In 2014, archaeologists were digging in the sands of Calvert Island, British Columbia when they made an unexpected discovery: a single footprint, seemingly belonging to a human, pressed into the clay below the surface. As Nicholas St. Fleur reports for the New York Times, the team recently announced that subsequent excavations revealed an additional 28 footprints, which are believed to be the oldest human tracks ever found in North America.

In a paper published in PLOS One, researchers write that the footprints are remarkably well preserved; some even have visible arch, toe and heel marks. The prints appear to have been made by at least three individuals, and based on the size of the tracks, researchers believe they belonged to two adults and a child. The team was also able to perform radiocarbon dating on sediments and two pieces of preserved wood found in the footprints, which revealed that the impressions are between 13,000 and 13,300 years old.

“This provides evidence that people were inhabiting the region at the end of the last ice age,” Duncan McLaren, an anthropologist from the Hakai Institute and University of Victoria and lead author of the study, tells St. Fleur.

Today, Canada’s Pacific Coast is covered in temperate rainforests and thick bogs, making it a difficult area for archaeologists to explore. But as Laura Geggel explains in Live Science, the region looked quite different at the end of the last ice age, around 11, 000 to 14,000 years ago. Large quantities of Earth’s water were contained in towering glaciers, and sea levels at Calvert Island may have been as much as 10 feet lower than they are today. Still, ancient humans would have needed a boat to access the island. In the new study, researchers suggest that the prints may have been made by people “disembarking from watercraft and moving towards a drier central activity area.”

The footprints may therefore offer additional evidence that the first settlers of North America came to the continent by following a route along the Pacific coastline, and not by crossing a land bridge that connected Asia and North America, as was once widely believed. Some researchers have theorized that these early colonizers were aided on their coastal journey by a “Kelp Highway”—underwater kelp forests that fostered diverse ecosystems and offered ancient humans a rich array of resources.

The prints add to a growing body of evidence that suggests ancient humans were thriving on North America’s Pacific coast during the last ice age. As Gemma Tarlach of Discover points out, Calvert Island is located just a few miles south of Triquet Island, home to one of the oldest known North American settlements—a 14,000-year-old village where archaeologists recently found fish hooks, stone tools, a hearth and other ancient relics.

And Calvert Island may hold more stories about the first humans to arrive in North America. The authors of the study write that it is likely “many more tracks exist in the surrounding and unexcavated sediments.”

Editor's Note March 30, 2018: The headline of this article has been updated to clarify that the footprints are the oldest known in North America.