Dinosaurs might not have gone extinct had the the asteroid that hit Earth some 66 million years ago and triggered the mass extinction of the giant animals struck somewhere else instead of crashing into the Yucatan Peninsula in Mexico, says a study. The impact of the asteroid, also known as the Chicxulub Impactor, caused a crater 180 km wide and heated organic matter in rocks and ejected it into the atmosphere, forming soot in the stratosphere. Soot is a strong, light-absorbing aerosol that caused global climate changes that triggered the mass extinction of dinosaurs, ammonites, and other animals, and led to the macroevolution of mammals and the appearance of humans.
Based on results of the new study, published in the journal Scientific Reports, the researchers said that the probability of the mass-extinction occurring was only 13 per cent. This is because the catastrophic chain of events could only have occurred if the asteroid had hit the hydrocarbon-rich areas occupying approximately 13 per cent of the Earth’s surface. Led by Professor Kunio Kaiho of Tohoku University in Japan, the researchers calculated the amount of soot in the stratosphere and estimated climate changes caused by soot using a global climate model
If the asteroid had hit a low-medium hydrocarbon area on Earth, mass extinction could not have occurred and the Mesozoic biota could have persisted beyond the Cretaceous/Paleogene boundary, said the study. The site of the asteroid impact, therefore, changed the history of life on Earth. According to the study, soot from hydrocarbon-rich areas caused global cooling of 8-11 degrees Celsius and cooling on land of 13-17 degrees Celsius. It also caused a decrease in precipitation by approximately 70-85 per cent on land and a decrease of approximately 5-7 degrees Celsius in seawater temperature at a 50-m water depth, leading to mass extinction of life forms including dinosaurs and ammonites.
At the time, these hydrocarbon-rich areas were marine coastal margins, where the productivity of marine algae was generally high and sedimentary rocks were thickly deposited. Therefore, these areas contained a high amount of organic matter, part of which became soot from the heat of the asteroid’s impact, the study said. Thus, the researchers concluded that the Chicxulub impact occurred in a hydrocarbon-rich area and is a rare case of mass extinction being caused at such an impact site.