(ORDO NEWS) — When the asteroid that wiped out the dinosaurs collided with Earth 66 million years ago, massive amounts of sulfur more than previously thought were ejected high above the earth into the stratosphere, a new study says.
Rising into the air, this huge cloud of sulfur-containing gases blotted out the Sun and cooled the Earth for decades or centuries before falling as deadly acid rain on Earth, changing the chemistry of the oceans for tens of thousands of years, longer than previously thought, the study says.
The results show that “we underestimated the amount of sulfur that was produced by the asteroid impact,” co-investigator James Witts, a lecturer in the School of Earth Sciences at the University of Bristol in the UK.
As a result, “the climate change associated with this has been much more significant than we previously thought.”
The fact that sulfur continued to fall to the Earth’s surface for so long could help explain why it took so long for life, especially marine life, to recover, as some of the sulfur that fell on land was then washed into the oceans, Witts said.
Related: What happened when the asteroid that killed the dinosaurs crashed into Earth?
The discovery of the researchers was completely accidental. “It was not at all what was planned,” Witts said.
The team originally planned to study the geochemistry of ancient shells in the Brazos River region of Falls County, Texas, a unique site that was underwater during the late Cretaceous extinction event when non-African dinosaurs died out.
It’s also near Chicxulub Crater in Mexico’s Yucatán Peninsula, where a 6-mile-wide (10 kilometers) asteroid hit. The researchers took several sediment samples on site, which they did not plan to do.
These samples were taken to the University of St Andrews in Scotland, where co-investigator Aubrey Mirror, a geochemist and geobiologist, analyzed different sulfur isotopes, or variations of sulfur that have different numbers of neutrons in their core.
The researchers found a “very unusual signal” – sulfur isotopes had unexpected tiny changes in mass, Witts said. These mass changes occur when sulfur enters the atmosphere and interacts with ultraviolet (UV) radiation.
“This can only happen in two cases: either in an atmosphere where there is no oxygen, or when there is so much sulfur that it rises very high into an atmosphere rich in oxygen,” Witts said.
The Earth is about 4.5 billion years old and was enveloped in an oxygen-rich atmosphere about 2.3 billion years ago.
“We are the first to see this in much more recent times,” at least in sediments that are not at the Earth’s poles, Witts said.
(This is because volcanic eruptions release sulfur high into the atmosphere, which can mix with snow and end up in high concentrations in ice cores at the poles, where there is no other sulfur or sulfate to dilute the signal, Witts said.)
“You won’t see [this signal] in marine rocks,” he said. “The sea has its own isotopic signature, which completely dilutes the tiny amounts of sulfur from these volcanoes.”
The fact that this signal is present in Cretaceous marine rocks shows that “there must have been a hell of a lot of sulfur in the atmosphere after this collision,” Witts said.
“And that, of course, has huge implications for impact-related climate change, because sulfur aerosols, as we know from modern volcanic eruptions, cause cooling.”
Most of the sulfur came from sulfur-rich limestone in the Yucatan Peninsula.
“If the asteroid had hit somewhere else, perhaps so much sulfur would not have entered the atmosphere, and the resulting climate change might not have been as severe,” Witts said. “And, therefore, extinction might not be so terrible.”
Previous estimates of sulfur aerosols released into the Earth’s atmosphere after an asteroid impact have ranged from 30 to 500 gigatons; according to climate models, this sulfur would have turned into sulfate aerosols that would have caused the Earth’s surface to cool 3.6 to 14.4 degrees Fahrenheit (2 to 8 degrees Celsius) within a few decades of the impact.
However, a new study suggests that since the amount of sulfur was higher, climate change could have been even more severe.
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