Something - global-scale combustion caused by a comet scraping our planet's atmosphere or a meteorite slamming into its surface - scorched the air, melted bedrock and altered the course of Earth's history. Exactly what it was is unclear, but this event jump-started what Kenneth Tankersley, an assistant professor of anthropology and geology at the University of Cincinnati, calls the last gasp of the last ice age.

"Imagine living in a time when you look outside and there are elephants walking around in Cincinnati," Tankersley says. "But by the time you're at the end of your years, there are no more elephants. It happens within your lifetime."

Tankersley explains what he and a team of international researchers found may have caused this catastrophic event in Earth's history in their research, "Evidence for Deposition of 10 Million Tonnes of Impact Spherules Across Four Continents 12,800 Years Ago," which was published in the Proceedings of the National Academy of Sciences.

The prestigious journal was established in 1914 and publishes innovative research reports from a broad range of scientific disciplines. Tankersley's research also was included in the History Channel series "The Universe: When Space Changed History" and will be featured in an upcoming film for The Weather Channel.

This research might indicate that it wasn't the cosmic collision that extinguished the mammoths and other species, Tankersley says, but the drastic change to their environment.

"The climate changed rapidly and profoundly. And coinciding with this very rapid global climate change was mass extinctions."

Putting A Finger On The End Of The Ice Age
Tankersley is an archaeological geologist. He uses geological techniques, in the field and laboratory, to solve archaeological questions. He's found a treasure trove of answers to some of those questions in Sheriden Cave in Wyandot County, Ohio. It's in that spot, 100 feet below the surface, where Tankersley has been studying geological layers that date to the Younger Dryas time period, about 13,000 years ago.

About 12,000 years before the Younger Dryas, the Earth was at the Last Glacial Maximum - the peak of the Ice Age. Millennia passed, and the climate began to warm. Then something happened that caused temperatures to suddenly reverse course, bringing about a century's worth of near-glacial climate that marked the start of the geologically brief Younger Dryas.

There are only about 20 archaeological sites in the world that date to this time period and only 12 in the United States - including Sheriden Cave.

"There aren't many places on the planet where you can actually put your finger on the end of the last ice age, and Sheriden Cave is one of those rare places where you can do that," Tankersley says.

Rock-Solid Evidence Of Cosmic Calamity
In studying this layer, Tankersley found ample evidence to support the theory that something came close enough to Earth to melt rock and produce other interesting geological phenomena. Foremost among the findings were carbon spherules. These tiny bits of carbon are formed when substances are burned at very high temperatures. The spherules exhibit characteristics that indicate their origin, whether that's from burning coal, lightning strikes, forest fires or something more extreme. Tankersley says the ones in his study could only have been formed from the combustion of rock.

The spherules also were found at 17 other sites across four continents - an estimated 10 million metric tons' worth - further supporting the idea that whatever changed Earth did so on a massive scale. It's unlikely that a wildfire or thunderstorm would leave a geological calling card that immense - covering about 50 million square kilometers.

"We know something came close enough to Earth and it was hot enough that it melted rock - that's what these carbon spherules are. In order to create this type of evidence that we see around the world, it was big," Tankersley says, contrasting the effects of an event so massive with the 1883 volcanic explosion on Krakatoa in Indonesia. "When Krakatoa blew its stack, Cincinnati had no summer. Imagine winter all year-round. That's just one little volcano blowing its top."

Other important findings include:
+ Micrometeorites: smaller pieces of meteorites or particles of cosmic dust that have made contact with the Earth's surface.

+ Nanodiamonds: microscopic diamonds formed when a carbon source is subjected to an extreme impact, often found in meteorite craters.

+ Lonsdaleite: a rare type of diamond, also called a hexagonal diamond, only found in non-terrestrial areas such as meteorite craters.

Three Choices At The Crossroads Of Oblivion
Tankersley says while the cosmic strike had an immediate and deadly effect, the long-term side effects were far more devastating - similar to Krakatoa's aftermath but many times worse - making it unique in modern human history.

