"YD impact debris across more than 10% of the planet" -- nanodiamonds in Lake Cuitzeo, Mexico, James Kennett and 15 coworkers, from 12.9 Ka impact event -- link to free full text of PNAS report: Rich Murray 2012.03.06
http://rmforall.blogspot.com/2012/03/yd-impact-debris-across-more-than-10-of.html
http://tech.groups.yahoo.com/group/astrodeep/message/95
"Based upon astrophysical observations and modeling,
Napier (48) proposed that YDB impact markers were produced
when Earth encountered a dense trail of material from a large
already fragmented comet.
His model predicts cluster airbursts
and/or small cratering impacts that could account for the wide
distribution of YD impact debris across more than 10% of the
planet, including Cuitzeo." [ PNAS report ]
Lake Cuitzeo 0.8--2.2 m deep,
19.940001 -101.140006 1.833 km el,
about 300--400 km^2, ~ 250 km NWW of Mexico City
http://cosmictusk.com/
[ George Howard blog ]
NOTE: This post will be “stuck” to the top of the page for the time being.
Related new material such as news articles and observations will be blogged subsequent to this post but will appear below.
The old “Drudge Siren” is getting quite a 1st quarter work out.
And from what I hear it is only the beginning.
West, Kennett, Bunch and nearly a dozen new experts from multiple disciplines are publishing a fundamental evidence-based challenge to critics of the Younger Dryas Impact Hypothesis this week in PNAS.
Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis
http://www.pnas.org/content/early/2012/03/01/1110614109.abstract
http://www.pnas.org/content/early/2012/03/01/1110614109.full.pdf+html
[ extracts from text at end of this post ]
Published online before print March 5, 2012,
doi: 10.1073/pnas.1110614109
PNAS March 5, 2012
Free via Open Access: OA
Show PDF in full window
OA Abstract
» Full Text (PDF)
Full Text + SI (Combined PDF)
Supporting Information
I.I.-A., J.L.B., G.D.-V., H.-C.L., T.E.B., A.W., S.X., and W.S.W. designed research;
I.I.-A., J.L.B., G.D.-V., H.-C.L., T.E.B., J.H.W., J.C.W., A.W., S.X., E.K.R., C.R.K., and W.S.W. performed research;
I.I.-A., J.L.B., G.D.-V., H.-C.L., P.S.D., T.E.B., J.H.W., J.C.W., R.B.F., A.W., J.P.K., C.M., S.X., E.K.R., and W.S.W. analyzed data;
and I.I.-A., J.L.B., G.D.-V., P.S.D., R.B.F., A.W., J.P.K., and C.M. wrote the paper.
The authors declare no conflict of interest.
*This Direct Submission article had a prearranged editor.
Freely available online through the PNAS open access option.
† Dates in calendar years before present, unless noted; ka ¼ kiloannum, or 1,000 calendar years
‡ Andronikov AV, Lauretta DS, Andronikva IE, Maxwell RJ,
On the possibility of a late Pleistocene, extraterrestrial impact:
LA-ICP-MS analysis of the black mat and Usselo Horizon samples,
74th Annual Meteoritical Society Meeting, August 8–12, 2011, London, UK,
Supplement, #5008.
1 To whom correspondence should be addressed. E-mail: jbischoff@usgs.gov
This article contains supporting information online at
www.pnas.org/lookup/suppl/doi:10.1073/pnas.1110614109/-/DCSupplemental
www.pnas.org/cgi/doi/10.1073/pnas.1110614109
PNAS Early Edition ∣ 1 of 10
GEOLOGY PNAS PLUS
Isabel Israde-Alcántara a,
James L. Bischoff b, 1,
Gabriela Domínguez-Vázquez c,
Hong-Chun Li d,
Paul S. DeCarli e,
Ted E. Bunch f,
James H. Wittke f,
James C. Weaver g,
Richard B. Firestone h,
Allen West i,
James P. Kennett j,
Chris Mercer k,
Sujing Xie l,
Eric K. Richman m,
Charles R. Kinzie n,
and Wendy S. Wolbach n,
a Departamento de Geología y Mineralogía, Edif. U-4.
