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CCNet 110/2003 - 21 November 2003
CONTROVERSIAL NEW CLAIM IN DEATH-BY-ASTEROID CASE
-------------------------------------------------
A longstanding mystery over what caused five great mass
extinctions,
including one that destroyed the dinosaurs, has grown with the
release
of two studies today in the journal Science. In one study,
researchers
make the bold claim that an asteroid is responsible for the death
of most
life on Earth in a catastrophic extinction 251 million years ago.
Other
scientists are not ready to accept the claim. "I get the gut
feeling it's
wrong," said geochemist Birger Schmitz of the University of
Goteborg in Sweden.
"It's astonishing, it's incredible, it's unbelievable,"
said Jeffrey Grossman
of the U.S. Geological Survey. All those adjectives apply,
Grossman later
told SPACE.com, if the findings prove to be accurate. "Like
all experiments
it's going to have to be replicated," he said. And that
replication is
relatively simple. Another group of researchers can go to the
same site in
Antarctica, bring back their own samples, and analyze them.
--Rob Britt, Space.com, 20 November 2003
(1) NEW EVIDENCE THAT IMPACT MAY HAVE TRIGGERED P/T MASS
EXTINCTION
Andrew Yee <ayee@nova.astro.utoronto.ca>
(2) CONTROVERSIAL NEW CLAIM IN DEATH-BY-ASTEROID CASE
Space.com, 20 November 2003
(3) DID ASTEROID IMPACT KILL 90% OF EARTH'S LIFE?
Associated Press, 20 November 2003
(4) ARE ASTEROIDS HISTORY'S GREATEST KILLERS?
National Geographic News, 20 November 2003
========
(1) NEW EVIDENCE THAT IMPACT MAY HAVE TRIGGERED P/T MASS
EXTINCTION
Andrew Yee <ayee@nova.astro.utoronto.ca>
Office of Public Relations
University of Rochester
Rochester, New York
MEDIA CONTACT:
Jonathan Sherwood (585) 273-4726
November 20, 2003
New Evidence that Earth's Greatest Extinction Caused by Ancient
Meteorite or Comet
Long before the dinosaurs ever lived, the planet experienced a
mass extinction
so severe it killed 90 percent of life on Earth, and researchers
at the
University of Rochester think they've identified the unlikely
culprit.
"An ancient meteorite body, one from the days when the solar
system was still
forming, struck the Earth 251 million years ago," says Asish
Basu, professor of
earth sciences in today's issue of Science. The research is the
latest volley in
a decades-long debate over what caused "The Great
Dying," the greatest
elimination of life in the planet's history.
While scientists have been wrangling over whether a meteor caused
this great
extinction ever since a meteor was fingered with the blame for
the later
dinosaur extinction, these new findings add weight to the
argument that a major
meteorite did strike the Earth 251 million years ago, likely
triggering climate
change and unprecedented volcanic activity. That one-two punch so
affected the
composition of the atmosphere that it took thousands of years to
recover --
leaving only a relative handful of plants and animals alive.
Two decades ago, Nobel laureate Luis Alvarez and his son, Walter,
detected huge
concentrations of iridium throughout the world in rock dated to
the end of the
dinosaur era. Iridium is only found in such concentrations in
asteroids, so they
concluded that a giant asteroid had struck the Earth at that
time, likely
leading to the downfall of the dinosaurs. The Alvarez claims were
at first
largely dismissed, but the evidence grew and today it is accepted
that their
interpretation was largely correct.
Basu added weight to the Alvarez claims in 1988 when he announced
the discovery
of "shocked quartz" -- special crystals that have split
along certain planes
indicative of a large impact -- immediately beneath the Deccan
Traps of India.
The Deccan Traps are areas of huge volcanic deposits that have
been dated to 65
million years ago, the time of the dinosaur extinction, so
finding shocked
quartz immediately beneath them suggests that a giant impact
preceded these
giant lava flows.
While a meteorite has been largely accepted as the source of the
dinosaurs'
demise, the root of The Great Dying has been a mystery. In 1991,
however, Basu
published a study in Science that showed a massive and ancient
lava flow in
Siberia dated precisely to that greatest of extinctions 251
million years ago.
The lava did not shoot out of the Earth like a giant volcano, but
oozed molten
rock for thousands of years -- so much lava, in fact, that if
spread evenly, it
would bury the surface of the Earth under 10 feet of magma.