In the cataclysm's wake, toxic gas poisoned the air and clouded the sky, causing temperatures to plummet. The roiling climate challenged the existence of plant and animal populations, and it produced what Tankersley has classified as "winners" and "losers" of the Younger Dryas. He says inhabitants of this time period had three choices: relocate to another environment where they could make a similar living; downsize or adjust their way of living to fit the current surroundings; or swiftly go extinct. "Winners" chose one of the first two options while "losers," such as the wooly mammoth, took the last.

"Whatever this was, it did not cause the extinctions," Tankersley says. "Rather, this likely caused climate change. And climate change forced this scenario: You can move, downsize or you can go extinct."

Humans at the time were just as resourceful and intelligent as we are today. If you transported a teenager from 13,000 years ago into the 21st century and gave her jeans, a T-shirt and a Facebook account, she'd blend right in on any college campus. Back in the Younger Dryas, with mammoth off the dinner table, humans were forced to adapt - which they did to great success.

Weather Report: Cloudy With A Chance Of Extinction
That lesson in survivability is one that Tankersley applies to humankind today.

"Whether we want to admit it or not, we're living right now in a period of very rapid and profound global climate change. We're also living in a time of mass extinction," Tankersley says. "So I would argue that a lot of the lessons for surviving climate change are actually in the past."

He says it's important to consider a sustainable livelihood. Humans of the Younger Dryas were hunter-gatherers. When catastrophe struck, these humans found news ways and new places to hunt game and gather wild plants. Evidence found in Sheriden Cave shows that most of the plants and animals living there also endured. Of the 70 species known to have lived there before the Younger Dryas, 68 were found there afterward. The two that didn't make it were the giant beaver and the flat-headed peccary, a sharp-toothed pig the size of a black bear.

Tankersley also cautions that the possibility of another massive cosmic event should not be ignored. Like earthquakes, tsunamis and volcanoes, these types of natural disasters do happen, and as history has shown, it can be to devastating effect.

"One additional catastrophic change that we often fail to think about - and it's beyond our control - is something from outer space," Tankersley says. "It's a reminder of how fragile we are. Imagine an explosion that happened today that went across four continents. The human species would go on. But it would be different. It would be a game changer."

]]> Thu, 23 MAY 2013 22:52:18 AEST Cleveland OH (SPX) May 13, 2013 - The water found on the moon, like that on Earth, came from small meteorites called carbonaceous chondrites in the first 100 million years or so after the solar system formed, researchers from Brown and Case Western Reserve universities and Carnegie Institution of Washington have found.

Evidence discovered within samples of moon dust returned by lunar crews of Apollo 15 and 17 dispels the theory that comets delivered the molecules.

The discovery's telltale sign is found in the ratio of an isotopic form of hydrogen, called deuterium, to standard hydrogen. The ratio in the Earth's water and in water from specks of volcanic glass trapped in crystals within moon dust match the ratio found in the chondrites. The proportions are far different from those in comet water.

The moon is thought to have formed from a disc of debris left when a giant object hit the Earth 4.5 billion years ago, very early in Earth's history. Scientists have long assumed that the heat from an impact of that size would cause hydrogen and other volatile elements to boil off into space, meaning the moon must have started off completely dry. But recently, NASA spacecraft and new research on samples from the Apollo missions have shown that the moon actually has water, both on and beneath its surface.

By showing that water on the moon and Earth came from the same source, this new study offers yet more evidence that the moon's water has been there all along, or nearly so.

"The simplest explanation for what we found is that there was water on the proto-Earth at the time of the giant impact," said Alberto Saal, a geochemist at Brown University and the study's lead author. "Some of that water survived the impact, and that's what we see in the moon."

Or, the proto-moon and proto-Earth were showered by the same family of carbonaceous chondrites soon after they separated, said James Van Orman, professor of earth, environmental and planetary sciences at Case Western Reserve, and a co-author.

The other authors are Erik Hauri, of the Carnegie Institution, and Malcolm Rutherford, from Brown.

To find the origin of the moon's water, the researchers looked at the trapped volcanic glass, referred to as a melt inclusion. The surrounding olivine crystals prevent water form escaping during an eruption, providing researchers an idea of what the inside of the moon is like.

