Microscopic diamonds suggest cosmic impact responsible for major period of climate change

Around 12,800 years ago, a sudden, catastrophic event plunged much of the Earth into a period of cold climatic conditions and drought. This drastic climate change-the Younger Dryas-coincided with the extinction of Pleistocene megafauna, such as the saber-tooth cats and the mastodon, and resulted in major declines in prehistoric human populations, including the termination of the Clovis culture.

With limited evidence, several rival theories have been proposed about the event that sparked this period, such as a collapse of the North American ice sheets, a major volcanic eruption, or a solar flare.


However, in a study published in The Journal of Geology, an international group of scientists analyzing existing and new evidence have determined a cosmic impact event, such as a comet or meteorite, to be the only plausible hypothesis to explain all the unusual occurrences at the onset of the Younger Dryas period.

Researchers from 21 universities in 6 countries believe the key to the mystery of the Big Freeze lies in nanodiamonds scattered across Europe, North America, and portions of South America, in a 50-million-square-kilometer area known as the Younger Dryas Boundary (YDB) field.

Microscopic nanodiamonds, melt-glass, carbon spherules, and other high-temperature materials are found in abundance throughout the YDB field, in a thin layer located only meters from the Earth’s surface. Because these materials formed at temperatures in excess of 2200 degrees Celsius, the fact they are present together so near to the surface suggests they were likely created by a major extraterrestrial impact event.

In addition to providing support for the cosmic impact event hypothesis, the study also offers evidence to reject alternate hypotheses for the formation of the YDB nanodiamonds, such as by wildfires, volcanism, or meteoric flux.

The team’s findings serve to settle the debate about the presence of nanodiamonds in the YDB field and challenge existing paradigms across multiple disciplines, including impact dynamics, archaeology, paleontology, limnology, and palynology.

Comet theory false; doesn’t explain Ice Age cold snap, Clovis changes, animal extinction

Controversy over what sparked the Younger Dryas, a brief return to near glacial conditions at the end of the Ice Age, includes a theory that it was caused by a comet hitting the Earth.

As proof, proponents point to sediments containing deposits they believe could result only from a cosmic impact.

Now a new study disproves that theory, said archaeologist David Meltzer, Southern Methodist University, Dallas. Meltzer is lead author on the study and an expert in the Clovis culture, the peoples who lived in North America at the end of the Ice Age.

Meltzer’s research team found that nearly all sediment layers purported to be from the Ice Age at 29 sites in North America and on three other continents are actually either much younger or much older.

Scientists agree that the brief episode at the end of the Ice Age – officially known as the Younger Dryas for a flower that flourished at that time – sparked widespread cooling of the Earth 12,800 years ago and that this cool period lasted for 1,000 years. But theories about the cause of this abrupt climate change are numerous. They range from changes in ocean circulation patterns caused by glacial meltwater entering the ocean to the cosmic-impact theory.

The cosmic-impact theory is said to be supported by the presence of geological indicators that are extraterrestrial in origin. However a review of the dating of the sediments at the 29 sites reported to have such indicators proves the cosmic-impact theory false, said Meltzer.

Meltzer and his co-authors found that only three of 29 sites commonly referenced to support the cosmic-impact theory actually date to the window of time for the Ice Age.

The findings, “Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago,” were reported May 12, 2014, in the Proceedings of the National Academy of Sciences.

Co-authors were Vance T. Holliday and D. Shane Miller, both from the University of Arizona; and Michael D. Cannon, SWCA Environmental Consultants Inc., Salt Lake City, Utah.

“The supposed impact markers are undated or significantly older or younger than 12,800 years ago,” report the authors. “Either there were many more impacts than supposed, including one as recently as 5 centuries ago, or, far more likely, these are not extraterrestrial impact markers.”

Dating of purported Younger Dryas sites proves unreliable


The Younger Dryas Impact Hypothesis rests heavily on the claim that there is a Younger Dryas boundary layer at 29 sites in the Americas and elsewhere that contains deposits of supposed extraterrestrial origin that date to a 300-year span centered on 12,800 years ago.

The deposits include magnetic grains with iridium, magnetic microspherules, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds, and fullerenes with extraterrestrial helium, all said to result from a comet or other cosmic event hitting the Earth.

