Unless I missed, it the author and certainly the nay sayers, don't mention mammoth tusk which were found with a spray of small flecks of meteoritic nickel-iron embedded in just one side. This suggests at lest some mammoths were up close witnesses to a good sized "shotgun-blast"/impact event if not "THE" impact( I think these tusk ages were off 200-300 years???).
The ice sheet over northeastern present day Canada was over two miles thick at this time. If much of the blast was Tunguska style--high over head and disintegration into powder-sized particles then Rare Earth Elements (REE) could be scattered by thermal currents well into the upper atmosphere and carried around the globe . What immediately fell should have been washed away by water channels in the melting ice. As there were many glacial lakes which emptied over North America at the time we should be looking in submarine slope cores for the missing REEs off the coasts of New York and New Jersey up to Newfoundland. A two mile thick ice sheet which has long melted is a fair explanation as to why we don't have a crater nor full spectrum REE assays in our samples.
Then there is the Clovis culture who's population abruptly disappeared from the archaeological record of North America all way from the Northeastern regions back into Texas and New Mexico for a hiatus of 400 years according to the dating of campfires; at 12,900 BP, there is a 400 year gap in Clovis --or any other human activity before we start finding occupied camps again. Many of these locations such as caves have the older fire hearths buried under the later ones--separated by you guessed it-- 400 years give or take. So humans tend to like the same shelter settings across time it seems.
As to Mammoths being hunted out of final existence--they likely were! The last Columbia Mammoths ( a pigmy island inhabiting race) died out as late as about 4000 years ago. As to death by comet vs that by human, the proportions of populations of both human and mammoth should have been equally wiped out regionally. Humans reproduce faster than elephants by 2 to 1 so once the balance had been reset by comet, extinction by human hand would have been a matter of time as human populations outpaced the large ice aged mammals.
Back to the article, some skepticism came from an expedition that found no spherules at SYD(Start of Younger Dryas) Clovis camps but after they returned to publish their work, it was clear that they sampled the wrong layers. Subsequent expeditions did return to selected sites and recovered spherules at the right dated layers. Not only spherules but "buckey-balls", the 64 carbon atom molecules associated with carbonaceous chondrite(CC) meteorites of which a couple of the CC clans have the same spectra and albedos as comets.
Research is a moving train and I believe any given writer's opinion depends on how old or how recent the studies he consults. It takes several years for each study to trickle down and get cited in subsequent studies. The other kink is even when a published study is discredited--there is no mechanism to go back and append the study unless an author chooses to do so. Human nature being what it is, most are loathe to do so and being their "suga-baby" aka (grant) money train, they are hold-outs unto their deaths that they did no wrong nor reached inaccurate conclusions.
On a personal note: For several seasons, I have been working in glacial outwash plain sand-deposit near Blakslee, PA which should contain "before through after" deposits of the 12,900 ybp event. This next summer will be my last season. I will then be looking for a researcher who will process my "dark cores". It seems that someone has developed a means to measure "stored photons" within sand/quartz grains and equate them to a deposition date-- so long as they are kept in total darkness throughout recovery and processing. Who'd a thunk, eah?
After aging we'll look at the samples for spherules, planar deformation features( PDFs) and buckey-balls; all impact evidence. This site is not far from the ancient Lake Sciota near present day Saylorsville, Monroe County, PA. Lake Sciota drained ..hummm..12,900 years ago when a mile high ice dam breached; emptying a basin about the size of Rhode Island. I think it is a fair assumption that any mammoth and mastodon herds grazing in the Broadhead Creek Valley were washed into the Lehigh River and into the Chesapeake via the Delaware River. Those that weren't directly flashed to a crisp.( Be it remembered that the casualty estimates are that all "upright life" in a 400 mile radius of Meteor Crater AZ was instantly killed by flash and over pressure when it hit 50-60k ybp)
This may be one of the culprits in the missing ice age mammal mystery. To my knowledge no large bones have been found near the terminal moraines of the maximum ice advance along Interstate 80. Those moraines have been dated to 12,900 ybp as well. Unless the ice sheet had been melted rapidly, it should have advanced rather than retreated under the cooling of the Younger Dryas. Cumulatively --spherules or not-- an impact/air bust seems to be the best fit which ties all the above observations together.
Eman
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