Research from 2011, led by Hauri, found that the melt inclusions have plenty of water-as much water, in fact, as lavas forming on the Earth's ocean floor. This study aimed to find the origin of that water. To do that, Saal and his colleagues looked at the isotopic composition of the hydrogen trapped in the inclusions.

Using a Cameca NanoSIMS 50L multicollector ion microprobe at Carnegie, the researchers measured the amount of deuterium in the samples compared to the amount of regular hydrogen. Deuterium has an extra neutron.

Water molecules originating from different places in the solar system have different amounts of deuterium. In general, things formed closer to the sun have less deuterium than things formed further out.

The investigators found that the deuterium/hydrogen ratio in the melt inclusions was relatively low and matched the ratio found in carbonaceous chondrites. These meteorites originated in the asteroid belt near Jupiter and are thought to be among the oldest objects in the solar system. That means the source of the water on the moon is primitive meteorites.

Comets, like meteorites, are known to carry water and other volatiles. But most comets were formed in the icy Oort Cloud, more than 1,000 times more distant than Neptune. Because comets formed so far from the sun, they tend to have high deuterium/hydrogen ratios-much higher ratios than in the moon's interior, where the samples in this study originated.

"The measurements themselves were very difficult," Hauri said, "but the new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and moon, and perhaps the entire inner solar system."

To determine the ratios that would currently be found deep in the moon's interior, Van Orman and Saal modeled the loss of gasses from inside melt inclusions and the influence of degassing on the deuterium.

The researchers also had to take into account the impact of cosmic rays-high-energy rays that carry charged particles-on the water trapped inside the inclusions.

The interaction produces more deuterium than hydrogen. In total, the effects proved to be small for the melt inclusions, and the ratios remained consistent with the those of the chondrites.

Recent research, Saal said, has found that as much as 98 percent of the water on Earth also comes from primitive meteorites, suggesting a common source for water on Earth and the moon. The easiest way to explain that, Saal said, is that the water was already present on the early Earth and was transferred to the moon.

The finding is not necessarily inconsistent with the idea that the moon was formed by a giant impact with the early Earth, but presents a problem. If the moon is made from material that came from the Earth, it makes sense that the water in both would share a common source, Saal said. However, there's still the question of how that water was able to survive such a violent collision.

"Our work suggests that even highly volatile elements may not be lost completely during a giant impact," said Van Orman. "We need to go back to the drawing board and discover more about what giant impacts do, and we also need a better handle on volatile inventories in the moon."

The research is published online in Science Express.

]]> Thu, 23 MAY 2013 22:52:18 AEST Paris (ESA) May 10, 2013 - In February, a speeding asteroid slammed into our atmosphere and exploded high over Russia's Ural region, injuring hundreds and causing millions of euros of damage. What should we do if we have a similar - or even bigger - strike in the future?

Of the more than 600 000 known asteroids in our Solar System, almost 10 000 are classified as near-Earth objects, or NEOs, because their orbits bring them relatively close to Earth's path.

Dramatic proof that any of these can strike Earth came on 15 February, when an unknown object thought to be 17-20 m in diameter arrived at 66 000 km/h and exploded high above Chelyabinsk, Russia, with 20-30 times the energy of the Hiroshima atomic bomb.

The resulting shock wave caused widespread damage and injuries, making it the largest known natural object to have entered the atmosphere since the 1908 Tunguska event, which destroyed a remote forest area of Siberia.

ESA watching out for Earth
"It's important that we become aware of the current and future position of NEOs, develop estimates on the likelihood of impacts and assess the possible consequences," says Detlef Koschny, Head of NEO activities in the Agency's Space Situational Awareness (SSA) Programme Office.

"More importantly, we must consider whether and how warning, mitigation and possible deflection actions can be taken. It's important not only for Europe, but for the rest of the planet, too."

One aspect of ESA's four-year-old effort requires the development of an integrated system to scan the sky nightly for as-yet-undiscovered NEOs.

Another important element is studying how mitigation measures can be applied in the case of smaller NEOs, and how to deflect any larger ones that may seriously threaten our home planet.

