Press Release

The Great Dying 250 Million Years Ago

By SpaceRef Editor
January 28, 2002
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250 million years ago something unknown wiped out most life on our planet.
Now scientists are finding buried clues to the mystery inside tiny capsules
of cosmic gas.

January 28, 2002: It was almost the perfect crime.

Some perpetrator — or perpetrators — committed murder on a scale unequaled
in the history of the world. They left few clues to their identity, and they
buried all the evidence under layers and layers of earth.

The case has gone unsolved for years — 250 million years, that is.

But now the pieces are starting to come together, thanks to a team of
NASA-funded sleuths who have found the “fingerprints” of the villain, or at
least of one of the accomplices

Above: Life was flourishing on the Earth about 250 million years ago, then
during a brief window of geologic time nearly all of it was wiped out. This
image is an artist’s impression of a Lower Permian swamp in Texas.

The terrible event had been lost in the amnesia of time for eons. It was
only recently that paleontologists, like hikers stumbling upon an unmarked
grave in the woods, noticed a startling pattern in the fossil record: Below
a certain point in the accumulated layers of earth, the rock shows signs of
an ancient world teeming with life. In more recent layers just above that
point, signs of life all but vanish.

Somehow, most of the life on Earth perished in a brief moment of geologic
time roughly 250 million years ago. Scientists call it the Permian-Triassic
extinction or “the Great Dying” — not to be confused with the better-known
Cretaceous-Tertiary extinction that signaled the end of the dinosaurs 65
million years ago. Whatever happened during the Permian-Triassic period was
much worse: No class of life was spared from the devastation. Trees, plants,
lizards, proto-mammals, insects, fish, mollusks, and microbes — all were
nearly wiped out. Roughly 9 in 10 marine species and 7 in 10 land species
vanished. Life on our planet almost came to an end.

Scientists have suggested many possible causes for the Great Dying: severe
volcanism, a nearby supernova, environmental changes wrought by the
formation of a super-continent, the devastating impact of a large asteroid
— or some combination of these. Proving which theory is correct has been
difficult. The trail has grown cold over the last quarter billion years;
much of the evidence has been destroyed.

“These rocks have been through a lot, geologically speaking, and a lot of
times they don’t preserve the (extinction) boundary very well,” says Luann
Becker, a geologist at the University of California, Santa Barbara. Indeed,
there are few 250 million-year-old rocks left on Earth. Most have been
recycled by our planet’s tectonic activity.

Undaunted, Becker led a NASA-funded science team to sites in Hungary, Japan
and China where such rocks still exist and have been exposed. There they
found telltale signs of a collision between our planet and an asteroid 6 to
12 km across — in other words, as big or bigger than Mt. Everest.

Many paleontologists have been skeptical of the theory that an asteroid
caused the extinction. Early studies of the fossil record suggested that the
die-out happened gradually over millions of years — not suddenly like an
impact event. But as their methods for dating the disappearance of species
has improved, estimates of its duration have shrunk from millions of years
to between 8,000 and 100,000 years. That’s a blink of the eye in geological

“I think paleontologists are now coming full circle and leading the way,
saying that the extinction was extremely abrupt,” Becker notes. “Life
vanished quickly on the scale of geologic time, and it takes something
catastrophic to do that.”

Such evidence is merely circumstantial — it doesn’t actually prove
anything. Becker’s evidence, however, is more direct and persuasive:

Deep inside Permian-Triassic rocks, Becker’s team found soccer ball-shaped
molecules called “fullerenes” (or “buckyballs”) with traces of helium and
argon gas trapped inside. The fullerenes held an unusual number of 3He and
36Ar atoms — isotopes that are more common in space than on Earth.
Something, like a comet or an asteroid, must have brought the fullerenes to
our planet.

Becker’s team had previously found such gas-bearing buckyballs in rock
layers associated with two known impact events: the 65 million-year-old
Cretaceous-Tertiary impact and the 1.8 billion-year-old Sudbury impact
crater in Ontario, Canada. They also found fullerenes containing similar
gases in some meteorites. Taken together, these clues make a compelling case
that a space rock struck the Earth at the time of the Great Dying.

But was an asteroid the killer, or merely an accomplice?

Many scientists believe that life was already struggling when the putative
space rock arrived. Our planet was in the throes of severe volcanism. In a
region that is now called Siberia, 1.5 million cubic kilometers of lava
flowed from an awesome fissure in the crust. (For comparison, Mt. St. Helens
unleashed about one cubic kilometer of lava in 1980.) Such an eruption would
have scorched vast expanses of land, clouded the atmosphere with dust, and
released climate-altering greenhouse gases.

World geography was also changing then. Plate tectonics pushed the
continents together to form the super-continent Pangea and the super-ocean
Panthalassa. Weather patterns and ocean currents shifted, many coastlines
and their shallow marine ecosystems vanished, sea levels dropped.

“If life suddenly has all these different things happen to it,” Becker says,
“and then you slam it with a rock the size of Mt. Everest — boy! That’s
just really bad luck.”

Was the “crime” then merely an accident? Perhaps so. Nevertheless, it’s wise
to identify the suspects — an ongoing process — before it happens again.

SpaceRef staff editor.