The bone does not look like much.

A fragment of horse jaw, brown with age, slightly mineralized, about the size of a large man’s hand.

It came out of a cold cave in the northern Yukon Territory of Canada, pulled from frozen sediment alongside the bones of mammoths, bison, and other animals of the last Ice Age.

For decades, it sat in a museum collection, catalogued and stored, one of thousands of faunal specimens from an excavation that had generated more controversy than conclusions.

Then a researcher placed it under a microscope.

The marks became visible only under magnification: narrow, clean-edged, parallel incisions running across the surface of the bone.

Not the crescentic bite marks left by carnivore teeth.

Not the rougher, irregular damage caused by trampling or rock fall.

Not the branching patterns of root etching.

Clean, linear, deliberate — the kind of marks that, in zooarchaeological analysis, carry a specific signature.

The signature of a stone tool.

The horse whose jaw produced that fragment lived during the Last Glacial Maximum — the coldest, harshest period of the last Ice Age, when ice sheets covered much of the Northern Hemisphere and sea levels were dramatically lower than today.

When the bone was submitted for accelerator mass spectrometry radiocarbon dating and the result was calibrated against the atmospheric radiocarbon record, the date that came back was approximately 24,000 years before present in calibrated calendar years.

Twenty-four thousand years ago, during the deep freeze of the Last Glacial Maximum, someone was in eastern Beringia.

Someone was butchering horses in what is now the northern Yukon.

And the evidence that they were there — cut marks on bone, directly dated — had been sitting in a collection for three decades before anyone with the right tools and the right questions looked at it carefully enough to see.

That is the story of Bluefish Caves.

And it is, in ways that ripple far beyond a single cave in the Yukon, one of the most consequential pieces of evidence in the long, contentious, still-unresolved debate about when and how the Americas were first peopled.