Next Ice Age delayed by rising CO2 levels


Future ice ages may be delayed by up to half a million years by our burning of fossil fuels. That is the implication of recent work by Dr Toby Tyrrell of the University of Southampton’s School of Ocean and Earth Science at the National Oceanography Centre, Southampton.



According to New Scientist magazine, which features Dr Tyrrell’s research this week, this work demonstrates the most far-reaching disruption of long-term planetary processes yet suggested for human activity.



Dr Tyrrell’s team used a mathematical model to study what would happen to marine chemistry in a world with ever-increasing supplies of the greenhouse gas, carbon dioxide.



The world’s oceans are absorbing CO2 from the atmosphere but in doing so they are becoming more acidic. This in turn is dissolving the calcium carbonate in the shells produced by surface-dwelling marine organisms, adding even more carbon to the oceans. The outcome is elevated carbon dioxide for far longer than previously assumed.



Computer modelling in 2004 by a then oceanography undergraduate student at the University, Stephanie Castle, first interested Dr Tyrrell and colleague Professor John Shepherd in the problem. They subsequently developed a theoretical analysis to validate the plausibility of the phenomenon.


The work, which is part-funded by the Natural Environment Research Council, confirms earlier ideas of David Archer of the University of Chicago, who first estimated the impact rising CO2 levels would have on the timing of the next ice age.



Dr Tyrrell said: ‘Our research shows why atmospheric CO2 will not return to pre-industrial levels after we stop burning fossil fuels. It shows that it if we use up all known fossil fuels it doesn’t matter at what rate we burn them. The result would be the same if we burned them at present rates or at more moderate rates; we would still get the same eventual ice-age-prevention result.’



Ice ages occur around every 100,000 years as the pattern of Earth’s orbit alters over time. Changes in the way the sun strikes the Earth allows for the growth of ice caps, plunging the Earth into an ice age. But it is not only variations in received sunlight that determine the descent into an ice age; levels of atmospheric CO2 are also important.



Humanity has to date burnt about 300 Gt C of fossil fuels. This work suggests that even if only 1000 Gt C (gigatonnes of carbon) are eventually burnt (out of total reserves of about 4000 Gt C) then it is likely that the next ice age will be skipped. Burning all recoverable fossil fuels could lead to avoidance of the next five ice ages.



Dr Tyrrell is a Reader in the University of Southampton’s School of Ocean and Earth Science. This research was first published in Tellus B, vol 59 p664.

Physicists aim to predict volcano eruption





Erupting Volcano
Erupting Volcano

University of St Andrews scientists have been awarded a three year grant to create an on-site life-saving device to help predict volcano eruption.



The work is funded by nearly £400K from the Natural Environment Research Council (NERC), bringing the team’s recent research funding to just over £1 million, following a £700K sub-contract from ERA Technology Limited for new work on military security.



The unmanned monitoring instrument, to be trialled at Montserrat in the West Indies, will be developed by the Millimetre Wave and High-Field ESR Group in the School of Physics and Astronomy.



The new volcano radar project builds on the success of the Group’s previous NERC funded project which developed the unique portable volcano mapping instrument ‘AVTIS’ (All-weather Volcano Topography Imaging Sensor). AVTIS uses millimetre waves to see through the smoke, gas and cloud that frequently cover volcanoes for months at a time to measure the size, shape and temperature of a growing volcanic lava dome. The Scots team will continue to work with a team of volcanologists from the Universities of Reading and Lancaster and the Montserrat Volcano Observatory (MVO) on the new AVTIS project, with the aim of helping MVO provide round the clock coverage of volcanic activity.


Dr David Macfarlane, lead scientist on the project explained, “AVTIS was the first millimetre wave instrument to ever be used on a volcano, proving the concept that a small battery powered radar could be used to map the lava dome from distances of up to six kilometres. We worked on the only active UK volcano, the lava dome at the Soufrière Hills in Montserrat. This type of volcano can change pretty quickly and the local observatory needs to know what is happening up on the mountain on a daily, if not hourly, basis. AVTIS measured the 3D shape of the lava dome, showing 60 metres growth over a ten day interval as well as gathering thermal images of the dome through thick cloud. It is the all-weather capability that sets this technology apart, allowing us to monitor the volcano from a safe distance all of the time”.



