Study provides new evidence ancient asteroid caused global firestorm on Earth

A new CU-Boulder study shows that an asteroid believed to have smacked Earth some 66 million years ago likely caused a global firestorm that led to extensive plant and animal extinctions. -  Illustration courtesy NASA/JPL
A new CU-Boulder study shows that an asteroid believed to have smacked Earth some 66 million years ago likely caused a global firestorm that led to extensive plant and animal extinctions. – Illustration courtesy NASA/JPL

A new look at conditions after a Manhattan-sized asteroid slammed into a region of Mexico in the dinosaur days indicates the event could have triggered a global firestorm that would have burned every twig, bush and tree on Earth and led to the extinction of 80 percent of all Earth’s species, says a new University of Colorado Boulder study.

Led by Douglas Robertson of the Cooperative Institute for Research in Environmental Sciences, or CIRES, the team used models that show the collision would have vaporized huge amounts of rock that were then blown high above Earth’s atmosphere. The re-entering ejected material would have heated the upper atmosphere enough to glow red for several hours at roughly 2,700 degrees Fahrenheit — about the temperature of an oven broiler element — killing every living thing not sheltered underground or underwater.

The CU-led team developed an alternate explanation for the fact that there is little charcoal found at the Cretaceous-Paleogene, or K-Pg, boundary some 66 million years ago when the asteroid struck Earth and the cataclysmic fires are believed to have occurred. The CU researchers found that similar studies had corrected their data for changing sedimentation rates. When the charcoal data were corrected for the same changing sedimentation rates they show an excess of charcoal, not a deficiency, Robertson said.

“Our data show the conditions back then are consistent with widespread fires across the planet,” said Robertson, a research scientist at CIRES, which is a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration. “Those conditions resulted in 100 percent extinction rates for about 80 percent of all life on Earth.”

A paper on the subject was published online this week in the Journal of Geophysical Research-Biogeosciences, a publication of the American Geophysical Union. Co-authors on the study include CIRES Interim Director William Lewis, CU Professor Brian Toon of the atmospheric and oceanic sciences department and the Laboratory for Atmospheric and Space Physics and Peter Sheehan of the Milwaukee Public Museum in Wisconsin.

Geological evidence indicates the asteroid collided with Earth about 66 million years ago and carved the Chicxulub crater in Mexico’s Yucatan Peninsula that is more than 110 miles in diameter. In 2010, experts from 33 institutions worldwide issued a report that concluded the impact at Chicxulub triggered mass extinctions, including dinosaurs, at the K-Pg boundary.

The conditions leading to the global firestorm were set up by the vaporization of rock following the impact, which condensed into sand-grain-sized spheres as they rose above the atmosphere. As the ejected material re-entered Earth’s atmosphere, it dumped enough heat in the upper atmosphere to trigger an infrared “heat pulse” so hot it caused the sky to glow red for several hours, even though part of the radiation was blocked from Earth by the falling material, he said.

But there was enough infrared radiation from the upper atmosphere that reached Earth’s surface to create searing conditions that likely ignited tinder, including dead leaves and pine needles. If a person was on Earth back then, it would have been like sitting in a broiler oven for two or three hours, said Robertson.

The amount of energy created by the infrared radiation the day of the asteroid-Earth collision is mind-boggling, said Robertson. “It’s likely that the total amount of infrared heat was equal to a 1 megaton bomb exploding every four miles over the entire Earth.”

A 1-megaton hydrogen bomb has about the same explosive power as 80 Hiroshima-type nuclear bombs, he said. The asteroid-Earth collision is thought to have generated about 100 million megatons of energy, said Robertson.

Some researchers have suggested that a layer of soot found at the K-Pg boundary layer roughly 66 million years ago was created by the impact itself. But Robertson and his colleagues calculated that the amount of soot was too high to have been created during the massive impact event and was consistent with the amount that would be expected from global fires.