International experts meeting in Spain
This week, Deimos Space, an industrial partner working for ESA on SSA, has invited top researchers from universities, research institutes, national space agencies and industry in Europe and the USA to discuss the state of the art in NEO impact effects and threat mitigation.

The meeting is taking place in Tres Cantos, Spain, near Madrid.

"A great deal of work remains to be done, for example, in computer modelling of impact effects, how airbursts differ from ground strikes, kinetic versus explosive deflection strategies and much more," says Gerhard Drolshagen, of the SSA Programme Office.

"The aim is to develop plans that will guide us in current and future NEO research and development."

Ultimately, ESA aims to develop the capability to integrate European current and new assets such as automated telescopes into a coordinated and more efficient NEO system that can provide nightly sky surveys and advanced warning.

"With this, we can work with our partner agencies, scientists, industry and international bodies like the UN to offer firm options to national governments and political decision-makers," says Nicolas Bobrinsky, Head of ESA's SSA Programme.

"Events like the Chelyabinsk strike show that the NEO hazard is not just theoretical, and we need to invest in practical measures today to address tomorrow's threats."

]]> Thu, 23 MAY 2013 22:52:18 AEST Boston MA (SPX) May 07, 2013 - The Tunguska impact event is one of the great mysteries of modern history. The basic facts are well known. On 30 June 1908, a vast and powerful explosion engulfed an isolated region of Siberia near the Podkamennaya Tunguska River.

The blast was 1000 times more powerful than the bomb dropped on Hiroshima, registered 5 on the Richter scale and is thought to have knocked down some 80 million trees over an area of 2000 square kilometres. The region is so isolated, however, that historians recorded only one death and just handful of eyewitness reports from nearby.

But the most mysterious aspect of this explosion is that it left no crater and scientists have long argued over what could have caused it.

The generally accepted theory is that the explosion was the result of a meteorite or comet exploding in the Earth's atmosphere. That could have caused an explosion of this magnitude without leaving a crater. Such an event would almost certainly have showered the region in fragments of the parent body but no convincing evidence has ever emerged.

In the 1930s, an expedition to the region led by the Russian mineralogist Leonid Kulik returned with a sample of melted glassy rock containing bubbles. Kulik considered this evidence of an impact event. But the sample was somehow lost and has never undergone modern analysis. As such, there is no current evidence of an impact in the form of meteorites.

That changes today with the extraordinary announcement by Andrei Zlobin from the Russian Academy of Sciences that he has found three rocks from the Tunguska region with the telltale characteristics of meteorites. If he is right, these rocks could finally help solve once and for all what kind of object struck Earth all those years ago.

Zlobin's story is remarkable in a number of ways. The area of greatest interest for meteor scientists is called the Suslov depression, which lies directly beneath the location of the air blast and is the place where meteorite debris was most likely to fall.

Dig into the peat bogs here and you can easily find layers that show clear evidence of the explosion. Zlobin said he dug more than ten prospect holes in the hope of finding meteorite fragments, but without success.

However, he had more luck exploring the bed of the local Khushmo River, where stones are likely to collect over a long period of time. He collected around 100 interesting specimens and returned to Moscow with them.

This expedition took place in 1988 and for some unexplained reason, Zlobin waited 20 years to examine his haul in detail. But in 2008, he sorted the collection and found three stones with clear evidence of melting and regmalypts, thumblike impressions found on the surface of meteorites which are caused by ablation as the hot rock falls through the atmosphere at high speed.

Zlobin and others have used tree ring evidence to estimate the temperatures that the blast created on the ground and says that these were not high enough to melt rocks on the surface. However, the fireball in the Earth's atmosphere would have been hot enough for this.

So Zlobin concludes that the rocks must be fragments of whatever body collided with Earth that day.

Zlobin has not yet carried out a detailed chemical analysis of the rocks that would reveal their chemical and isotopic composition. So the world will have to wait for this to get a better idea of the nature of the body.

However, the stony fragments do not rule out a comet since the nucleus could easily contain rock fragments, says Zlobin. Indeed he has calculated that the density of the impactor must have been about 0.6 grams per cubic centimetre, which is about the same as nucleus of Halley's comet. Zlobin says that together the evidence seems "excellent confirmation of cometary origin of the Tunguska impact."