He added, “The first instrument had to be manned, using a laptop computer to control the scanning, and could only operate for about eight hours before the batteries ran out. This new funding will allow us to build an unmanned version that lives on the volcano crater rim with its own power supply, beaming the radar images and data back to the observatory every few minutes using WiFi technology. With constant coverage of the evolving lava dome we aim to capture the all of the significant activity leading up to an eruption and eventually we hope to be able to help predict where and when the volcano might explode. In Montserrat, where we’ll trial the instrument, people are continuing to be evacuated from their homes as the volcano continues to grow and becomes ever more dangerous so there is a real need for this technology”.



Dr Duncan Robertson, also of the Millimetre Wave and High-Field ESR Group said, “We’re absolutely delighted to have won this funding which will allow us to expand significantly our activities in electromagnetics research. The awards reflect our continuing capability to deliver state-of-the-art instruments for tackling novel measurement problems”.



Dr Graham Smith, group leader added, “Much of this has been made possible by leveraging expertise and technology developed during our other successful research projects, in particular the £2.6m HIPER Basic Technology project, building a next-generation, ultrafast, millimetre wave spectrometer used for probing electron structure, particularly in chemical and biological samples”.

Volcanic Activity Key to Oxygen-rich Atmosphere





An artist's cross-section of an underwater volcano and the processes that drive them. Submarine volcanoes can sometimes form islands. - Image Credit: Zina Deretsky, National Science Foundation
An artist’s cross-section of an underwater volcano and the processes that drive them. Submarine volcanoes can sometimes form islands. – Image Credit: Zina Deretsky, National Science Foundation

Next time you catch a breath, be thankful, for a change, that the Earth’s surface is dotted with volcanoes.



National Science Foundation-funded research published this week in the journal Nature indicates that billions of years ago, when the Earth was home largely to undersea volcanoes, some previously unknown agent was removing the gas.



The researchers suggest that mixture of gases and lavas produced by submarine volcanoes scrubbed oxygen from the atmosphere and bound it into oxygen-containing minerals.



Lee R. Kump, a professor of geosciences at Penn State University, working with a colleague at the University of Western Australia, looked at the geologic record from the Archaean–a geologic period from 3.8 to 2.5 billion years before the present day–and the Palaeoproterozoic– geologic era immediately following that featured profound global change that included the breakup and formation of two supercontinents. They found that in the Archean there was a dearth of terrestrial volcanoes, while in the Palaeoproterozoic, although submarine volcanoes continued to be common, the population of terrestrial volcanoes increased dramatically.


“The rise of oxygen allowed for the evolution of complex oxygen-breathing life forms,” Kump said.



Terrestrial volcanoes could become much more common because land masses stabilized and the current system of tectonics regime took shape.



Because submarine volcanoes erupt at lower temperatures than terrestrial volcanoes, they are more efficient at converting–or “reducing”–oxygen. As long as the reducing ability of the submarine volcanoes was larger than the amounts of oxygen created, the atmosphere had no oxygen. When terrestrial volcanoes began to dominate, oxygen levels increased.



The change over time caused an atmospheric shift from oxygen-free to oxygen-rich, the researchers argue, with profound implications for life on the planet.

The wandering of the magnetic north pole


Fairbanks adventurer Roger Siglin has journeyed close to the magnetic north pole. Near Resolute, in the northern area of Canada now known as Nunavut, Siglin was 300 miles from the magnetic north pole, the wandering spot on Earth’s surface that attracts compass needles and confounds scientists.



There, his compass needle dipped like a divining rod over water. “I had to tilt the compass quite a bit to keep the needle from hitting the face,” said Siglin, whose snowmachine odysseys have taken him thousands of miles in the high Arctic.



The magnetic north pole is now somewhere centered on the Arctic Ocean north of Canada, approximately latitude 82 degrees north and longitude 114 degrees west. It won’t be there long. The magnetic pole migrates about 10 kilometers northwest each year. Scientists at the U.S. Geological Survey say the magnetic north pole has strayed around the north for thousands of years, at one point dropping to the latitude of Anchorage.



Within Earth is a core that resembles a ball of molten iron and nickel slightly smaller than the moon. When the core rotates, the sloshing of molten iron and nickel produces an electric current, and with it a magnetic force. Ground zero for this force is the elusive spot known as the magnetic north pole.


In 1600, Sir William Gilbert, a doctor for Queen Elizabeth I, was the first to suggest Earth behaved like a giant magnet. In 1829, Sir John Ross commanded an expedition to find the North West Passage from the Atlantic to the Pacific. He didn’t make it. Ice trapped his ship in Canada’s Arctic for four years. Before the ships were able to retreat to England, Ross’s nephew, James Ross, discovered the magnetic north pole.



