Two Supernovae Showered Earth with Radioactive Debris

Wednesday, 06 April 2016 - 5:18PM
Earth
Wednesday, 06 April 2016 - 5:18PM
Two Supernovae Showered Earth with Radioactive Debris
Supernovae are, by nature, catastrophic cosmic events, but they're usually too far away to have a direct effect on our planet. Now, a new study claims that a pair of recent supernovae left a layer of radioactive debris at the bottom of Earth's oceans.

Scientists have long been theorizing that supernovae could have a direct impact on Earth if they were close enough; if one were within 26 light years from Earth, for example, it would wipe out all life on this planet. Luckily, the two supernovae in question were a little further away than that, at least several hundred million light years away, but they were the first that have been confirmed to directly interact with our planet.

The new study, published today in Nature, contends that radioactive material found on the ocean floor (which has a half-life of up to 100 million years), may have traveled to Earth after being trapped in interstellar dust grains that penetrated our Solar System. At least one of these radionuclides, known as 60Fe, is known to be emitted from stellar explosions, and was found by the researchers to originate from multiple interstellar events. 

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"The signal measured implies that a few per cent of fresh 60Fe was captured in dust and deposited on Earth," the authors wrote. "Our findings indicate multiple supernova and massive-star events during the last ten million years at distances of up to 100 parsecs."
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Another study published in Nature today details exactly how close those nearby stellar events were. Adrian Mellott and his colleagues modeled how radioactive isotopes such as iron-60 reached Earth, and found that the closest and most recent explosion occurred 326 light years away and occurred between 3.2 and 1.7 million years ago. This would have been close enough to see in the night sky, and would have appeared to be a very bright star.

The researchers also theorize that this more recent supernova might have had an impact on the evolution of life on Earth. This event coincided with the advent of the Pleistocene era, which cooled our planet significantly. Scientists don't know for sure, but there's a possibility that this era could have been instigated by this supernova, as they have the ability to impact our climate.

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"We don't have any concrete evidence that any one event is tied to a supernovae," Mellott told Gizmodo. "But the odds are, one or more are."
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