Ice Age blast 'ravaged America'

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Ice Age blast 'ravaged America'

Postby Tomyhoi on May 21st, 2007, 12:38 pm 

A controversial new idea suggests that a large space rock exploded over North America 13,000 years ago.
The blast may have wiped out one of America's first Stone Age cultures as well as the continent's big mammals such as the mammoth and the mastodon.

The blast, from a comet or asteroid, caused a major bout of climatic cooling which may also have affected human cultures emerging in Europe and Asia.

Scientists will outline their evidence this week at a meeting in Mexico.

Their impact theory shouldn't be dismissed; it deserves further investigation

Jeff Severinghaus, Scripps Institution of Oceanography
The evidence comes from layers of sediment at more than 20 sites across North America.

These sediments contain exotic materials: tiny spheres of glass and carbon, ultra-small specks of diamond - called nanodiamond - and amounts of the rare element iridium that are too high to have come from Earth.

All, they argue, point to the explosion 12,900 years ago of an extraterrestrial object up to 5km across.

No crater remains, possibly because the Laurentide Ice Sheet, which blanketed thousands of sq km of North America during the last Ice Age, was thick enough to mask the impact.

Another possibility is that it exploded in the air.

Climate cooling

The rocks studied by the researchers have a black layer which, they argue, is the charcoal deposited by wildfires which swept the continent after the explosion.


The Clovis people developed an advanced stone tool technology
The blast would not only have generated enormous amounts of heat, that could have given rise to wildfires across the continent but also brought about a period of climate cooling that lasted 1,000 years - an event known as the Younger Dryas.

Professor James Kennett, from the University of California in Santa Barbara (UCSB), said the explosion could be to blame for the extinction of several large North American mammals at the end of the last Ice Age.

"All the elephants, including the mastodon and the mammoth, all the ground sloths, including the giant ground sloth - which, when standing on its hind legs, would have been as big as a mammoth," he told the BBC.

"All the horses went out, all the North American camels went out. There were large carnivores like the sabre-toothed cat and an enormous bear called the short-faced bear."

Professor Kennett said this could have had an enormous impact on human populations.

Population decline

According to the traditional view, humans crossed from north-east Asia to America at the end of the last Ice Age, across a land bridge which - at the time - connected Siberia to Alaska.


The extinction of large North American beasts is a puzzle
The Clovis culture was one of the earliest known cultures in the continent. These proficient hunter-gatherers developed a distinctive thin, fluted spear head known as the Clovis point, which is regarded as one of the most sophisticated stone tools ever developed.

Archaeologists have found evidence from the Topper site in South Carolina, US, that Clovis populations here went through a population collapse.

But there is no evidence of a similar decline in other parts of the continent. The Clovis culture does vanish from the archaeological record abruptly, but it is replaced by a myriad of different local hunter-gatherer cultures.


The Tunguska event devastated parts of Siberia in 1908
Jeff Severinghaus, a palaeoclimatologist at Scripps Institution of Oceanography in California, told Nature magazine: "Their impact theory shouldn't be dismissed; it deserves further investigation."

According to the new idea, the comet would have caused widespread melting of the North American ice sheet. The waters would have poured into the Atlantic, disrupting its currents.

This, they say, could have caused the 1,000 year-long Younger Dryas cold spell, which also affected Asia and Europe.

The Younger Dryas has been linked by some researchers to changes in the living patterns of people living in the Middle East which led to the beginning of farming.

A massive explosion near the Tunguska river, Siberia, in 1908, is also thought to have been caused by a space rock exploding in the atmosphere. It felled 80 million trees over an area of 2,000 sq km.

The new theory will be presented and debated at the American Geophysical Union's Joint Meeting in Acapulco, Mexico, this week.


Source: http://news.bbc.co.uk/2/hi/science/nature/6676461.stm
[img:203:152]http://upload8.postimage.org/442391/_42952177_comstrike_bbc_203.jpg[/img]
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Postby psionic11 on May 21st, 2007, 2:04 pm 

Hmm. I thought this was the prevailing theory already... I wonder which theory this is going to replace then?
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Postby Lincoln on May 21st, 2007, 2:30 pm 

The "impact caused the Lesser Dryas" idea is not commonly held. The Lesser Dryas clearly happened. Tunguska clearly happened. But this isn't the same thing at all.