Study provides new evidence ancient asteroid caused global firestorm on Earth

A new CU-Boulder study shows that an asteroid believed to have smacked Earth some 66 million years ago likely caused a global firestorm that led to extensive plant and animal extinctions. -  Illustration courtesy NASA/JPL
A new CU-Boulder study shows that an asteroid believed to have smacked Earth some 66 million years ago likely caused a global firestorm that led to extensive plant and animal extinctions. – Illustration courtesy NASA/JPL

A new look at conditions after a Manhattan-sized asteroid slammed into a region of Mexico in the dinosaur days indicates the event could have triggered a global firestorm that would have burned every twig, bush and tree on Earth and led to the extinction of 80 percent of all Earth’s species, says a new University of Colorado Boulder study.

Led by Douglas Robertson of the Cooperative Institute for Research in Environmental Sciences, or CIRES, the team used models that show the collision would have vaporized huge amounts of rock that were then blown high above Earth’s atmosphere. The re-entering ejected material would have heated the upper atmosphere enough to glow red for several hours at roughly 2,700 degrees Fahrenheit — about the temperature of an oven broiler element — killing every living thing not sheltered underground or underwater.

The CU-led team developed an alternate explanation for the fact that there is little charcoal found at the Cretaceous-Paleogene, or K-Pg, boundary some 66 million years ago when the asteroid struck Earth and the cataclysmic fires are believed to have occurred. The CU researchers found that similar studies had corrected their data for changing sedimentation rates. When the charcoal data were corrected for the same changing sedimentation rates they show an excess of charcoal, not a deficiency, Robertson said.

“Our data show the conditions back then are consistent with widespread fires across the planet,” said Robertson, a research scientist at CIRES, which is a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration. “Those conditions resulted in 100 percent extinction rates for about 80 percent of all life on Earth.”

A paper on the subject was published online this week in the Journal of Geophysical Research-Biogeosciences, a publication of the American Geophysical Union. Co-authors on the study include CIRES Interim Director William Lewis, CU Professor Brian Toon of the atmospheric and oceanic sciences department and the Laboratory for Atmospheric and Space Physics and Peter Sheehan of the Milwaukee Public Museum in Wisconsin.

Geological evidence indicates the asteroid collided with Earth about 66 million years ago and carved the Chicxulub crater in Mexico’s Yucatan Peninsula that is more than 110 miles in diameter. In 2010, experts from 33 institutions worldwide issued a report that concluded the impact at Chicxulub triggered mass extinctions, including dinosaurs, at the K-Pg boundary.

The conditions leading to the global firestorm were set up by the vaporization of rock following the impact, which condensed into sand-grain-sized spheres as they rose above the atmosphere. As the ejected material re-entered Earth’s atmosphere, it dumped enough heat in the upper atmosphere to trigger an infrared “heat pulse” so hot it caused the sky to glow red for several hours, even though part of the radiation was blocked from Earth by the falling material, he said.

But there was enough infrared radiation from the upper atmosphere that reached Earth’s surface to create searing conditions that likely ignited tinder, including dead leaves and pine needles. If a person was on Earth back then, it would have been like sitting in a broiler oven for two or three hours, said Robertson.

The amount of energy created by the infrared radiation the day of the asteroid-Earth collision is mind-boggling, said Robertson. “It’s likely that the total amount of infrared heat was equal to a 1 megaton bomb exploding every four miles over the entire Earth.”

A 1-megaton hydrogen bomb has about the same explosive power as 80 Hiroshima-type nuclear bombs, he said. The asteroid-Earth collision is thought to have generated about 100 million megatons of energy, said Robertson.

Some researchers have suggested that a layer of soot found at the K-Pg boundary layer roughly 66 million years ago was created by the impact itself. But Robertson and his colleagues calculated that the amount of soot was too high to have been created during the massive impact event and was consistent with the amount that would be expected from global fires.

Scientists conclude asteroid ended the age of dinosaurs

University of Alaska Fairbanks scientist Michael Whalen is part of a team of distinguished scientists who recently compiled a wide swath of evidence striking a definitive blow in the ongoing battle over what killed the dinosaurs.

In a review published in the March 5 issue of the journal Science, the research group reaffirmed the recently challenged theory that an asteroid ended the age of the dinosaurs.

