The Permian Extinction - the worst extinction in history
Previous research showed the extinction wiped out nearly 90 percent of sea
species and 70 percent of vertebrate animal species on land. That made it
far worse than the Cretaceous-Tertiary extinction of the dinosaurs and
many other creatures 65 million years ago an event often blamed on the
impact of a perhaps 6-mile- (10-kilometer-) wide asteroid.
In the September 8 issue of the journal Science, Ward and colleagues
concluded the Permian-Triassic catastrophe also stripped Earth of many
rooted plants, triggering severe erosion.
As a result, sedimentary rocks from that time show that large meandering
rivers throughout South Africas Karoo Basin took on a braided,
multichannel appearance, resembling streams in areas devastated by Mount
St. Helens big eruption or areas logged by clear-cutting.
in the Past
about 65 million years ago, probably caused or aggravated by impact
of several-mile-wide asteroid that created the Chicxulub crater now hidden
on the Yucatan Peninsula and beneath the Gulf of Mexico. Some argue for
other causes, including gradual climate change or flood-like volcanic
eruptions of basalt lava from Indias Deccan Traps. The extinction killed
16 percent of marine families, 47 percent of marine genera (the
classification above species) and 18 percent of land vertebrate families,
including the dinosaurs. End Triassic extinction,
roughly 199 million to 214 million years ago, most likely caused by
massive floods of lava erupting from the central Atlantic magmatic
province -- an event that triggered the opening of the Atlantic Ocean. The
volcanism may have led to deadly global warming. Rocks from the eruptions
now are found in the eastern United States, eastern Brazil, North Africa
and Spain. The death toll: 22 percent of marine families, 52 percent of
marine genera. Vertebrate deaths are unclear. Permian-Triassic extinction,
about 251 million years ago. Many scientists suspect a comet or
asteroid impact, although direct evidence has not been found. Others
believe the cause was flood volcanism from the Siberian Traps and related
loss of oxygen in the seas. Still others believe the impact triggered the
volcanism and also may have done so during the Cretaceous-Tertiary
extinction. The Permian-Triassic catastrophe was Earths worst mass
extinction, killing 95 percent of all species, 53 percent of marine
families, 84 percent of marine genera and an estimated 70 percent of land
species such as plants, insects and vertebrate animals. Late Devonian extinction,
about 364 million years ago, cause unknown. It killed 22 percent of
marine families and 57 percent of marine genera. Erwin said little is
known about land organisms at the time.
about 439 million years ago, caused by a drop in sea levels as
glaciers formed, then by rising sea levels as glaciers melted. The toll:
25 percent of marine families and 60 percent of marine genera.
Studies Suggest -
Permian Extinction Quick
Studies suggesting the permian extinction was quick
The new study is the latest in a series showing the Permian-Triassic
catastrophe was quick at least in geological terms and extremely nasty.
But it has not settled debate among those who advocate various theories of
what caused the extinction: an object whacking Earth, floods of lava from
the Siberian Traps, climate change, and/or deadly radiation from a nearby
supernova or other cosmic explosion.
In July, Doug Erwin of the Smithsonian Institutions National Museum of
Natural History published a study in Science in which marine rocks from
China revealed the Permian-Triassic extinction happened in less than
And in Julys issue of the journal Geology, a study of seafloor rocks now
in the Austrian Alps concluded the extinction happened in less than 60,000
years and perhaps in less than 8,000 years, said the main author,
planetary scientist Michael Rampino of New York University.
Because the rock layers do not permit finer dissection of time, the
findings are consistent with the extinction being triggered by an impact
that happened during "a single bad day," Erwin said.
"The mass extinction at the end of the Permian Period was catastrophic and
sudden," ravaging sea and land life, Rampino said. "The only thing we know
of that can cause an extinction like this is a large impact of an asteroid
or comet. But we still havent found conclusive evidence that an impact
Rampino said the object "would have to be bigger one and a half to twice
as big" as the 6-mile- (10-kilometer-) wide asteroid usually blamed for
the dinosaurs extinction.