Instituto de Investigaciones Metalúrgicas,
Universidad Michoacana de San Nicólas de Hidalgo,
C. P. 58060, Morelia, Michoacán, México;
b US Geological Survey, Menlo Park, CA, 94025;
c Facultad de Biología,
Universidad Michoacana de San Nicólas Hidalgo
C. P. 58060, Morelia, Michoacán, México;
d Department of Geosciences,
National Taiwan University, Taipei 106,
Taiwan, Republic of China;
e SRI International, Menlo Park, CA 94025;
f Geology Program,
School of Earth Science and Environmental Sustainability,
Northern Arizona University, Flagstaff AZ 86011;
g Wyss Institute for Biologically Inspired Engineering,
Harvard University, Cambridge, MA 02138;
h Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
i GeoScience Consulting, Dewey, AZ 86327;
j Department of Earth Science and Marine Science Institute,
University of California, Santa Barbara, CA 93106;
k National Institute for Materials Science,
1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan;
l CAMCOR High Resolution and MicroAnalytical Facilities,
University of Oregon, Eugene, OR 97403;
m Materials Science Institute,
University of Oregon, Eugene, Oregon 97403;
and n Department of Chemistry, DePaul University,
Chicago, IL 60614
Edited* by Steven M. Stanley, University of Hawaii, Honolulu, HI,
and approved January 31, 2012 (received for review July 13, 2011)
We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact.
These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial.
Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences.
Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record.
This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core.
Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond:
n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance.
This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe.
We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism.
It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.
UPDATE #4: Space.com has a piece with some quotes from Ted Bunch.
UPDATE #3: Orange County a register has nice write-up with some new quotes from Jim Kennett.
UPDATE #2: See post below for breaking article from Popular Science on the new evidence from Mexico
UPDATE #1: The paper is published and unrestricted on the PNAS website here, and also below.
http://cosmictusk.com/ucsb-press-release/#comments
http://www.ia.ucsb.edu/pa/display.aspx?pkey=2662
PRESS RELEASE
Study Jointly Led by UCSB Researcher Supports Theory of Extraterrestrial Impact
March 5, 2012
(Santa Barbara, Calif.) -- A 16-member international team of researchers that includes James Kennett, professor of earth science at UC Santa Barbara, has identified a nearly 13,000-year-old layer of thin, dark sediment buried in the floor of Lake Cuitzeo in central Mexico.
The sediment layer contains an exotic assemblage of materials, including nanodiamonds, impact spherules, and more, which, according to the researchers, are the result of a cosmic body impacting Earth.
These new data are the latest to strongly support of a controversial hypothesis proposing that a major cosmic impact with Earth occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas.
The researchers' findings appear today in the Proceedings of the National Academy of Sciences.
Conducting a wide range of exhaustive tests, the researchers conclusively identified a family of nanodiamonds, including the impact form of nanodiamonds called lonsdaleite, which is unique to cosmic impact.
The researchers also found spherules that had collided at high velocities with other spherules during the chaos of impact.
Such features, Kennett noted, could not have formed through anthropogenic, volcanic, or other natural terrestrial processes.
"These materials form only through cosmic impact," he said.
The data suggest that a comet or asteroid -- likely a large, previously fragmented body, greater than several hundred meters in diameter -- entered the atmosphere at a relatively shallow angle.
The heat at impact burned biomass, melted surface rocks, and caused major environmental disruption.
"These results are consistent with earlier reported discoveries throughout North America of abrupt ecosystem change, megafaunal extinction, and human cultural change and population reduction," Kennett explained.
The sediment layer identified by the researchers is of the same age as that previously reported at numerous locations throughout North America, Greenland, and Western Europe.
The current discovery extends the known range of the nanodiamond-rich layer into Mexico and the tropics.
In addition, it is the first reported for true lake deposits.
In the entire geologic record, there are only two known continent-wide layers with abundance peaks in nanodiamonds, impact spherules, and aciniform soot. These are in the 65-million-year-old Cretaceous-Paleogene boundary layer that coincided with major extinctions, including the dinosaurs and ammonites; and the Younger Dryas boundary event at 12,900 years ago, closely associated with the extinctions of many large North American animals, including mammoths, mastodons, saber-tooth cats, and dire wolves.
"The timing of the impact event coincided with the most extraordinary biotic and environmental changes over Mexico and Central America during the last approximately 20,000 years, as recorded by others in several regional lake deposits," said Kennett.