Clearly there is more work to be done here, particularly the chemical analysis perhaps with international cooperation and corroboration.

Then there is also the puzzle of why Zlobin has waited so long to analyse his samples. It's not hard to imagine that the political changes that engulfed the Soviet Union in the year after his expedition may have played a role in this, but it still requires some explaining.

Nevertheless, this has the potential to help clear up one of the outstanding mysteries of the 20th century and finally determine the origin of the largest Earth impact in recorded history.

Ref: Discovery of Probably Tunguska Meteorites at the Bottom of Khushmo River's Shoal

]]> Thu, 23 MAY 2013 22:52:18 AEST Moscow (UPI) May 3, 2013 - A Russian researcher says stones he found in 1988 may be fragments of the largest celestial body to hit the Earth in recorded history.

Andrei Zlobin of the Vernadsky State Geological Museum at the Russian Academy of Sciences in central Siberia says the stones he found in a river in 1988 may have been part of the so-called Tunguska meteorite that exploded over the area in 1908.

Although the Tunguska blast was 1,000 times more powerful than the nuclear bomb that destroyed Hiroshima in 1945, scientists have so far failed to find any fragments of the celestial body that caused it.

Some scientists believe it was an ice asteroid or comet that exploded in the atmosphere and evaporated, leaving no traces on the surface below.

But Zlobin says three stones found in the Khushmo River near the impact's site have traces of melting and indentations often formed during a meteorite's passing through the atmosphere.

The samples are still pending a chemical analysis.

Even if a link to the Tunguska event is confirmed, the samples would not necessarily disprove the ice comet theory because the comet's nucleus could have contained small stones, experts said.

]]> Thu, 23 MAY 2013 22:52:18 AEST Huntsville AL (SPX) Apr 25, 2013 - April 19, 2013: Anticipation is building as Comet ISON plunges into the inner solar system for a close encounter with the sun in November 2013. Blasted at point-blank range by solar radiation, the sungrazer will likely become one of the finest comets in many years.

When NASA's Swift spacecraft observed the comet in January 2013, it was still near the orbit of Jupiter, but already very active. More than 112,000 pounds of dust were spewing from the comet's nucleus every minute.

It turns out, some of that dust might end up on Earth.

Veteran meteor researcher Paul Wiegert of the University of Western Ontario has been using a computer to model the trajectory of dust ejected by Comet ISON, and his findings suggest that an unusual meteor shower could be in the offing.

"For several days around January 12, 2014, Earth will pass through a stream of fine-grained debris from Comet ISON," says Wiegert. "The resulting shower could have some interesting properties.

According to Wiegert's computer models, the debris stream is populated with extremely tiny grains of dust, no more than a few microns wide, pushed toward Earth by the gentle radiation pressure of the sun. They will be hitting at a speed of 56 km/s or 125,000 mph. Because the particles are so small, Earth's upper atmosphere will rapidly slow them to a stop.

"Instead of burning up in a flash of light, they will drift gently down to the Earth below," he says.

Don't expect to notice. The invisible rain of comet dust, if it occurs, would be very slow. It can take months or even years for fine dust to settle out of the high atmosphere.

While the dust is "up there," it could produce noctilucent clouds (NLCs).

NLCs are icy clouds that glow electric-blue as they float more than 80 km above Earth's poles. Recent data from NASA's AIM spacecraft suggests that NLCs are seeded by space dust. Tiny meteoroids act as nucleating points where water molecules gather; the resulting ice crystals assemble into clouds at the edge of space itself.

This is still speculative, but Comet ISON could provide the seeds for a noctilucent display. Electric-blue ripples over Earth's polar regions might be the only visible sign that a shower is underway.

Wiegert notes another curiosity: "The shower is going to hit our planet from two directions at once."

When Earth passes through the debris stream, we will encounter two populations of comet dust. One swarm of dust will be following the Comet ISON into the sun. Another swarm will be moving in the opposite direction, pushed away from the sun by solar radiation pressure. The streams will pepper opposite sides of Earth simultaneously.

"In my experience, this kind of double whammy is unprecedented," says Wiegert.