Further testing by Basu and Robert Poreda, professor of earth and
environmental
sciences at the University, and also co-author of the current
Science research,
showed that both the Siberian and Indian lava had come from as
deep as 1,800
miles beneath the surface.
"These were not just examples of local magma bubbling
through the crust,"
explains Poreda. "Something brought this lava all the way up
from near the
Earth's core."
To find what might have caused the Siberian flows meant finding
rock samples 251
million years old-not an easy prospect since oceanic tectonic
plates that make
up 70 percent of the Earth's surface are younger than that.
Oceanic plates slide
underneath continental plates as they move, thus carrying any
evidence far
beyond the reach of humans. From an area in Antarctica called
Graphite Peak,
Basu and Poreda took rock from a stratum that sat between a layer
that contained
many fossils and a layer nearly devoid of fossils called the
Permian/Triassic,
or P/T boundary. One of the fossils that had gone from prominence
to sudden
disappearance was Glossopteris flora, a plant that was widely
known to have been
wiped out in The Great Dying. This reassured the team that they
had the right
rock from the right period. Previous tests by Poreda on this same
layer found
shocked quartz and fullerenes, cage-like molecules, containing
atoms of
extraterrestrial gases, which again hinted at a meteorite or
comet strike. These
results, however, were disputed by some researchers.
Coming at the problem from another angle, Basu and Poreda
separated out the
magnetic particles from the samples from Graphite Peak and from a
source of P/T
strata in Meishan, China, and Japan. To their surprise they found
that the
grains that sorted out contained an iron alloy that does not
occur on Earth.
Some 40 pieces were tiny fragments of meteorite 4.56 billion
years old, while
other grains displayed metallic characteristics that were more
indicative of
being formed by extreme heat, such as that in a severe meteorite
impact. The
very fact that these grains had not deteriorated from weathering
means they must
have been buried quickly under sedimentary deposits, again,
indicative of a
major impact.
"At the end of the Permian era, Antarctica was close to its
present position as
the southernmost part of the ancient supercontinent, Pangea,
while south China
was at the equator and Japan was to the north of the
equator," explains Basu.
"Such a wide, global distribution of these metal grains in
the P/T boundary
strongly suggests that these grains mark a major impact of a
celestial body at
that time."
Critics of the P/T impact theory may point to the lack of
iridium, the element
that is so rare on Earth but common in asteroids and which
alerted Alvarez to
the possibility of a meteorite as the death knell for the
dinosaurs. The
Rochester team's work shows strong evidence that not all
collisions with
extraterrestrial bodies will leave an iridium footprint. Basu
suggests that a
collision with a comet, which may have a meteoric core, would be
low in iridium.
Thus the culprit that wiped out nine of every 10 creatures on the
Earth and
nearly ended life when it was just taking hold may have been
created before the
Earth itself was fully formed.
Basu and Poreda plan to continue searching for evidence of a
catastrophic impact
in the P/T layer in different sites around the world. They hope
that if enough
samples from enough locations show evidence of a major impact,
then scientists
will be able to construct the exact scenarios of how the two
largest mass
extinctions in history were caused by meteorite collisions.
Along with Basu and Poreda, the co-authors of the paper are
Michail I. Petaev
and Stein B. Jacobsen of Harvard University, and Luann Becker of
the University
of California, Santa Barbara.
============
(2) CONTROVERSIAL NEW CLAIM IN DEATH-BY-ASTEROID CASE
Space.com, 20 November 2003
http://www.space.com/scienceastronomy/mass_extinction_031120.html
By Robert Roy Britt
A longstanding mystery over what caused five great mass
extinctions, including one that destroyed the dinosaurs, has
grown with the release of two studies today in the journal
Science.
In one study, researchers make the bold claim that an asteroid is
responsible for the death of most life on Earth in a catastrophic
extinction 251 million years ago. Other scientists are not ready
to accept the claim.
Many experts have become convinced over the past two decades that
the dinosaurs were exterminated 65 million years ago by an
asteroid impact. Some findings suggest other mass extinctions,
such as the one 251 million years ago, might also have been
caused by rocks from space.
But the evidence is scant. Volcanic activity remains a suspect in
the extinction cases, and a growing scientific minority is
skeptical of the whole death-by-space-rock scenario.