"These changes were large, abrupt, and unprecedented, and had been recorded and identified by earlier investigators as a ‘time of crisis.' "
Other scientists contributing to the research include
Isabel Israde-Alcántara and Gabriela Dominguez-Vásquez of the Universidad Michoacana de San Nicólas de Hidalgo;
James L. Bischoff of the U.S. Geological Survey;
Hong-Chun Li of National Taiwan University;
Paul S. DeCarli of SRI International;
Ted E. Bunch and James H. Wittke of Northern Arizona University;
James C. Weaver of Harvard University;
Richard B. Firestone of Lawrence Berkeley National Laboratory;
Allen West of GeoScience Consulting;
Chris Mercer of the National Institute for Materials Science;
Sujing Zie and Eric K. Richman of the University of Oregon, Eugene;
and Charles R. Kinzie and Wendy S. Wolbach of DePaul University.
http://www.ia.ucsb.edu/pa/image.aspx?pkey=2662&Position=1
James Kennett
http://www.ia.ucsb.edu/pa/image.aspx?pkey=2662&Position=2
† Center image: The ‘tectonic' effects of the collision of one spherule with another during the cosmic impact.
http://www.ia.ucsb.edu/pa/image.aspx?pkey=2662&Position=3
†† Bottom image: Images of single and twinned nanodiamonds show the atomic lattice framework of the nanodiamonds. Each dot represents a single atom.
Copyright © The Regents of the University of California, All Rights Reserved.
UC Santa Barbara, Santa Barbara, CA 93106 (805) 893-8000
http://cosmictusk.com/tree-falls-in-forest-and-one-hand-claps-science-press-picks-the-new-mexican-black-mat-study/
This just in from Popular Science, link here.
http://www.popsci.com/science/article/2012-03/space-rock-impact-could-have-caused-ancient-cooldown-new-evidence-says
By Rebecca Boyle, Posted 03.05.2012 at 3:25 pm, 9 Comments
Massive Extraterrestrial Rock Hit Earth 13 Millennia Ago, According to Nano-Evidence
About 13,000 years ago, a chunk of a comet or asteroid hurtled into the atmosphere at a shallow angle, superheating the atmosphere around it as it careened toward the surface. The air grew hot enough to ignite plant material and melt rock below the object’s flight path. Within a few microseconds, atmospheric oxygen was consumed and the freed carbon atoms condensed into nanodiamond crystals.
An air shock followed several seconds later, lofting these nanodiamonds and other carbon particles into the atmosphere, spreading them around. Mega mammals starved, unable to forage on the scorched earth, and human populations dwindled. The shock on the atmosphere was enough to lower global temperatures for a thousand years.
This is according to a new study of ancient Mexican nanodiamonds, and it’s another salvo in a longstanding ancient-climate dispute. The study bolsters the controversial argument that an asteroid impact might have chilled the planet during the Younger Dryas, an abrupt and very short cold interval that started about 12,900 years back.
Paleo-climatologists have been arguing about the genesis of this period for half a decade now. Some hypothesize it was the result of collapsing North American ice sheets, which disrupted the heat conveyor of the North Atlantic. Others argue it was because melting ice changed the landscape, which in turn changed the jet stream. And another theory, first posed in 2007, holds that something hit the Earth and set North America on fire. This theory was proposed after a study of ancient sediments in multiple sites, in which geologists noticed an organic-rich layer of material called a “black mat.” Later, researchers led by University of Oregon archaeologist Douglas Kennett found high concentrations of nanodiamonds -- a material associated with high-temperature collisions of material.
The theory soon drew a firestorm of criticism, with a concurrent paper dismissing the nanodiamond results as a false positive. The nanodiamond theory was all but ignored by mid-2011 after many groups of scientists could neither corroborate nor replicate the results. Now comes Isabel Israde-Alcántara et al., writing in the same journal that published the nanodiamond refutation.
This time, the researchers studied a different location -- a lake in central Mexico instead of Greenland -- and used a different set of techniques to take their measurements. The team studied a 10-centimeter-thick, carbon-rich layer dating to 12,900 years ago, which contained nanodiamonds, carbon spherules and other material. Israde-Alcántara and colleagues at the Universidad Michoacana de San Nicólas de Hidalgo in Mexico and the U.S. Geological Survey report their results in the Proceedings of the National Academy of Sciences.
The sediment layer came from a a 27-meter-long core sample drilled from Lake Cuitzeo as part of a paleoclimate study. The team focused on several microparticles they attribute to widespread burning -- such as carbon particulates -- and nanodiamonds, which they measured using even more precise techniques than Kennett et al. two years ago.
These particles can’t be explained by any terrestrial mechanisms, the authors say. They rule out a rain shower of cosmic particles; wildfires; volcanism; human-related activities; and even particle misidentification (like finding fool’s nanodiamonds). They say a cosmic impact is the only viable hypothesis.
This is surely not the last word on this subject, however. We will stay on top of the nanodiamond hunt.
http://www.ocregister.com/news/impact-343336-kennett-years.html
Orange County Register NEWS
Published: March 6, 2012 Updated: 11:32 a.m.
