A gigantic supernova explosion may have triggered mass extinctions for creatures living in Earth's prehistoric oceans some 2.6 million years ago, according to a new research published in Astrobiology.
Marine animals like the Megalodon, a fearsome shark around 10.5 meters (34 ft) long and with huge jaws full of sharp, pointed teeth, suddenly disappeared during the late Pliocene. Around the same time, scientists from the University of Kansas and the Federal University of São Carlos, noted a peak in the iron-60 isotope in ancient seabeds.
"As far back as mid-1990s, people said, 'Hey, look for iron-60. It is a telltale because there is no other way for it to get to Earth, but from a supernova. "Because iron-60 is radioactive, if it was formed with Earth it would be long gone by now. So, it must have been rained down on us, "explained Adrian Melott, lead author of the paper and a physics and astronomy professor at the University of Kansas.
"There is some debate about whether there was only one supernova really near or a whole chain of them. I kind of favor a combo of the two – a big chain with one that was unusually powerful and close. If you look at the iron-60 residue, there's a huge spike 2.6 million years ago, but there's a scattered clear back 10 million years. "
The team believes that a supernova located 150 light years away from a chain of supernovae bursts and covered Earth in a shroud of deadly cosmic ray radiation. This was amplified, Melott said, because the Solar System is right on the edge of an interstellar medium called Local Bubble.
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The Local Bubble extends about 300 light years across and contains the two main clouds of dust and gas: Local Interstellar Cloud and G-Cloud. "It's basically very hot, very low-density gas – almost all the gas clouds have been swept out of it. The best way to produce a bubble is that a whole bunch of supernovae blows it bigger and bigger, and that seems to fit well with the idea of a chain, "said Melott.
As the supernovae ejected cosmic rays, these beams of energetic particles would have repeatedly bounced off the clouds to create a "cosmic-ray bath" that would have lasted 10,000 to 100,000 years, he postulates. Some of that radiation, such as cosmic ray muons, would have leaked onto Earth, and over time it could have led to genetic mutations and cancers.
Muons pass through Earth all the time, but during peak iron – 60 times the number would have been enough to cause health problems for animal life. The researchers estimate that the cancer rate would increase by about 50 percent for animals that were as big as humans, and rise even higher for larger creatures. Animals like the mgalodone would have absorbed enough radiation to develop cancers and die prematurely.
"There has not been any good explanation for the marine megafaunal extinction," Melott said. "This could be one. It's this paradigm change – we know something happened and when it happened, so for the first time we can really dig in and look for things in a definite way. We now can get really defined about what the effects of radiation would be in a way that was not possible before. "