More than a meteor likely killed dinosaurs 65 million years ago
http://www.eurekalert.org/pub_releases/2006-10/nsf-mta102606.php
Growing evidence shows a series of natural events caused extinction
October 17, 2006 -- Growing evidence shows that the dinosaurs and their contemporaries were not wiped out by the famed Chicxulub meteor impact alone, according to a paleontologist who says multiple meteor impacts, massive volcanism in India and climate changes culminated in the end of the Cretaceous Period.
The Chicxulub impact may have been the lesser and earlier of a series of meteor impacts and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University paleontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany.
A final, much larger and still unidentified impact 65.5 million years ago appears to have been the last straw, said Keller, exterminating two-thirds of all species in one of the largest mass extinction events in the history of life. It's that impact - not Chicxulub - that left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles, Keller believes.
"The Chicxulub impact alone could not have caused the mass extinction," said Keller, "because this impact predates the mass extinction."
Keller is scheduled to present that evidence at the annual meeting of the Geological Society of America (GSA) in Philadelphia, on Tuesday, October 24, 2006.
"Chicxulub is one of thousands of impact craters on Earth's surface and in its subsurface," said H. Richard Lane, program director in the National Science Foundation (NSF) Division of Earth Sciences, which funded the research. "The evidence found by Keller and colleagues suggests that there is more to learn about what caused the major extinction event millions of years ago, and the demise of the dinosaurs at the end of the Cretaceous."
Marine sediments drilled from the Chicxulub crater itself, as well as from a site in Texas along the Brazos River and from outcrops in northeastern Mexico, reveal that Chicxulub hit Earth 300,000 years before the mass extinction. Microscopic marine animals were left virtually unscathed, said Keller.
"In all these localities we can analyze their microfossils in the sediments directly above and below the Chicxulub impact layer, and cannot find any significant biotic effect," said Keller. "We cannot attribute any specific extinctions to this impact."
The story that seems to be taking shape, according to Keller, is that Chicxulub, though violent, actually conspired with the prolonged and gigantic volcanic eruptions of the Deccan Flood Basalts in India, as well as with climate change, to nudge species towards the brink. They were then pushed over with a second large meteor impact.
The Deccan volcanism released vast amount of greenhouse gases into the atmosphere over a period of more than a million years leading up to the mass extinction. By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom, Keller said.
"On land it must have been 7-8 degrees warmer," she said. "This greenhouse warming is well-documented. The temperature rise was rapid over about 20,000 years, and it stayed warm for about 100,000 years, then cooled back to normal well before the mass extinction."
Where's the crater? "I wish I knew," said Keller.
New Recipe: How to Make a Mass Extinction
Michael Schirber
Special to LiveScience
Apocalypses may not be all fire and brimstone. A growing number of paleontologists say that Earth-smashing meteors cannot take all the blame for the many mass extinctions that dot our planet's fossil record. The true causes seem to be more complex.
"The [meteor] impact model has been so successful because it's easy to explain and easy to understand," said Nan Arens of Hobart and William Smith College in Geneva, NY. "However, the simple answer isn't always the best one."
At the annual meeting of the Geological Society of America this week in Philadelphia, Arens and others argued that the combined punch of volcanoes, climate change and impacts leaves many species teetering on the brink of extinction. One final blow brings collapse.
The same scenario could be happening now.
Dino disappearance
The most famous of all giant space rocks is the one that presumably killed off the non-avian dinosaurs 65 million years ago, in the so-called K-T extinction event. But this may not be the whole story.
For several years, Gerta Keller of Princeton University and her colleagues have been arguing that the widely-accepted dino-killer-a space rock that left a 100-mile-wide crater around Chicxulub, Mexico-happened 300,000 years too soon. Keller therefore believes that this impact was just one of several smoking guns.
"Impacts by themselves simply don't cause major mass extinctions," she told LiveScience.
