Archaeologists have long debated when and how the first people made it to North America from Asia.
Researchers previously thought early humans crossed the Bering land bridge from Siberia to Canada 13,000 years ago.
But artifacts discovered in a Mexican cave shift the timeline, revealing people may have been in North America 30,000 years ago.
The land bridge was impassable at that time, so the research suggests the first Americans arrived by sea.
New evidence suggests people have been living in North America twice as long as archaeologists previously thought.
Stone tools and artifacts discovered in a remote cave in Zacatecas, Mexico, offer evidence that humans were on the continent as far back as 32,000 years ago, during the last ice age.
That upends the idea that the first people arrived in North America between 18,000 and 13,000 years ago after continent-hopping from modern-day Siberia via the Bering land bridge. The new finding, described in a study in the journal Nature on Wednesday, pushes that timeline back at least 15,000 years. It also shatters our previous understanding of how humans arrived in the North America: Since the land bridge was blocked during the last ice age and only opened after the ice started to recede, the new timeline means early people likely made their way on the ocean.