Meltzer and his colleagues tested that hypothesis by investigating the existing stratigraphic and chronological data sets reported in the published scientific literature and accepted as proof by cosmic-impact proponents, to determine if these markers dated to the onset of the Younger Dryas.

They sorted the 29 sites by the availability of radiometric or numeric ages and then the type of age control, if available, and whether the age control is secure.

The researchers found that three sites lack absolute age control: at Chobot, Alberta, the three Clovis points found lack stratigraphic context, and the majority of other diagnostic artifacts are younger than Clovis by thousands of years; at Morley, Alberta, ridges are assumed without evidence to be chronologically correlated with Ice Age hills 2,600 kilometers away; and at Paw Paw Cove, Maryland, horizontal integrity of the Clovis artifacts found is compromised, according to that site’s principal archaeologist.

The remaining 26 sites have radiometric or other potential numeric ages, but only three date to the Younger Dryas boundary layer.

At eight of those sites, the ages are unrelated to the supposed Younger Dryas boundary layer, as for example at Gainey, Michigan, where extensive stratigraphic mixing of artifacts found at the site makes it impossible to know their position to the supposed Younger Dryas boundary layer. Where direct dating did occur, it’s sometime after the 16th century A.D.

At Wally’s Beach, Alberta, a radiocarbon age of 10,980 purportedly dates extraterrestrial impact markers from sediment in the skull of an extinct horse. In actuality, the date is from an extinct musk ox, and the fossil yielding the supposed impact markers was not dated, nor is there evidence to suggest that the fossils from Wally’s Beach are all of the same age or date to the Younger Dryas onset.

At nearly a dozen other sites, the authors report, the chronological results are neither reliable nor valid as a result of significant statistical flaws in the analysis, the omission of ages from the models, and the disregard of statistical uncertainty that accompanies all radiometric dates.

For example, at Lake Cuitzeo, Mexico, Meltzer and his team used the data of previous researchers and applied a fifth-order polynomial regression, but it returned a different equation that put the cosmic-impact markers at a depth well above that which would mark the Younger Dryas onset.

The authors go on to point out that inferences about the ages of supposed Younger Dryas boundary layers are unsupported by replication in more cases than not.

In North America, the Ice Age was marked by the mass extinction of several dozen genera of large mammals, including mammoths, mastodons, American horses, Western camels, two types of deer, ancient bison, giant beaver, giant bears, sabre-toothed cats, giant bears, American cheetahs, and many other animals, as well as plants.

Prehistoric climate change due to cosmic crash in Canada

An artist's rendition of mastodons, camels and a ground sloth before the environmental changes of the Younger Dryas led to their extinction. -  Barry Roal Carlsen, University of Wisconsin
An artist’s rendition of mastodons, camels and a ground sloth before the environmental changes of the Younger Dryas led to their extinction. – Barry Roal Carlsen, University of Wisconsin

For the first time, a dramatic global climate shift has been linked to the impact in Quebec of an asteroid or comet, Dartmouth researchers and their colleagues report in a new study. The cataclysmic event wiped out many of the planet’s large mammals and may have prompted humans to start gathering and growing some of their food rather than solely hunting big game.

The findings appear next week in the online Early Edition of the Proceedings of the National Academy of Sciences. A preprint of the article is available to journalists starting Wednesday, Aug. 28, at http://www.eurekalert.org/account.php.

The impact occurred about 12,900 years ago, at the beginning of the Younger Dryas period, and marks an abrupt global change to a colder, dryer climate with far-reaching effects on both animals and humans. In North America, the big animals all vanished, including mastodons, camels, giant ground sloths and saber-toothed cats. Their human hunters, known to archaeologists as the Clovis people, set aside their heavy-duty spears and turned to a hunter-gatherer subsistence diet of roots, berries and smaller game.

“The Younger Dryas cooling impacted human history in a profound manner,” says Dartmouth Professor Mukul Sharma, a co-author of the study. “Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture.”

It is not disputed that these powerful environmental changes occurred, but there has long been controversy over their cause. The classic view of the Younger Dryas cooling interlude has been that an ice dam in the North American ice sheet ruptured, releasing a massive quantity of freshwater into the Atlantic Ocean. The sudden influx is thought to have shut down the ocean currents that move tropical water northward, resulting in the cold, dry climate of the Younger Dryas.

