Wildfires are getting worse. Parts of the United States, scientists say, are experiencing wildfires three times as often — and four times as big — as they were 20 years ago. This summer alone, smoke from Canadian blazes turned North American skies an unearthly orange, “fire whirls” were seen in the Mojave Desert and raging flames in Maui led to disaster.

Records of the distant past can reveal what once drove increased fire activity and what can happen as a result. In a new study published Thursday in the journal Science, a group of paleontologists that analyzed fossil records at La Brea Tar Pits, a famous excavation site in Southern California, concluded that the disappearance of sabertooth cats, dire wolves and other large mammals in this region nearly 13,000 years ago was linked to rising temperatures and increased fire activity spurred by people.

“We implicate humans as being the primary cause of the tipping point,” said Robin O’Keefe, an evolutionary biologist at Marshall University. “What happened in La Brea, is it happening now? Well, that’s a really good question — and I think we should figure it out.”

Earth has seen five mass extinction events so far; some scientists argue that the disappearance of large mammals at the end of the last ice age was the start of a sixth. “It was the biggest extinction event since an asteroid slammed into Earth and wiped out all the dinosaurs,” said Emily Lindsey, a paleoecologist at La Brea Tar Pits and Museum and author of the new study, adding that the disappearance could very well represent “the first pulse” in a sixth mass extinction.