Did cosmic impact kill the mammoths?
By PAT BRENNAN / ORANGE COUNTY REGISTER
A series of strikes by an asteroid or comet might solve a prehistoric mystery: Why did a long list of creatures, from mammoths and saber-toothed cats to horses and camels, vanish suddenly from North America nearly 13,000 years ago?
Relying on a meticulous analysis of fragments, including tiny diamonds of submicroscopic size, from a dark layer of sediment in a Mexican lake, a new study suggests that large objects from space might have caused the continental-sized catastrophe.
And while the impact is "dinky" compared to the massive strike that wiped out the dinosaurs 65 million years ago, it would have been enough to profoundly alter the course of evolution in the Americas.
"This is the standout event in terms of environmental and biotic change," said James Kennett, an earth science professor at UC Santa Barbara and an author of the new study. "All the horses in North America, all the camels, the mastodon, short-faced bear, giant beaver, dire wolf, saber-toothed cats -- the disappearances converge very abruptly at or close to 12.9 (thousand years ago)."
Humans, too, suffered steep population declines, with the Clovis culture seeming to vanish, along with human presence in California, during a sharp cooling episode known as the Younger Dryas.
"It's a bit of a puzzle why the cooling even occurred," Kennett said. "We argued the cooling occurred as a result of the impact."
Kennett and an international, 16-member team examined "nanodiamonds" that form only during cosmic impacts, along with "impact spherules" that had crashed together at high speed and remained fused -- again an effect seen only in impacts from space bodies.
And, while there are hints of a crater in the Gulf of St. Lawrence that might be related to the event, Kennett says his team's hypothesis does not require an impact crater.
Instead, the strikes -- perhaps a series of strikes from a comet or asteroid that had broken up -- could have taken place above the ground, much like the Tunguska event over Siberia in 1908 that leveled trees across 800 square miles.
Evidence of the strike, or strikes, is scattered across western Europe as well as North and South America, though the European material is made up of nanodiamonds so light they could have been carried there by wind.
The material analyzed by the team came from Lake Cuitzeo in central Mexico.
"It's really a cometary cloud that intersected Earth at that time," Kennett said. "That's our hypothesis. We're finding, as we do more work on this, essentially the larger it's getting."
Relying on detailed geochemistry as well as careful analysis of the lattice-like structure inside the nanodiamonds, the team was able to rule out other possible origins for the material -- volcanoes or stray bits falling into the atmosphere from space.
While Kennett is careful to point out that the new study includes only evidence of the extraterrestrial impact, and makes no direct link to animal extinctions, the match between the timing of the many disappearances of large creatures and the timing of the impact is extraordinary.
It even includes the pygmy mammoths that once inhabited California's Channel Islands.
"The youngest known pygmy mammoth is dated to 12.9 (thousand years ago)," he said. "They go right up to 12.9, then they're gone."
More familiar creatures such as grizzly bears and 3lk might have reinvaded the continent after the cosmic impacts. But compared to the spectacular period before, the later North American fauna begins to look a little impoverished.
"What we have left is wimpish compared with Africa," Kennett said. "It's sad. But we lost all these wonderful animals, including the giant sloths."
The study, one of a series on the impacts 12,900 years ago, was published Monday in the Proceedings of the National Academy of Sciences.
http://www.space.com/14793-comet-earth-impact-younger-dryas.html?utm_content=SPACEdotcom&utm_campaign=seo%2Bblitz&utm_source=twitter.com&utm_medium=social%2Bmedia
Comet May Have Collided With Earth 13,000 Years Ago
by Clara Moskowitz, SPACE.com Assistant Managing Editor
Date: 06 March 2012 Time: 06:05 AM ET
Central Mexico’s Lake Cuitzeo contains melted rock formations and nanodiamonds that suggest a comet impacted Earth around 12,900 years ago, scientists say.
CREDIT: Israde et al. (2012)
New evidence supports the idea that a huge space rock collided with our planet about 13,000 years ago and broke up in Earth's atmosphere, a new study suggests.
This impact would have been powerful enough to melt the ground, and could have killed off many large mammals and humans. It may even have set off a period of unusual cold called the Younger Dryas that began at that time, researchers say.
The idea that Earth experienced an asteroid or comet impact at the start of the Younger Dryas has been controversial, in part because there is no smoking-gun impact crater left behind as with other known events in our planet's past. But researchers say it's common for space rocks to disintegrate in the heat of a planet's atmosphere before they can reach the ground.
