Deep in the bottom sediments of a leafy lake, archaeologists have found more evidence that an asteroid blew up over South Carolina as people lived below.
The lesson of White Pond is simple: Sooner or later another one may too.
"The big question is what did it do? What effect did it have on humans?," said Chris Moore, a South Carolina Institute of Archaeology and Anthropology researcher, who led the core-sample study at the private pond near Elgin.
"We have ideas. But we certainly don't have good answers," he said.
The Clovis people camped in this central South Carolina region near present-day Kershaw about 13,000 years ago, hunting huge tusked elephantine creatures. But those early people and much of their game seemed to vanish at about the same time, evidently decimated by the blast and fumes of a comet that landed or blew apart in the Earth's atmosphere — the sort of catastrophe widely thought to be a disaster of the far past, millions of years ago.
Platinum testing and radiocarbon dating of the core samples told the tale, again, as it has at other sites in the state, across the country and the world.
"This wasn't like the dinosaur extinction 66 million years ago. We have some animals and some humans that survived," Moore said.
But the blast ignited wildfires, and threw a mass of soot into the atmosphere that blocked out the sun, likely for months. Plant and animal traces in the core samples dropped off immediately.
Conventional thinking had been that the Clovis people declined as the mastodons, mammoths and saber-toothed tigers they hunted died out in a cooling climate. But more recent archaeological findings have been challenging the notion, and suspicions have turned to the sky.
After Harvard University researchers in 2013 found rare concentrations of platinum in Greenland ice core samples — suggesting a comet or asteroid impact — Moore and nine other researchers began digging at a dozen sites around the East and far West.
The abnormal concentrations of platinum in late Clovis-era soils across the continent points to the likelihood of a vast, catastrophic asteroid or comet impact. A 19-mile-wide crater has now been found under a glacier in Greenland that "might be the smoking gun," Moore said.
The White Pond sediments are the latest confirmation. The organic-rich soils, which include the spore of large animals, helped narrow the timeline to about 12,800 years ago. The study was published last week in Scientific Reports.
The asteroid, combined with a rapid cooling at the time that led to an ice age and possibly overhunting, could well have doomed both the mastodons and the Clovis, Moore said.
Before White Pond, Moore dug at other locations in South Carolina, including the Topper site — an ancient quarry unearthed in the woods near Allendale that already was renowned for Clovis findings. The White Pond site is famous among archaeologists for a groundbreaking pollen study that showed how plant life changed across 20,000 years.
The find stokes curiosity of what life was like before the present day and what that can teach us, said institute archaeologist Al Goodyear, who co-authored the study.
Asteroid impacts aren't in the distant past. In 2013, a blast in the sky over Siberia, Russia, injured nearly 1,500 people and put more than 100 in the hospital.
"That was the real deal," Goodyear said. "The Earth's history has been one of terrestrial impacts. There are going to be more to come. What was happening to humans in this ancient past?"
The institute team is continuing to study the ancient soils, hoping to come up with more answers about the fate of the Clovis people.