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.”

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.”

Earth’s iron core is surprisingly weak, Stanford researchers say

The massive ball of iron sitting at the center of Earth is not quite as “rock-solid” as has been thought, say two Stanford mineral physicists. By conducting experiments that simulate the immense pressures deep in the planet’s interior, the researchers determined that iron in Earth’s inner core is only about 40 percent as strong as previous studies estimated.

This is the first time scientists have been able to experimentally measure the effect of such intense pressure – as high as 3 million times the pressure Earth’s atmosphere exerts at sea level – in a laboratory. A paper presenting the results of their study is available online in Nature Geoscience.

“The strength of iron under these extreme pressures is startlingly weak,” said Arianna Gleason, a postdoctoral researcher in the department of Geological and Environmental Sciences, and lead author of the paper. Wendy Mao, an assistant professor in the department, is the co-author.

“This strength measurement can help us understand how the core deforms over long time scales, which influences how we think about Earth’s evolution and planetary evolution in general,” Gleason said.

Until now, almost all of what is known about Earth’s inner core came from studies tracking seismic waves as they travel from the surface of the planet through the interior. Those studies have shown that the travel time through the inner core isn’t the same in every direction, indicating that the inner core itself is not uniform. Over time and subjected to great pressure, the core has developed a sort of fabric as grains of iron elongate and align lengthwise in parallel formations.

The ease and speed with which iron grains in the inner core can deform and align would have influenced the evolution of the early Earth and development of the geomagnetic field. The field is generated by the circulation of liquid iron in the outer core around the solid inner core and shields Earth from the full intensity of solar radiation. Without the geomagnetic field, life – at least as we know it – would not be possible on Earth.

“The development of the inner core would certainly have some effect on the geomagnetic field, but just what effect and the magnitude of the effect, we can’t say,” said Mao. “That is very speculative.”

Gleason and Mao conducted their experiments using a diamond anvil cell – a device that can exert immense pressure on tiny samples clenched between two diamonds. They subjected minute amounts of pure iron to pressures between 200 and 300 gigapascals (equivalent to the pressure of 2 million to 3 million Earth atmospheres). Previous experimental studies were conducted in the range of only 10 gigapascals.

“We really pushed the limit here in terms of experimental conditions,” Gleason said. “Pioneering advancements in pressure-generation techniques and improvements in detector sensitivity, for example, used at large X-ray synchrotron facilities, such as Argonne National Lab, have allowed us to make these new measurements.”

In addition to intense pressures, the inner core also has extreme temperatures. The boundary between the inner and outer core has temperatures comparable to the surface of the sun. Simultaneously simulating both the pressure and temperature at the inner core isn’t yet possible in the laboratory, though Gleason and Mao are working on that for future studies. (For this study, Gleason mathematically extrapolated from their pressure data to factor in the effect of temperature.)

Gleason and Mao expect their findings will help other researchers set more realistic variables for conducting their own experiments.

“People modeling the inner core haven’t had many experimental constraints, because it’s so difficult to make measurements under those conditions,” Mao said. “There really weren’t constraints on how strong the core was, so this is really a fundamental new constraint.”

Earth’s iron core is surprisingly weak, Stanford researchers say

The massive ball of iron sitting at the center of Earth is not quite as “rock-solid” as has been thought, say two Stanford mineral physicists. By conducting experiments that simulate the immense pressures deep in the planet’s interior, the researchers determined that iron in Earth’s inner core is only about 40 percent as strong as previous studies estimated.

This is the first time scientists have been able to experimentally measure the effect of such intense pressure – as high as 3 million times the pressure Earth’s atmosphere exerts at sea level – in a laboratory. A paper presenting the results of their study is available online in Nature Geoscience.

“The strength of iron under these extreme pressures is startlingly weak,” said Arianna Gleason, a postdoctoral researcher in the department of Geological and Environmental Sciences, and lead author of the paper. Wendy Mao, an assistant professor in the department, is the co-author.

“This strength measurement can help us understand how the core deforms over long time scales, which influences how we think about Earth’s evolution and planetary evolution in general,” Gleason said.

Until now, almost all of what is known about Earth’s inner core came from studies tracking seismic waves as they travel from the surface of the planet through the interior. Those studies have shown that the travel time through the inner core isn’t the same in every direction, indicating that the inner core itself is not uniform. Over time and subjected to great pressure, the core has developed a sort of fabric as grains of iron elongate and align lengthwise in parallel formations.

