... A new study by Kunio Kaiho and colleagues published in the journal Scientific Reports suggests a possible explanation. The K-Pg boundary contains soot. Although originally thought to be produced by wildfires, studies of its chemistry suggest that it is actually derived from burning hydrocarbons (crude oil). This fact seems puzzling until you consider that the Gulf of Mexico contains vast oil reserves. The Jurassic Cantarell oil field, the largest in Mexico, is nearby and, in fact, the Chicxulub crater was only discovered because geologists were mapping the area in search of oil.
As the Chicxulub asteroid tore into the earth, it released the oil locked in the rock. The Deepwater Horizon spill produced 4.9 million barrels of oil from just a tiny hole in the ocean floor. The Chicxulub crater was 180 kilometers across. The intense heat of the impact would have burned the oil to create clouds of black soot and shot them into the stratosphere. Critically, tiny soot particles can stay up in the atmosphere for years. But was there enough to block out the sun?
The researchers from Tohoku University in Japan studied the chemistry of soot at the K-Pg boundary and then estimated the amount of soot produced by impact. The total burned carbon produced was on the order of 1.8 to 60 billion tons.
They then used computer models to estimate the effects on the climate. Their models showed that the soot would have been highly effective in blocking light. Depending on the amount of soot, sunlight would have been reduced by 50% to 90%, and the global temperature would have cooled by between 6°C and 18°C, with cooling being especially severe towards the poles. Cooler temperatures would have also reduced rainfall, leading to widespread drought.
Critically, the soot cloud would stay aloft for years. The darkness and cooling were most severe in the first few years, but it would have taken a decade for light levels to slowly return to normal, and even longer for the climate to return to normal.
The research also helps put a time limit on the dinosaur extinction, suggesting the bulk of it took place in a span of less than ten years.
This could also explain why other asteroid impacts aren't associated with mass extinctions. It may have been the unlucky coincidence of a huge oil field and a giant asteroid impact that made Chicxulub so deadly.
There is a certain irony in the possibility that the same oil that did in the dinosaurs is now being used to run our own civilization – and perhaps threatening it as well. Kunio Kaiho et al.
Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction, Scientific Reports (2016).