The new study uncovered 40 extraterrestrial mineral fragments in
the Antarctic, indicating the asteroid impact 251 million years
ago. The timing coincides with the well-documented
Permian-Triassic mass extinction, the worst of five major events
scientists have identified through fossil records. Some 90
percent of all species disappeared, by some accounts.
Scientists generally agree that the newfound tiny grains, called
chondritic meteorite fragments, are indeed from space. But
agreement stops there.
Too good to be true?
Study leader Asish Basu, a geochemist at the University of
Rochester, and his colleagues are puzzled by their own discovery
but have arrived at a conclusion nonetheless.
"It appears to us that the two largest mass extinctions in
Earth history [65 million and 251 million years ago] were both
caused by catastrophic collisions with chondritic
meteoroids," the researchers write.
The pristine state of the fragments, however, does not make sense
to other researchers. They should have long ago become
indistinguishable soil, conventional wisdom holds. The fragments
were collected from a layer dated to the Permian-Triassic
boundary in time. They were embedded in rock 4-8 inches (10-20
centimeters) beneath the surface.
In a related analysis in Science by the science writer Richard
Kerr, other scientists say they are stunned that the fragments
survived for a quarter-billion years.
"I get the gut feeling it's wrong," said geochemist
Birger Schmitz of the University of Goteborg in Sweden.
"It's astonishing, it's incredible, it's unbelievable,"
said Jeffrey Grossman of the U.S. Geological Survey. All those
adjectives apply, Grossman later told SPACE.com, if the findings
prove to be accurate. "Like all experiments it's going to
have to be replicated," he said. And that replication is
relatively simple. Another group of researchers can go to the
same site in Antarctica, bring back their own samples, and
analyze them.
Basu stands by the results. He insists the fragments were
properly analyzed and that contamination in the sample was ruled
out.
"We discovered them," Basu said in a telephone
interview today. "Therefore they are there. Time will tell
why they are there."
Basu added that the purpose of his team's scientific paper was
not to explain how the grains held up over time. "The grains
are there. Nobody can challenge that," he said. "We
have to figure out how they survived."
Basu's team is back in Antarctica looking for more of the
fragments. He said further research could solve the mystery.
Another culprit
Meanwhile, other researchers have been working to understand what
role volcanoes might play in mass extinctions.
Deadly climate-altering gases spewed by volcanic eruptions could
be the main culprit behind mass death, some figure. Others
suppose volcanoes play just a supporting role. There is also the
question of whether asteroid impacts trigger the volcanic
activity and so are the root of all this evil either way.
Another new study in the journal suggests volcanoes might not be
as deadly as some believe. And, if correct, it rules out the
possibility that the dino-killing asteroid triggered intense
volcanic activity known to have occurred in the era.
Researchers agree that at some time near the dinosaur extinction
event 65 million years ago, a vast outpouring of volcanic
material created a feature in India called the Deccan Traps, a
bed of lava that covers an area about the size of Oregon and
Washington states combined. But the timing has not been pinned
down.
The Deccan volcanism occurred about 500,000 years before the end
of the dinosaurs, according to the new research, by Greg Ravizza
of the University of Hawaii and Bernhard Peucker-Ehrenbrink from
the Woods Hole Oceanographic Institution.
The volcanoes loaded the air with carbon dioxide, fueling global
warming, these scientists presume. Death of some species would
have weakened the biological chain supporting dinosaurs.
Volcanic activity might have made life difficult for dinosaurs,
it seems, but an asteroid impact remains the prime suspect in
their demise.
Copyright 2003, Space.com
===========
(3) DID ASTEROID IMPACT KILL 90% OF EARTH'S LIFE?
Associated Press, 20 November 2003
http://www.thestar.com/NASApp/cs/ContentServer?pagename=thestar/Layout/Article_Type1&c=Article&cid=1069369353526&call_pageid=968332188854&col=968705899037
WASHINGTON (AP) - A massive asteroid may have collided with the
Earth 251 million years ago and killed 90 per cent of all life,
an extinction even more severe than the meteorite impact that
snuffed out the dinosaurs 66 million years ago.
A new study, based on meteorite fragments found in Antarctica,
suggests the Permian-Triassic event, the greatest extinction in
the planet's history, may have been triggered by a mountain-sized
space rock that smashed into a southern land mass.
"It appears to us that the two largest mass extinctions in
Earth history ... were both caused by catastrophic
collisions" with meteoroids, the researchers say in their
study appearing this week in the journal Science.