The ease and speed with which iron grains in the inner core can deform and align would have influenced the evolution of the early Earth and development of the geomagnetic field. The field is generated by the circulation of liquid iron in the outer core around the solid inner core and shields Earth from the full intensity of solar radiation. Without the geomagnetic field, life – at least as we know it – would not be possible on Earth.

“The development of the inner core would certainly have some effect on the geomagnetic field, but just what effect and the magnitude of the effect, we can’t say,” said Mao. “That is very speculative.”

Gleason and Mao conducted their experiments using a diamond anvil cell – a device that can exert immense pressure on tiny samples clenched between two diamonds. They subjected minute amounts of pure iron to pressures between 200 and 300 gigapascals (equivalent to the pressure of 2 million to 3 million Earth atmospheres). Previous experimental studies were conducted in the range of only 10 gigapascals.

“We really pushed the limit here in terms of experimental conditions,” Gleason said. “Pioneering advancements in pressure-generation techniques and improvements in detector sensitivity, for example, used at large X-ray synchrotron facilities, such as Argonne National Lab, have allowed us to make these new measurements.”

In addition to intense pressures, the inner core also has extreme temperatures. The boundary between the inner and outer core has temperatures comparable to the surface of the sun. Simultaneously simulating both the pressure and temperature at the inner core isn’t yet possible in the laboratory, though Gleason and Mao are working on that for future studies. (For this study, Gleason mathematically extrapolated from their pressure data to factor in the effect of temperature.)

Gleason and Mao expect their findings will help other researchers set more realistic variables for conducting their own experiments.

“People modeling the inner core haven’t had many experimental constraints, because it’s so difficult to make measurements under those conditions,” Mao said. “There really weren’t constraints on how strong the core was, so this is really a fundamental new constraint.”

Scientist finds topography of Eastern Seaboard muddles ancient sea level changes

The distortion of the ancient shoreline and flooding surface of the U.S. Atlantic Coastal Plain are the direct result of fluctuations in topography in the region and could have implications on understanding long-term climate change, according to a new study.

Sedimentary rocks from Virginia through Florida show marine flooding during the mid-Pliocene Epoch, which correlates to approximately 4 million years ago. Several wave-cut scarps, (rock exposures) which originally would have been horizontal, are now draped over a warped surface with up to 60 meters variation.

Nathan Simmons of Lawrence Livermore National Laboratory and colleagues from the University of Chicago, Université du Québec à Montréal, Syracuse University, Harvard University and the University of Texas at Austin modeled the active topography using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial adjustment, account for the current architecture of the coastal plain and nearby shelf.

The results appear in the May 16 edition of Science Express, and will appear at a later date in Science Magazine,

“Our simulations of dynamic topography of the Eastern Seaboard have implications for inferences of global long-term sea-level change,” Simmons said.

The eastern coast of the United States is considered an archetypal Atlantic-type or passive-type continental margin.

“The highlight is that mantle flow is a major component in distorting the Earth’s surface over geologic time, even in so-called ‘passive’ continental margins,” Simmons said. “Reconstructing long-term global sea-level change based on stratigraphic relations must account for this effect. In other words, did the water level change or did the ground move? This could have implications on understanding very long-term climate change.”

The mantle is not a passive player in determining long-term sea level changes. Mantle flow influences surface topography, through perturbations of the dynamic topography, in a manner that varies both spatially and temporally. As a result, it is it difficult to invert for the global long-term sea level signal and, in turn, the size of the Antarctic Ice Sheet, using east coast shoreline data.

Simmons said the new results provide another powerful piece of evidence that mantle flow is intimately involved in shaping the Earth’s surface and must be considered when attempting to unravel numerous long-term Earth processes such as sea-level variations over millions of years.

Scientist finds topography of Eastern Seaboard muddles ancient sea level changes

The distortion of the ancient shoreline and flooding surface of the U.S. Atlantic Coastal Plain are the direct result of fluctuations in topography in the region and could have implications on understanding long-term climate change, according to a new study.

Sedimentary rocks from Virginia through Florida show marine flooding during the mid-Pliocene Epoch, which correlates to approximately 4 million years ago. Several wave-cut scarps, (rock exposures) which originally would have been horizontal, are now draped over a warped surface with up to 60 meters variation.

Nathan Simmons of Lawrence Livermore National Laboratory and colleagues from the University of Chicago, Université du Québec à Montréal, Syracuse University, Harvard University and the University of Texas at Austin modeled the active topography using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial adjustment, account for the current architecture of the coastal plain and nearby shelf.