This hypothesis will be hard to substantiate.
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Postby Forest_Dump on May 21st, 2007, 3:36 pm 

It will be very hard to demonstrate. We have Clovis equivalents very well dated in eastern North America at a yonger age. We also have technological continuity between Clovis and the more recent Folsum as well as eastern North American equivalents. We even have more recent dates on mastodons suggesting they lived to around 10,000 b.p. And the funny thing about the Topper site is that, although still not published, most arguments I have heard about it are far older. I will look forward to seeing how a site that is supposed to prove pre-Clovis (which is still questionable) can also tell us about post-Clovis. Still, it is worth hearing more about.
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Postby Tomyhoi on May 21st, 2007, 3:39 pm 

Rocks deposited during the Cretaceous Period and Tertiary Period are separated by a thin clay layer that is visible at several sites around the world. A team of scientists led by Luis Alvarez (a Nobel Prize-winning physicist) and his son Walter (a geologist) discovered that the clay layer contains a strikingly high concentration of iridium, an element that is much more common in meteorites than in Earth's crustal rocks. Like meteorites, asteroids and comets also have relatively large abundances of iridium. Consequently, they proposed that an impacting asteroid or comet hit the Earth, generating the iridium anomaly, and causing the mass extinction event. The discovery of high iridium concentrations in the clay layer at several places around the world suggested the impact was a large one.

Many doubted the Alvarez Hypothesis, but it is generally accepted today. I will wait to see the paper to be presented this week, before forming an opinion. At this stage, it seems to answer many questions about the extiction of Mammoths, Mastodons, Giant Sloths, Saber-toothed tigers, Melting of the North American Ice Cap, etc.
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Postby Lincoln on May 21st, 2007, 3:47 pm 

I know about Alvarez' work.

But we're talking a vastly different order of magnitude in energy release and a much different length of time involved. This is the reason that this physical mechanism will be difficult to establish. I'm not claiming it to be wrong, nor am I claiming the work is substandard. I just think even a super-Tunguska event won't leave a dramatic trace, especially in the absence of an impact crater.

Chixculub was an entirely different beast. Soot from the forest fires caused by the heat of the impact is found in Wyoming.

But it's an interesting hypothesis. We'll see how the debate unfolds.
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Postby Tomyhoi on May 21st, 2007, 4:30 pm 

As North America was covered by an estimated 10,000 feet of Ice at the time, it will be very difficult to find direct evidence of an impact. If it exploded before impact it would be more difficult to prove. But what they claim to have found-
"The evidence comes from layers of sediment at more than 20 sites across North America.

These sediments contain exotic materials: tiny spheres of glass and carbon, ultra-small specks of diamond - called nanodiamond - and amounts of the rare element iridium that are too high to have come from Earth. "

sounds like an impact.
Also I have read that 17 million years ago, there was an impact at the OR-CA-NE Junction that became what we know today as the Yellowsone Volcano. Shocked Quartz Crystals were reported from ths site. And North America moved in the past 17 million years consistent with initial crater and the volcano being at its present location. Supposedly it impacted at a low angle from the South and opened cracks that explain the Eastern Washington Basalt Flows that occured at approximately he same time. Asteroid impacts may have played a larger role in Earth's History than we realize.
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Postby Tomyhoi on May 23rd, 2007, 3:21 pm 

