Gamma-Ray Burst Caused Mass Extinction?

April 3, 2009

A brilliant burst of gamma rays may have caused a mass extinction event on Earth 440 million years ago—and a similar celestial catastrophe could happen again, according to a new study.

Most gamma-ray bursts are thought to be streams of high-energy radiation produced when the core of a very massive star collapses.

The new computer model shows that a gamma-ray burst aimed at Earth could deplete the ozone layer, cause acid rain, and initiate a round of global cooling from as far as 6,500 light-years away.

Such a disaster may have been responsible for the mass die-off of 70 percent of the marine creatures that thrived during the Ordovician period (488 to 443 million years ago), suggests study leader Brian Thomas, an astrophysicist at Washburn University in Kansas.

The simulation also shows that a significant gamma-ray burst is likely to go off within range of Earth every billion years or so, although the stream of radiation would have to be lined up just right to affect the planet.

Currently WR104, a massive star 8,000 light-years away in the constellation Sagittarius, is in position to be a potential threat, Thomas noted.

But the study, which has been submitted to the International Journal of Astrobiology, isn't necessarily sending other astrophysicists into a panic.

"There is certainly no harm in looking at what a gamma-ray burst might do if it were close enough to us, as this author has done. That's the way science works," said David Thompson, a NASA astrophysicist and deputy project director on the Fermi Gamma-ray Space Telescope.

But Thompson compares the risk to Earth from a future gamma-ray burst to "the danger I might face if I found a polar bear in my closet in Bowie, Maryland.

"It could happen, but it is so unlikely that it is not worth worrying about."

Lingering Damage

Study author Thomas' former graduate advisor, Adrian Melott, first proposed in 2004 that a gamma-ray burst near Earth wiped out Ordovician life. Since then, both researchers have been tackling pieces of the puzzle.

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