An exploding star may have destroyed part of Earth's protective ozone layer two million years ago, devastating some forms of ancient marine life, according to a new theory presented at this week's meeting of the American Astronomical Society.
The new theory brings together puzzling clues from several different fields of research, including paleontology, geology, and astronomy.
Narciso Benitez, an associate research scientist in astronomy at Johns Hopkins University, said the "missing smoking gun" that brought the clues together was the revelation that a stellar cluster with many large, short-lived stars prone to producing supernovae had passed near Earth's solar system several million years ago.
That discovery, made by co-author and Space Telescope Science Institute astronomer Jesus Maiz-Apellaniz, led Benitez to check the scientific record for potential effects of nearby supernovae on Earth.
"Nobody had realized that this cluster of stars that Jesus had tracked, which is known as the Scorpius-Centaurus OB association, could have been so close to Earth during the past several million years," Benitez said.
"And when I did a search," he added, "one of the first things that popped out was a 1999 finding where a team of German astronomers led by Klaus Knie detected the presence of a highly unusual isotope of iron in samples of the Earth's crust drilled from the deep ocean bottom."
Knie had proposed that the iron isotope was debris from a recent supernova explosion that took place close to Earth. But astronomers had no plausible candidates for such a nearby explosion until Maiz-Apellaniz's work with the Scorpius-Centaurus association, which is also being presented at this week's meeting of the American Astronomical Society.
Benitez compared data produced by Maiz-Apellaniz and Knie's results, and found "very good agreement, both in the amount of iron deposited and in its time distribution."
Ancient Records
Benitez consulted with his wife, Matilde Canelles, an immunologist at the U.S. National Institutes of Health who had done her master's thesis on microscopic algae, to learn if the paleontological record included an extinction that had unusual characteristics suggestive of a potential link to a supernova.
"Such an extinction would have had especially pronounced effects on the plankton and the marine organisms," Benitez said.
Canelles pointed out that evidence existed for a widespread extinction of plankton and other marine organisms about two million years ago, and noted that scientists are still debating the possible causes of the event.