The Clovis people of North America, flourishing some 13,000 years ago, had a mastery of stone weaponry that stood them in good stead against the constant threat of large carnivores, such as American lions and giant short-faced bears. It's unlikely, however, that they thought death would come from the sky.
According to results presented by a team of 25 researchers this week at the American Geophysical Union meeting in Acapulco, Mexico, that's where the Clovis people's doom came from. Citing several lines of evidence, the team suggests that a wayward comet hurtled into Earth's atmosphere around 12,900 years ago, fractured into pieces and exploded in giant fireballs. Debris seems to have settled as far afield as Europe.
Jim Kennett, an oceanographer at the University of California, Santa Barbara, and one of the team's three principal investigators, claims immense wildfires scorched North America in the aftermath, killing large populations of mammals and bringing an abrupt end to the Clovis culture. "The entire continent was on fire," he says.
Lead team member Richard Firestone, a nuclear analytical chemist at the Lawrence Berkeley National Laboratory in California, says the evidence lies in a narrow 12,900-year-old carbon-rich layer of sediment found at eight well-dated Clovis-era sites and a peppering of sediment cores across North America, as well as one site in Belgium.
In this layer the team detected several different types of extraterrestrial debris, including nanodiamonds that are only ever found on Earth in meteorites; tiny carbon spherules that form when molten droplets cool rapidly in air; and cage-like carbon molecules containing the rare isotope helium-3, far more abundant in the cosmos than on Earth.
"You might find some other explanation for these individually," says Firestone, "but taken together, it's pretty clear that there was an impact." The team says the agent of destruction was probably a comet, since the key sediment layer lacks both the high nickel and iridium levels characteristic of asteroid impacts.
Intense controversyThe team's findings will almost certainly stir intense controversy and debate, for many geologists remain sceptical of impact hypotheses in general.
"There is a tendency in this field to label any circular feature a crater," says geomorphologist Michael Oskin of the University of North Carolina in Chapel Hill. But Asish Basu, a geochemist at the University of Rochester, New York, thinks the team's methods are sound, and finds the case for an extraterrestrial explosion convincing. "I think it is a very straightforward case of an impact."
Exactly where the explosion might have occurred is uncertain, but several clues point to the north of the continent. Levels of the apparent extraterrestrial debris, for example, are highest at the Gainey archaeological site in Michigan, just beyond the southern reach of North America's primary ice sheet 12,900 years ago. Moreover, levels decrease the further you go from Gainey, suggesting that the comet blew up largely over Canada – perhaps over Ontario or the Hudson Bay region.
However, this cosmic wallop does not seem to have left behind any obvious crater. In all probability, says Arizona-based geophysicist and team member Allen West, "whatever hit us was a low-density object" that fragmented as it entered the atmosphere. The disintegrating pieces could then have blown up in a series of massive aerial explosions. Alternatively, some might have crashed into the 3-kilometre-thick ice sheet. West notes that such craters "would have been ice-walled and basically melted away at the end of the last ice age", leaving few traces.
If the team's impact theory holds up under scrutiny it could help explain three mysterious events that coincided around 12,900 years ago.
Cold spellAt this key time, the climate changed abruptly in the northern hemisphere, suddenly cooling in a period known as the Younger Dryas. In addition, the distinctive Clovis culture seems to have vanished in North America, while at least 35 genera of the continent's mammals went extinct – including mammoths, mastodons, camels, ground sloths and horses.
For years, many researchers have chalked up the onset of the Younger Dryas to a major change in North America's plumbing. Near the end of the last ice age, meltwater from the continent's principal ice sheet flooded into proglacial lakes in the centre of North America, and from there drained southward into the Mississippi river.
But by 12,900 years ago, the ice had retreated sufficiently from the northern Atlantic coast to let meltwater rush suddenly eastward. As an estimated 9500 cubic kilometres of fresh water poured into the Atlantic, it switched off the ocean's salinity-driven "conveyor belt" current, shutting down the Gulf Stream that carries heat from the tropics to eastern North America. It was this that triggered the Younger Dryas cooling, say many palaeoclimate experts.
However, some of the comet proponents now propose a different trigger for the cold spell. The massive airbursts over Canada could have destabilised the continental ice sheet, opening new drainage channels to the east. Additionally, dust and debris from the explosions may have darkened the ice, absorbing solar heat and accelerating melting. "What we suggest is that the meltwater outflow from the proglacial lakes and from the temporarily melting ice sheet was the result of extraterrestrial impact," says Kennett.
The comet-strike also offers a third and radical hypothesis for the massive extinction of mammals, which for years palaeontologists have blamed on the sudden Younger Dryas freeze, combined with the hunting prowess of newly arrived Clovis bands. In the 12,900-year-old carbon-rich layer at Murray Springs, Arizona, and in sediment cores taken from the Carolina Bays (see "Marks of a comet?", below), chemist Wendy Wolbach of DePaul University in Chicago has detected significant quantities of soot – a product of the intense heat of wildfires.
Raging wildfiresMoreover, geologist Luanne Becker at the University of California, Santa Barbara, has detected a chemical signature of wildfire – polycyclic aromatic hydrocarbons – in samples taken from three of the team's study sites. Kennett and other team members say this suggests the cometary explosions ignited wildfires that swept across much of southern North America, wiping out large populations of animals. "I don't want to sound catastrophic here," he says, "but this is wild stuff. There is significant evidence of massive biomass burning."
If they are right, the cataclysm could also have devastated bands of Clovis hunters. Archaeologist Al Goodyear of the University of South Carolina, Columbia, reported at the Acapulco meeting that there is indirect evidence of a human disaster in what is now the south-eastern US. Chert points fashioned in the distinctive Clovis style disappear, and a new type of tool appears in the archaeological record: redstone points, judged on stylistic grounds to date from 12,750 years ago. Numbers of Clovis points outnumber redstones by 4 to 1. "If the number of points are diagnostic of the number of people there, which is a pretty reasonable assumption," notes West, "there was at least a 70 per cent decline" in the human population in the region.
Nonetheless, many researchers are likely to greet such apocalyptic scenarios with deep scepticism. Palaeontologist Paul Koch of the University of California, Santa Cruz, says he is intrigued by the new evidence of an impact, but he is far from persuaded by some of the team's sweeping claims. "I'm not convinced yet there were [widespread] wildfires," says Koch. "But if an impact just triggered the Younger Dryas, that in itself is a pretty big issue."
Gerta Keller, a Princeton University geologist, has similar reservations. "Some of the conclusions may be a bit over the top," she says, particularly the claims of continent-wide fires. Kennett and his colleagues are braced for the critics. "You watch it," he jokes, "there will be blood on the streets."
Comets and Asteroids - Learn more about the threat to human civilisation in our special report.
From issue 2591 of New Scientist magazine, 22 May 2007, page 28-33
MARKS OF A COMET?
If a comet really did blow up over North America 12,900 years ago, did the blast leave any traces other than microscopic extraterrestrial debris? Proponents have yet to find any, but they speculate that three areas might bear some traces – the Great Lakes, Hudson Bay and the Carolinas in the south-eastern US.

