Did a Comet Really Kill the Mammoths 12,900 Years Ago?
Did the planetary upheaval 12,900 years ago come from the heavens—or Earth?
Published September 10, 2013
Why did mammoths, mastodons, and other mega-beasts vanish from North America?
Was it because:
1) humans killed them;
2) they couldn’t hack the climate after the Ice Age ended; or
3) an exploding comet ignited continent-wide wildfires, sent hundred-mile-an-hour winds and tornadoes howling across the land, and shattered the North American ice sheet, while also maybe gouging out the Great Lakes?
Let’s talk about option number three.
The idea that a comet struck Earth 12,900 years ago, at the beginning of a strange interlude of climate cooling called the Younger Dryas was first proposed in 2007. In the bitter scientific debate that has flared sporadically ever since, the latest evidence includes:
Tiny, glassy “spherules” of rock found in a Pennsylvania flowerbed by a woman who had seen a NOVA program about the comet hypothesis. In a paper that got wide coverage last week, Dartmouth researchers argue that those spherules were hurled to Pennsylvania by an impact in Quebec 12,900 years ago.
Traces of platinum deposited on the Greenland ice cap at about the same time. Harvard researchers argue that the platinum probably came from an extraterrestrial object—not a comet, however, but a rare type of iron-rich meteorite.
Spherules in Syria. In their latest paper, some of the original proponents of the impact hypothesis now say it deposited 10 million metric tons of spherules over an area of 20 million square miles, stretching from Syria through Europe to the west coast of North America.
Some opponents of the hypothesis—and there are many—want so badly for it to go away that they have attempted to declare it dead. “My only comment is that the pro-impact literature is, at this point, fringe science being promoted by a single journal,” one of them, Nicholas Pinter of Southern Illinois University, said last week. The journal in question is Proceedings of the National Academy of Science.
Other researchers are trying to keep an open mind.
“Most people were trying to disprove this,” said Wallace Broecker, a geochemist and climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Now they’re going to have to realize there’s some truth to it”—though maybe only a spherule or two.
Continue reading NatGeo actually calls Wally Broecker to discuss evidence for cosmic impact at Younger Dryas start
Tip of the Hat: Thomas Lee Ellifritz
Nanodiamond Quantification in Pre-Younger Dryas to Recent Age Deposits Along Bull Creek, Oklahoma, USA
Leland C. Bement, Andrew S. Madden, Brian J. Carter, Alexander Simms, Andrew L. Swindle, Hanna M. Alexander, Scott Fine, and Mourad Benamara, Geological Society of America 125th Anniversayr Annual Meeting, 27-30 October 2013, Denver, Colorado, USA, Paper No. 306-8
Sediments recording the Younger Dryas and time immediately before and afterwards reveal a rich story of dramatic regional changes in climate, human cultural artifacts, and floral and faunal patterns. Previously, Firestone et al. (2007) suggested such changes resulted in large part due to an extraterrestrial impact event. Nanodiamonds were suggested as one line of evidence, as they are associated both with meteorites and other impact events from the geologic record. The Bull Creek, OK drainage basin includes nearly continuous alluvial and aeolian sediments from prior to the Younger Dryas through recent time. Whole-sediment digestions performed on a series of samples dated across this time frame, including both a continuous profile in one location and other sites selected due to their sedimentological or cultural significance. Sediment residues were found to contain nanodiamond spikes (190 ppm) primarily in two horizons: the Younger Dryas and the most recent late Holocene. Much lower levels of nanodiamonds were found in some other layers, while no nanodiamonds were identified in many others. The total distribution of nanodiamonds was not correlated with sediment depositional type, duration of exposure, or evidence for cultural disturbance and fire. The Younger Dryas nanodiamond spike was associated with sediments with some of the shortest surface exposure ages, while the late Holocene nanodiamond spike was associated with the longest surface exposure age. With respect to the impact hypothesis, these results both confirm the presence of a nanodiamond spike associated with the Younger Dryas and indicate that these nanodiamonds were deposited over a geologically short duration. On the other hand, large carbonaceous grains putatively identified as hexagonal diamonds were found to be more consistent with graphene/graphane mixtures.
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A meteor or comet impact near Quebec heaved a rain of hot melted rock along North America’s Atlantic Coast about 12,900 years ago, a new study claims.
Scientists have traced the geochemical signature of the BB-sized spherules that rained down back to their source, the 1.5-billion-year-old Quebecia terrane in northeastern Canada near the Gulf of Saint Lawrence. At the time of the impact, the region was covered by a continental ice sheet, like Antarctica and Greenland are today.
“We have provided evidence for an impact on top of the ice sheet,” said study co-author Mukul Sharma, a geochemist at Dartmouth College in Hanover, N.H. The results were published today (Sept. 2) in the journal Proceedings of the National Academy of Sciences…..
See entire NBC article here
…..Scientists on the other side of the impact theory debate are not so sure.
“At this point, the pro-impact literature is fringe science being promoted by a single journal,” said Nicholas Pinter, a geologist at Southern Illinois University in Carbondale, who was not involved in the PNAS research.