The asteroid impact that led to the demise of the dinosaurs would only have resulted in a mass extinction in areas rich in hydrocarbons, occupying approximately 13% of the Earth’s surface, according to a study in Scientific Reports.
66 million years ago the Chicxulub asteroid impact, in what is now Mexico, led to an ecosystem collapse including the devastation of land vegetation, and the extinction of dinosaurs and approximately 75% of all land and sea animals. Previous research has shown that the burning of hydrocarbons in rocks as a result of the asteroid impact produced stratospheric soot and sulphate aerosols causing extreme global cooling and drought. However, the quantities of hydrocarbons and sulphur in rocks varies widely depending on the location, suggesting that the probability of an extinction event was dependent on the impact site.
Kunio Kaiho and Naga Oshima calculated the amount of stratospheric soot and sulphate that would be formed by a virtual asteroid impact, depending on the amount of hydrocarbon and sulphate present in the ground. Using five quantities of black carbon (equivalent to soot), 20, 200, 500, 1500, and 2600 teragrams (Tg), the authors estimated the effect on the climate caused by an asteroid impact. They found that in areas of the earth with a high or very high concentration of hydrocarbons (equivalent to 230-590 Tg of black carbon and 590-2,300 Tg of black carbon entering the stratosphere), the resulting decrease in global mean surface air temperature would produce the conditions responsible for a mass extinction. However, in areas with lower concentrations of hydrocarbons, a mass extinction would not have occurred. The authors calculate that approximately 13% of the earth’s surface meets the requirements that would have caused this mass extinction.