Keller advocates a scenario in which the Chicxulub meteor combined with volcanoes in India and global warming to unsettle the ecologic balance. She has compiled data prior to K-T event that show many species shrinking in size-a sign of an unhealthy environment.
Keller speculates that a second, currently unidentified meteor crashed after Chicxulub. This impact, in conjunction with a surge in volcanism, "dealt the final blow to a Cretaceous biota already on the brink of extinction," Keller said.
Great Dying
A similar environmental deterioration may have preceded the biggest retreat in life's history.
The P-T extinction event, or Great Dying, occurred 251 million years ago when up to 90 percent of all species were snuffed out. David Bottjer's group from the University of Southern California has studied the fossil record and found clear signs that species were in peril long before they disappeared.
The reason: "The Earth got sick," Bottjer said.
The illness began when Siberian volcanoes triggered global warming, he explained. This reduced ocean circulation and the oxygen supply. These hazardous conditions were a boon for sulfur-eating microbes, which released toxic hydrogen sulfide into the atmosphere, finishing off most of the life that remained.
Common diagnosis
A sick Earth succumbing to a final shock is apparently a common extinction formula. Arens and her colleagues analyzed geologic data from the last 488 million years and found more species died out when the environment was first stressed and then stung.
Specifically, the researchers compared stress-inducing volcanic activity and catastrophic meteor impacts. Only when the Earth experienced both did extinction rates significantly increase.
"Periods of stress are going to reduce population sizes," Arens said. With reduced numbers, "species are vulnerable to pulse catastrophes."
On the flip side, an unstressed environment is resilient to geologic and climatic disasters because life is diverse and geographically spread out.
And now?
Applying their model to the present, Arens and her collaborators speculate that human activity has both stressed the environment with agriculture and shocked it with fossil fuel burning.
Whether or not this is an accurate description, both Bottjer and Keller agree that we are in a precarious situation.
"Under [current] conditions any disaster that might strike (impact or volcanism or major greenhouse warming), which ordinarily would not cause major extinctions, will put much of Earth's biota at risk of extinction," Keller said.
LiveScience.com Fri Oct 27,
http://www.eurekalert.org/pub_releases/2006-10/nsf-mta102606.php
Growing evidence shows a series of natural events caused extinction
October 17, 2006 -- Growing evidence shows that the dinosaurs and their contemporaries were not wiped out by the famed Chicxulub meteor impact alone, according to a paleontologist who says multiple meteor impacts, massive volcanism in India and climate changes culminated in the end of the Cretaceous Period.
The Chicxulub impact may have been the lesser and earlier of a series of meteor impacts and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University paleontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany.
A final, much larger and still unidentified impact 65.5 million years ago appears to have been the last straw, said Keller, exterminating two-thirds of all species in one of the largest mass extinction events in the history of life. It's that impact - not Chicxulub - that left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles, Keller believes.
"The Chicxulub impact alone could not have caused the mass extinction," said Keller, "because this impact predates the mass extinction."
Keller is scheduled to present that evidence at the annual meeting of the Geological Society of America (GSA) in Philadelphia, on Tuesday, October 24, 2006.
"Chicxulub is one of thousands of impact craters on Earth's surface and in its subsurface," said H. Richard Lane, program director in the National Science Foundation (NSF) Division of Earth Sciences, which funded the research. "The evidence found by Keller and colleagues suggests that there is more to learn about what caused the major extinction event millions of years ago, and the demise of the dinosaurs at the end of the Cretaceous."
Marine sediments drilled from the Chicxulub crater itself, as well as from a site in Texas along the Brazos River and from outcrops in northeastern Mexico, reveal that Chicxulub hit Earth 300,000 years before the mass extinction. Microscopic marine animals were left virtually unscathed, said Keller.
"In all these localities we can analyze their microfossils in the sediments directly above and below the Chicxulub impact layer, and cannot find any significant biotic effect," said Keller. "We cannot attribute any specific extinctions to this impact."
