Analysis of sediment found in a central Texas cave in the US shows volcanic eruptions responsible for the cooling of the Earth around 13,000 years ago, say researchers. Some researchers believed the event - which cooled the Earth by about 3 degrees Centigrade, a huge amount - was caused by an extraterrestrial impact with the Earth, such as a meteor collision. But the current study, published in the journal Science Advances, shows the evidence left in layers of sediment in Hall's Cave was almost certainly the result of volcanic eruptions.
According to the research team, Hall's Cave, located in the Texas hill country, has a sediment record extending over 20,000 years and they first began researching the cave in 2017. "One big question was, did an extraterrestrial impact occur near the end of the last ice age, about 13,000 years ago as the ice sheets covering Canada were melting, and cause an abrupt cooling that thrust the northern hemisphere back into the ice age for an extra 1,200 years?" said study researcher Michael Waters from the Texas A&M University in the US.
The research team took every avenue they could to come up with an alternative explanation, or even avoid this conclusion. A volcanic eruption had been considered one possible explanation but was generally dismissed because there was no associated geochemical fingerprint, the researchers said.
After a volcano erupts, the global spread of aerosols reflects incoming solar radiation away from Earth and may lead to global cooling post-eruption for one to five years, depending on the size and timescales of the eruption, they added.
"The Younger Dryas, which occurred about 13,000 years ago, disrupted distinct warming at the end of the last ice age," the study authors wrote. The Earth's climate may have been at a tipping point at the end of the Younger Dryas, possibly from the ice sheet discharge into the North Atlantic Ocean, enhanced snow cover and powerful volcanic eruptions that may have in combination led to intense Northern Hemisphere cooling.
The team completed the isotopic analysis of sediments collected from Hall's Cave. They found that elements such as iridium, ruthenium, platinum, palladium and rhenium were not present in the correct proportions, meaning that a meteor or asteroid could not have caused the event.
"The isotope analysis and the relative proportion of the elements matched those that were found in previous volcanic gases," the authors wrote.