But Sharma and his co-authors have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation. The report focuses on spherules, or droplets of solidified molten rock expelled by the impact of a comet or meteor. The spherules in question were recovered from Younger Dryas boundary layers at sites in Pennsylvania and New Jersey, the layers having been deposited at the beginning of the period. The geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma and his colleagues argue the impact took place.

“We have for the first time narrowed down the region where a Younger Dryas impact did take place,” says Sharma, “even though we have not yet found its crater.” There is a known impact crater in Quebec – the 4-kilometer wide Corossal crater — but based on the team’s mineralogical and geochemical studies, it is not the impact source for the material found in Pennsylvania and New Jersey.

People have written about many impacts in different parts of the world based on the presence of spherules. “It may well have taken multiple concurrent impacts to bring about the extensive environmental changes of the Younger Dryas,” says Sharma. “However, to date no impact craters have been found and our research will help track one of them down.”

Comprehensive analysis of impact spherules supports theory of cosmic impact 12,800 years ago

This is UCSB Earth Sciences professor emeritus James Kennett. -  Courtesy photo
This is UCSB Earth Sciences professor emeritus James Kennett. – Courtesy photo

About 12,800 years ago when the Earth was warming and emerging from the last ice age, a dramatic and anomalous event occurred that abruptly reversed climatic conditions back to near-glacial state. According to James Kennett, UC Santa Barbara emeritus professor in earth sciences, this climate switch fundamentally — and remarkably — occurred in only one year, heralding the onset of the Younger Dryas cool episode.

The cause of this cooling has been much debated, especially because it closely coincided with the abrupt extinction of the majority of the large animals then inhabiting the Americas, as well as the disappearance of the prehistoric Clovis culture, known for its big game hunting.

“What then did cause the extinction of most of these big animals, including mammoths, mastodons, giant ground sloths, American camel and horse, and saber- toothed cats?” asked Kennett, pointing to Charles Darwin’s 1845 assessment of the significance of climate change. “Did these extinctions result from human overkill, climatic change or some catastrophic event?” The long debate that has followed, Kennett noted, has recently been stimulated by a growing body of evidence in support of a theory that a major cosmic impact event was involved, a theory proposed by the scientific team that includes Kennett himself.

Now, in one of the most comprehensive related investigations ever, the group has documented a wide distribution of microspherules widely distributed in a layer over 50 million square kilometers on four continents, including North America, including Arlington Canyon on Santa Rosa Island in the Channel Islands. This layer — the Younger Dryas Boundary (YDB) layer — also contains peak abundances of other exotic materials, including nanodiamonds and other unusual forms of carbon such as fullerenes, as well as melt-glass and iridium. This new evidence in support of the cosmic impact theory appeared recently in a paper in the Proceedings of the National Academy of the Sciences.

This cosmic impact, said Kennett, caused major environmental degradation over wide areas through numerous processes that include continent-wide wildfires and a major increase in atmospheric dust load that blocked the sun long enough to cause starvation of larger animals.

Investigating 18 sites across North America, Europe and the Middle East, Kennett and 28 colleagues from 24 institutions analyzed the spherules, tiny spheres formed by the high temperature melting of rocks and soils that then cooled or quenched rapidly in the atmosphere. The process results from enormous heat and pressures in blasts generated by the cosmic impact, somewhat similar to those produced during atomic explosions, Kennett explained.

But spherules do not form from cosmic collisions alone. Volcanic activity, lightning strikes, and coal seam fires all can create the tiny spheres. So to differentiate between impact spherules and those formed by other processes, the research team utilized scanning electron microscopy and energy dispersive spectrometry on nearly 700 spherule samples collected from the YDB layer. The YDB layer also corresponds with the end of the Clovis age, and is commonly associated with other features such as an overlying “black mat” — a thin, dark carbon-rich sedimentary layer — as well as the youngest known Clovis archeological material and megafaunal remains, and abundant charcoal that indicates massive biomass burning resulting from impact.

