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CCNet 77/2003 - 26 September 2003
"CHICXULUB IMPACT CRATER NOT RELATED TO K/T MASS EXTINCTION"

[Gerta] Keller has accumulated evidence suggesting that the Chicxulub
crater probably did not coincide with the K/T boundary. Instead, the
impact that caused the Chicxulub crater was likely smaller than
originally believed and probably occurred 300,000 years before the mass
extinction. The final dinosaur-killer probably struck Earth somewhere else
and remains undiscovered, said Keller.... If the majority of scientists
eventually reduce their estimates of the damage done by a single asteroid,
that shift in thinking could influence the current-day debate on how much
attention should be given to tracking and diverting Earth-bound asteroids
and comets in the future.
--Steven Schultz, Princeton University, 25 Sept. 2003

This affair has become an object lesson on how partisan and unethical the
whole dinosaur controversy has become. Young scientists are now refusing to
get involved in this field because no matter what they say it will offend
someone and damage their careers. It's like the nature-nurture debate.
No matter what you say, someone will hate you for it.
--Norman MacLeod, Natural History Museum, 7 Sept. 2003

(1) "CHICXULUB IMPACT CRATER NOT RELATED TO K/T MASS EXTINCTION"

Ron Baalke <info@jpl.nasa.gov>

http://www.princeton.edu/pr/news/03/q3/0925-keller.htm

Princeton University
Office of Communications
22 Chambers St.
Princeton, New Jersey 08542
Telephone 609-258-3601; Fax 609-258-1301

For immediate release: September 25, 2003
Contact: Steven Schultz, (609) 258-5729, sschultz@princeton.edu

Princeton paleontologist produces evidence for new theory on
dinosaur extinction

PRINCETON, N.J. -- As a paleontologist, Gerta Keller has studied
many aspects of the history of life on Earth. But the question
capturing her attention lately is one so basic it has passed the
lips of generations of 6-year-olds: What killed the dinosaurs?

The answers she has been uncovering for the last decade have
stirred an adult-sized debate that puts Keller at odds with many
scientists who study the question. Keller, a professor in
Princeton's Department of Geosciences, is among a minority of
scientists who believe that the story of the dinosaurs' demise is
much more complicated than the familiar and dominant theory that a
single asteroid hit Earth 65 million years ago and caused the mass
extinction known as the Cretacious-Tertiary, or K/T, boundary.

Keller and a growing number of colleagues around the world are
turning up evidence that, rather than a single event, an intensive
period of volcanic eruptions as well as a series of asteroid
impacts are likely to have stressed the world ecosystem to the
breaking point. Although an asteroid or comet probably struck Earth
at the time of the dinosaur extinction, it most likely was, as
Keller says, "the straw that broke the camel's back" and not the
sole cause.

Perhaps more controversially, Keller and colleagues contend that
the "straw" -- that final impact -- is probably not what most
scientists believe it is. For more than a decade, the prevailing
theory has centered on a massive impact crater in Mexico. In 1990,
scientists proposed that the Chicxulub crater, as it became known,
was the remnant of the fateful dinosaur-killing event and that
theory has since become dogma.

Keller has accumulated evidence, including results released this
year, suggesting that the Chicxulub crater probably did not
coincide with the K/T boundary. Instead, the impact that caused the
Chicxulub crater was likely smaller than originally believed and
probably occurred 300,000 years before the mass extinction. The
final dinosaur-killer probably struck Earth somewhere else and
remains undiscovered, said Keller.

These views have not made Keller a popular figure at meteorite
impact meetings. "For a long time she's been in a very
uncomfortable minority," said Vincent Courtillot, a geological
physicist at Université Paris 7. The view that there was anything
more than a single impact at work in the mass extinction of 65
million years ago "has been battered meeting after meeting by a
majority of very renowned scientists," said Courtillot.

The implications of Keller's ideas extend beyond the downfall of
ankylosaurus and company. Reviving an emphasis on volcanism, which
was the leading hypothesis before the asteroid theory, could
influence the way scientists think about the Earth's many episodes
of greenhouse warming, which mostly have been caused by periods of
volcanic eruptions. In addition, if the majority of scientists
eventually reduce their estimates of the damage done by a single
asteroid, that shift in thinking could influence the current-day
debate on how much attention should be given to tracking and
diverting Earth-bound asteroids and comets in the future.