Bill Cooke, lead scientist at NASA's Meteoroid Environment Office, says there's little danger to Earth-orbiting spacecraft. "These particles are just too small to penetrate the walls of our satellites, and they don't stand a chance against the heavy shielding of the ISS." However, he adds, mission operators will be alert around January 12th for possible anomalies.

Sky watchers should probably be alert, too. The odds of seeing anything are low, but Comet ISON could prove full of surprises.

]]> Thu, 23 MAY 2013 22:52:18 AEST Chicago (UPI) Apr 11, 2013 - Chicago's Field Museum of Natural History says it has obtained 234 pieces of the meteorite that slammed into Russia's Urals region in February.

The donation of the fragments comes from Terry Boudreaux, a philanthropist specializing in meteorites who sent a team to Russia the day after the huge meteorite exploded over the Urals city of Chelyabinsk to buy pieces gathered by locals, RIA Novosti reported Wednesday.

"The local villagers actually went out in three feet of snow on their snow skis and looked for holes in the snow. They would dig down with plastic shovels and find these little pieces and throw them in their pockets," Boudreaux told abclocal.go.com.

The Field Museum, which put around 2.2 pounds of Chelyabinsk fragments on display Wednesday, has a meteorite collection of some 6,500 fragments.

"I expected we would get a piece like this," said Field Museum scientist and assistant curator of meteorite studies Philipp Heck. "But we got more than a kilogram (2.2 pounds) of pieces there laid out on the table there."

The Chelyabinsk meteorite caused a massive sonic boom that blew out windows and damaged thousands of buildings around the city, injuring 1,500 people in the area.

"This event was probably a once in a 100 year event and made people realize how vulnerable we are to meteorite impacts," the Field Museum said in a statement.

]]> Thu, 23 MAY 2013 22:52:18 AEST Hanover NH (SPX) Apr 05, 2013 - In a geological moment about 66 million years ago, something killed off almost all the dinosaurs and some 70 percent of all other species living on Earth. Only those dinosaurs related to birds appear to have survived. Most scientists agree that the culprit in this extinction was extraterrestrial, and the prevailing opinion has been that the party crasher was an asteroid.

Not so, say two Dartmouth researchers. Professors Jason Moore and Mukul Sharma of the Department of Earth Sciences favor another explanation, asserting that a high-velocity comet led to the demise of the dinosaurs.

Recently, asteroids have been in the headlines. On February 15, 2013, an asteroid exploded in the skies over Siberia. Later that day, another swept past the Earth in what some regard as a close call-just 17,000 miles away.

The asteroid impact theory of extinction began with discoveries by the late physicist and Nobel Laureate Luis Alvarez and his son, the geologist Walter Alvarez, a professor at the University of California, Berkeley. In 1980 they identified extremely high concentrations of the element iridium in a layer of rock known as the K-Pg (formerly called K-T) boundary. The layer marks the end of the Cretaceous period (abbreviated "K"), the epoch of the dinosaurs, and the beginning of the Paleogene period, with its notable absence of the large lizards.

While iridium is rare in the Earth's crust, it is a common trace element in rocky space debris such as asteroids. Based on the elevated levels of iridium found worldwide in the boundary layer, the Alvarezes suggested that this signaled a major asteroid strike around the time of the K-Pg boundary-about 66 million years ago. Debate surrounded their theory until 2010, when a panel of 41 scientists published a report in support of the Alvarezes' theory. The panel confirmed that a major asteroid impact had occurred at the K-Pg boundary and was responsible for mass extinctions.

The scientific community today looks to the deeply buried and partially submerged, 110-mile wide Chicxulub crater in Mexico's Yucatan as the place where the death-dealing asteroid landed. The 66-million-year age of Chicxulub, discovered in 1990, coincides with the KT boundary, leading to the conclusion that what caused the crater also wiped out the dinosaurs.

Moore and Sharma do agree with fellow scientists that Chicxulub was the impact zone, but dispute the characterization of the object from space as an asteroid. In a paper presented to the 44th Lunar and Planetary Conference on March 22, 2013, they described their somewhat controversial findings.