The results, according to Kennett, are compelling. Examinations of the YDB spherules revealed that while they are consistent with the type of sediment found on the surface of the earth in their areas at the time of impact, they are geochemically dissimilar from volcanic materials. Tests on their remanent magnetism — the remaining magnetism after the removal of an electric or magnetic influence — also demonstrated that the spherules could not have formed naturally during lightning strikes.

“Because requisite formation temperatures for the impact spherules are greater than 2,200 degrees Celsius, this finding precludes all but a high temperature cosmic impact event as a natural formation mechanism for melted silica and other minerals,” Kennett explained. Experiments by the group have for the first time demonstrated that silica-rich spherules can also form through high temperature incineration of plants, such as oaks, pines, and reeds, because these are known to contain biologically formed silica.

Additionally, according to the study, the surface textures of these spherules are consistent with high temperatures and high-velocity impacts, and they are often fused to other spherules. An estimated 10 million metric tons of impact spherules were deposited across nine countries in the four continents studied. However, the true breadth of the YDB strewnfield is unknown, indicating an impact of major proportions.

“Based on geochemical measurements and morphological observations, this paper offers compelling evidence to reject alternate hypotheses that YDB spherules formed by volcanic or human activity; from the ongoing natural accumulation of space dust; lightning strikes; or by slow geochemical accumulation in sediments,” said Kennett.

“This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event.”

Greenland ice may exaggerate magnitude of 13,000-year-old deep freeze

Ice samples pulled from nearly a mile below the surface of Greenland glaciers have long served as a historical thermometer, adding temperature data to studies of the local conditions up to the Northern Hemisphere’s climate.

But the method — comparing the ratio of oxygen isotopes buried as snow fell over millennia — may not be such a straightforward indicator of air temperature.

“We don’t believe the ice cores can be interpreted purely as a signal of temperature,” says Anders Carlson, a University of Wisconsin-Madison geosciences professor. “You have to consider where the precipitation that formed the ice came from.”

According to a study published today by the Proceedings of the National Academy of Sciences, the Greenland ice core drifts notably from other records of Northern Hemisphere temperatures during the Younger Dryas, a period beginning nearly 13,000 years ago of cooling so abrupt it’s believed to be unmatched since.

Such periods of speedy cooling and warming are of special interest to climate scientists, who are teasing out the mechanisms of high-speed change to better understand and predict the changes occurring in our own time.

In the case of the Younger Dryas, average temperatures — based on the Greenland ice — plummeted as much as 15 degrees Celsius in a few centuries, and then shot back up nearly as much (over just decades) about 1,000 years later.

“In terms of temperature during the Younger Dryas, the only thing that looks like Greenland ice cores are Greenland ice cores,” Carlson says. “They are supposed to be iconic for the Northern Hemisphere, but we have four other records that do not agree with the Greenland ice cores for that time. That abrupt cooling is there, just not to the same degree.”

Working with UW-Madison climatologist Zhengyu Liu, collaborators at the National Center for Atmospheric Research and others, Carlson found their computer climate model breaking down on the Younger Dryas.

While it could reliably recreate temperatures in the Oldest Dryas — a similar cooling period about 18,000 years ago — they just couldn’t find a lever in the model that would simulate a Younger Dryas that matched the Greenland ice cores.

“You can totally turn off ocean circulation, have Arctic sea ice advance all the way across the North Atlantic, and you still will have a warmer climate during the Younger Dryas than the Oldest Dryas because of the carbon dioxide,” Carlson say.

By the time the Younger Dryas rolled around, there was more carbon dioxide in the air — about 50 parts per million more. The warming effects of that much CO2 overwhelmed the rest of the conditions that make the Oldest and Younger Dryas so alike, and demonstrates a heightened sensitivity for Arctic temperatures to rising greenhouse gases in the atmosphere.

The researchers zeroed in on the Northern Hemisphere’s temperature outlier, Greenland ice cores, and found that the conversion of oxygen isotope ratio to temperature typically used on the ice cores did not account for the sort of crash climate change occurring during the Younger Dryas. It assumes prevailing winds and jet streams and storm tracks are providing the moisture for Greenland precipitation from the Atlantic Ocean.

“The Laurentide ice sheet, which covered much of North America down into the northern United States, is getting smaller as the Younger Dryas approaches,” Carlson says. “That’s like taking out a mountain of ice three kilometers high. As that melts, it allows more Pacific Ocean moisture to cross the continent and hit the Greenland ice sheet.”

