A team of international researchers, including two Northern Arizona University geologists, reports evidence that a comet or low-density object barreling toward Earth exploded in the upper atmosphere and triggered a devastating swath of destruction that wiped out most of the large animals, their habitat and humans of that period.
“The detonation either fried them or compressed them because of the shock wave,” said Ted Bunch, NAU adjunct professor of geology and former NASA researcher who specializes in impact craters. “It was a mini nuclear winter.”
Bunch and Jim Wittke, a geologic materials analyst at NAU, are co-authors of the paper, which fingers an extraterrestrial impact 12,900 years ago for the mass extinctions at the end of the Ice Age. The paper was just released online in the
Proceedings of the National Academy of Sciences. The research team includes several members of the U.S. National Academy of Sciences and researchers from Hungary and the Netherlands.
No one has found a giant crater in the Earth that could attest to such a cataclysmic impact 13,000 years ago, but the research team offers evidence of a comet, two and a half to three miles in diameter, that detonated 30 to 60 miles above the earth, triggering a massive shockwave, firestorms and a subsequent drastic cooling effect across most of North America and northern Europe.
“The comet may have broken up into smaller pieces as it neared the Earth and then these pieces detonated in various places above two continents,” Bunch said.
The evidence for multiple detonations comes from a four-inch-thick “black mat” of carbon-rich material that appears as far north as Canada, Greenland and Europe to as far south as the Channel Islands off the coast of California and eastward to the Carolinas. Two sites exist in Arizona at Murray Springs and Lehner Ranch, both near Sierra Vista.
Evidence of mammoths and other megafauna and early human hunters, known as the Clovis culture, are found beneath the black mat but are missing entirely within or above it. This led the research team to conclude an extraterrestrial impact wiped out many of the inhabitants of the Late Pleistocene. Bunch notes that some animals may have survived in protected niches.
The black mat was formed by ponding of water and algal blooms and contains carbon, soot and glassy carbon—remnants of burned materials. Some of these remnants are extraterrestrial in nature. For example, the research team has identified fullerenes, spherical carbon cages resembling a soccer ball, which are formed in shock events outside the Earth’s atmosphere. Trapped inside the fullerenes is a concentration of helium 3 that is many times greater than what is found in the Earth’s atmosphere.
The black mat also has turned up nanodiamonds, which are formed in the interstellar medium outside the solar system, by or by a high-explosive detonation.
“Either these things came in with the impactor or they were made during impact detonation. We have no other explanation for their presence,” Bunch said.
The magnitude of the detonations would have been huge.
“A hydrogen bomb is the equivalent of about 100 to 1,000 megatons,” Bunch said. “The detonations we’re talking about would be about 10 million megatons. That’s larger than the simultaneous detonation of all the world’s nuclear bombs past and present.”
The research team believes the detonations destabilized a vast ice sheet, known as the Laurentide Ice Sheet, that covered most of what was then Canada and the northern United States. Heat from the detonation and firestorms would have melted much of the ice sheet, releasing water vapor into the atmosphere.
“The result was rapid cooling of about eight degrees over the next 100 years,” Bunch said. The melting of the ice sheet and subsequent climate change would explain the water-based nature of the black mat.
Catastrophic extraterrestrial impacts are not new. Scientists theorize a much larger asteroid impact annihilated the dinosaurs and about 85 percent of the Earth’s biomass about 65 million years ago. The most recent incident, known as the Tunguska event, occurred in 1908 in Russia. The Tunguska explosion was an airburst of a comet or meteorite estimated at 10-15-megatons that destroyed tens of millions of trees across more than 800 square miles.
Bunch says impact airbursts may be more common than previously thought with possibly two or three such events having occurred over the last 100,000 years. And more are sure to follow.
Source: Northern Arizona University
Related stories:
New climate record shows century-long droughts in eastern North America
A stalagmite in a West Virginia cave has yielded the most detailed geological record to date on climate cycles in eastern North America over the past 7,000 years. The new study confirms that during periods when Earth received less solar radiation, the Atlantic Ocean cooled, icebergs increased and precipitation fell, creating a series of century-long droughts.
New evidence implicates humans in prehistoric animal extinctions
Research led by UK and Australian scientists sheds new light on the role that our ancestors played in the extinction of Australia's prehistoric animals. The study, published this week in the journal
Proceedings of the National Academy of Sciences of the USA, provides the first evidence that Tasmania's giant kangaroos and marsupial 'rhinos' and 'leopards' were still roaming the island when humans first arrived. The findings suggest that the mass extinction of Tasmania's large prehistoric animals was the result of human hunting, and not climate change as previously believed.
Running slows the aging clock, researchers find
Regular running slows the effects of aging, according to a new study from Stanford University School of Medicine that has tracked 500 older runners for more than 20 years. Elderly runners have fewer disabilities, a longer span of active life and are half as likely as aging nonrunners to die early deaths, the research found.
A Flash of Insight: LCROSS Mission Update
There are places on the Moon where the sun hasn't shined for millions of years. Dark polar craters too deep for sunlight to penetrate are luna incognita, the realm of the unknown, and in their inky depths, researchers believe, may lie a treasure of great value. NASA is about to light one up.
Now That's Cool: Engineers Out to Thaw the Mysteries of Ice
(PhysOrg.com) -- "Ye canna change the laws of physics!" Scotty warned Captain Kirk on Star Trek. But engineers and physicists at the University of Maryland may rewrite one of them.
Professor talks about latest in Younger Dryas work in Science article
University of Cincinnati Professor of Geology Tom Lowell is featured in the July 18 issue of Science, discussing the latest research into the question of whether the significant climate change event about 12,900 years ago known as Younger Dryas impacted the climate all around the globe.
Scientists demonstrate the sharpest measurement of ice crystals in clouds
Scientists have created an instrument designed to help determine the shapes and sizes of tiny ice crystals typical of those found in high-altitude clouds, down to the micron level (comparable to the tiniest cells in the human body), according to a new study in
Optics Letters, a journal published by the Optical Society. The data produced using this instrument likely will help improve computer models used to predict climate change.
Orbiter's HiRISE Camera Saw Phoenix Heat Shield in Freefall on Landing Day
Scientists running the High Resolution Imaging Science Experiment, known as HiRISE, on NASA's Mars Reconnaissance Orbiter have processed more details in an amazing image their camera captured as the Phoenix spacecraft descended through Mars' atmosphere during its landing on May 25, 2008.
