Chixculub: cold, darkness and soot did it for dinosaurs (Introduction)

by David Turell , Sunday, March 22, 2020, 00:03 (1498 days ago) @ David Turell

Soot is the latest conclusion of a new study:

https://phys.org/news/2020-03-darkness-cold-responsible-dinosaur-killing-extinction.html

"A new study in AGU's journal Geophysical Research Letters simulates the contributions of the impact's sulfur, dust, and soot emissions to the extreme darkness and cold of the impact winter. The results show the cold would have been severe but likely not devastating enough to drive a mass extinction. However, soot emissions from global forest fires darkened the sky enough to kill off photosynthesizers at the base of the food web for well over a year, according to the study.

"'This low light seems to be a really big signal that would potentially be devastating to life," said Clay Tabor, a geoscientist at the University of Connecticut and lead author of the new study. "It seems like these low light conditions are a probable explanation for a large part of the extinction."

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"The Chicxulub asteroid impact spewed clouds of ejecta into the upper atmosphere that then rained back down to Earth. The returning particles would have had enough energy to broil Earth's surface and ignite global forest fires. Soot from the fires, along with sulfur compounds and dust, blocked out sunlight, causing an impact winter lasting several years. Previous research estimates average global temperatures plummeted by at least 26 degrees Celsius (47 degrees Fahrenheit).

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"Their results suggest soot emissions from global fires absorbed the most sunlight for the longest amount of time. The model showed soot particles were so good at absorbing sunlight that photosynthesis levels dropped to below one percent of normal for well over a year.
"Based on the properties of soot and its ability to effectively absorb incoming sunlight, it did a very good job at blocking sunlight from reaching the surface," Tabor said. "In comparison to the dust, which didn't stay in the atmosphere for nearly as long, and the sulfur, which didn't block as much light, the soot could actually block almost all light from reaching the surface for at least a year."

"The darkness would have been devastating to photosynthesizers and could explain the mass extinction through a collapse of the food web, according to the researchers. All life on Earth depends on photosynthesizers like plants and algae that harvest energy from sunlight.
Interestingly, the temperature drop likely wasn't as disturbing to life as the darkness, according to the study.

"'It's interesting that in their model, soot doesn't necessarily cause a much larger cooling when compared other types of aerosol particles produced by the impact-but soot does cause surface sunlight to decline a lot more," said Manoj Joshi, a climate dynamics professor at the University of East Anglia in the United Kingdom who was not connected to the new study."

Comment: However it happened, the dinos are gone