Asish Basu, a professor of Earth sciences at the University of
Rochester, said proof of a massive impact 251 million years ago
is in the chemistry found in rocky fragments recovered on
Graphite Peak in Antarctica. He said the fragments were found at
a geological horizon, or layer, that was laid down at the start
of the Permian-Triassic extinction. Analysis shows the fragments
have chemical ratios that are unique to meteorites.
"The only place you would find the chemical composition that
we found in these fragments is in very primitive,
4.6-billion-year-old meteorites, as old as our Earth," said
Basu, the first author of the study.
Basu said the Permian-Triassic asteroid was probably bigger than
the 10-kilometre-wide space rock that is thought to have killed
the dinosaurs.
Such an impact could cause a huge fireball and send billions of
tonnes of dust into the atmosphere, enough to darken the sun for
months. It also would have laid down a layer of dust bearing the
same chemical composition as the meteorite.
The dinosaur-killing asteroid left a thin layer of the element
iridium across the globe. But Basu said iridium was not found in
the fragments recovered from the Antarctica, suggesting the
earlier Permian-Triassic asteroid had a different composition.
Basu said specimens recovered from Permian-Triassic rock
formations in China, however, have a chemistry that matches that
of the meteorite fragments found in Antarctica, a discovery that
supports the impact theory. Also, shocked quartz, a telltale sign
of an asteroid impact, has been found at both sites, he said.
At the time of the Permian-Triassic event, Africa, South America,
India, Australia and Antarctica were joined in a giant continent
called Pangea. Just where the asteroid hit in that land mass is
uncertain, Basu said, but it could have been near what is now
western Australia.
Life on Earth 251 million years ago was far different from what
it is now or what it was when dinosaurs lived.
"There were no large animals then, but there were lots of
species living on the land and in the sea, and there were
plants," said Basu. The most dominant plant, which is found
commonly in fossil beds from the Permian-Triassic, was a giant
fern called glossopteris. In the geological layers following the
impact, that fern is absent from the fossil record.
"That was the last blooming of that plant," said Basu.
"After that, it was gone forever from the planet."
Massive outflows of lava, called flood basalt, occurred around
the time of both the Permian-Triassic and the dinosaur
extinctions. The outflow continued for thousands of years and
thickly covered hundreds of kilometres. Basu said it is possible
that asteroid impacts triggered both eruptions of lava, but the
connection has yet to be proven.
Some experts are skeptical that Basu and his co-authors have
found 251-million-year-old meteorite metals, although nobody
questions that the material did come from outer space. The
surprise is that the specimens survived the weathering on Earth
for so long.
"Nobody has even seen anything like this before," said
Jeffrey Grossman, a researcher with the United States Geologic
Survey in Reston, Va. "It is incredibly fresh and that is
astonishing."
David Kring, a planetary geologist at the University of Arizona,
said it is clear that material found by Basu and his team is from
an asteroid, "but it is unlike the debris we have seen in
other impact ejecta."
As a result, said Kring, "there are enough questions ...
that I don't think one can say that an impact is conclusively
linked to the Permian-Triassic extinction. We need to go back and
test the hypothesis."
Copyright 2003, AP
===========
(4) ARE ASTEROIDS HISTOR'S GREATEST KILLERS?
National Geographic News, 20 November 2003
http://news.nationalgeographic.com/news/2003/11/1120_031120_massextinctions.html
John Roach
Catastrophic asteroid impacts are gaining a credible edge over
violent volcanic eruptions as the greatest killers Earth has ever
seen, according to two pieces of scientific detective work
reported in tomorrow's issue of the journal Science.
The first cataclysm in question occurred about 250 million years
ago, when according to the fossil record more than 90 percent of
Earth's marine species and 70 percent of life on land perished.
The event is known as the Permian-Triassic (P-T for short) mass
extinction, named because it falls on the boundary between the
two geological eras.
The second event, known as the Cretaceous-Tertiary (K-T) mass
extinction, occurred about 65 million years ago, leading to the
demise of the dinosaurs and most of the creatures and plants that
lived with them.
The geologic record shows that cataclysmic volcanic eruptions
occurred around the same time as two periods of mass extinctions.
But recent research shows that asteroids may have had a more
significant impact on prehistoric flora and fauna. The Ida
asteroid, the 1991 eruption of Mt. Pinatubo in the Philippines,
and a magnified meteorite fragment are shown above.
