While the popular Netflix film “Don’t Look Up” has heightened public awareness about the potentially disastrous repercussions of an asteroid impact on planet Earth, a new study reveals how the Chicxulub impact 66 million years ago wiped out 75 percent of all species on the planet, including dinosaurs.
A massive asteroid with a diameter of about 10 kilometers collided with Mexico’s northern Yucatán peninsula, ejecting material the size of Connecticut and more than twice the height of Mt. Everest and dispersing it throughout the world.
“The impact blast and fallout ignited widespread fires, which together with rock dust, soot and volatiles ejected from the crater, blotted out the sun globally in an impact winter that may have lasted years, resulting in the extinction,” explains Christopher Junium.
Scientists have long suspected small sulfate particles in the stratosphere as the principal cause of huge climate change and mass extinction, but they were unsure of the sulfur’s fate.
“There has been uncertainty regarding how much reached the stratosphere where its effects on climate would have been greatly magnified,” adds Junium.
In a study published this month in PNAS, researchers from Syracuse University, the University of St Andrews in Scotland, the University of Bristol in England, and Texas A&M University link high levels of stratospheric sulfur to the impact and its location, which was rich in the sulfate mineral gypsum.
While comets, asteroids, and other planetary bodies have collided with Earth many times over its history, the geologic record indicates nothing about how these collisions altered the trajectory of life. The Chicxulub impact was unique in changing the biosphere’s equilibrium and in the geologic record left behind, a thin layer of silt known as the K-Pg boundary, which can be found in marine and terrestrial rocks all over the planet.
The crew did fieldwork along the Brazos River in Central Texas, collecting and analyzing rock samples that document the Chicxulub impact’s immediate aftermath. Researchers were able to detect the specific transformations that sulfur aerosols go through when they climb above the ozone layer and are exposed to UV radiation, establishing diagnostic signs in the stable isotopes of the sulfur gases, thanks to new geochemical techniques.
“The unique fingerprints we’ve measured in these impact sediments provide the first direct evidence for the importance of sulfur aerosols in catastrophic climate change and cooling,” adds Aubrey Zerkle, an expert in sulfur isotopes and the sulfur cycle.
According to Junium, the presence of these signs requires a large amount of sulfur aerosols in the stratosphere, which gradually returned to Earth as acid rain and washed into shallow marine oceans after the impact.
“These sulfur aerosols would have extended the duration of post-impact climate change, taking an already beleaguered biosphere to the brink of collapse,” according to him.
Image Credit: Benjamin Uveges
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