When Norwegian Roald Amundsen found the same point during the first successful trip through the Northwest Passage 70 years later, magnetic north was 30 miles north of where Ross found it. Amundsen’s journey proved that the magnetic north pole moves. Scientists still aren’t sure why it moves, or even why the Earth is similar to a giant bar magnet.



The magnetic north pole isn’t the same as the geographic north pole, the center of Earth’s axis. The discrepancy makes topographic maps a bit more confusing, requiring compass users to adjust for declination, the difference between geographic (true) north and magnetic north. Because the magnetic north pole is always changing, USGS updates its maps every five years. Most handheld GPS units adjust themselves automatically for declination, which varies wildly with location. In Fairbanks, for example, magnetic north is about 21 degrees east of true north. New York City is about 13 degrees west. On the island of Attu in the Aleutians, quirks in Earth’s magnetic field make adjusting a compass for declination unnecessary-true north there is the same as magnetic north.



The magnetic north pole’s constant movement assures the truthfulness of what James Ross wrote upon first discovering its location 173 years ago: “Nature had erected no monument to denote the spot which she had chosen as the center of one of her great and dark powers.”

Strong Evidence Points to Earth’s Proximity to Sun as Ice Age Trigger





The Dome Fuji deep ice core, Antarctica, with drill. This ice was retrieved from a depth of 1,332 meters (4,370 feet), which was deposited about 89,000 years ago. - Photo: Dr. Hideaki Motoyama, National Institute of Polar Research, Japan
The Dome Fuji deep ice core, Antarctica, with drill. This ice was retrieved from a depth of 1,332 meters (4,370 feet), which was deposited about 89,000 years ago. – Photo: Dr. Hideaki Motoyama, National Institute of Polar Research, Japan

When do ice ages begin? In June, of course.



Analysis of Antarctic ice cores led by Kenji Kawamura, a visiting scientist at Scripps Institution of Oceanography, UC San Diego, shows that the last four great ice age cycles began when Earth’s distance from the sun during its annual orbit became great enough to prevent summertime melts of glacial ice. The absence of those melts allowed buildups of the ice over periods of time that would become characterized as glacial periods.



Results of the study appear in the Aug. 23 edition of the journal Nature.



Jeff Severinghaus, a Scripps geoscientist and co-author of the paper, said the finding validates a theory formalized in the 1940s but first postulated in the 19th Century. The work also helps clarify the role of carbon dioxide in global warming and cooling episodes past and present, he said.



“This is a significant finding because people have been asking for 100 years the question of why are there ice ages,” Severinghaus said.



A premise advanced in the 1940s known as the Milankovitch theory, named after the Serbian geophysicist Milutin Milankovitch, proposed that ice ages start and end in connection with changes in summer insolation, or exposure to sunlight, in the high latitudes of the Northern Hemisphere. To test it, Kawamura used ice core samples taken thousands of miles to the south in Antarctica at a station known as Dome Fuji.


Scientists studying paleoclimate often use gases trapped in ice cores to reconstruct climatic conditions from hundreds of thousands of years in the past, digging thousands of meters deep into ice sheets. By measuring the ratio of oxygen and nitrogen in the cores, Kawamura’s team was able to show that the ice cores record how much sunlight fell on Antarctica in summers going back 360,000 years. The team’s method enabled the researchers to use precise astronomical calculations to compare the timing of climate change with sunshine intensity at any spot on the planet.



Kawamura, a former postdoctoral researcher at Scripps, used the oxygen-nitrogen ratio data to create a climate timeline that was used to validate the calculations Milankovitch had created decades earlier. The team found a correlation between ice age onsets and terminations, and variations in the season of Earth’s closest approach to the sun. Earth’s closest pass, or perihelion, happens to fall in June about every 23,000 years. When the shape of Earth’s orbit did not allow it to approach as closely to the sun in that month, the relatively cold summer on Earth encouraged the spread of ice sheets on the Northern Hemisphere’s land surface. Periods in which Earth passed relatively close in Northern Hemisphere summer accelerated melt and brought an end to ice ages.



“When we start to come to the point of closest approach in June, that’s when the big ice melts off,” said Severinghaus.



Kawamura said the new timeline will serve as a guide that will allow researchers to test climate forecast models of the effects of carbon dioxide levels in the atmosphere. The team found that the changes in Earth’s orbit that terminate ice ages amplify their own effect on climate through a series of steps that leads to more carbon dioxide being released from the oceans into the air. This secondary effect, or feedback, has accounted for as much as 30 percent of the warming seen as ice ages of the past have come to an end.