The results appear in the May 16 edition of Science Express, and will appear at a later date in Science Magazine,

“Our simulations of dynamic topography of the Eastern Seaboard have implications for inferences of global long-term sea-level change,” Simmons said.

The eastern coast of the United States is considered an archetypal Atlantic-type or passive-type continental margin.

“The highlight is that mantle flow is a major component in distorting the Earth’s surface over geologic time, even in so-called ‘passive’ continental margins,” Simmons said. “Reconstructing long-term global sea-level change based on stratigraphic relations must account for this effect. In other words, did the water level change or did the ground move? This could have implications on understanding very long-term climate change.”

The mantle is not a passive player in determining long-term sea level changes. Mantle flow influences surface topography, through perturbations of the dynamic topography, in a manner that varies both spatially and temporally. As a result, it is it difficult to invert for the global long-term sea level signal and, in turn, the size of the Antarctic Ice Sheet, using east coast shoreline data.

Simmons said the new results provide another powerful piece of evidence that mantle flow is intimately involved in shaping the Earth’s surface and must be considered when attempting to unravel numerous long-term Earth processes such as sea-level variations over millions of years.

GOCE Earth explorer satellite to look at the Earth’s surface and core





GOCE positioned on the rotary table for alignment check, during launch campaign at the Plesetsk Cosmodrome. - Credits: ESA
GOCE positioned on the rotary table for alignment check, during launch campaign at the Plesetsk Cosmodrome. – Credits: ESA

The European Space Agency is about to launch the most sophisticated mission ever to investigate the Earth’s gravitational field and to map the reference shape of our planet – the geoid – with unprecedented resolution and accuracy.



The Gravity field and steady-state Ocean Circulation Explorer (GOCE) will be placed onto a low altitude near sun-synchronous orbit by a Russian Rockot vehicle launched from the Plesetsk Cosmodrome in Northern Russia, some 800 km north of Moscow. Lift-off is scheduled to take place at 16:21 CEST (14:21 UTC) on Wednesday 10 September. The launcher is operated by Eurockot Launch Services, a joint venture between EADS Astrium and the Khrunichev Space Centre (Russia).



ESA’s 1-tonne spacecraft carries a set of six state-of-the-art high-sensitivity accelerometers to measure the components of the gravity field along all three axes. The data collected will provide a high-resolution map of the geoid (the reference surface of the planet) and of gravitational anomalies. Such a map will not only greatly improve our knowledge and understanding of the Earth’s internal structure, but will also be used as a much better reference for ocean and climate studies, including sea-level changes, oceanic circulation and ice caps dynamics survey. Numerous applications are expected in climatology, oceanography and geophysics, as well as for geodetic and positioning activities.



To make this mission possible, ESA, its industrial partners (45 European companies led by Thales Alenia Space) and the science community had to overcome an impressive technical challenge by designing a satellite that will orbit the Earth close enough to gather high-accuracy gravitational data while being able to filter out disturbances caused by the remaining traces of the atmosphere in low Earth orbit (at an altitude of only 260 km). This resulted in a slender 5-m-long arrowhead shape for aerodynamics with low power ion thrusters to compensate for the atmospheric drag.


GOCE is the first Core Mission of the Earth Explorer programme undertaken by ESA in 1999 to foster research on the Earth’s atmosphere, biosphere, hydrosphere, cryosphere and interior, on their interactions and on the impact of human activities on these natural processes. It will be the first in a whole series of Earth Explorer missions with five launches to take place within the next two years.



Two more Core Missions, selected to address specific topics of major public concern are already under development: ADM-Aeolus for atmospheric dynamics (2010), and EarthCARE to investigate the Earth’s radiative balance (2013). Three smaller Earth Explorer Opportunity Missions are also in preparation: CryoSat-2 to measure ice sheet thickness (2009), SMOS to study soil moisture and ocean salinity (2009) and Swarm to survey the evolution of the magnetic field (2010).



On the occasion of the launch of GOCE, ESA will open a Press Centre at ESA/ESRIN in Frascati, Italy from 14:00 to 20:00, hosting a launch event from 15:30 to 18:15.



A live televised transmission of the launch will bring images from Plesetsk and from mission control at ESA/ESOC in Darmstadt, Germany to broadcasters (further details on the TV transmission at http://television.esa.int). ESA senior management and programme specialists will be on hand at ESRIN for explanations and interviews. The general public can also follow the video transmission web-streamed at: http://www.esa.int/goce.