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.

Asks Reilly:

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.

SOURCES:
Discovery News

Paleobiology

The data fits with the extinction of the dinosaurs 65 million years ago and another extinction at the end of the Paleocene period, 35 million years ago. It also means our planet's probably in for another life-ending black eye in the not too-distant future.

But what's Galactic density got to do with comet impacts? As the solar system moves through denser parts of the galaxy the extra gravitational pull upsets comets orbiting the Sun, sending them hurtling towards Earth. The theory's been tossed around for a while (and there are other good ones, like supervolcanoes, that haven't been discounted yet) but this new evidence makes it seems a little more believable.

It sucks to think that gravity — a pretty immutable force of nature — will be the source of our demise rather than something we can avoid, like global warming or nuclear war. But the study suggests there may be a silver lining to our extinction: comet impacts could be the driving force behind panspermia:

While the "bounce" effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.

Centre director Professor Chandra Wickramasinghe said: "This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale."

Source: Cardiff University via Science Blog

Image: The Alien Next Door