The story that seems to be taking shape, according to Keller, is that Chicxulub, though violent, actually conspired with the prolonged and gigantic volcanic eruptions of the Deccan Flood Basalts in India, as well as with climate change, to nudge species towards the brink. They were then pushed over with a second large meteor impact.
The Deccan volcanism released vast amount of greenhouse gases into the atmosphere over a period of more than a million years leading up to the mass extinction. By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom, Keller said.
"On land it must have been 7-8 degrees warmer," she said. "This greenhouse warming is well-documented. The temperature rise was rapid over about 20,000 years, and it stayed warm for about 100,000 years, then cooled back to normal well before the mass extinction."
Where's the crater? "I wish I knew," said Keller.
New Recipe: How to Make a Mass Extinction
Michael Schirber
Special to LiveScience
Apocalypses may not be all fire and brimstone. A growing number of paleontologists say that Earth-smashing meteors cannot take all the blame for the many mass extinctions that dot our planet's fossil record. The true causes seem to be more complex.
"The [meteor] impact model has been so successful because it's easy to explain and easy to understand," said Nan Arens of Hobart and William Smith College in Geneva, NY. "However, the simple answer isn't always the best one."
At the annual meeting of the Geological Society of America this week in Philadelphia, Arens and others argued that the combined punch of volcanoes, climate change and impacts leaves many species teetering on the brink of extinction. One final blow brings collapse.
The same scenario could be happening now.
Dino disappearance
The most famous of all giant space rocks is the one that presumably killed off the non-avian dinosaurs 65 million years ago, in the so-called K-T extinction event. But this may not be the whole story.
For several years, Gerta Keller of Princeton University and her colleagues have been arguing that the widely-accepted dino-killer-a space rock that left a 100-mile-wide crater around Chicxulub, Mexico-happened 300,000 years too soon. Keller therefore believes that this impact was just one of several smoking guns.
"Impacts by themselves simply don't cause major mass extinctions," she told LiveScience.
Keller advocates a scenario in which the Chicxulub meteor combined with volcanoes in India and global warming to unsettle the ecologic balance. She has compiled data prior to K-T event that show many species shrinking in size-a sign of an unhealthy environment.
Keller speculates that a second, currently unidentified meteor crashed after Chicxulub. This impact, in conjunction with a surge in volcanism, "dealt the final blow to a Cretaceous biota already on the brink of extinction," Keller said.
Great Dying
A similar environmental deterioration may have preceded the biggest retreat in life's history.
The P-T extinction event, or Great Dying, occurred 251 million years ago when up to 90 percent of all species were snuffed out. David Bottjer's group from the University of Southern California has studied the fossil record and found clear signs that species were in peril long before they disappeared.
The reason: "The Earth got sick," Bottjer said.
The illness began when Siberian volcanoes triggered global warming, he explained. This reduced ocean circulation and the oxygen supply. These hazardous conditions were a boon for sulfur-eating microbes, which released toxic hydrogen sulfide into the atmosphere, finishing off most of the life that remained.
Common diagnosis
A sick Earth succumbing to a final shock is apparently a common extinction formula. Arens and her colleagues analyzed geologic data from the last 488 million years and found more species died out when the environment was first stressed and then stung.
Specifically, the researchers compared stress-inducing volcanic activity and catastrophic meteor impacts. Only when the Earth experienced both did extinction rates significantly increase.
"Periods of stress are going to reduce population sizes," Arens said. With reduced numbers, "species are vulnerable to pulse catastrophes."
On the flip side, an unstressed environment is resilient to geologic and climatic disasters because life is diverse and geographically spread out.
And now?
Applying their model to the present, Arens and her collaborators speculate that human activity has both stressed the environment with agriculture and shocked it with fossil fuel burning.
Whether or not this is an accurate description, both Bottjer and Keller agree that we are in a precarious situation.
"Under [current] conditions any disaster that might strike (impact or volcanism or major greenhouse warming), which ordinarily would not cause major extinctions, will put much of Earth's biota at risk of extinction," Keller said.
LiveScience.com Fri Oct 27,