Most geologists believe that the Great Lakes were scoured out by glaciation, but the comet-blast team's principle author, Richard Firestone, notes that there are "four large holes in the lakes which are deeper than Death Valley, so we kind of suspect that pieces of this impact did penetrate them".

The team is also keen to investigate a 400-kilometre-long anomaly on the bottom of Hudson Bay, which they suggest may be part of a crater rim.

Then there are the Carolina Bays, thousands of oval depressions scattered along the Atlantic coast, most of them pointing towards the Great Lakes region. While many researchers are convinced that local winds scooped out these bays, team member Allen West suggests that a shock wave from the comet launched tornado-like winds that carved out the bays. Geomorphologist Michael Oskin of the University of North Carolina, Chapel Hill, flatly dismisses the idea. "In my opinion, the shock wave idea is grasping at straws – searching for an extraordinary origin for what are in fact quite ordinary [wind] features."

Source: http://space.newscientist.com/article/d ... icans.html
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Postby Forest_Dump on May 23rd, 2007, 5:28 pm 

Well, I can't say much about the prospect of a comet strike but I can comment on the idea that there was any kind of decline of Clovis people in the northeast. There definitely was not. The Great Lakes Clovis equivalent is indeed the Gainey point, named after the Gainey site which has been worked on by a Michigan archaeologist named Don Simon (who does good work). Gainey points are reasonably common as surface collected artifacts in the Great Lakes region (although most do not get reported) but few sites have been found, excavated and published. The following is often known as the Parkhill Phase and Parkhill points are clearly and unambiguously only slightly different from Gainey (it does take a trained eye to spot the differences). An equivalent further south is the "Cumberland" point style. Based on number of sites and surface collected sites, it would be hard to argue that there wasn't a significant population increase in the lower Great Lakes region. I am also familiar with Al Goodyear and his work and he is well-known for his work on Dalton sites in the southeast which date a little later still. In fact, Goodyear was one of the ones who demonstrated that Dalton developed from Gainey and later fluted point styles. I don't know yet how strong the evidence is for a comet strike and cannot comment on that. But I can say with a great deal of confidence that there is no evidence of a population decline in the lower Great Lakes - if anything there was a noticeable increase in population at this time.
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Postby goingtothedogs on June 6th, 2007, 5:25 pm 

Tomyhoi wrote: Also I have read that 17 million years ago, there was an impact at the OR-CA-NE Junction that became what we know today as the Yellowsone Volcano. .


I understood tha the Yellowstone site is supposed to be a mantel plume????
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Postby Tomyhoi on June 6th, 2007, 6:12 pm 

Yes, it is a mantle plume which resulted from an Impact Crater deep enough to expose the Mantle, which then melted without the weight of the Crust on it, forming a Plume.
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Extraterrestrial Impact Likely Source Of Sudden Ice Age Exti

Postby Tomyhoi on September 25th, 2007, 3:38 am 

At the end of the Pleistocene era, woolly mammoths roamed North America along with a cast of fantastic creatures – giant sloths, saber-toothed cats, camels, lions, tapirs and the incredible teratorn, a condor with a 16-foot wingspan.

