Adapted from an article in the LA Times (July 15, 2016):
A layer of soot deposited after the K/T extinction event may explain why dinosaurs but not everything else died. (See The Cosmos, A Closer Look 8.5, p. 220.)
Researchers from Japan argue that the 6-mile-wide asteroid slammed into an oil field in the present day Yucatán Peninsula and triggered an inferno that launched a massive cloud of smoke into the sky. The resulting layer of soot that enveloped the globe would have been just the right thing to kill the dinosaurs and most other land-dwelling creatures.
Previous theories have postulated that the asteroid sparked the mass extinction by releasing high levels of sulfuric acid particles in the atmosphere. The particles would have caused complete darkness, near-freezing temperatures and acid rain. However, sulfuric acid particles don’t hang around for very long — and if they did, the results would have been catastrophic for many species besides dinosaurs. Instead, soot from the immense fire caused by the Chicxulub impact was a prime candidate.
The scientists collected soot samples from the thin band of rock that marks the timing of the extinction of dinosaurs and found the same composition from locations around the world. They hypothesize that soot was slowly deposited on land in the five years following the massive collision. The powdery substance is primarily made of black carbon that results from incineration of organic matter.
The tiny particles are about a million times more light-absorbing than carbon dioxide. They would have blocked about 85% of sunlight from reaching Earth and cut rainfall by nearly 80%, creating near-drought conditions, as well as causing temperatures to plummet. In this post-asteroid wasteland, plants began to die off, cutting off the food supply to creatures higher up the food chain — such as the dinosaurs — while allowing smaller mammals, birds and aquatic creatures to survive.
Link: the LA Times article