The scientists first reported their suspicions about the event in 2007. Now, they say, a new site in Central Mexico's Lake Cuitzeo displays telltale signs of an impact, including melted rock formations called spherules and microscopic diamonds that could only have formed under extreme temperatures.
The researchers, led by Isabel Israde-Alcántara of Mexico's Universidad Michoacana de San Nicólas de Hidalgo, published their findings online March 5 in the journal Proceedings of the National Academy of Sciences.
This scanning electron microscope image shows a magnetic impact spherule likely to have been created by an asteroid or comet impact 12,900 years ago, researchers say.
CREDIT: Israde et al. (2012)
Buried evidence
"If you don't have a crater, you're a little bit lost," said space scientist Ted Bunch of Northern Arizona University, a member of the research team. "Here what we have is something similar to an aerial bomb blast. With these aerial bursts, with time all the evidence is wiped away unless it's buried." [Best Close Encounters of the Comet Kind]
In addition to the Mexican site, the scientists have found signs of an impact in Canada, the United States, Russia, Syria and various sites in Europe. And all of these bits of evidence were found buried in a thin layer of rock that dates to precisely 12,900 years ago.
"If you have an event like this in a 1- or 2-inch layer that dates to exactly the same age over a very large area, and you have high-temperature materials and nanodiamonds in there, the evidence pretty well points to an event that as pretty disastrous," Bunch told SPACE.com.
This wouldn't have been the only aerial impact event ever to hit Earth. Scientists think a space rock exploded over Siberia in 1908, flattening 500,000 acres (2,000 square kilometers) of forest in what's known as the Tunguska event.
Heat flash
If a comet, which would have been traveling at about 30 miles per second, impacted Earth's atmosphere, it would have created a flash of extreme heat reaching about 3,000 to 4,000 degrees Fahrenheit (1,600 to 2,200 degrees Celsius).
In addition to melting the ground, such temperatures would have proven cataclysmic to many kinds of life.
At the same time that the impact may have taken place -- 12,900 years ago -- Earth was beginning a mini ice age. It is known that many large animals, such as the mammoth and the saber-toothed cat, did not survive this age. There's even evidence of a population decline in humans living in North America at the time, called the Clovis culture.
The researchers aren't claiming that the comet impact caused the climate changes at the time, but Bunch said such an event would have had a significant effect on Earth's climate.
"We're not going to come out and say it did do it, but it's more than a coincidence that the timing happened exactly the time that a lot of climatic conditions occurred and you had the loss of various species," Bunch said.
Still, the researchers predict some skeptics will remain unconvinced that Earth was hit by space rock during the Younger Dryas.
"There's always going to be theoretical and statistical people who would never believe it even if they were there," Bunch said."I think what we're trying to do is open up a vista there for people to examine the data themselves and make their own conclusions."
[ from the paper: ]
We present data from Lake Cuitzeo in central Mexico (19.94 °N,
101.14 °W) in support of evidence for the Younger Dryas
(YD) impact hypothesis, as first presented at the 2007 Meeting
of the American Geophysical Union in Acapulco, Mexico.
There, a consortium of scientists reported geochemical and
mineralogical evidence from multiple terrestrial sites ascribed
to extraterrestrial (ET) impacts and/or airbursts (1).
Their first evidence was the discovery at well-dated Clovis-era
archeological sites in North America
of abundant magnetic spherules (MSp)
and carbon spherules (CSp) in a thin layer (0.5 to 5 cm) called
the Younger Dryas boundary layer (YDB),
dating to 12.9 0.1 kaBP (calibrated, or calendar years)
or 10.9 14C kaBP (radiocarbon years) † (1–3).
The YDB is commonly located directly
beneath or at the base of an organic-rich layer, or “black
mat,” broadly distributed across North America (1).
Later, abundant
nanodiamonds (NDs) were discovered by Kennett et al.
(2, 3) in the YDB layer at numerous locations.
NDs also were detected at the margin of the Greenland Ice Sheet
in a layer that dates to the approximate YD onset (4).
These discoveries led to the hypothesis that one or more fragments
of a comet or asteroid impacted the Laurentide Ice Sheet
and/or created atmospheric airbursts (1)
that initiated the abrupt YD cooling at 12.9 ka,
caused widespread biomass burning, and contributed
to the extinction of Late Pleistocene megafauna and to major
declines in human populations (5).
Some independent workers have been unable to reproduce
earlier YDB results for MSp, CSp, and NDs (6–8), as summarized
in a “News Focus” piece in Science (9), which claims that the
YDB evidence is “not reproducible” by independent researchers.
