A rapid cooling event 13,000 years ago was triggered by volcanism, rather than the impact of a fragmented comet or asteroid, according to a new study. Researchers found evidence of the volcanic activity in sediment collected from a cave in central Texas.
Some studies have suggested that an extraterrestrial impact, such as a meteor collision, abruptly shifted Earth into a state of intense cooling as the last ice age ended. However, the current study has found evidence of volcanism in layers of cave sediment that date back to a time when the cooling event would have been kicked off.
Study co-author Michael Waters is the director of The Center for The Study of the First Americans and a professor at Texas A&M University.
Professor Waters said that Hall’s Cave, located in the Texas hill country, has a sediment record extending over 20,000 years. He first began researching the cave in 2017.
“It is an exceptional record that offers a unique opportunity for interdisciplinary cooperation to investigate a number of important research questions,” said Professor Waters.
“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?”
The cooling event likely led to the extinction of large mammals such as mammoths and camels in North America.
“This work shows that the geochemical signature associated with the cooling event is not unique but occurred four times between 9,000 and 15,000 years ago,” said Professor Alan Brandon of the University of Houston.
“Thus, the trigger for this cooling event didn’t come from space. Prior geochemical evidence for a large meteor exploding in the atmosphere instead reflects a period of major volcanic eruptions.”
“I was skeptical,” said Professor Brandon. “We took every avenue we 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.”
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, said the researchers.
The Younger Dryas is one of the best examples of sudden climate change. This period reversed gradual warming after the Late Glacial Interstadial, the last ice age, about 13,000 years ago. The Younger Dryas lasted about 1,200 years, and then ended as abruptly as it began.
Study co-author Professor Steven Forman explained that the Earth’s climate may have been at a tipping point, 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.
“This period of rapid cooling coincides with the extinction of a number of species, including camels and horses, and the appearance of the Clovis archaeological tradition,” said Professor Waters.
Professor Brandon and study lead author Nan Sun analyzed the sediments collected from Hall’s Cave. They found that elements such as iridium, ruthenium, platinum, palladium and rhenium were not in the consistent quantities that would be present if an asteroid strike was responsible for the event.
“The isotope analysis and the relative proportion of the elements matched those that were found in previous volcanic gases,” said Sun.
The researchers explained that volcanic eruptions cause their most severe cooling near the source, usually in the year of the eruption, with substantially less cooling in the years after the eruption.
Since the Younger Dryas cooling lasted about 1,200 years, the experts determined that volcanic eruptions initiated the cooling, but other Earth system changes were needed to sustain the extended cold period.
According to Professor Waters, the bottom line is that “the chemical anomalies found in sediments dating to the beginning of the Younger Dryas are the result of volcanism and not an extraterrestrial impact.”
The study is published in the journal Science Advances.