The two oceans have distinctly different ratios of oxygen isotopes, allowing for a different isotope ratio where the water falls as snow.

“We ran an oxygen isotope-enabled atmosphere model, so we could simulate what these ice cores are actually recording, and it can match the actual oxygen isotopes in the ice core even though the temperature doesn’t cool as much,” Carlson says. “That, to us, means the source of precipitation has changed in Greenland across the last deglatiation. And therefore that the strict interpretation of this iconic record as purely temperature of snowfall above this ice sheet is wrong.”

By the study’s findings, Greenland temperatures may not have cooled as significantly as climate headed into the Younger Dryas relative to the Oldest Dryas, because of the rise in atmospheric carbon dioxide that had occurred since the Oldest Dryas.

“You can say at the end of the Younger Dryas it warmed 10, plus or minus five, degrees Celsius. But what happened on this pathway into the event, you can’t see,” Carlson says.

It’s a fresh reminder from an ancient ice core that climate science is full of nuance, according to Carlson.

“Abrupt climate changes have happened, but they come with complex shifts in the way climate inputs like moisture moved around,” he says. “You can’t take one difference and interpret it solely as changes in temperature, and that’s what we’re seeing here in the Greenland ice cores.”

Study finds new evidence supporting theory of extraterrestrial impact

This is James Kennett. -  UCSB
This is James Kennett. – UCSB

An 18-member international team of researchers that includes James Kennett, professor of earth science at UC Santa Barbara, has discovered melt-glass material in a thin layer of sedimentary rock in Pennsylvania, South Carolina, and Syria. According to the researchers, the material — which dates back nearly 13,000 years — was formed at temperatures of 1,700 to 2,200 degrees Celsius (3,100 to 3,600 degrees Fahrenheit), and is the result of a cosmic body impacting Earth.

These new data are the latest to strongly support the controversial Younger Dryas Boundary (YDB) hypothesis, which proposes that a cosmic impact occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas. This episode occurred at or close to the time of major extinction of the North American megafauna, including mammoths and giant ground sloths; and the disappearance of the prehistoric and widely distributed Clovis culture. The researchers’ findings appear today in the Proceedings of the National Academy of Sciences.

“These scientists have identified three contemporaneous levels more than 12,000 years ago, on two continents yielding siliceous scoria-like objects (SLO’s),” said H. Richard Lane, program director of National Science Foundation’s Division of Earth Sciences, which funded the research. “SLO’s are indicative of high-energy cosmic airbursts/impacts, bolstering the contention that these events induced the beginning of the Younger Dryas. That time was a major departure in biotic, human and climate history.”

Morphological and geochemical evidence of the melt-glass confirms that the material is not cosmic, volcanic, or of human-made origin. “The very high temperature melt-glass appears identical to that produced in known cosmic impact events such as Meteor Crater in Arizona, and the Australasian tektite field,” said Kennett.

“The melt material also matches melt-glass produced by the Trinity nuclear airburst of 1945 in Socorro, New Mexico,” he continued. “The extreme temperatures required are equal to those of an atomic bomb blast, high enough to make sand melt and boil.”

The material evidence supporting the YDB cosmic impact hypothesis spans three continents, and covers nearly one-third of the planet, from California to Western Europe, and into the Middle East. The discovery extends the range of evidence into Germany and Syria, the easternmost site yet identified in the northern hemisphere. The researchers have yet to identify a limit to the debris field of the impact.

“Because these three sites in North America and the Middle East are separated by 1,000 to 10,000 kilometers, there were most likely three or more major impact/airburst epicenters for the YDB impact event, likely caused by a swarm of cosmic objects that were fragments of either a meteorite or comet,” said Kennett.

The PNAS paper also presents examples of recent independent research that supports the YDB cosmic impact hypothesis, and supports two independent groups that found melt-glass in the YDB layers in Arizona and Venezuela. “The results strongly refute the assertion of some critics that ‘no one can replicate’ the YDB evidence, or that the materials simply fell from space non-catastrophically,” Kennett noted.

