in what is today India.
But other extinctions are problematic. The greatest dying in geologic history, the Permian-Triassic extinction, killed 90 percent of all life on Earth, but there is no record of an impact. Instead, all signs point to a 200,000-year-long volcanic eruption in Siberia as the murder weapon.
Arens and West's work also suggests that Earth may be headed for a new mass extinction, because climate change is a common form of press event, and all we really need is one big pulse event to reach the total apocalypse tipping point.