Eons ago, down in the southernmost reaches of what is now Chile, a child stepped in a patch of mud. Unless kids have changed a lot since ancient times, this was probably not a remarkable event.
But last month, as a team of scientists scoured this site - known as Monte Verde - that small footprint began to take on an enormous significance.
After 20 years of excavation and carbon dating, and a firsthand inspection last month by some of his most skeptical colleagues, University of Kentucky archaeologist Tom Dillehay has established that Monte Verde is the oldest known human settlement in the Americas.
Not only is this small encampment of about 25 inhabitants 13 centuries older than any other known American settlement, its discovery near the continent's southern tip negates nearly 60 years of scientific consensus.
Previously, archaeologists believed the first Americans arrived here by crossing a now-submerged land bridge at Alaska's Bering Strait about 11,200 years ago. The estimated age of the Monte Verde site, about 12,500 years, renders that theory obsolete.
It's the kind of discovery that will color the work of researchers for years to come. "Once you have a new benchmark in science," says Dena Dincauze, a University of Massachusetts anthropologist, "you have to attach it to everything else."
Indeed, that's what happened in the 1930s when archaeologists unearthed human tools with a distinctive fluted point at a site in northeast New Mexico. In subsequent years, researchers discovered similar "Clovis" tools in several digs throughout North America, concluding that a single tribe of nomads crossed the Bering Strait at one time and peopled the entire continent.
The Monte Verde discovery directly challenges that theory and reopens the debate about when and how the Americas were colonized. Some scientists argue that early peoples may have sailed across the Pacific Ocean or crossed the Bering Strait and migrated down the coast. Another theory says that the strait was crossed, but far earlier than once thought. It has been proved that the strait was traversable for a brief time about 20,000 years ago.
Monte Verde also adds a few new daubs to the scientific portrait of the first American colonists. The Chilean site, located about 500 miles south of Santiago, was immaculately preserved by chance when a nearby stream backed up and submerged the encampment in a peat bog.
Although there were no Clovis tools found here, the site contains some artifacts never before seen at an early American site: remnants of hide-covered huts, bits of rope, a chunk of mastodon meat, digging sticks, finely crafted tools of bone and tusk, clumps of seaweed used as medicine, and the now-famous footprint.
In addition, Dr. Dillehay says he has found another set of human-like artifacts at a deeper level that he believes could be as old as 33,000 years. If this discovery can be verified, he says, it might suggest that the continent was once home to an entirely separate species of early humans.
Still, some experts say that Monte Verde's ultimate relevance will depend on how much corroborating evidence is unearthed in years to come. "It's pretty clear now that at a fairly early point in time, two different groups of people existed on the continent," says Vance Haynes, an anthropologist at the University of Arizona. "It's a significant discovery, but we'll look back on it with even more favor as more sites are found."