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What might have happened?
According to the theory, a comet broke apart in the atmosphere above what is now eastern North America, producing massive, multiple explosions as its pieces slammed into the surface with more force than all the world's nuclear weapons combined.
What's the evidence?
The fallout from the explosions would have dusted the Earth with microscopic nanodiamonds, magnetic particles, iridium and black carbon. All of those substances have been found in a layer of soil, found continent-wide, dated to about 12,900 years ago.
How was life affected by it?
The explosions and resulting climate change could explain the sudden disappearance of large mammals, such as mammoths and mastodons, at that same time period. Also, it could explain the abrupt end in the archaeological records of the Clovis people, the first to populate North America.
For the second time in less than a decade, a South Carolina river bluff holds evidence pointing to a theory with history-rewriting potential.
Microscopic soil particles from the Topper site near Allendale might hold a tiny key to a big theory: that comet-caused explosions wiped out the mammoths and mastodons, prompted the last ice age and decimated the first human culture in North America about 12,900 years ago.
The comet theory first began generating a buzz at an international meeting of geophysicists in Mexico in May. The findings were published this month in the Proceedings of the National Academy of Sciences. They are about to go mainstream, with a National Geographic Channel segment tonight. The History Channel will film for a future show at Topper this week.
"People are fascinated by it," said Allen West, an Arizona geophysicist and one of the leaders of the comet team, who is speaking Wednesday at USC. "It has diamonds and giant elephants and Indians. Any new catastrophe theory that comes along gets plenty of attention."
The new theory holds that a comet broke apart in the atmosphere above what is now eastern North America, producing multiple explosions and wildfires as the pieces smashed into the surface.
Scientists, led by Richard Firestone of the Lawrence Berkeley National Laboratory in Berkeley, Calif., took soil samples from throughout North America and in Belgium. In a layer dating to about 12,900 years ago, they found high levels of iridium, nanodiamonds and glass-like carbon that could have been caused by a comet explosion and subsequent fires.
The Topper site, on the banks of the Savannah River, provided compelling evidence, in part because of earlier findings there by Al Goodyear of the S.C. Institute of Archaeology and Anthropology at USC.
Goodyear drew international attention in 2004 when stone points found at Topper that apparently were sharpened by humans were carbon dated to nearly 50,000 years ago. That put human beings in North America thousands of years earlier than thought. For generations, scientists have thought the first humans arrived 13,000 years ago via a land bridge from Asia.
Goodyear's work at Topper, along with similar finds in Brazil and Chile, prompted scientific reconsideration of when humans arrived in North America. It also led to skepticism by scientists who didn't buy Goodyear's theory. In that regard, he found kindred spirits in the comet group.
"This is a pretty wild theory," Goodyear said with a chuckle. "I'm glad I'm not doing this one."
He welcomed West to dig at Topper. At the same depth as Topper's undeniable Clovis artifacts, West found high concentrations of iridium, nanodiamonds and glasslike carbon.
West's findings prompted Goodyear to do his own study on the disappearance of Clovis points. These stone tools, used for hunting and scraping, are found throughout North America only in soil dating back about 13,000 years or more.
The Clovis points stopped showing up in soil layers dating back to 12,900 years ago. Not long after that, a different style of points began showing up from people scientists have dubbed the Redstone culture. Most experts suspect a surviving remnant of the Clovis culture grew into the Redstone culture.
Goodyear's recent study found there were four times as many Clovis points as Redstone points at similar sites. That would indicate a huge population drop from the Clovis to Redstone cultures, possibly caused by some natural catastrophe.
Goodyear's findings put him squarely on the side of the comet theory, and he's not the only one to be swayed, West said.
"It has been pretty quickly embraced," West said. "People weren't comfortable with the existing theories on the disappearance of the large mammals and the Clovis people."
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