Moore notes that in the past geochemists toiled away, isolated from their geophysicist colleagues, each focused on his or her particular area of expertise. "There hadn't been a concerted synthesis of all the data from these two camps," says Moore. "That's what we've tried to do."

The Dartmouth duo compiled all the published data on iridium from the K-Pg boundary. They also included the K-Pg data on osmium-another element common in space rock. In sifting through all this they found a wide range of variability, so consequently kept only the figures they demonstrated to be most reliable. "Because we are bringing a fresh set of eyes into this field, we feel our decisions are objective and unbiased," says Sharma.

For example, they deleted data drawn from deep ocean cores where there were very high amounts of iridium. "We discovered that even then there was a huge variation. It was much worse in the oceans than on the continents," Sharma said. "We figured out that the oceanic variations are likely caused by preferential concentration of iridium bearing minerals in marine sediments."

In the final analysis, the overall trace element levels were much lower than those that scientists had been using for decades and being this low weakened the argument for an asteroid impact explanation. However, a comet explanation reconciles the conflicting evidence of a huge impact crater with the revised, lower iridium/osmium levels at the K-Pg boundary.

"We are proposing a comet because that conclusion hits a 'sweet spot.' Comets have a lower percentage of iridium and osmium than asteroids, relative to their mass, yet a high-velocity comet would have sufficient energy to create a 110-mile-wide crater," says Moore. "Comets travel much faster than asteroids, so they have more energy on impact, which in combination with their being partially ice means they are not contributing as much iridium or osmium."

Moore attributes much of the early resistance to a comet impact theory to a lack of knowledge about comets in general. "We weren't certain whether they were dirty snowballs or icy dirt balls," he says. "Today, we are inclined toward the icy dirt ball description."

Comet composition and physical structure were unknown, but with the advent of NASA missions to comets like "Deep Impact" in 2010, a much larger database has been developed. "We now have a much better understanding of what a comet may be like and it is still consistent with the K-Pg boundary data we are seeing," Moore adds.

Sharma says that, "In synthesizing the data generated by two very disparate fields of research-geochemistry and geophysics-we are now 99.9 percent sure that what we are dealing with is a 66-million-year-old comet impact-not an asteroid."

]]> Thu, 23 MAY 2013 22:52:18 AEST Boulder CO (SPX) Mar 29, 2013 - 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.

]]> Thu, 23 MAY 2013 22:52:18 AEST London, UK (SPX) Mar 28, 2013 - About 66 million years ago a mountain-sized asteroid hit what is now the Yucatan in Mexico at exactly the time of the Cretaceous-Paleogene (K-Pg) mass extinction. Evidence for the asteroid impact comes from sediments in the K-Pg boundary layer, but the details of the event, including what precisely caused the mass extinction, are still being debated.

Some scientists have hypothesized that since the ejecta from the impact would have heated up dramatically as it reentered the Earth's atmosphere, the resulting infrared radiation from the upper atmosphere would have ignited fires around the globe and killed everything except those animals and plants that were sheltered underground or underwater.

Other scientists have challenged the global fire hypothesis on the basis of several lines of evidence, including absence of charcoal -- which would be a sign of widespread fires -- in the K-Pg boundary sediments. They also suggested that the soot observed in the debris layer actually originated from the impact site itself, not from widespread fires caused by reentering ejecta.

Robertson et al. show that the apparent lack of charcoal in the K-Pg boundary layer resulted from changes in sedimentation rates: When the charcoal data are corrected for the known changes in sedimentation rates, they exhibit an excess of charcoal, not a deficiency.

They also show that the mass of soot that could have been released from the impact site itself is far too small to account for the observed soot in the K-Pg layer.

In addition, they argue that since the physical models show that the radiant energy reaching the ground from the reentering ejecta would be sufficient to ignite tinder, it would thereby spark widespread fires.

The authors also review other evidence for and against the firestorm hypothesis and conclude that all of the data can be explained in ways that are consistent with widespread fires.

Journal of Geophysical Research-Planets, doi:10.1002/jgrg.20018, 2013 "K/Pg extinction: Reevaluation of the heat/fire hypothesis".

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