He added that the archaeological site in Syria where the melt-glass material was found — Abu Hureyra, in the Euphrates Valley — is one of the few sites of its kind that record the transition from nomadic hunter-gatherers to farmer-hunters who live in permanent villages. “Archeologists and anthropologists consider this area the ‘birthplace of agriculture,’ which occurred close to 12,900 years ago,” Kennett said.

“The presence of a thick charcoal layer in the ancient village in Syria indicates a major fire associated with the melt-glass and impact spherules 12,900 years ago,” he continued. “Evidence suggests that the effects on that settlement and its inhabitants would have been severe.”

Impact hypothesis loses its sparkle

Tyrone Daulton is pictured with the transmission electron microscrope he used to search in vain for shock-synthesized nanodiamonds, evidence that a extraterrestrial object such as a meteorite killed off North American megafauna. -  Tyrone Daulton
Tyrone Daulton is pictured with the transmission electron microscrope he used to search in vain for shock-synthesized nanodiamonds, evidence that a extraterrestrial object such as a meteorite killed off North American megafauna. – Tyrone Daulton

About 12,900 years ago, a sudden cold snap interrupted the gradual warming that had followed the last Ice Age. The cold lasted for the 1,300-year interval known as the Younger Dryas (YD) before the climate began to warm again.

In North America, large animals known as megafauna, such as mammoths, mastodons, saber-tooth tigers and giant short-faced bears, became extinct. The Paleo-Indian culture known as the Clovis culture for distinctively shaped fluted stone spear points abruptly vanished, eventually replaced by more localized regional cultures.

What had happened?

One theory is that either a comet airburst or a meteor impact somewhere in North America set off massive environmental changes that killed animals and disrupted human communities.

In sedimentary deposits dating to the beginning of the YD, impact proponents have reported finding carbon spherules containing tiny nano-scale diamonds, which they thought to be created by shock metamorphism or chemical vapor deposition when the impactor struck.

The nanodiamonds included lonsdaleite, an unusal form of diamond that has a hexagonal lattice rather than the usual cubic crystal lattice. Lonsdaleite is particularly interesting because it has been found inside meteorites and at known impact sites.

In the August 30 issue of the Proceedings of the National Academy of Sciences, a team of scientists led by Tyrone Daulton, PhD, a research scientist in the physics department at Washington University in St. Louis, reported that they could find no diamonds in YD boundary layer material.

Daulton and his colleagues, including Nicholas Pinter, PhD, professor of geology at Southern Illinois University In Carbondale and Andrew C. Scott, PhD, professor of applied paleobotany of Royal Holloway University of London, show that the material reported as diamond is instead forms of carbon related to commonplace graphite, the material used for pencils.

“Of all the evidence reported for a YD impact event, the presence of hexagonal diamond in YD boundary sediments represented the strongest evidence suggesting shock processing,” Daulton, who is also a member of WUSTL’s Center for Materials Innovation, says.

However, a close examination of carbon spherules from the YD boundary using transmission electron microscopy by the Daulton team found no nanodiamonds. Instead, graphene- and graphene/graphane-oxide aggregates were found in all the specimens examined (including carbon spherules dated from before the YD to the present). Importantly, the researchers demonstrated that previous YD studies misidentified graphene/graphane-oxides as hexagonal diamond and likely misidentified graphene as cubic diamond.

The YD impact hypothesis was in trouble already before this latest finding. Many other lines of evidence – including: fullerenes, extraterrestrial forms of helium, purported spikes in radioactivity and iridium, and claims of unique spikes in magnetic meteorite particles – had already been discredited. According to Pinter, “nanodiamonds were the last man standing.”

“We should always have a skeptical attitude to new theories and test them thoroughly,” Scott says, “and if the evidence goes against them they should be abandoned.”

Ice sheet melt identified as trigger of Big Freeze

Mapped extent of the Cordillerian and Laurentide icesheets at around 14,750 years ago (after Dyke et al 2003)
Mapped extent of the Cordillerian and Laurentide icesheets at around 14,750 years ago (after Dyke et al 2003)

The main cause of a rapid global cooling period, known as the Big Freeze or Younger Dryas – which occurred nearly 13,000 years ago – has been identified thanks to the help of an academic at the University of Sheffield.

A new paper, which is published in Nature today (1 April 2010), has identified a mega-flood path across North America which channeled melt-water from a giant ice sheet into the oceans and triggering the Younger Dryas cold snap.