Keller does not work with big fossils such as dinosaur bones
commonly associated with paleontology. Instead, her expertise is in
one-celled organisms, called foraminifera, which pervade the oceans
and evolved rapidly through geologic periods. Some species exist
for only a couple hundred thousand years before others replace
them, so the fossil remains of short-lived species constitute a
timeline by which surrounding geologic features can be dated.

In a series of field trips to Mexico and other parts of the world,
Keller has accumulated several lines of evidence to support her
view of the K/T extinction. She has found, for example, populations
of pre-K/T foraminifera that lived on top of the impact fallout
from Chicxulub. (The fallout is visible as a layer of glassy beads
of molten rock that rained down after the impact.) These fossils
indicate that this impact came about 300,000 years before the mass
extinction.

The latest evidence came last year from an expedition by an
international team of scientists who drilled 1,511 meters into the
Chicxulub crater looking for definitive evidence of its size and
age. Although interpretations of the drilling samples vary, Keller
contends that the results contradict nearly every established
assumption about Chicxulub and confirm that the Cretaceous period
persisted for 300,000 years after the impact. In addition, the
Chicxulub crater appears to be much smaller than originally thought
-- less than 120 kilometers in diameter compared with the original
estimates of 180 to 300 kilometers.

Keller and colleagues are now studying the effects of powerful
volcanic eruptions that began more than 500,000 years before the
K/T boundary and caused a period of global warming. At sites in the
Indian Ocean, Madagascar, Israel and Egypt, they are finding
evidence that volcanism caused biotic stress almost as severe as
the K/T mass extinction itself. These results suggest that asteroid
impacts and volcanism may be hard to distinguish based on their
effects on plant and animal life and that the K/T mass extinction
could be the result of both, said Keller.

Note: A longer version of this news release appeared in the
Princeton Weekly Bulletin: http://www.princeton.edu/pr/pwb/03/0922/

(2) WHAT KILLED THE DINOSAURS? GERTA KELLER REKINDLES K/T CONTROVERSY

Princeton University Weekly Bulletin, 25 Sept. 2003
http://www.princeton.edu/pr/pwb/03/0922/

Dinosaur dust-up: Princeton paleontologist produces evidence for new theory on extinction
By Steven Schultz

Princeton NJ -- As a paleontologist, Gerta Keller has studied many aspects of the history of life on Earth. But the question capturing her attention lately is one so basic it has passed the lips of generations of 6-year-olds: What killed the dinosaurs?

The answers she has been uncovering for the last decade have stirred an adult-sized debate that puts Keller at odds with many scientists who study the question. Keller, a professor in Princeton's Department of Geosciences, is among a minority of scientists who believe that the story of the dinosaurs' demise is much more complicated than the familiar and dominant theory that a single asteroid hit Earth 65 million years ago and caused a mass extinction.

Keller and a growing number of colleagues around the world are turning up evidence that, rather than a single event, an intensive period of volcanic eruptions as well as a series of asteroid impacts are likely to have stressed the world ecosystem to the breaking point. Although an asteroid or comet probably struck Earth at the time of the dinosaur extinction, it most likely was, as Keller says, "the straw that broke the camel's back" and not the sole cause.

Perhaps more controversially, Keller and colleagues contend that the "straw" -- that final impact -- is probably not what most scientists believe it is. For more than a decade, the prevailing theory has centered on a massive impact crater in Mexico. In 1990, scientists proposed that the Chicxulub crater, as it became known, was the remnant of the fateful dinosaur-killing event and that theory has since become dogma.

Keller has accumulated evidence, including results released this year, suggesting that the Chicxulub crater probably did not coincide with the dinosaur extinction. Instead, the impact that caused the Chicxulub crater was likely smaller than originally believed and probably occurred 300,000 years before the mass extinction. The final dinosaur-killer probably struck Earth somewhere else and remains undiscovered, said Keller.

These views have not made Keller a popular figure at meteorite impact meetings. "For a long time she's been in a very uncomfortable minority," said Vincent Courtillot, a geological physicist at Université Paris 7. The view that there was anything more than a single impact at work in the mass extinction of 65 million years ago "has been battered meeting after meeting by a majority of very renowned scientists," said Courtillot.

The implications of Keller's ideas extend beyond the downfall of ankylosaurus and company. Reviving an emphasis on volcanism, which was the leading hypothesis before the asteroid theory, could influence the way scientists think about the Earth's many episodes of greenhouse warming, which mostly have been caused by periods of volcanic eruptions. In addition, if the majority of scientists eventually reduce their estimates of the damage done by a single asteroid, that shift in thinking could influence the current-day debate on how much attention should be given to tracking and diverting Earth-bound asteroids and comets in the future.