About 12,900 years ago, these megafauna disappeared from the fossil record, as did evidence of human remains. The cause of the mass extinction and the human migration is a mystery. Now a team of scientists, including Brown University planetary geologist Peter Schultz, provides evidence that an asteroid impact likely caused the sudden climate changes that killed off the mammoths and other majestic beasts of prehistory.

In the Proceedings of the National Academy of Sciences, the international team lays out its theory that the mass extinctions in North America were caused by one or more extraterrestrial objects – comets or meteorites – that exploded over the Earth or slammed into it, triggering catastrophic climate change.

The scientists believe that evidence for these extraterrestrial impacts is hidden in a dark layer of dirt sometimes called a black mat. Found in more than 50 sites around North America, this puzzling slice of geological history is a mere three centimeters deep and filled with carbon, which lends the layer its dark color. This black mat has been found in archaeological digs in Canada and California, Arizona and South Carolina – even in a research site in Belgium.

The formation of this layer dates back 12,900 years and coincides with the abrupt cooling of the Younger Dryas period, sometimes called the “Big Freeze.” This coincidence intrigued the researchers, led by Richard Firestone of Lawrence Berkeley National Laboratory, who thought that the black mat might be related to the mass extinctions.

So the researchers studied black mat sediment samples from 10 archaeological sites dating back to the Clovis people, the first human inhabitants of the New World. Researchers conducted geochemical analysis of the samples to determine their makeup and also ran carbon dating tests to determine the age of the samples.

Directly beneath the black mat, researchers found high concentrations of magnetic grains containing iridium, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds and fullerenes packed with extraterrestrial helium – all of which are evidence for an extraterrestrial impact and the raging wildfires that might have followed.

Schultz, professor of geological sciences at Brown and an impact specialist, said the most provocative evidence for an extraterrestrial impact was the discovery of nanodiamonds, microscopic bits of diamond formed only from the kind of intense pressure you’d get from a comet or meteorite slamming into the Earth.

“We don’t have a smoking gun for our theory, but we sure have a lot of shell casings,” Schultz said. “Taken together, the markers found in the samples offer intriguing evidence that North America had a major impact event about 12,900 years ago.”

Schultz admits that there is little decisive evidence about the actual details about the impact and its effects. Scientists suspect that a carbon-rich asteroid or comets were the culprits. The objects would have exploded over North America or slammed into it, or both, shattering and melting ice sheets, sparking extreme wildfires, and fueling hurricane-force winds – all of which could have contributed to changes in climate that led to the cooling of the Younger Dryas period.

“Our theory isn’t a slam dunk,” Schultz said. “We need to study a lot more sediments to get a lot more evidence. But what is sobering about this theory of ours is that this impact would be so recent. Not so long ago, something may have fallen from the sky and profoundly changed our climate and our culture.”

The U.S. Department of Energy and the National Science Foundation funded the work.

Note: This story has been adapted from a news release issued by Brown University.

Source: http://www.sciencedaily.com/releases/20 ... 172959.htm
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Could this be related to the Impact?

Postby Tomyhoi on December 2nd, 2007, 4:07 am 

Prehistoric Forest Emerges From Farmer's Pond
ScienceDaily (Dec. 1, 2007) — Dennis Myllyla thought he’d struck a fine bargain with the Michigan Department of Transportation. MDOT would get fill for nearby highway construction by dredging a pond on his farm near Arnheim, Mich., and Myllyla would get the pond.

Neither Myllyla nor MDOT expected to find a prehistoric forest too. But that’s exactly what they uncovered, about 15 feet down.

“We ran into logs, lots of logs. It was like a forest down there,” said Myllyla, who has been farming in the Arnheim area since 1948.

Forestry consultant Justin Miller was on site when the MDOT heavy equipment operators found themselves dredging up more logs than sand. Miller, who had been preparing a management plan for the forested sections of Myllyla’s property, was a 2000 graduate of Michigan Technological University’s School of Forest Resources and Environmental Science, and he knew just whom to call.

“I’ll rush right down and take a look,” James Schmierer responded. The forester from Michigan Tech was there within 24 hours.

What he saw amazed him. “We find a lot of trees lying on the forest floor, but this was the first time I’ve seen so many trees thousands of years old and so well preserved in the soil,” he said. Dozens were tangled together, some of them 20 feet long and more than 2 feet in diameter.

