Looking to the deep-sea crusts of the Earth’s oceans, an international team of astronomers has found radioactive evidence that one or more supernovae explosions occurred in the planet’s solar neighborhood between 1.7 and 3.2 million years ago. The resulting radioactive debris from the explosion showered the Earth, ending up at the bottom of the oceans, including the Pacific, Atlantic, and Indian.
The research was published today in Nature.
For the study, the researchers analyzed 120 ocean-floor samples from the past 11 million years. Using Australia National University’s Heavy-Ion Accelerator, they found evidence of iron-60, which has a half-life of 2.6 million years and is interstellar in origin. The iron-60’s age was determined by the decay of radioactive isotopes beryllium-10 and aluminium-26.
According to the researchers, iron-60 is substantially less abundant than the iron that exists on Earth.
“We were very surprised that there was debris clearly spread across 1.5 million years,” said study author Anton Wallner, of the Australian National University, in a statement. “It suggests there were a series of supernovae, one after another.”
Wallner noted it’s intriguing the explosions seemed to occur while the Earth was transitioning from the warm Pliocene to the cool Pleistocene period. The researchers believe these supernovae occurred around 300 light-years away. Their brightness would be comparable to that of the moon.
To figure out where the supernovae’s locations are, the researchers looked to the Local Bubble, “In which the solar system is embedded, (and which) originated from 14 to 20 supernovae within a moving group, whose surviving members are now in the Scorpius-Centaurus stellar association,” according to the researchers.
The Verge reported that only two of those supernovae explosions splashed the Earth with iron-60.
The closer explosion is believed to have occurred around 2.3 million years ago at a distance of 296 light-years. The other occurred around 1.5 million years ago about 313 light-years away.
University of Illinois astronomer Brian Fields, who was not involved in the study, told The Verge that the new work is all theoretical, meaning there are other ways iron-60 could’ve gotten to Earth. But “it’s a nice sort of piece of detective work,” Fields told the media outlet.
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