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| An artistic expression of how a large impact might have looked (Carsten Egestal Thuesen / GEUS) |
That’s a question that has been hotly debated by scientists since 2007, with the Topper archaeological site, located on the Savannah River in western Allendale County, South Carolina, right in the middle of the comet impact controversy. The new study provides further evidence that it may not be such a far-fetched notion.
In 2007, archaeologists led by Dr Richard Firestone of the Lawrence Berkeley National Laboratory found spherules of metals and nano-sized diamonds in a layer of sediment dating 12,900 years ago at 10 of 12 archaeological sites. The mix of particles is thought to be the result of an extraterrestrial object, such as a comet or meteorite, exploding in the Earth’s atmosphere. Among the sites examined was the Topper, one of the most pristine sites in the United States for research on Clovis, one of the earliest ancient peoples.
“This independent study is yet another example of how the Topper site with its various interdisciplinary studies has connected ancient human archaeology with significant studies of the Pleistocene,” said Dr Albert Goodyear, an archaeologist with University of South Carolina and co-author on the new study. “It’s both exciting and gratifying.”
Younger-Dryas is what scientists refer to as the period of extreme cooling that began around 12,900 years ago and lasted 1,300 years. While that brief Ice age has been well-documented – occurring during a period of progressive solar warming after the last Ice age – the reasons for it have long remained unclear.
Dr Firestone’s team presented a provocative theory: that a major impact event – perhaps a comet – was the catalyst. His copious sampling and detailed analysis of sediments at a layer in the earth dated to 12,900 years ago, also called the Younger-Dryas Boundary (YDB), provided evidence of micro-particles, such as iron, silica, iridium and nano-diamonds. The particles are believed to be consistent with a massive impact that could have killed off the Clovis people and the large North American animals of the day. Thirty-six species, including the mastodon, mammoth and saber-toothed tiger, went extinct.
Dr Malcolm LeCompte, a research associate professor at Elizabeth City State University and lead author of the new study, began independent study in 2008 using and further refining Dr Firestone’s sampling and sorting methods at two sites common to the three studies: Blackwater Draw in New Mexico and Topper. He also took samples at Paw Paw Cove in Maryland.
At each site he found the same microscopic spherules, which are the diameter of a human hair and distinct in appearance. He describes their look as tiny black ball bearings with a marred surface pattern that resulted from being crystalized in a molten state and then rapidly cooled. The investigation also confirmed that the spherules were not of cosmic origin but were formed from earth materials due to an extreme impact.
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| Left: Dr Tariq Ghaffar of the Public Broadcasting System’s Time Team America excavating pedestals capped by debitage at the Topper archeological site (Albert Goodyear / Meg Galliard). Right: spherules picked from the YDB layer at the Topper site (Topper), the Blackwater Draw site (BWD-D and BWD-D/C), and the Paw Paw Cove site (PPC) (Malcolm A. LeCompte et al) |
“What we had at Topper and nowhere else were pieces of manufacturing debris from stone tool making by the Clovis people. Topper was an active and ancient quarry at the time,” Dr LeCompte said. “Al Goodyear was instrumental in our approach to getting samples at Topper.”
Dr Goodyear showed Dr LeCompte where the Clovis level was in order to accurately guide his sampling of sediments for the Younger Dryas Boundary layer. He advised him to sample around Clovis artifacts and then to carefully lift them to test the sediment directly underneath.
“If debris was raining down from the atmosphere, the artifacts should have acted as a shield preventing spherules from accumulating in the layer underneath. It turns out it really worked!” Dr Goodyear said. “There were up to 30 times more spherules at and just above the Clovis surface than beneath the artifacts.”
Dr LeCompte said the finding is “critical and what makes the paper and study so exciting. The other sites didn’t have artifacts because they weren’t tool-making quarries like Topper.”
“While the comet hypothesis and its possible impact on Clovis people isn’t resolved,” Dr Goodyear said. “This independent study lends greater credibility to the claim that a major impact event happened at the Younger Dryas Boundary 12,900 years ago.”
“The so-called extra-terrestrial impact hypothesis adds to the mystery of what happened at the YDB with its sudden and unexplained reversion to an ice age climate, the rapid and seemingly simultaneous loss of many Pleistocene animals, such as mammoths and mastodons, as well as the demise of what archaeologists call the Clovis culture,” Dr Goodyear said. “There’s always more to learn about the past, and Topper continues to function as a portal to these fascinating mysteries.”
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