“What could bury a whole forest 15 feet underground?” Schmierer wondered. “It had to be a single catastrophic, violent event, and it must have happened a long time ago for 15 feet of soil to build up.”

Schmierer and his colleague, Michael Hyslop, a GIS analyst and instructor of geomorphology and vegetation at Michigan Tech, speculate that the trees were either transported or mowed down by the last glacier to move across the Keweenaw, before Lake Superior covered the peninsula. “That would make them more than 10,000 years old,” he said.

Schmierer and Hyslop have recovered some of the logs and are hoping to carbon-date them. Schmierer also hopes to identify the species of tree.

“If I had to guess, I’d say it was an elm,” said Miller, “but I really don’t know. I’ll be real curious to find out how old they are and what species.”

Schmierer plans to make two displays from chunks of the ancient trees, one to put on exhibit at Alberta Village, the Michigan Tech School of Forestry’s field site, and the other for the atrium of the U.J. Noblet Forestry Building on campus.

“And Michigan Tech is going to give me one as a momento,” said Myllyla
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Postby Forest_Dump on December 2nd, 2007, 9:49 am 

Definitely need more information here. If these are elms, then it is unlikely that they were that close to the glaciers. Vegetation histories based on pollen cores indicate that elm first appears around 10,500 B.P. (not recalibrated) and reaches a maximum around 8,500 B.P. before decling somewhat around 1000 B.P Given the reported size of these trees, I would suspect they would not be the earliest. The mechanism for burial is not that clear. Land slides, local flooding because of changes due to drainage from isostatic rebound, etc., could be factors long after the ice fronts were gone. More solid species identification (should be child's play given the reported size of the logs), AMS dating and a taphonomic study of the burial mechanism would all help clear this up. But at this point, I suspect the direct link to glacial movements (or the comet) are purely uninformed speculation.
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Ancient flood brought Gulf Stream to a halt

Postby Tomyhoi on December 9th, 2007, 11:37 pm 

It was the biggest climate event of the last 10,000 years and caused the most dramatic change in the weather since humans began farming. And it may yet hold important lessons about climate change in the 21st century.

Just over 8000 years ago, a huge glacial lake in Canada burst, and an estimated 100,000 cubic kilometres of fresh water rushed into the North Atlantic. Researchers now say they know for sure that this catastrophic event shut down the Gulf Stream and cooled parts of the northern hemisphere by several degrees for more than a hundred years.

They say the findings show modelling studies are right to suggest that something similar could happen with equal abruptness as the planet warms under human influence. The film The Day After Tomorrow, which portrays such a scenario, may have exaggerated – but not by much.

Lake Agassiz was a giant lake that formed at the end of the last ice age as the huge Laurentide ice sheet melted (see a simulation of the process). The lake occupied most of the modern-day Canadian Midwest between the Hudson Bay and the US border.

Freshwater flood
Climate historians have previously established that the lake burst suddenly, emptying down the Hudson Strait and into the Labrador Sea west of Greenland.

This is very close to a key point in the global ocean circulation system, where Atlantic water brought north on the Gulf Stream freezes, and dense, saline, leftover water plunges to the ocean floor.

Investigators have speculated that the huge slug of water from the emptying lake could have refreshed the ocean water so much that this plunging ceased, shutting down the circulation, including the Gulf Stream, which keeps countries around the North Atlantic warm.

That, they said, would explain why Greenland ice cores show temperatures in the area plummeting by up to 8 °C.

Now Helga Kleiven at the University of Bergen in Norway and colleagues claim to have found proof that this is exactly what happened.

Abrupt changes
They carried out a detailed study of sediments on the floor of the Labrador Sea and found clear signs of major changes exactly when the lake emptied and the temperatures dropped.

The changes include a flood of fine sediment from the land, coinciding with a sharp drop in the amount of particles of magnetite normally carried to the area by deep ocean currents. The study also shows that the changes were abrupt, happening within a decade or so, in warm climate conditions not unlike those of today.

Modern concerns arise because melting ice, especially on Greenland and in Siberia, is making the North Atlantic less saline. Oceanographers worry that this might eventually be sufficient to shut down the ocean circulation, says Kleiven, just as happened 8000 years ago, "particularly given the concerns about the impact of future warming on the Greenland ice sheet."

The next step, Kleiven believes, is to use the findings to work out exactly how much freshwater may be needed to shut down the circulation.