Refuting this view, multiple groups have confirmed the presence
of abundant YDB markers, although sometimes proposing alternate
hypotheses for their origin.
For example, Mahaney et al. (10–12) independently identified
glassy spherules, CSps, high temperature melt-rocks, shocked quartz,
and a YDB black mat analogue in the Venezuelan Andes.
Those authors conclude the cause was
“either an asteroid or comet event that reached
far into South America” at 12.9 ka.
At Murray Springs, Arizona,
Haynes et al. (13) observed highly elevated concentrations of
YDB MSp and iridium.
Abundances of MSp were 340 × higher
than reported by Firestone et al. (1) and iridium was 34 × higher,
an extraordinary enrichment of 3,000 × crustal abundance.
Those authors stated that their findings are “consistent with their
(Firestone et al.’s) data.”
In YDB sediments from North America and Europe,
Andronikov et al. (2011) reported anomalous enrichments
in rare earth elements (REE) and “overall higher concentrations
of both Os and Ir [osmium and iridium]” that could
“support the hypothesis that an impact occurred shortly before
the beginning of the YD cooling 12.9 ka.” ‡.
Tian et al. (14) observed abundant cubic NDs at Lommel, Belgium,
and concluded that
“our findings confirm … the existence of diamond
nanoparticles also in this European YDB layer.”
The NDs occur within the same layer in which Firestone et al. (1)
found impact related materials.
Similarly, at a YDB site in the Netherlands,
Van Hoesel et al. § observed
“carbon aggregates [consistent with] nanodiamond.”
Recently, Higgins et al. ¶ independently announced
a 4- to 4.5-km-wide YDB candidate crater named Corossol
in the Gulf of St. Lawrence, containing basal sedimentary
fill dating to 12.9 ka.
If confirmed, it will be the largest known
crater in North and South America within the last 35 million years.
Because of the controversial nature of the YD impact debate,
we have examined a diverse assemblage of YDB markers at Lake
Cuitzeo using a more comprehensive array of analytical techniques
than in previous investigations.
In addition, different researchers at
multiple institutions confirmed the key results.
5 Van Hoesel A, Hoek W, Braadbaart F, van der Plicht H, Drury MR,
Nanodiamonds and the Usselo layer, INQUA XVIII, July 21–27, 2011,
Bern Switzerland, #1556.
¶ Higgins MD, et al.,
Bathymetric and petrological evidence for a young (Pleistocene?) 4-km diameter impact crater in the Gulf of Saint Lawrence, Canada,
42nd Lunar and Planetary Science Conference, March 7–11, 2011,
The Woodlands, TX, 1504 LPI Contribution No. 1608.
∥ http://www.calpal.de
.....Comets.
Based upon astrophysical observations and modeling,
Napier (48) proposed that YDB impact markers were produced
when Earth encountered a dense trail of material from a large
already fragmented comet.
His model predicts cluster airbursts
and/or small cratering impacts that could account for the wide
distribution of YD impact debris across more than 10% of the
planet, including Cuitzeo.
Most comets eventually break up as
they transit the inner solar system, and previously unknown fragmented
comets are discovered by space-borne telescopes, such as
the Solar and Heliospheric Observatory, on average every 4 y.
As evidence, Earth is bombarded at an average rate of once every 5 d
by one of 72 meteor streams or “showers,” massive clouds of debris
from fragmented comets.
These well-known meteor showers,
e.g., Perseids, Geminids, Taurids, etc., are highly dispersed, but in
the recent geologic past, each stream was far more condensed,
containing many large, potentially destructive fragments.
Currently, the Taurid Complex contains 19 large near-earth Apollo
asteroids, with diameters ranging from approximately 1.5 km
(6063 Jason) to approximately 5 km (4184 Cuno) (48).
None of these currently threatens Earth but may do so in the future.
Impact Dynamics.
Earth has been subjected to a continuous,
although intermittent bombardment by impactors with diameters
ranging from microns to tens of kilometers; velocities range from
approximately 11 km∕s to 73 km∕s with typical values of 17 km∕s
for asteroids and 51 km∕s for comets.
The term “cosmic impact”
evokes images of craters ranging from the 50-kyr-old, 1-km-diameter
Meteor Crater to the 2-billion-year-old, 200-km-diameter
Vredefort crater (49, 50).
For these crater-forming events that
have peak impact pressures in the range of hundreds of GPa,
impact dynamics and shock wave metamorphic effects are well
understood (49, 50).