Scientists first proposed the asteroid impact theory of dinosaur mass extinction 30 years ago. The discovery of a massive crater at Chicxulub [CHICK-shuh-loob], in Mexico’s Yucatán Peninsula in 1991, strengthened that hypothesis. The Chicxulub crater is more than 120 miles wide-about the distance from Fairbanks to the Arctic Circle-and scientists believe it was created when an asteroid more than six miles wide crashed into Earth 65 million years ago. The cataclysmic impact-a million times more powerful than the largest nuclear bomb ever tested-triggered massive earthquakes, atmospheric discharge and oceanic upheaval. The ensuing mass extinction ended both the reign of the dinosaurs and the Cretaceous period, which gave way to the Paleogene period. This theory, having steadily accumulated evidence, was thought to be a near-consensus view.

Recently, however, in a series of articles, researchers posed an alternate hypothesis for the mass extinction. Some scientists claim that long-term volcanic activity at the Deccan Traps, in what is now India, caused acid rain and global cooling, gradually making life untenable for the dinosaurs and other large animals. They also suggest that the Chicxulub impact occurred some 300,000 years before the mass extinctions.

The alternate hypothesis spurred Whalen and other Chicxulub impact proponents to respond. The current Science article dispels the Deccan Traps hypothesis, arguing that the geological record favors the Chicxulub impact event theory.

“It’s as tight a case for a synchronous chain of events as we can find in the fossil record,” Whalen said.

Whalen is an associate professor at the UAF geology and geophysics department and the Geophysical Institute. He first began studying the Chicxulub site in 2002. His expertise is in carbonate rock, or limestone-a handy specialty, as limestone forms the layers above the Cretaceous-Paleogene geological boundary in the Chicxulub crater. He studied a 2001 core from the crater and compared it to seismic data gathered in 2006. His analysis offered insight on the geography of the area prior to impact, how it changed during the impact and the eventual infill of the crater by limestones deposited after the impact event.

Experts reaffirm asteroid impact caused mass extinction

An artist's rendering of the moment of impact when an enormous space rock struck the Yucatán peninsula at the end of the Cretaceous Period. Credit: Don Davis, NASA.
An artist’s rendering of the moment of impact when an enormous space rock struck the Yucatán peninsula at the end of the Cretaceous Period. Credit: Don Davis, NASA.

Responding to challenges to the hypothesis that an asteroid impact caused a mass extinction on Earth 65 million years, a panel of 41 scientists re-analyzed data and provided new evidence, concluding that an impact in Mexico was indeed the cause of the mass extinction.

Reporters are invited to a live embargoed webcast with one of the study’s co-authors on March 3. Details below.

Thirty years ago, Luis Alvarez, Jan Smit and their coworkers suggested a large meteorite slammed into Earth 65 million years ago and caused one of the most severe mass extinctions in Earth’s history, ending the age of the dinosaurs. In 1991, a more than 200-kilometer-wide impact crater was discovered in Yucatan, Mexico, that coincided with the extinctions. Since then, the impact hypothesis has gained overwhelming acceptance within the scientific community.

Still in recent years, a few scientists have challenged this hypothesis. To address their claims, a panel of 41 experts from Europe, the U.S., Mexico, Canada and Japan provide new data from the analysis of ocean drilling and continental sites and re-analyze the relevant literature in the field, including the most recent research. In a review paper in the March 5 edition of the journal Science, they find that alternative hypotheses are inadequate to explain the abrupt mass extinction and that the impact hypothesis has grown stronger than ever.

The fossil record clearly shows a mass extinction event across the planet at about 65.5 million years ago. Because this change is so dramatic, geologists use it to define the end of the Cretaceous period and the start of the Paleogene period (formerly called the Tertiary period). They refer to the time of the extinctions as the K-Pg boundary.

Some scientists have suggested that the Chicxulub (“chik-shoo-loob”) impact in Mexico happened 300,000 years before the K-Pg boundary and therefore, came too early to have been the major cause of extinctions.

They point to deposits at sites around the Gulf of Mexico with a layer of tiny glass-like blobs of melted impact material that, according to their interpretation, was deposited at about 300,000 years before the K-Pg boundary mass extinction. As an alternative, they suggest the Deccan Traps -unusually active volcanoes in what is now India-led to global cooling and acid rain, and were the major cause of mass extinction, not the Chicxulub impact in Mexico.

