Jacques van Oene
April 6th 05, 10:01 PM
Dolores Beasley/Gretchen Cook-Anderson April 6, 2005
Headquarters, Washington
(Phone: 202/358-1753/0836)
Susan Hendrix
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-7745)
Release 05-094
EXPLOSIONS IN SPACE MAY HAVE INITIATED ANCIENT EXTINCTION ON EARTH
Scientists at NASA and the University of Kansas say that a mass
extinction on Earth hundreds of millions of years ago could have been
triggered by a star explosion called a gamma-ray burst. The scientists do
not have direct evidence that such a burst activated the ancient extinction.
The strength of their work is their atmospheric modeling -- essentially a
"what if" scenario.
The scientists calculated that gamma-ray radiation from a relatively nearby
star explosion, hitting the Earth for only ten seconds, could deplete up to
half of the atmosphere's protective ozone layer. Recovery could take at
least five years. With the ozone layer damaged, ultraviolet 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.
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, Lawrence. "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," Melott added.
A scientific paper describing this finding appears in Astrophysical Journal
Letters. The lead author is Brian Thomas, a Ph.D. candidate at University of
Kansas.
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
In the new work, the team used detailed computer models to calculate the
effects of a nearby gamma-ray burst on the atmosphere and the consequences
for life.
Thomas, with Dr. Charles Jackman of NASA's Goddard Space Flight Center in
Greenbelt, Md., calculated the effect of a nearby gamma-ray burst on the
Earth's atmosphere. Gamma- rays, a high-energy form of light, can break
molecular nitrogen (N2) into nitrogen atoms, which react with molecular
oxygen (O2) to form nitric oxide (NO). NO will destroy ozone (O3) and
produce nitrogen dioxide (NO2). NO2 will then react with atomic oxygen to
reform NO. More NO means more ozone destruction. Computer models show that
up to half the ozone layer is destroyed within weeks. Five years on, at
least 10 percent is still destroyed.
Next,researchers calculated the effect of ultraviolet radiation on life.
Deep-sea creatures living several feet below water would be protected.
Surface-dwelling plankton and other life near the surface, however, would
not survive. Plankton is the foundation of the marine food chain.
Dr. Bruce Lieberman, a paleontologist at the University of Kansas,
originated the idea that a gamma-ray burst specifically could have caused
the great Ordovician extinction, 200 million years before the dinosaurs. An
ice age is thought to have caused this extinction. However, gamma-ray burst
could have caused a fast die-out early on and also could have triggered the
significant drop in surface temperature on Earth.
"One unknown variable is the rate of local gamma-ray bursts," Thomas said.
"The bursts we detect today originated far away billions of years ago,
before the Earth formed. Among the billions of stars in our Galaxy, there's
a good chance that a massive one relatively nearby exploded and sent gamma
rays our way," he added.
The Swift mission, launched in November 2004, will help determine recent
burst rates.
For images, movies, and more information via the Internet:
http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html
- end -
--
--------------
Jacques :-)
www.spacepatches.info
Headquarters, Washington
(Phone: 202/358-1753/0836)
Susan Hendrix
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-7745)
Release 05-094
EXPLOSIONS IN SPACE MAY HAVE INITIATED ANCIENT EXTINCTION ON EARTH
Scientists at NASA and the University of Kansas say that a mass
extinction on Earth hundreds of millions of years ago could have been
triggered by a star explosion called a gamma-ray burst. The scientists do
not have direct evidence that such a burst activated the ancient extinction.
The strength of their work is their atmospheric modeling -- essentially a
"what if" scenario.
The scientists calculated that gamma-ray radiation from a relatively nearby
star explosion, hitting the Earth for only ten seconds, could deplete up to
half of the atmosphere's protective ozone layer. Recovery could take at
least five years. With the ozone layer damaged, ultraviolet 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.
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, Lawrence. "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," Melott added.
A scientific paper describing this finding appears in Astrophysical Journal
Letters. The lead author is Brian Thomas, a Ph.D. candidate at University of
Kansas.
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
In the new work, the team used detailed computer models to calculate the
effects of a nearby gamma-ray burst on the atmosphere and the consequences
for life.
Thomas, with Dr. Charles Jackman of NASA's Goddard Space Flight Center in
Greenbelt, Md., calculated the effect of a nearby gamma-ray burst on the
Earth's atmosphere. Gamma- rays, a high-energy form of light, can break
molecular nitrogen (N2) into nitrogen atoms, which react with molecular
oxygen (O2) to form nitric oxide (NO). NO will destroy ozone (O3) and
produce nitrogen dioxide (NO2). NO2 will then react with atomic oxygen to
reform NO. More NO means more ozone destruction. Computer models show that
up to half the ozone layer is destroyed within weeks. Five years on, at
least 10 percent is still destroyed.
Next,researchers calculated the effect of ultraviolet radiation on life.
Deep-sea creatures living several feet below water would be protected.
Surface-dwelling plankton and other life near the surface, however, would
not survive. Plankton is the foundation of the marine food chain.
Dr. Bruce Lieberman, a paleontologist at the University of Kansas,
originated the idea that a gamma-ray burst specifically could have caused
the great Ordovician extinction, 200 million years before the dinosaurs. An
ice age is thought to have caused this extinction. However, gamma-ray burst
could have caused a fast die-out early on and also could have triggered the
significant drop in surface temperature on Earth.
"One unknown variable is the rate of local gamma-ray bursts," Thomas said.
"The bursts we detect today originated far away billions of years ago,
before the Earth formed. Among the billions of stars in our Galaxy, there's
a good chance that a massive one relatively nearby exploded and sent gamma
rays our way," he added.
The Swift mission, launched in November 2004, will help determine recent
burst rates.
For images, movies, and more information via the Internet:
http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html
- end -
--
--------------
Jacques :-)
www.spacepatches.info