“An important point is that climate models should be validated with the past climate so that we can better predict what will happen in the future with rising CO2 levels,” said Kawamura. “For that, my new timescale can distinguish the contribution to past climate change from insolation change and CO2.”



In addition to Kawamura and Severinghaus, authors of the report included Takakiyo Nakazawa, Shuji Aoki, Koji Matsumoto, and Hisakazu Nakata of Tohoku University, Sendai, Japan; Frederic Parrenin of Laboratoire de Glaciologie et Geophysique de l’Environment in Grenoble, France; Lorraine Lisiecki and Maureen Raymo of Boston University; Ryu Uemura, Hideaki Motoyama, Shuji Fujita, Kumiko Goto-Azuma, Yoshiyuki Fujii, and Okitsugu Watanabe of the National Institute of Polar Research in Tokyo, Japan; Manuel Hutterli of the British Antarctic Survey in Cambridge, England; and Francoise Vimeux and Jean Jouzel of Laboratoire des Sciences du Climat et de l’Environment in Gif-sur-Yvette, France.



The research was supported by a Grant-in-Aid for Creative Scientific Research and a Grant-in-Aid for Young Scientists from the Ministry of Education, Science, Sports and Culture in Japan, the Gary Comer Science and Education Foundation and the National Science Foundation.

New Breakthroughs in Geological Dating Imminent


A breakthrough in geological dating can be expected within the next few years, combining existing methods to yield higher accuracy over longer time scales closer to the earth’s origin. This will bring great benefits not just for earth sciences, but also for other fields that rely on accurate dating over geological time. The developments ushering in a new generation of dating methods were discussed at a recent workshop on geochronological timing organised by the European Science Foundation (ESF).



The earth sciences rely on highly accurate timing to unravel past causes and effects, and understand the forces driving many events from ice ages to mass extinctions. Other scientific disciplines, such as evolutionary biology and climate science, in turn depend on accurate timing of geological processes to provide a baseline for their investigations. While significant progress has been made over recent decades, great uncertainties remain that are inhibiting investigations of major past events and formative processes in the earth sciences. In the case of the dinosaur extinction, knowledge of how long the process took would help resolve whether this was caused by a sudden asteroid strike or more gradually following a period of intense volcanic activity for example.



There was intense interest therefore in the ESF workshop, which came six years after the launch of an international project in the same field, called EARTHTIME. The workshop was organised to recognise and boost Europe’s leading position in geochronology. It identified the need to improve the three main dating methods currently used, and cross-calibrate between them where possible to yield even greater accuracy, according to Klaudia Kuiper, scientific convenor of the ESF workshop. “The main outcome is that we first aim to work on the improvement of the numerical tools to calibrate the Geological Time Scale,” said Kuiper.



Although these methods currently achieve high-sounding accuracies in the order of 0.5 percent to 1 percent, this can equate to an error of several million years over geological time scales. The objective is to reduce the error to better than 0.1 percent, in other words below an error of 100,000 years over a 100 million year time scale.


The three main tools currently used for dating geological events are argon-argon dating, uranium/lead dating, and astronomical methods. Argon-argon dating measures the level of decay from an isotope of potassium to argon, which occurs predictably over time, also taking account of the proportions of the two different isotopes of argon that form during the process.



Uranium/lead dating, one of the oldest and most refined methods, also exploits radioactive decay. However in this case the measurement is based on a correlation between the decay of two isotopes of uranium occurring at different rates, boosting the accuracy as result.



Astronomical timing is quite different, exploiting long term cyclical changes in the earth’s orbit and axis. These cause climate changes that can be measured in sediment deposits, providing a dating method that can be correlated with geological events.



The methods each have pros and cons. Astronomical dating is highly accurate, but only over relatively short times on a geological scale, up to at most 250 million years, which is just 5 percent of the earth’s age. Radiometric dating can span the earth’s whole history back to 4.5 billion years ago, but with less accuracy, and some uncertainties. Currently the astronomical timing is used for events in the last 23 million years, then argon-argon back to 100 million years, and uranium/lead for older events.