However, the reviewers find that what appears to be a series of layers neatly laid down over 300,000 years near the impact site were actually violently churned and then dumped in a thick pile in a very short time. Models suggest the impact at Chicxulub was a million times more energetic than the largest nuclear bomb ever tested. An impact of this size would eject material at high velocity around the world, cause earthquakes of magnitude >10, continental shelf collapse, landslides, gravity flows, mass wasting and tsunamis and produce a relatively thick and complex sequence of deposits close to Chicxulub.

“If we are to unravel the sequence of events across the K-Pg boundary, perhaps the last place in the world we should look is close to the Chicxulub impact site, where the sedimentary deposits will be most disturbed,” write the reviewers.

In addition, the reviewers note, as you go farther from the impact site, these layers become thinner and the amount of ejected material decreases until it becomes one layer that can be found globally exactly at the K-Pg boundary coincident with the mass extinction. Moreover, the ejecta within the global K-Pg layer is compositionally linked to the specific sediments and crystalline rocks at Chicxulub.

The reviewers find that despite evidence for relatively active volcanism in India, marine and terrestrial ecosystems showed only minor changes within the 500,000 years before the K-Pg boundary. Then, precisely at the boundary, there was an abrupt and major decrease in productivity (a measure of the sheer mass of living things) and species diversity.

The Deccan hypothesis is further weakened by a review of models of atmospheric chemistry. Although significant volumes of sulfur may be emitted during each volcanic eruption and form aerosols in the stratosphere, these sulfur aerosols fall out rapidly and any adverse environmental effects are apparently only short-lasting. In comparison, during the Chicxulub impact, much larger volumes of sulfur, dust and soot were released in a much shorter time, leading to extreme environmental perturbations (such as darkening or cooling).

“Combining all available data from different science disciplines led us to conclude that a large asteroid impact 65 million years ago in modern-day Mexico was the major cause of the mass extinctions,” says Peter Schulte, assistant professor at the University of Erlangen in Germany and lead author of the review paper.

Far from Chicxulub, the geologic record clearly shows a single large meteorite hit the Earth exactly at the K-Pg boundary. Thickening of the K-Pg boundary layer towards Chicxulub shows Chicxulub was the impact site. The significant changes in Earth’s ecosystems all occur precisely at this boundary and thus, say the reviewers, a large asteroid impact into the sulfate-rich sediments at Chicxulub remains the most plausible cause for the K-Pg boundary mass extinction.

Several mechanisms have been proposed to explain why the impact was so deadly. In February 2008, Sean Gulick and Gail Christeson, research scientists at The University of Texas at Austin’s Institute for Geophysics, and their colleagues published a study in the journal Nature Geoscience finding that the asteroid landed in deeper water than previously assumed and therefore released more water vapor and sulfate aerosols into the atmosphere. Gulick, a co-author of the new review paper in Science, said this could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain). That finding and many others strengthen the case for the impact hypothesis.

New blow for dinosaur-killing asteroid theory

Computer generated gravity map image of the Chixulub Crater in Mexico.- Credit: NASA
Computer generated gravity map image of the Chixulub Crater in Mexico.- Credit: NASA

The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.

The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.

When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the “smoking gun” responsible for the mass extinction event that took place 65 million years ago.

It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.

However, a number of scientists have since disagreed with this interpretation.

The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.

“Keller and colleagues continue to amass detailed stratigraphic information supporting new thinking about the Chicxulub impact, and the mass extinction at the end of the Cretaceous,” says H. Richard Lane, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “The two may not be linked after all.”

From El Penon and other localities in Mexico, says Keller, “we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval.”

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

“The problem with the tsunami interpretation,” says Keller, “is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period.”

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

The scientists also found evidence that the Chicxulub impact didn’t have the dramatic impact on species diversity that has been suggested.

At one site at El Penon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules.

“We found that not a single species went extinct as a result of the Chicxulub impact,” says Keller.

This conclusion should not come as too great a surprise, she says. None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect.