Working back in time

Unlike many children today who lap up a steady diet of dinosaur-related books, toys and television programs, Keller knew nothing of the creatures when growing up in Liechtenstein and Switzerland. She became interested in paleontology in the 1970s as a graduate student in earth sciences at Stanford University and began studying the periodic episodes of extinctions and abrupt climate changes that punctuate Earth's 4 billion years.

"I am interested in major events in Earth's history," said Keller. "How did they change life on Earth? What caused the big changes in evolution?"

Keller does not work with big fossils such as dinosaur bones commonly associated with paleontology. Instead, her expertise is in one-celled organisms, called foraminifera, which pervade the oceans and evolved rapidly through geologic periods. Some species exist for only a couple hundred thousand years before others replace them, so the fossil remains of short-lived species constitute a timeline by which surrounding geologic features can be dated.

Princeton geophysicist Jason Morgan said Keller's detailed analysis of these microorganisms gives her work real credibility. "It's not like finding an isolated dinosaur bone," said Morgan. "You have thousands of organisms in a single sample. You can do real statistics on them."

Keller first used fossilized foraminifera to study climate changes in the last several hundred thousand years. Then, going to work for the U.S. Geological Survey, she became interested in earlier periods and began working her way backward in time. "I'm now down to 100 million years and can't go much further," she said, noting that these microorganism records extend back only about 200 million years.

The time of the dinosaur extinction is known as the Cretaceous-Tertiary boundary, or K/T for short. In addition to dinosaurs, many other forms of life were wiped out, including all tropical and subtropical species of foraminifera. Looking at ocean sediments from before and after the K/T boundary "is like day and night," Keller said, because so much life disappeared.

At many locations around the world, the K/T boundary is clearly visible in rock formations, which contain a thin layer of clay rich in the element iridium. Because iridium is more common in asteroids and comets than on Earth, scientists, led by father and son Luis and Walter Alvarez, proposed in l980 that an asteroid or comet must have struck Earth just at the K/T boundary. When the Chicxulub impact crater was discovered in 1990, it appeared to be a likely source for the iridium and seemed to confirm the hypothesis.

Several lines of evidence

Keller began studying the K/T boundary several years after coming to Princeton in 1984 and soon suspected that the story might not be so straightforward. In a series of field trips to Mexico and other parts of the world, she has accumulated several lines of evidence. She has found, for example, populations of pre-K/T foraminifera that lived on top of the impact fallout from Chicxulub. (The fallout is visible as a layer of glassy beads of molten rock that rained down after the impact.) These fossils indicate that this impact came about 300,000 years before the mass extinction.

In other studies spread across a range of excavation sites, Keller has found evidence that the ecological disruption caused by the Chicxulub impact may not have been as severe as originally thought. She found normal marine sediments lying directly on top of the fallout layer, suggesting that there were no tsunami waves or other major disturbances.

In addition, Keller and her students conducted studies throughout Mexico, Guatemala and Haiti (see related story below) that revealed signs of as many as three meteorite impacts: the Chicxulub impact, evidenced by the fallout of glass beads; the K/T impact with its iridium layer and mass extinction; and probably a third smaller impact, evidenced by another iridium layer about 100,000 years after the mass extinction.

The latest evidence came last year from an expedition by an international team of scientists who drilled 1,511 meters into the Chicxulub crater looking for definitive evidence of its size and age. Although interpretations of the drilling samples vary, Keller contends that the results contradict nearly every established assumption about Chicxulub and confirm that the Cretaceous period persisted for 300,000 years after the impact. In addition, the Chicxulub crater appears to be much smaller than originally thought -- less than 120 kilometers in diameter compared with the original estimates of 180 to 300 kilometers.

Keller and colleagues are now studying the effects of powerful volcanic eruptions that began more than 500,000 years before the K/T boundary and caused a period of global warming. At sites in the Indian Ocean, Madagascar, Israel and Egypt, they are finding evidence that volcanism caused biotic stress almost as severe as the K/T mass extinction itself. These results suggest that asteroid impacts and volcanism may be hard to distinguish based on their effects on plant and animal life and that the K/T mass extinction could be the result of both, said Keller.