Journal reference: Science Express (DOI: 10.1126/science.1148924)

Source: http://environment.newscientist.com/art ... -halt.html
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Postby Removed user on December 10th, 2007, 4:02 am 

I’m not familiar with flood events into the Atlantic Ocean but I am somewhat familiar with the mechanisms of thermohaline currents and quite familiar with the Missoula Floods of the Northwestern U.S. If a similar amount of cold glacial lake waters as were released into the Pacific Ocean by the Missoula Floods were released into the North Atlantic then without a doubt they would disrupt the global thermohaline current, almost certaintly causing widespread climate shifts.

http://en.wikipedia.org/wiki/Thermohaline_circulation
http://en.wikipedia.org/wiki/Missoula_Floods
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Postby Removed user on December 10th, 2007, 4:35 am 

Forest_Dump wrote:Definitely need more information here. If these are elms, then it is unlikely that they were that close to the glaciers...


If the trees appear to be "elms” but could not have been then they may be the closely related hackberry Celtis sp. I’ve found fossilized hackberry seeds on Pleistocene digs and a little research reveals the genus to have been widespread in North America since the Eocene.

http://books.google.com/books?id=8fqv1F ... 2Ze74IX5aU

I have no idea about a "space rock" explosion 13,000 years ago but every time I've dug in Kansas I've run into bentonite and I know that a volcanic explosion 13,000 years ago left a 5 kilometer wide crater at Yellowstone. Massive volcanic activity is generally associated with climate cooling.

http://volcano.und.edu/vwdocs/Gases/climate.html
Last edited by Removed user on December 10th, 2007, 11:17 am, edited 1 time in total.
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Postby Forest_Dump on December 10th, 2007, 7:18 am 

I have to admit I don't know much about the draining of Lake Agassiz. I know that there were earlier "releases" from glacial lakes and changes in flows. For example, Lakes Hough and Stanley (in the Georgian Bay and Lake Huron basins respectively) originally drained east through the French River channel and down the Ottawa valley. In fact, before the isostatic rebound, the Ottawa valley was depressed enough that there were marine mammals there. I have heard people speculating about a flood that would have filled Lakes Erie and Ontario basins early in the Holocene and possibly Lakes Tonnawanda and Wainfleet which in turn were standing until the Niagara Gorge eroded back far enough to release them much later. However, this one is new to me although I suspect I will be hearing more about it in the near future.
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Postby psionic11 on December 11th, 2007, 2:19 am 

/quick aside on...

Forest, I must admit to a certain admiration of your knowledge base. Is it de rigeur that an anthropologist must be well-versed in world history, archaelogy/paleontology, the life sciences, some geology and hard science, and the soft sciences like psychology and sociology, proto-language and philosophy? Not to mention your literature and academic credentials and references...

Can you be a professional and yet dabble in every other major field of knowledge... and get paid for it?! If so, I may have to re-think my life-course, excepting the major goals of computer science and outdoors sports...

/quick aside off....
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Postby Removed user on December 11th, 2007, 6:55 am 

There has been some contention as to which discipline should fall under the purview of another since the days when scientists were not even recognized as such but instead called natural philosophers. Lately, however, many are throwing this archaic jousting aside, realizing that some issues are just too complex to be addressed within a single field of study.

Anthropology, as you note, contains or utilizes knowledge from many other disciplines. Another such “inter” discipline is Environmental Science, which takes from such diverse fields as Physics, Chemistry, Astronomy, Geology, Geography, Climatology, Ecology, Oceanography, Agronomy, Medicine, Demography, Political Science, and, yes, even Anthropology to study human interactions with the environment.

I have a cousin who is essentially the Environmental Science equivalent of Forrest Dump as she runs a private consulting firm that contracts both with private industry and the EPA to perform environmental impact studies. She is even more extensively educated then I, as she has a handful of Master's degrees in diverse subject areas.
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Postby Forest_Dump on December 11th, 2007, 7:28 am 

