A recent archaeological discovery challenges current theories about human history.

Archaeologists have uncovered a 1.5-million-year-old stone tool in a location where, according to existing knowledge, humans have only been present for the past 150,000 (!) years, the Daily Star reports. Could this mean it’s time to rewrite the history books?

Who could have lived in Sulawesi at that time?

In recent years, researchers have been increasingly focused on the Indonesian island of Sulawesi, where this shockingly ancient tool was discovered. The find raises serious questions about which human ancestor might have lived in the region at that time. Archaeologists have been excavating in Wallacea, the island group situated between the Asian and Australian continental shelves.

What makes these newly unearthed tools particularly remarkable is that they were made from flint, a very hard, fine-grained sedimentary rock that requires considerable skill to shape. Laboratory analysis determined the tools were created between 1.04 and 1.48 million years ago, which is hundreds of thousands of years before any known appearance of Homo sapiens.

Clues of an unknown human species?

While Homo erectus, a distant ancestor of modern humans, did exist during this period, Sulawesi has yielded very few ancient human-related remains. Until now, the oldest evidence of human presence there dated back just 150,000 years. This new find suggests that an unknown human species may have settled the island much earlier, though exactly who they were remains unclear.

This discovery could also breathe new life into research on the so-called “hobbit humans,” specifically the Homo luzonensis and Homo floresiensis, whose origins are still being investigated. These mysterious, small-statured hominins lived on the nearby islands of Luzon and Flores, but it’s possible that their shared ancestor may have once roamed Sulawesi as well.