The scientists ran computer models simulating the amount of soot that asteroid impacts would have generated depending on the amount of hydrocarbons in the ground. They next estimated the climate effects caused by these different impact scenarios.
The researchers calculated the level of climate change needed to cause a mass extinction was a 14.4 to 18 degrees Fahrenheit (8 to 10 degrees Celsius) drop in global average surface air temperatures. This would involve an asteroid impact sending 385 million tons (350 million metric tons) of soot into the stratosphere.
The scientists found that a mass extinction would have occurred from the impact only if it had hit 13 percent of the surface of the Earth, including both land and oceans.