65-million-year-old asteroid impact triggered a global hail of carbon beads





Carbon cenospheres are tiny, carbon-rich particles that form when coal and heavy fuel are heated intensely. Scientists have now learned that cenospheres can form in the wake of asteroid impacts, too. - Photo by: Mark Harvey
Carbon cenospheres are tiny, carbon-rich particles that form when coal and heavy fuel are heated intensely. Scientists have now learned that cenospheres can form in the wake of asteroid impacts, too. – Photo by: Mark Harvey

The asteroid presumed to have wiped out the dinosaurs struck the Earth with such force that carbon deep in the Earth’s crust liquefied, rocketed skyward, and formed tiny airborne beads that blanketed the planet, say scientists from the U.S., U.K., Italy, and New Zealand in this month’s Geology.



The beads, known to geologists as carbon cenospheres, cannot be formed through the combustion of plant matter, contradicting a hypothesis that the cenospheres are the charred remains of an Earth on fire. If confirmed, the discovery suggests environmental circumstances accompanying the 65-million-year-old extinction event were slightly less dramatic than previously thought.



“Carbon embedded in the rocks was vaporized by the impact, eventually forming new carbon structures in the atmosphere,” said Indiana University Bloomington geologist Simon Brassell, study coauthor and former adviser to the paper’s lead author, Mark Harvey.



The carbon cenospheres were deposited 65 million years ago next to a thin layer of the element iridium — an element more likely to be found in Solar System asteroids than in the Earth’s crust. The iridium-laden dust is believed to be the shattered remains of the 200-km-wide asteroid’s impact. Like the iridium layer, the carbon cenospheres are apparently common. They’ve been found in Canada, Spain, Denmark and New Zealand.



But the cenospheres’ origin presented a double mystery. The cenospheres had been known to geologists only as a sign of modern times — they form during the intense combustion of coal and crude oil. Equally baffling, there were no power plants burning coal or crude oil 65 million years ago, and natural burial processes affecting organic matter from even older ages — such as coals from the 300-million-year-old Carboniferous Period — had simply not been cooked long or hot enough.



“Carbon cenospheres are a classic indicator of industrial activity,” Harvey said. “The first appearance of the carbon cenospheres defines the onset of the industrial revolution.”



The scientists concluded the cenospheres could have been created by a new process, the violent pulverization of the Earth’s carbon-rich crust.


Geologists do believe the Earth burned in spots as molten rock and super-hot ash fell out of the sky and onto flammable plant matter. But the charcoal-ized products of these fires only appear in some places on Earth, and are more often found near the asteroid impact site of Chicxulub Crater, just west of Mexico’s Yucatan Peninsula. Some geologists had thought all carbon particles resulting from the impact was ash from global scale forest fires, but the present research strongly contradicts that assumption.



The scientists examined rock samples from eight marine locations in New Zealand, Italy, Denmark and Spain. They also examined carbon-rich particles from five non-marine locations in the U.S. and Canada. Following chemical and microscopic analysis, the researchers concluded the particles were carbon cenospheres, similar to the ones produced by industrial combustion.



The scientists also found that the farther the sample site was from the Chicxulub Crater, the smaller the cenospheres tended to be. That observation is consistent with the expectation that particles were produced by the asteroid impact, since once the particles are ejected, heavier particles should fall back to Earth sooner (and travel shorter distances) than lighter particles.



Last, the scientists estimated the total mass of carbon cenospheres ejected by the asteroid collision, assuming a global distribution, to be perhaps as much as 900 quadrillion kilograms. Whether or not the carbon cenospheres are truly ubiquitous, however, needs further corroboration.



“There are still clues to unravel about the events occurring around the time of the impact,” Brassell said. “And there are aspects of the Earth’s natural carbon cycle that we didn’t previously consider.”



Harvey is interested in the unique properties of the cenospheres themselves. “Perhaps we can generate and study carbon cenospheres to better understand them,” he said. “We also need to look for the cenospheres in other parts of the world and also around the time of other extinction events.”



Harvey conducted the research while he was a master’s student at IU Bloomington. He is now a geoscientist for Sinclair Knight Merz in New Zealand. Claire Belcher (University of London) and Alessandro Montanari (Coldigioco Geological Observatory) also contributed to the study. It was funded by the Geological Society of America, the Indiana University Department of Geological Sciences, and the Society for Organic Petrology.