Softening opposition

Because her results are among the first to quantify the biotic effects of volcanism, they may also help other scientists understand the likely effects of greenhouse warming resulting from volcanism or other causes, Keller said.

Together Keller's results give her hope that her ideas may gain greater recognition, but she remains cautious about how many people she is likely to convince. "When you have such a large group of scientists who became famous based on the idea that a single impact at Chicxulub caused the K/T mass extinction, you can't easily change their minds," she said.

Courtillot, whose views largely concur with Keller's, is optimistic that the opposition may be softening, particularly concerning the role of volcanism in the K/T extinction. "Recent years are vindicating our minority views -- at least I hope that is the case," he said.

In the meantime, Keller has further studies planned, including trips to extract sediments from Brazil, the Indian Ocean and the Middle East. She hopes these samples could broaden and clarify the story of the last days of the dinosaurs. "We want to nail it down as far away from Chicxulub as possible," she said.

(3) I'VE GOT A BONE TO PICK WITH YOU, SAY FEUDING DINOSAUR EXPERTS

The Observer, 7 Sept. 2003
http://observer.guardian.co.uk/international/story/0,6903,1037002,00.html

Robin McKie, science editor

The world's biggest bang wiped out the dinosaurs in a cataclysm that swathed our planet in choking dust - or at least that is what many palaeontologists claim. Others say dinosaurs died out gradually as Earth's climate and geology changed.

It sounds a typical academic dispute - but last week it erupted into open warfare. Allegations have been made of deceit and unethical behaviour. One scientist is even alleged to have held back inconvenient evidence.

'This affair has become an object lesson on how partisan and unethical the whole dinosaur controversy has become,' said Dr Norman MacLeod, keeper of palaeontology at London's Natural History Museum. 'Young scientists are now refusing to get involved in this field because no matter what they say it will offend someone and dam age their careers. It's like the nature-nurture debate. No matter what you say, someone will hate you for it.'

The furore focuses on a massive drilling project set up to study the Chicxulub crater in Yucatán. Buried under half a mile of rock, the crater was created 65 million years ago when Earth was hit by a meteorite 10 miles in diameter. The blast would have blotted out the sun for decades, or even centuries, many researchers claim. Given that around this time the dinosaurs became extinct, many scientists made a direct link. Denied sunlight and food, most of the world's animals would have starved, and choked, to death.

But others disagree. Volcanoes, global warming or sea level changes were responsible, they say - pointing to evidence that most dinosaurs became extinct before the explosion and to the fact that many large animals such as alligators survived this alleged catastrophe. Things weren't that bad, they say.

In a bid to resolve the dispute, a £2 million project was launched in Yucatán two years ago. Researchers drilled a pipe into the Earth's crust to bring back samples of the meteor and crater wall. By studying what happened just before and just after the meteorite impact, scientists would glean critical insights, it was argued. For example, it would show if all life was extinguished in the millennia that followed the impact.

In 2002 the first samples were brought up. To the disgust of Mexican geologists, and to many scientists who doubted the Big Blast theory, these were entrusted to Jan Smit, a geologist at the Free University of Amsterdam and a leading supporter of the meteorite hypothesis. Promising to cut up the samples and distribute them to project scientists, Smit left with the precious Chicxulub remains. A year later, many scientists were still seeking the promised samples. 'We were dismayed,' geochemist Erika Elswick of Indiana University in Bloomington states in the current issue of Nature . 'There was no explanation given, no apology.'

Eventually some samples were sent out, but most were too small for experiments. Dismay turned to fury. Researcher Gerta Keller, of Princeton University, pressed Smit and at last got a good set of samples. At the European Union of Geosciences conference in Nice, she presented her results, which were a bombshell. Her research, Keller claimed, clearly showed that marine plankton, far from being killed off by debris blotting out the sun, thrived for hundreds of thousands of years after the crater was created. The meteor that struck at Chicxulub was not responsible for mass extinctions, she concluded.

Nor is Keller reticent in her interpretation of Smit's behaviour. 'He tried to postpone our results so that he could remain unchallenged at that meeting,' she states in Nature . Smit dismisses the allegation as 'ridiculous'. He blames the delays on his busy schedule and poor communications by those running the project. He also claims Keller misidentified some fossils in her samples.

The row is far from over. Project scientists are preparing papers containing results of studies of the samples they obtained from Smit and these will be published in a special issue of Meteoritics and Planetary Science next year. Few doubt it will resolve the issue. As MacLeod says: 'It's no longer about science. It's about reputations.'