This new theory shakes up the popular belief that has been held in place for some 20 years. It was a widely accepted fact Homo neanderthalensis persisted in southern Iberia while modern humans (homo sapiens) were advancing in the same region. But the international study, in which researchers from the Spanish National Distance Education University (UNED) participated, pokes holes in that hypothesis.

If the new evidence holds any weight, then the popular theory that modern humans and Neanderthals co-existed—and possibly even interbred—for millennia has just been shot down, especially as another hugely accepted theory shows modern humans didn’t settle in the region until 42,000 years ago.

The new study used the improved dating method “ultrafiltration,” a technique that removes modern carbon that can contaminate ancient collagen in bones. Using the new method, lead researcher Dr. Rachel Wood, of Australian National University (ANU), and her colleagues tested 215 bones from 11 sites where previous radiocarbon dating had supported the later survival of Neanderthals. The study is published today (Feb. 4) in the journal Proceedings of the National Academy of Sciences (PNAS).

The team found the vast majority of the bones contained insufficient collagen to be successfully dated. But of those that could be tested, Wood and her colleagues found enough evidence that placed the earliest record to be about 50,000 years ago at two separate sites.

Wood said the new evidence doesn’t completely exclude the possibility that Neanderthals lived until 35,000 years ago. Because radiocarbon testing couldn’t be accurately completed on many of the fossils, it’s possible some may have been from a later period. But for the two of the 11 sites examined, Wood says the evidence suggests Neanderthals died out 50,000 years ago.