An ET impact is the only natural mechanism
known to produce major coeval abundances in cubic NDs, lons
daleite, and quench-melted MSp, both of which co-occur in impact
events, including Ries crater and the KPg (39).
Based on hundreds of shock-recovery experiments by one of
the authors of this article (DeCarli), the formation of lonsdaleite
in graphite-bearing gneisses in the Ries, Popigai, and other impact
craters is in complete accord with static high-pressure data
on solid–solid transformation of graphite to lonsdaleite and cubic
NDs (29–31).
However, this transformation does not readily explain
the NDs found at the KPg boundary or in the YDB.
Based on available evidence, it seems unlikely that the YDB NDs
formed by shock compression of terrestrial graphite, and instead,
our preferred mechanism invokes the interaction of an ETobject
with Earth’s atmosphere (49).
If incoming objects are relatively small,
virtually all kinetic energy is transferred to the atmosphere
at high altitudes, creating an air shock with temperatures up to
tens of thousands degrees Kelvin.
These are the familiar shooting stars,
the remains of which may be collected as cosmic dust.
Although shock pressures due to solid–air interaction are modest
at high altitudes, larger objects may be disrupted and fragmented
as pressure builds due to increasing atmospheric density at lower
altitudes.
This breakup is especially likely if the object was loosely
consolidated or low density like a comet.
When an incoming ET
object encounters the atmosphere and breaks apart, individual
pieces rapidly decelerate due to the marked increase in the ratio
of cross-sectional area to mass.
Area of the luminous air shock is
correspondingly increased, with the result that the object appears
to “explode” in a fireball.
For an object traveling at 30 km∕s,
air shock pressure would be
approximately 20 MPa at 20 km altitude,
approximately 170 MPa at 10 km,
and approximately 900 MPa at sea level.
For an air shock of 170 MPa, the pressure exceeds unconfined
compressive strengths of many rocks.
These energetic events are often termed “atmospheric impacts”
to distinguish them from more familiar crater-forming events.
For example, the craterless Tunguska event in Siberia
in 1908 appears to be such an atmospheric impact.
Estimates of energy associated with this event range from
3 to 24 megatons of TNT (51, 52), powerful enough to produce
an air shock that
leveled approximately 80 million trees across 2,000 km^2 of forest.
At a distance of 60 km, the air shock was still able to knock
down a Siberian trader (53), and thermal radiation was intense
enough to char his clothing (49).
Even though the Tunguska atmospheric impact formed no known crater,
it produced MSp (54) and lonsdaleite (55).
Studies of such atmospheric impacts indicate
that Tunguska-sized events up to 24 megatons occur about
once every 220 y (52).
Similar but smaller effects occurred during
the Trinity atomic bomb test in 1945, an aerial burst that also left
no crater yet produced glassy surficial sheet melt, along with
rounded and teardrop-like glassy spherules (56).
Such an atmospheric impact scenario
is also the best explanation for other well known
events with no known craters, including the Libyan Desert
glass field and Dakhleh Oasis glass in Egypt.
In the Australasian
tektite field (780 ka), microspherules and tektites are strewn
across 10–30% of Earth’s surface, producing the world’s largest
ejecta field and yet, there is no known crater.
Wasson (57) proposed
that the Australasian field resulted from an atmospheric
impact by a comet approximately 1 km in diameter, striking
Earth’s atmosphere at an oblique angle.
The amount of kinetic energy transferred during an atmospheric
impact via air shock depends upon the cross-sectional
area of the object, its velocity, and its mass.
Air shock pressure depends upon the velocity of the object
and the density of air at altitude.
Shock front temperature is limited to approximately
20,000 K by dissociation of air molecules ahead of front (58),
and effective duration of the intense thermal pulse can be of
the order of seconds.
Whether an object disintegrates in flight
depends upon its strength, size, shape, velocity, and angle of
entry.
In the case of a comet that is a dusty porous snowball having
little strength, a 20-km-diameter comet traveling at 40 km∕s
would not disintegrate in the Earth’s atmosphere;
the front of the comet would impact Earth before the shock
from atmospheric impact reached the rear of the comet.
However, comets with dimensions
of tens of meters will disintegrate at high altitude.
Weissman (59) estimated that a comet would have to be >350 m
in diameter to penetrate Earth’s atmosphere and form a crater,
depending upon angle, velocity, etc.
Such an event would be at
least 500 × more energetic than the Tunguska event.
YD Impact Model.
Based on current data, we propose the following
preliminary model for formation of the YDB NDs and MSp.
A comet or asteroid, possibly a previously fragmented object that was
once greater than several hundred meters in diameter, entered the
atmosphere at a relatively shallow angle ( > 5° and < 30°).
