Details of their research were discussed at the 44th Lunar and Planetary Science Conference in The Woodlands, Texas, the BBC said.
The scientists said they believe a comet smashed into the planet.
The conclusion came after a study showed that the object that hit Earth and produced the large crater in Mexico was smaller than previously thought, the scientists said.
"So we said: How do we get something that has enough energy to generate that size of crater but has much less rocky material? That brings us to comets," said Jason Moore of Dartmouth College.
The event killed off roughly 70 percent of all species on Earth in a short period of time and would have also triggered fires, earthquakes and tsunamis, the BBC said.