More than 13,000 years ago, two adults and a child walked around a fire pit on Calvert Island, off the coast of British Columbia.
The footprints they left in soft clay near the shore were soon covered with black sand, which hid them until a team of archeologists led by Dr. Daryl Fedje and Dr. Duncan McLaren unearthed them recently, exposing what are believed to be the oldest footprints ever found in North America.
The find adds to a growing body of evidence that the first people didn't arrive in the Americas via an ice-free corridor east of the Rockies about 12,000 years ago, but rather followed a route down the Pacific Coast much earlier.
"It makes the hair on the back of your head stand up," Dr. McLaren said of the moment the archeologists from the Hakai Institute and the University of Victoria made their discovery.
"When we started finding them, the excitement in the air was electric. It was really quite amazing," he said Monday. "You know there is no doubt in my mind what we were finding. It was just really cool."
The first find was made by Dr. Fedje last year, but it was an obscure, single print and its age wasn't known. The pit was closed up at the end of the season before radiocarbon dating was done. Over the winter they got the first evidence they were looking at something extremely old.
"It came back at 13,200 years ago," Dr. McLaren said.
"This year we decided to go back and open up the same area … and that's where we discovered a [fire] hearth feature and a dozen footprints … I'm certain there's more there," he said. "Some are obscure and some are overlapping. But in some cases you could see individual toes and heels."
He said the recently discovered prints seem to be focused around the fire pit, which has only been partially uncovered.
"It looks more like a family group hanging out around a hearth. There are several different sizes of footprints, and from what we can tell there are three different individuals represented. A larger adult, a smaller adult and a child's footprints as well," he said. "We could see toe prints [in one sample] and that is most likely barefoot, but there could be some kind of a moccasin [on others] … there may have been footwear, but we can't say for sure."
In recent years, archeologists have steadily been pushing back the date of the earliest human presence on the Pacific Coast.
Last year Dr. Fedje and Dr. Quentin Mackie of University of Victoria found a stone fishing weir estimated to be at least 13,700 years old submerged in the waters off Haida Gwaii.
Dr. Fedje has described the investigation of ancient coastline sites as "incredibly difficult" because the retreat of the glaciers meant sea levels rose, drowning many of the locations.
Dr. McLaren said the Calvert Island site is below the high-tide mark, which made things harder for the archeologists.
"Unfortunately, we are working in the intertidal zone, so you are racing against the tides when you are excavating there," he said. "It's a fairly remote place where you don't have massive caissons [to hold back the water] or anything like that. So you are torn between these two fields: One that you should go very slowly and excavate very delicately, and the other is that you have to rush because the tide is coming in."
Dr. Tom Dillehay, of Vanderbilt University in Tennessee, said the Calvert Island discovery is interesting, but more evidence is needed before it is scientifically verified and its importance can be evaluated.
Dr. Dillehay, who led the research that uncovered ancient footprints at Monte Verde in southern Chile, said making such a find is a startling experience.
"When we uncovered the footprint people were just stunned," he said. "It is nice to have this kind of extra signature associated with an archeological record. … It kind of adds a human element to it that goes beyond just the [stone tool] artifacts."
Dr. Dillehay didn't want to speculate, but said it would be interesting to compare the Calvert Island footprints to those from Monte Verde, which in 1997 was confirmed as the oldest known site of human occupation in the Americas, to see if they suggest a link between ancient people in Chile and those in B.C.