Thermal radiation from the air shock reaching Earth’s surface was intense
enough to pyrolyze biomass and melt silicate minerals below the
flight path of the impactor (60).
Pyrolytic products were oxidized,
locally depleting the atmosphere of oxygen, and within microseconds,
residual free carbon condensed into diamond-like crystal
structures, CSp, carbon onions, and aciniform soot.
This involved a CVD-like process similar to diamond-formation
during TNT detonation.
In some cases, carbon onions grew around the NDs and
other nanomaterials.
At the same time, iron-rich and silicate materials
may have melted to form MSp.
Several seconds later, depending on the height of the thermal
radiation source, the air shock arrived.
NDs, MSp, CSp, and other markers were lofted by the
shock-heated air into the upper atmosphere,
where prevailing winds distributed them across the
Northern and Southern Hemispheres.
We suggest that the above
model can account for the observed YDB markers.
.....Summary
Synchronous peaks in multiple YDB markers dating to 12.9 ka
were previously found at numerous sites across North and South
America and in Western Europe.
At Lake Cuitzeo, magnetic impact
spherules, CSps, and NDs form abundance peaks within a
10 cm layer of sediment that dates to the early part of the YD,
beginning at 12.9 ka.
These peaks coincide with anomalous environmental,
geochemical, and biotic changes evident at Lake Cuitzeo
and in other regional records, consistent with the occurrence of
an unusual event.
Analyses of YDB acid-resistant extracts using
STEM, EDS, HRTEM, SAD, FFT, EELS, and EFTEM indicate
that Lake Cuitzeo nanoparticles are dominantly crystalline carbon
and display d-spacings that match various ND allotropes, including
lonsdaleite.
These results are consistent with reports of abundant
NDs in the YDB in North America and Western Europe.
Although the origin of these YDB markers remains speculative,
any viable hypothesis must account for coeval abundance
peaks in NDs, magnetic impact spherules, CSps, and charcoal
in Lake Cuitzeo, along with apparently synchronous peaks at
other sites, spanning a wide area of Earth’s surface.
Multiple hypotheses have been proposed to explain these YDB peaks
in markers, and all but one can be rejected.
For example, the magnetic
impact spherules and NDs cannot result from the influx of
cosmic material or from any known regular terrestrial mechanism,
including wildfires, volcanism, anthropogenesis, or alternatively,
misidentification of proxies.
Currently, only one known event, a cosmic impact,
can explain the diverse, widely distributed
assemblage of proxies.
In the entire geologic record, there are
only two known continent-wide layers with abundance peaks in
NDs, impact spherules, CSps, and aciniform soot, and those
are the KPg impact boundary at 65 Ma and the YDB boundary
at 12.9 ka.
ACKNOWLEDGMENTS.
Robert Rosenbauer and Pamela Campbell [US Geological Survey (USGS)] performed GC-MS analyses of extractable organic matter from the anomalous interval.
We gratefully acknowledge Ming Xie for assistance with HRTEM analyses at University of Oregon’s CAMCOR transmission electron microscopy facility,
supported by grants from W.M. Keck Foundation,
M.J. Murdock Charitable Trust,
Oregon Nanoscience and Microtechnologies Institute,
and Air Force Research Laboratory (agreement #FA8650-05-1-5041).
R.B.F.’s efforts were supported, in part, by US Department of Energy Contract DE-AC02-05CH11231.
Research by J.P.K. was supported in part by US National Science Foundation grant #OCE-0825322, Marine Geology and Geophysics.
Various parts of the manuscript were improved as a result of collegial reviews by
David Hodell (Cambridge University),
Anthony Irving (University of Washington),
John Barron,
John Hagstrum,
and Scott Starratt (USGS).
10 m broken rock hill with black glazes, W of Rancho Alegre Road, S of
Coyote Trail, W of Hwy 14, S of Santa Fe, New Mexico, tour of 50
photos 1 MB size each via DropBox: Rich Murray 2011.07.28 2011.08.03
http://rmforall.blogspot.com/2011/08/10-m-broken-rock-hill-with-black-glazes.html
http://rmforall.blogspot.com/2011/08/35479730-106085926-1865-km-el-top-10-m.html
photos 3-5 of 50
http://tech.groups.yahoo.com/group/astrodeep/message/92
Rich Murray,
MA Boston University Graduate School 1967 psychology,
BS MIT 1964 history and physics,
254-A Donax Avenue, Imperial Beach, CA 91932
rmforall@gmail.com
505-819-7388
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