WASHINGTON — Researchers have found evidence that a comet or space rock smashed into Earth 56 million years ago, perhaps setting off a massive warming that began around that time.

It’s a suggestion that is causing much debate among scientists, many of whom question the link. Researchers study the mysterious ancient warming to better understand current man-made climate change and Earth’s future.

About 56 million years ago Earth warmed by about 9 to 14 degrees and then returned to normal, all in about 100,000 years. This helped lead to some extinctions and the rise of mammals. Theories about the cause have pointed to increased carbon in the atmosphere from many erupting volcanoes; a Greenland volcano that cooked a huge coal deposit; and sudden methane releases from underwater. But a new study in the journal Science suggests a link to a cosmic crash.

At the same time Earth started getting hotter, it seems to have been hit by a space object that sent debris flying around North America and maybe around the world, according to an examination of soil cores. The scientists didn’t find the space rock or comet or a crater; instead, they found what they said were nearby rocks superheated by the crash.

Study lead author Morgan Schaller, an Earth sciences professor at Rensselaer Polytechnic Institute, isn’t quite saying the crash caused the massive carbon jump and the warming, but it’s awfully suspicious timing, he said.