In 1997, University of Oregon paleontologist Gregory Retallack reported
finding elevated iridium levels and shocked quartz crystals in
Permian-Triassic rocks telltale signs of an impact.
"Unfortunately, we have not found a good candidate crater," he said.
Ward said a comet made of ice "would be almost invisible geologically."
Australian scientists said they found a 75-mile- (120-kilometer-) wide
crater in western Australia that might be from an impact that caused the
Permian-Triassic extinction or a later extinction at the end of the
Triassic Period roughly 200 million years ago.
But Rampino said the age of that crater is so poorly known that "it is
impossible to tie that impact to this [Permian-Triassic] extinction."
Nevertheless, Retallack favors impact as the cause, perhaps with the
impact triggering an undersea release of methane that robbed the oceans of
life-sustaining oxygen. He says the impact also may have triggered massive
eruptions from volcanic vents named the Siberian Traps.
"There is no evidence of an impact" at Permian-Triassic time, Erwin said.
"So while the data are consistent with an impact, there is nothing that
tells us it was an impact," and massive volcanic eruptions may be a more
Rampino said the Siberian volcanic eruptions lasted hundreds of thousands
of years, so "if the extinctions were gradual over a half million years,
we might suspect volcanism or changes in climate caused by volcanic
eruptions. But the fact the extinctions were so sudden and catastrophic
argues against a volcanic interpretation."
Possible Cause of the Permian Extinction
A crater that could be the possible cause of the Permian Extinction
An apparent crater as big as Ohio has been found in Antarctica. Scientists
think it was carved by a space rock that caused the greatest mass
extinction on Earth, 250 million years ago.
The crater, buried beneath a half-mile of ice and discovered by some
serious airborne and satellite sleuthing, is more than twice as big as the
one involved in the demise of the dinosaurs.
The crater's location, in the Wilkes Land region of East Antarctica, south
of Australia, suggests it might have instigated the breakup of the
so-called Gondwana supercontinent, which pushed Australia northward, the
"This Wilkes Land impact is much bigger than the impact that killed the
dinosaurs, and probably would have caused catastrophic damage at the
time," said Ralph von Frese, a professor of geological sciences at Ohio
How they found it
The crater is about 300 miles wide. It was found by looking at differences
in density that show up in gravity measurements taken with NASA's GRACE
satellites. Researchers spotted a mass concentration, which they call a
masconâ€”dense stuff that welled up from the mantle, likely in an impact.
"If I saw this same mascon signal on the Moon, I'd expect to see a crater
around it," Frese said. (The Moon, with no atmosphere, retains a record of
ancient impacts in the visible craters there.)
So Frese and colleagues overlaid data from airborne radar images that
showed a 300-mile wide sub-surface, circular ridge. The mascon fit neatly
inside the circle.
"And when we looked at the ice-probing airborne radar, there it was," he
The Permian-Triassic extinction, as it is known, wiped out most life on
land and in the oceans. Researchers have long suspected a space rock might
have been involved. Some scientists have blamed volcanic activity or other
The die-off set up conditions that eventually allowed dinosaurs to rule
The newfound crater is more than twice the size of the Chicxulub crater in
the Yucatan peninsula, which marks the impact that may have ultimately
killed the dinosaurs 65 million years ago. The Chicxulub space rock is
thought to have been 6 miles wide, while the Wilkes Land meteor could have
been up to 30 miles wide, the researchers said.
Postdoctoral researcher Laramie Potts assisted in the discovery.
The work was financed by NASA and the National Science Foundation. The
discovery, announced today, was initially presented in a poster paper at
the recent American Geophysical Union Joint Assembly meeting in Baltimore.
The researchers say further work is needed to confirm the finding. One way
to do that would be to go there and collect rock from the crater to see if
its structure matches what would be expected from such a colossal impact.