Seismic Images Show Dinosaur-killing Meteor Made Bigger Splash





A new study reveals that the asteroid that killed the dinosaurs landed in deeper water than once thought, perhaps explaining why its effects were so severe. Inset: 1996 (black) and 2005 (red) seismic surveys are shown over the Bouguer gravity anomaly map showing the buried Chicxulub impact crater. (Credit: Map from Nature Geoscience / Illustration courtesy of NASA)
A new study reveals that the asteroid that killed the dinosaurs landed in deeper water than once thought, perhaps explaining why its effects were so severe. Inset: 1996 (black) and 2005 (red) seismic surveys are shown over the Bouguer gravity anomaly map showing the buried Chicxulub impact crater. (Credit: Map from Nature Geoscience / Illustration courtesy of NASA)

The most detailed three-dimensional seismic images yet of the Chicxulub crater, a mostly submerged and buried impact crater on the Mexico coast, may modify a theory explaining the extinction of 70 percent of life on Earth 65 million years ago.



The Chicxulub crater was formed when an asteroid struck on the coast of the Yucatan Peninsula. Most scientists agree the impact played a major role in the “KT Extinction Event” that caused the extinction of most life on Earth, including the dinosaurs.



According to Sean Gulick, a research scientist at the Institute for Geophysics at The University of Texas at Austin’s Jackson School of Geosciences and principal investigator for the project, the new images reveal the asteroid landed in deeper water than previously assumed and therefore released about 6.5 times more water vapor into the atmosphere.



The impact site also contained sulfur-rich sediments called evaporites, which would have reacted with water vapor to produce sulfate aerosols. According to Gulick, an increase in the atmospheric concentration of the compounds could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain). Earlier studies had suggested both effects might result from the impact, but to a lesser degree.



“The greater amount of water vapor and consequent potential increase in sulfate aerosols needs to be taken into account for models of extinction mechanisms,” says Gulick.



An increase in acid rain might help explain why reef and surface dwelling ocean creatures were affected along with large vertebrates on land and in the sea. As it fell on the water, acid rain could have turned the oceans more acidic. There is some evidence that marine organisms more resistant to a range of pH survived while those more sensitive did not.



Gulick says the mass extinction event was probably not caused by just one mechanism, but rather a combination of environmental changes acting on different time scales, in different locations. For example, many large land animals might have been baked to death within hours or days of the impact as ejected material fell from the sky, heating the atmosphere and setting off firestorms. More gradual changes in climate and acidity might have had a larger impact in the oceans.





A new study reveals that the asteroid that killed the dinosaurs landed in deeper water than once thought, perhaps explaining why its effects were so severe. Inset: 1996 (black) and 2005 (red) seismic surveys are shown over the Bouguer gravity anomaly map showing the buried Chicxulub impact crater. (Credit: Map from Nature Geoscience / Illustration courtesy of NASA)
A new study reveals that the asteroid that killed the dinosaurs landed in deeper water than once thought, perhaps explaining why its effects were so severe. Inset: 1996 (black) and 2005 (red) seismic surveys are shown over the Bouguer gravity anomaly map showing the buried Chicxulub impact crater. (Credit: Map from Nature Geoscience / Illustration courtesy of NASA)

Gulick and collaborators originally set out to learn more about the trajectory of the asteroid. They had hoped the crater’s structure in the subsurface would hold a tell-tale signature. Instead, the structure seemed to be most strongly shaped by the pre-impact conditions of the target site.



“We discovered that the shallow structure of the crater was determined much more by what the impact site was like before impact than by the trajectory of the impactor,” says Gulick.



If scientists can determine the trajectory, it will tell them where to look for the biggest environmental consequences of impact, because most of the hazardous, shock-heated and fast-moving material would have been thrown out of the crater downrange from the impact.



Researchers at Imperial College in London are already using computer models to search for possible signatures in impact craters that could indicate trajectory regardless of the initial surface conditions at the impact site.



“As someone who simulates impact events using computers, this work provides valuable new constraints on both the pre-impact target structure and the final geometry of the cratered crust at Chicxulub,” says Gareth Collins, a research fellow at Imperial College.



The study “Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater” appears in the February 2008 print edition of the journal Nature Geoscience.



Collaborators on the project included Gail Christeson of the Institute for Geophysics, Penny Barton at the University of Cambridge, Joanna Morgan and Mike Warner at Imperial College, and several graduate students.