The research team, which included Dr Mark Bateman from the University of Sheffield’s Department of Geography, discovered that a mega-flood, caused by the melting of the Laurentide ice sheet, which covered much of North America, was routed up into Canada and into the Arctic Ocean.

This resulted in huge amounts of fresh water mixing with the salt water of the Arctic Ocean. As a result, more sea-ice was created which flowed into the North Atlantic, causing the northward continuation of the Gulf Stream to shut down.

Without the heat being brought across the Atlantic by the Gulf Stream, temperatures in Europe plunged from similar to what they are today, back to glacial temperatures with average winter temperatures of -25oC. This cooling event has become known as the Younger Dryas period with cold conditions lasting about 1400 years. The cold of the Younger Dryas affected many places across the continent, including Yorkshire in the Vale of York and North Lincolnshire which became arctic deserts with sand dunes and no vegetation.

Before now, scientists have speculated that the mega-flood was the main cause of the abrupt cooling period, but the path of the flood waters has long been debated and no convincing evidence had been found establishing a route from the ice-sheet to the North Atlantic.

The research team studied a large number of cliff sections along the Mackenzie Delta and examined the sediments within them. They found that many of the cliff sections showed evidence of sediment erosion. This evidence spanned over a large region at many altitudes, which could only be explained by a mega-flood from the over-spilling of Lake Agassiz, which was at times bigger than the UK, at the front of the Laurentide Ice-sheet rather than a normal flood of the river.

Dr Bateman, who has been researching past environmental changes both in the UK and elsewhere in the world for almost 20 years, runs the luminescence dating lab at Sheffield. The lab was able to take the MacKenzie Delta sediment samples from above and below the mega-flood deposits, and find out when the mega-flood occurred, enabling its occurrence to be attributed to the start of the Younger Dryas.

The study will help shed light on the implications of fresh water input into the North Atlantic today. There are current concerns that changes in the salinity of the ocean today, could cause another shut down of the Gulf Stream. Current climate changes, including global warming, may be altering the planetary system which regulates evaporation and precipitation, and moves fresh water around the globe.

The findings, which show the cause, location, timing and magnitude of the mega-flood, will enable scientists to better understand how sensitive both oceans and climates are to fresh-water inputs and the potential climate changes which may ensue if the North Atlantic continues to alter.

Dr Mark Bateman, from the University of Sheffield’s Centre for International Drylands Research at the Department of Geography, said: “The findings of this paper through the combination of luminescence dating, landscape elevation models and sedimentary evidence allows an insight into what must have been one of the most catastrophic geological events in recent earth’s history. They also show how events within the Earth-climate system in North America had huge impacts in Europe.”

Absence of evidence for a meteorite impact event 13,000 years ago

The woolly mammoth was one of the large mammals that became extinct in North America at the onset of the Younger Dryas approx. 13,000 years ago. -  Image of Woolly Mammoth at the Royal BC Museum, Victoria, British Columbia courtesy Wikipedia Commons
The woolly mammoth was one of the large mammals that became extinct in North America at the onset of the Younger Dryas approx. 13,000 years ago. – Image of Woolly Mammoth at the Royal BC Museum, Victoria, British Columbia courtesy Wikipedia Commons

An international team of scientists led by researchers at the University of Hawaii at Manoa have found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas ~13000 years ago.

The Younger Dryas is an abrupt cooling event in Earth’s history. It coincided with the extinction of many large mammals including the woolly mammoth, the saber toothed jaguar and many sloths. This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America. This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorise that an impact event was instead the instigator of this climate shift. A team led by Fran├žois Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this theory, to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas. Their results will be published in the December 7th early online edition of the prestigious journal the Proceedings of the National Academy of Sciences.

The idea that an impact event may have been the instigator for this cooling period was appealing because of several alleged impact markers, especially the high iridium concentrations that the previous team reported. However, it is difficult for proponents of this theory to explain why no impact crater of this age is known. “There is a black mat layer across North America which is correlated to the Younger Dryas climatic shift seen in Greenland ice cores dated at 13 thousand years ago by radio carbon,” explains Paquay. “Initially I thought this type of layer could be associated with an impact event because concentration in the proxies of widespread wildfires are sky high. That plus very high levels of iridium (which is one indicator used to indicate extraterrestrial impact events). So the theory was conceptually appealing, but because of the missing impact site, the idea of one or multiple airburst arose.”