Further progress can be made by combining these methods, with astronomical dating already being used to calibrate radiometric timing over the last 10 million years where the former is highly accurate. According to Kuipers, such progress will usher in a new generation of Geological Time Scale (GTS) measurements that will in turn yield fresh insights into critical events during the earth’s history. Kuipers believed these could be just as exciting as some of the insights enabled by the previous generation of dating technologies, such as timing of the great ice ages of the Pleistocene between about 2 million and 11,000 years ago. The hope is that the new generation of timing methods will enable older events to be dated accurately.

Research challenges theory on New Zealand prehistory


A combination of geological and biological findings are lending weight to the possibility that the Chatham Islands were under water until three million years ago, and that New Zealand’s flora and fauna may have evolved in another large island near New Zealand.



Traditional thinking is that the islands of New Zealand split from the ancient super-continent Gondwanaland about 85 million years ago, and stayed above the oceans since then. This is challenged by the findings of the multidisciplinary project that has been researching the Chathams, named the Chatham Islands Emergent Ark Survey. The team of biologists and geologists includes Dr Steve Trewick, Senior Lecturer at the Allan Wilson Centre for Molecular Ecology and Evolution. Dr Trewick was part of a team who visited the islands in 2004.



Findings include identification of remnants of deepwater limestone from about three million years ago, overlaid by beach deposits of sand, indicating that the Chathams may be much younger than previously thought. A further significant discovery was the previously unmapped formation in the southwest corner of the Chathams, volcanic rocks of a type that erupted and accumulated on the seashore. By using fossils from within the rocks and radiometric ageing, researchers found the formation was deposited between 2.5 million and 4.5 million years ago. The rocks were originally on the seabed, but now form the highest point on the Chathams, indicating that the entire land area was under the sea until uplift about two million years ago raised it to above the water level.


Biological findings now coming to hand are compatible with the geological findings, indicating that Chatham Islands birds and plants have been separated from their New Zealand relatives for up to three million years.



The final report on the Marsden-funded project is due next year. Participants include staff from Otago, Lincoln and Massey universities and GNS Science.

For earthquakes ‘speed kills’


High-speed ruptures travelling along straight fault lines could explain why some earthquakes are more destructive than others, according to an Oxford University scientist. In this week’s Science, Professor Shamita Das suggests that ruptures in the Earth’s surface moving at 6km per second could make future earthquakes along California’s San Andreas fault much more destructive than current models predict.



Professor Das compared data from the 1906 California earthquake with data from a similar earthquake that occurred in 2001 in Kunlunshan, Tibet. The comparison suggests that, in both, the long straight portions of the fault enabled ruptures to travel twice as fast as the original ‘shear’ wave travelling through the rock. Such ‘super-shear’ waves were once thought to be impossible but could now explain why similar magnitudes of earthquake can cause much greater devastation in some areas than others.



“Long straight faults are more likely to reach high rupture speeds,” said Professor Das of the Department of Earth Sciences. “The fault starts from rest, then accelerates to the maximum permissible speed and continues at this speed until it reaches an obstacle such as a large ‘bend’. If the next earthquake in southern California follows the same pattern as the ones in California in 1857 and 1906, and in Tibet in 2001, a super-shear rupture travelling southward would strongly focus shock waves on Santa Barbara and Los Angeles.”


The 2001 Kunlunshan earthquake is of particular interest to scientists because it was so well preserved owing to its remote location and dry desert environment. Studies of the earthquake revealed telltale off-fault open cracks only at the portions where it was found to have a very high rupture speed. “These cracks confirm that the earthquake reached super-shear speeds on the long, straight section of the fault. This is the first earthquake where such direct evidence is available and it is exactly the kind of evidence that we do not have for the similar earthquake in California 1906, due to the heavy rains and rapid rebuilding that occurred there immediately afterwards.”



Professor Das believes that future research into rupture speeds could take scientists one step closer to predicting the potential impact of earthquakes in particular regions. She commented: “It appears that the 1857 and 1906 California earthquakes may have propagated faster than was previously thought. If this is the case then we need to apply the same analysis to other similar faults around the world. By developing a measure of the ‘straightness’ of faults and finding and recording evidence such as off-fault open cracks we hope to better understand these potentially devastating phenomena.” The full article, entitled ‘The Need to Study Speed’, is published in Science on 17 August 2007.

Tectonic Plates Like Variable Thermostat





View of the San Andreas Fault on the Carrizo Plain in central California
View of the San Andreas Fault on the Carrizo Plain in central California

Like a quilt that loses heat between squares, the earth’s system of tectonic plates lets warmth out at every stitch.



But a new study in PNAS Early Edition finds the current blanket much improved over the leaky patchwork of 60 million years ago.



