Super Unlucky: Dinosaur Killing Asteroid Had to Hit a Sweet Spot to Cause Extinction Event

Kaiho clarified the relationship between the findings and concluded that the significant cooling and mass-extinction event could have only have occurred if the asteroid had hit hydrocarbon-rich areas occupying approximately 13 percent of the Earth’s surface (orange areas in Fig. 1).

If the asteroid had hit a low-medium hydrocarbon area on Earth (occupying approximately 87 percent of the Earth’s surface), mass extinction could not have occurred and the Mesozoic biota could have persisted beyond the Cretaceous/Paleogene boundary.

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°C and cooling on land of 13-17°C. It also caused a decrease in precipitation by approximately 70-85 percent on land and a decrease of approximately 5-7°C 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.

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. Kaiho and Oshima are doing further studies to clarify the frequency of all the cooling events by impacts.

Kaiho’s team is analyzing climate change caused by large volcanic eruptions that may have contributed to other mass extinctions. It is hoped that the results will lead to further understanding of the processes behind those mass extinctions.

Contacts and sources:
Kunio Kaiho
Tohoku University