A new study suggests the Neanderthals started dying off long before a massive volcanic eruption caused Europe to freeze over, which means the most likely cause of their demise was competition with modern humans.

How the Neanderthals -- an extinct species that closely resembles humans -- died has been the subject of years of debate within the archeological community.

In one camp are those who argue it was evolution that did them in. Modern humans simply won out as the dominant species.

In the other camp are those who believe that climate change, sparked in large part by a massive volcanic eruption in Italy, wiped them off the face of the planet.

The volcano erupted in what is now Naples, covering much of Europe in ash. This, combined with a cold spell that hit the Northern Hemisphere, combined to create what's called a "volcanic winter," which destroyed the Neanderthals -- or so the theory goes.

But a team of 40 European researchers led by geographer John Lowe of Royal Holloway, University of London, claims to have debunked the climate theory altogether.

That's because they've discovered the big eruption actually happened 40,000 years ago. By then, the Neanderthals were mostly already extinct. Early modern humans from Africa, or possibly the Middle East, had already replaced them in most of Europe.

The team determined this via a new method, pioneered at Royal Holloway and Oxford, that links layers of volcanic glass invisible to the naked eye -- called cryptotephra -- to specific volcanic eruptions.

"Our evidence indicates that, on a continental scale, modern humans were a greater competitive threat to indigenous populations than the largest known volcanic eruption in Europe, even if combined with the deleterious effects of climate cooling," the study, published in the Proceedings of the National Academy of Sciences, concludes.