The study, appearing online the week of Aug. 13-17, shows that heat flowed out of Earth’s mantle at a high rate 60 million years ago, when small tectonic plates made up the Pacific basin.



The reason, the authors said, is that much of the heat from the mantle escapes near the ridges between newly formed plates. Those areas are thinner and allow more heat to pass.



The smaller the plates, the greater the heat loss from the mantle on which they float, said geophysicists from the University of Southern California, Johns Hopkins University and the University of Michigan at Ann Arbor.



Several small plates have more area close to the ridge — and allow more heat to pass — than one large plate, explained lead author Thorsten Becker, assistant professor of earth sciences at USC.



“When you go back 60 million years there were a bunch more smaller plates in the Pacific basin,” Becker said.



Using seafloor age reconstructions published last year, Becker and his co-authors found that heat flow out of the mantle in the last 60 million years was greater than previously estimated.


They also found that heat flow is relatively low now that the Pacific basin consists mainly of one large plate.



Becker added that variations in heat flow would not necessarily affect surface temperature, which depends on many factors, including solar activity and greenhouse gases in the atmosphere.



However, Becker said, a leaky tectonic quilt on average would lead to greater volcanic activity, earthquakes and plate movement. This would affect almost every aspect of Earth’s geography, from sea level to erosion to climate.



“There’s sort of a chain of things that follows from a good mechanical understanding of how plate tectonics works,” he said.



Like previous estimates of heat flow, the new study raises a nagging question. If heat loss for the past few billion years was comparable to Becker’s estimate, the mantle would have had to be impossibly hot at the beginning of Earth’s history.



Becker’s study, which implies an even greater rate of heat loss, shows that previous models designed to avert a “thermal catastrophe” do not work.



“A different solution to the thermal catastrophe needs to be found,” he said.



Becker’s co-authors were Frank Corsetti, USC associate professor of earth sciences, USC graduate student Sean Lloyd, Clint Conrad of Johns Hopkins University and Carolina Lithgow-Bertelloni of the University of Michigan at Ann Arbor.

Comet May Have Exploded Over North America 13,000 Years Ago





A 'black mat' of algal growth in Arizona marks a line of extinction at 12,900 years ago; Clovis points and mammoth skeletons were found at the line but not above it. - Photo Credit: Allen West, UCSB
A ‘black mat’ of algal growth in Arizona marks a line of extinction at 12,900 years ago; Clovis points and mammoth skeletons were found at the line but not above it. – Photo Credit: Allen West, UCSB

New scientific findings suggest that a large comet may have exploded over North America 12,900 years ago, explaining riddles that scientists have wrestled with for decades, including an abrupt cooling of much of the planet and the extinction of large mammals.



The discovery was made by scientists from the University of California at Santa Barbara and their colleagues. James Kennett, a paleoceanographer at the university, said that the discovery may explain some of the highly debated geologic controversies of recent decades.



The period in question is called the Younger Dryas, an interval of abrupt cooling that lasted for about 1,000 years and occurred at the beginning of an inter-glacial warm period. Evidence for the temperature change is recorded in marine sediments and ice cores.



According to the scientists, the comet before fragmentation must have been about four kilometers across, and either exploded in the atmosphere or had fragments hit the Laurentide ice sheet in the northeastern North America.



Wildfires across the continent would have resulted from the fiery impact, killing off vegetation that was the food supply of many of larger mammals like the woolly mammoths, causing them to go extinct.



Since the Clovis people of North America hunted the mammoths as a major source of their food, they too would have been affected by the impact. Their culture eventually died out.


The scientific team visited more than a dozen archaeological sites in North America, where they found high concentrations of iridium, an element that is rare on Earth, and is almost exclusively associated with extraterrestrial objects such as comets and meteorites.



They also found metallic microspherules in the comet fragments; these microspherules contained nano-diamonds. The comet also carried carbon molecules called fullerenes (buckyballs), with gases trapped inside that indicated an extraterrestrial origin.



The team concluded that the impact of the comet likely destabilized a large portion of the Laurentide ice sheet, causing a high volume of freshwater to flow into the north Atlantic and Arctic Oceans.



“This, in turn, would have caused a major disruption of the ocean’s circulation, leading to a cooler atmosphere and the glaciation of the Younger Dryas period,” said Kennett. “We found evidence of the impact as far west as the Santa Barbara Channel Islands.”



NSF’s Paleoclimate Program funded the research.