In the 1920s, archaeologists dug up a trove of ancient artifacts near Clovis, New Mexico. What humans had known about their past was changed forever. These artifacts were the oldest man-made objects found on the Western Hemisphere, and the discovery led to a theory that the first humans to set foot in the Americas did so around about 13,000 years ago, and that they made and used tools like the ones found near Clovis.

Now a group of archaeologists from Texas State University are offering some of the most convincing evidence yet to challenge this “Clovis First” theory. They’ve recently discovered about 150,000 artifacts near at the Gault Archaeological Site near Killeen, Texas. What they’ve found could change what we know about the timeline of human history.

Tom Williams is one of the archaeologists who has been working at Gault, and he doesn’t mince words when he talks about the significance of this research.

“It really is changing the paradigm that we currently consider for the earliest human occupation in the Americas,” Williams says.

The search for artifacts older than the Clovis ones began at the Gault site in 2007, and since then, Williams and his team have found about 150,000 technological tools that range from hide-scrapers, to blade cores, which were used to create long knives out of flint, to projectile points.

“These projectile points are particularly interesting because they don’t look like Clovis,” Williams says. “And at the moment they appear to be unique in the archaeological record in the earliest part of prehistory in North America.”

Williams conservatively estimates that these artifacts could be 16,000-20,000 years old, which would put them at about 3,000 years older than any Clovis artifact. The age of the tools found at Gault suggests that humans arrived in North America much earlier than what was previously thought. They’re utterly unique.

“Right now we find no other technology that looks like this assemblage,” Williams says.

For Williams, finds like this illuminate one of archaeology’s great appeals.

“One of the things with archaeology is you never know what’s down beneath the earth,” Williams says.