To corroborate the theory, Paquay and his colleagues decided to take a three-pronged approach. The first was to replicate the original researchers data, the second step was to look for other tracers, specifically osmium isotopes, of extraterrestrial matter in those rocks, and the third step was to look for these concentrations in other settings. “Because there are so many aspects to the impact theory, we decided to just focus on geochemical evidence that was associated with it, like the concentration of iridium and other platinum group elements, and the osmium isotopes,” says Paquay. “We also decided to look in very high resolution sediment cores across North America, and yet we could find nothing in our data to support their theory.”

The team includes American, Belgian and Canadian researchers. Analysis of the sediments was done both at UHM and in Belgium, using the same sediments from the same interval and indepedently did the analysis work and got similar results. Both the marine and terrestrial sediment records do not indicate that an impact event was the trigger for the transition into the Younger Dryas cold period. “The marine and terrestrial record both complement each other to support this finding,” concludes Paquay. “That’s what makes the beauty of this study.”

Charcoal evidence tracks climate changes in Younger Dryas

A new study reports that charcoal particles left by wildfires in sediments of 35 North American lake beds don’t readily support the theory that comets exploding over the continent 12,900 years ago sparked a cooling period known as the Younger Dryas.

The study — appearing online this week ahead of regular publication in the Proceedings of the National Academy of Sciences — however, did find clear links between abrupt climate changes and fire activity during the transition between the last Ice Age and the warm interglacial period that began 11,700 years ago. These links are also consistent with the impacts of climate-change conditions on wildfires during recent decades in North America, the researchers noted.

Charcoal particles, along with tree pollen, provide snapshots of types of vegetation and frequencies of wildfire activity in a given area, said study co-author Patrick J. Bartlein, a professor of geography at the University of Oregon. His doctoral student Jennifer R. Marlon led the collaborative study of 23 co-authors (including seven current or former UO students) at institutions in the U.S., Canada and Europe.

“The charcoal data don’t support the idea of widespread fires at the beginning of the Younger Dryas interval,” Bartlein said. “The results don’t reject the comet hypothesis, but do suggest that one element of it — widespread fires — didn’t occur. Instead, the data show that biomass burning tracked general climate changes closely. Biomass burning increased as conditions warmed during deglaciation until the beginning of the Younger Dryas cold interval at 12,900 years ago, leveled off during the cool interval, and then increased again as warming resumed after the end of the cold interval, about 11,700 years ago.”

The fires that left the charcoal records reflect the impact of climate changes independent of potential contributions of early Paleoindians who may have been living on the continent. Proponents of the comet theory suggest Clovis culture may have been dramatically disrupted across the continent.

Marlon began the National Science Foundation-sponsored study of charcoal-pollen records soon after the comet theory was proposed in PNAS by an international team of 26 researchers led by Richard B. Firestone. A co-author of that study, UO archaeologist Douglas Kennett, in the Jan. 2 issue of Science, documented the existence of possible comet-triggered nanodiamond-rich soil at six North American sites dating to 12,900 years ago in apparent support of the hypothesis. The formation of nanodiamonds requires intense pressure and heat, much higher than those of biomass wildfires but possible in comet explosions.

“We had the data to look for widespread fires if they had occurred,” Marlon said, “but what we saw instead was a general increase in biomass burning whenever the climate warmed.”

The lakes containing the charcoal are in Alaska (3 sites), British Columbia (7), U.S. Pacific Northwest (6), the Sierra Nevada (3), northern U.S. Rocky Mountains (6), Southwest (4), Midwest (2), Northeast (3 sites in Quebec), and Southeast (1). Thirty of the samples came from the Global Charcoal Database; another five were drawn from more recent research by co-authors currently studying sediments from the Younger Dryas.

The new study’s conclusion that climate is a major control of wildfires matched that of a study published last year in Nature Geosciences by the same researchers on global biomass burning over the last 2,000 years. “Together,” Bartlein said, “these studies suggest that episodes of global warming are accompanied by increases in wildfires.”