Well, thanks. Actually, one way or another I suppose you do have to cover a lot of these fields. My teaching generally requires covering human evolution, basics of evolutionary theory and primatology plus the archaeological "history" of the world. I try to make full use (and add to over time) the teaching collections which includes lots of casts. And you need to read up and study these things so you know your stuff in class - can't be fumbling for a reference all the time. But the "four field" approach to anthropology includes linguistics and ethnography. Plus, I have to deal with FN people, etc. That can be tricky. Ethnography, for a while, did include a lot of concern about psychology (non-western folk) but not my strong suit and sociology seems to be anthropology but confined to the "west" (and I did have to read a lot of Weber and Durkheim - helpful if you end up having to read Foucault). When doing my grad studies I also sat in on a lot of philosophy classes - I guess I took it seriously that you Master in Science but Doctor in Philosophy. Sitting in on lectures (no promises about doing the readings) was sometimes better than watching TV for an hour and I did try to model my lectures on what I saw a physics prof do - he was incredibly entertaining. "Theory" became big in archaeology in the 60s and is still considered pretty important. Big questions included whether archaeology is a historical science (like geology and astronomy) or more traditional history (had to read Collingwood to Braudel for that longue duree perspective). A lot of philosophy of science was written by chemists and physicists exploring their historical perspectives of science. So, proto-language? While linguistics is not one of my strong suits, I need to be able to cover it for 1st year, archaeology does sometimes try to link past societies to "language stocks" and, when I had to do my language requirement (most students hate this and sometimes it seems anachronistic), I decided to, at the same time, wonder about the Whorf-Sapir hypothesis about whether language structures thought. Which is not far from the big question of whether culture in internally generated or externally generated which I end up wondering about when I have to look at and identify a projectile point out in a muddy field that is stylistically similar to others half a continent away. I don't think there is much special about all of this, it is all inter-linked. But like everything, you get out what you put in. Some do the minimal required but I think it is my responcibility to keep up with what is going on in the field - rhetorically, would you want a doctor who didn't keep up to speed with what is going on in the field and wasn't capable of being flexible and critical? I think a key is do everything you have to and then do more of the things you should and add some things just because you can (like sit in on other courses at the school you attend - just don't feel you need to add the readings or other work. That can add stress while you can always sit in again next year.)
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Supercomputers Offer New Explanation Of Tunguska Disaster

Postby Tomyhoi on December 19th, 2007, 9:11 am 

The stunning amount of forest devastation at Tunguska a century ago in Siberia may have been caused by an asteroid only a fraction as large as previously published estimates, Sandia National Laboratories supercomputer simulations suggest.
“The asteroid that caused the extensive damage was much smaller than we had thought,” says Sandia principal investigator Mark Boslough of the impact that occurred June 30, 1908. “That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed.”

Because smaller asteroids approach Earth statistically more frequently than larger ones, he says, “We should be making more efforts at detecting the smaller ones than we have till now.”

The new simulation — which more closely matches the widely known facts of destruction than earlier models — shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball.

This causes stronger blast waves and thermal radiation pulses at the surface than would be predicted by an explosion limited to the height at which the blast was initiated.

“Our understanding was oversimplified,” says Boslough, “We no longer have to make the same simplifying assumptions, because present-day supercomputers allow us to do things with high resolution in 3-D. Everything gets clearer as you look at things with more refined tools.”

The new interpretation also accounts for the fact that winds were amplified above ridgelines where trees tended to be blown down, and that the forest at the time of the explosion, according to foresters, was not healthy. Thus previous scientific estimates had overstated the devastation caused by the asteroid, since topographic and ecologic factors contributing to the result had not been taken into account.

“There’s actually less devastation than previously thought,” says Boslough, “but it was caused by a far smaller asteroid. Unfortunately, it’s not a complete wash in terms of the potential hazard, because there are more smaller asteroids than larger ones.”

Boslough and colleagues achieved fame more than a decade ago by accurately predicting that that the fireball caused by the intersection of the comet Shoemaker-Levy 9 with Jupiter would be observable from Earth.

Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth’s atmosphere. As it penetrates deeper, the more and more resistant atmospheric wall causes it to explode as an airburst that precipitates the downward flow of heated gas.

Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.

“Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion,” says Boslough.

One of most prominent papers in estimating frequency of impact was published five years ago in Nature by Sandia researcher Dick Spalding and his colleagues, from satellite data on explosions in atmosphere. “They can count those events and estimate frequencies of arrival through probabilistic arguments,” says Boslough.

The work was presented at the American Geophysical Union meeting in San Francisco on Dec. 11. A paper on the phenomenon, co-authored by Sandia researcher Dave Crawford and entitled “Low–altitude airbursts and the impact threat” has been accepted for publication in the International Journal of Impact Engineering.

The research was paid for by Sandia’s Laboratory-Directed Research and Development office.

Adapted from materials provided by DOE/Sandia National Laboratories.


[img:200:240]http://www.postimage.org/Pq2LKwRA.jpg[/img]
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