"When a huge asteroid slammed into the Earth 65 million years ago, it began a catastrophic chain of events that caused the extinction of the dinosaurs, and 75% of the species on Earth. One devastating aspect of the event was when hot debris rained down, starting enormous wildfires across the entire planet. Scientists from the Southwest Research Institute have come up with a model that calculates how large an impact had to be to cause massive fires. A crater 85 km (52 miles) across probably caused continent-wide fires, and a crater 135 km (83 miles) across could ignite fires around the whole world."
Universe Today - What Impact Would Set the World on Fire?
