Scientists at NASA believe that gamma-ray burst might have caused a mass extinction on Earth hundreds of million years ago. They say that gamma-ray radiation from a relatively nearby star, besides our Sun, could deplete up to half of our ozone layer within ten seconds. Recovery could take at least five years.
When this happens UV radiation from the Sun could kill much of the life on land and near the surface of oceans and lakes, and disrupt the food chain.
With the ozone layer damaged for up to five years, harmful ultraviolet radiation from the Sun would kill smaller life-forms and disrupt the food chain. Scientists say that a gamma-ray burst might have caused the Ordovician extinction 450 million years ago, some 200 million years before dinosaurs.
Scientists say that a ten-second burst of gamma rays from a massive star explosion within 6,000 light years from Earth could have triggered a mass extinction hundreds of millions of years ago. In this artist's conception we see the gamma rays hitting the Earth's atmosphere. (The expanding shell is pictured as blue, but gamma rays are actually invisible.) The gamma rays initiate changes in the atmosphere that deplete ozone and create a brown smog of NO2.
Gamma-ray bursts in our Milky Way galaxy are indeed rare, but the scientists estimate that at least one nearby likely hit the Earth in the past billion years. Life on Earth is thought to have appeared at least 3.5 billion years ago. This research, supported by a NASA Astrobiology grant, represents a thorough analysis of the "mass extinction" hypothesis first announced by members of this science team in September 2003.
"A gamma-ray burst originating within 6,000 light years from Earth would have a devastating effect on life," said Dr. Adrian Melott of the Department of Physics and Astronomy at the University of Kansas. "We don't know exactly when one came, but we're rather sure it did come -- and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage."
Gamma-ray bursts are the most powerful explosions known. Most originate in distant galaxies, and a large percentage likely arise from explosions of stars over 15 times more massive than our Sun. A burst creates two oppositely-directed beams of gamma rays that race off into space.
Thomas says that a gamma-ray burst may have caused the Ordovician extinction 450 million years ago, killing 60 percent of all marine invertebrates. Life was largely confined to the sea, although there is evidence of primitive land plants during this period. Read more at NASA