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Stellar explosions may have played a bigger role in the history of Earth’s climate than scientists thought.
Nearby supernova have left a number of possible footprints in the tree-ring log here on Earth over the past 40,000 years, potentially disrupting our planet’s climate multiple times over this time span, a new study reports.
“These are extreme events and their potential effects appear to match tree ring records,” study author Robert Brakenridge, a senior research associate at the Arctic and Alpine Research Institute at the University of Colorado Boulder, he said in a statement.
Supernova Photos: Fantastic images of stellar explosions
Brakenridge has compiled a list of 18 supernovae – violent explosions that mark the death of certain types of stars – that occurred within approximately 4,900 light years of Earth. He then compared the estimated timing of these cosmic events with the carbon-14 peaks, as observed in the record of the tree ring.
Carbon-14 is a radioactive isotope of carbon that contains eight neutrons in its atomic nucleus instead of the usual six. Carbon-14 is rare on Earth and is not found here naturally without some external influence, namely, high-energy radiation from deep space, which can convert some of the “normal” carbon in our atmosphere into carbon-14 ( which explains why this isotope is also known as radiocarbon).
“There is generally a constant amount year after year,” Brakenridge said. “The trees rise carbon dioxideand some of that carbon will be radiocarbon. “
However, the amount of radiocarbon is not always constant. Scientists have identified spikes in the tree ring log, which have generally been attributed to powerful glows from our sun. But Brakenridge suspected that supernovae might be involved, so he investigated a possible link.
And he found one tempting but uncertain: Eight of the closest supernovae on his list occurred around the same time as a short radiocarbon peak. The association was particularly strong for four supernovae, including one 13,000 years ago that ended the life of a star in the constellation of Vela about 815 light-years from Earth.
Shortly after that explosion, radiocarbon levels briefly increased by about 3% in Earth’s atmosphere, Brakenridge found.
The results are not conclusive given the various uncertainties involved. For example, it is difficult to accurately date supernovae; the inferred timing of the Vela explosion could be shortened by as much as 1,500 years, Brakenridge said. But he thinks the new results, which were posted online last week in the International Journal of Astrobiology, show that further research on the supernova-radiocarbon link is needed.
“What keeps me going is when I look at the Earth record and say, ‘My God, the predicted and modeled effects seem to be there,” Brakenridge said.
He is not the only scientist to suggest that supernovae may have significantly affected life on Earth. Other studies have speculated that explosions of nearby stars have caused or contributed to some mass extinctions, altering the atmosphere of our planet and causing climate change.
Mike Wall is the author of “Out there“(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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