According to the geological record, bouts of extreme volcanism
occurred around the same time as these mass extinctions and many
scientists have suggested that the volcanic activity is directly
responsible for the loss of life.
However, the discovery and analysis over the past few decades of
a crater from an asteroid impact about 65 million years ago, and
of meteorite fragments from an apparent asteroid impact about 250
million years ago, is leading some scientists to believe that the
impact events, not volcanism, were the primary cause of the
extinctions.
Two studies published in the November 21 issue of Science support
these theories. One study presents further evidence for an impact
event about 250 million years ago and the second study suggests
that the volcanism around the K-T boundary was probably not a
major contributor to the K-T mass extinction.
Asteroid Impacts
In 1991 scientists located a 112-mile-wide (180-kilometer-wide)
and 3,000-foot-deep (900-meter-deep) crater on Mexico's Yucatán
Peninsula that appeared to have been made by a giant comet or
asteroid that slammed into the Earth about 65 million years ago.
The collision has gained favor as the cause of the K-T mass
extinction and is referred to as the "dinosaur killer."
Now, a team of scientists led by Asish Basu, a geochemist at the
University of Rochester in New York, has found dozens of unusual
mineral grains from two rock samples taken from Graphite Peak,
Antarctica, that they say are pieces of a meteorite that impacted
Earth 250 million years ago.
"We analyzed them and they seem to be pieces of
extraterrestrial material," said Basu.
The researchers also found bits of nearly pure metallic iron in
the Antarctic rock that they say is of neither terrestrial nor
extraterrestrial origin. Rather, they say the particles resemble
those reported by Kunio Kaiho of Tohoku University in Sendai,
Japan, from the P-T boundary in Meishan, China, that formed as an
impact cloud condensed.
A third, controversial, impact marker-clusters of carbon atoms
called buckyballs-have also shown up at Graphite Peak, co-authors
of the Science paper Luann Becker of the University of
California, Santa Barbara and Robert Poredea of the University of
Rochester reported earlier this year in the journal Astrobiology.
Basu and his colleagues suggest in Science that the material from
Asia and Antarctica is from an impact event associated with the
P-T mass extinction just as the impact crater in the Yucatán is
now widely associated with K-T mass extinction.
Gregory Retallack, a geologist at the University of Oregon in
Eugene who in 1995 collected one of the Antarctic samples
analyzed by Basu and colleagues, also concluded that the rocks
contained evidence of an asteroid impact.
"This new paper is a splendid corroboration of our earlier
work," he said in an e-mail sent from Antarctica where he is
currently searching for more impact beds associated with the P-T
boundary.
Meanwhile, Basu and his colleagues are actively searching for an
impact crater associated with the P-T mass extinction. Such a
find, said Basu, would further clarify whether the impact
occurred and, if so, its association with the mass extinction.
"The search is going on. So far in the published literature
no one has found it, but we are working on it actively. We are
working on it right now," he said.
Volcanic Isotopes
In a second Science study, geochemists analyzing the ratios of
two osmium isotopes in seawater suggest that the bout of violent
volcanic activity around the K-T boundary likely caused a major
global warming event but was probably not a major contributor to
the demise of the dinosaurs.
Greg Ravizza, a co-author of the study at the University of
Hawaii in Honolulu, said the finding substantiates earlier
studies based on analysis of the past climate by bringing more
resolution to when the volcanism occurred in relation to the
impact event.
"It's the first thing we have that substantiates the
previous interpretations of the paleoclimate," he said.
The finding suggests that while the period of volcanism spanned
the K-T impact event, the bulk of the volcanism occurred several
hundred thousand years before the asteroid slammed into the
Yucatán, causing the mass die off.
Ravizza said he would like to apply the dating technique he and
his colleague Bernhard Peucker-Ehrenbrink of the Woods Hole
Oceanographic Institution in Massachusetts used to the volcanism
at the P-T boundary as well, but 250-million-year-old sediments
on the seafloor are not well preserved.
Such work, if eventually possible, will help answer the still
outstanding question of how significant a contribution the
volcanism at the P-T boundary made to the mass extinction, versus
the contribution of the impact.
Basu said it may even be possible that the volcanism at the P-T
boundary is directly linked to the impact event. "That is
the $64 million question," he said. "People are trying
to figure out whether an impact could trigger volcanism. That
would be a double punch."
Copyright 2003, National Geographic News
-----------
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