Supernova blame for mass extinction?

Extinction of large marine animals 2.6 million years ago could have had cosmic causes

Was a stellar explosion at 150 light-years away responsible for mass extinctions 2.6 million years ago? © NASA
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Cosmic ray shower: A star explosion could have caused mass extinction 2.6 million years ago. For only 150 light-years away, a supernova took place, bombarding the earth with cosmic radiation. In particular, large marine animals such as the giant shark megalodon could be affected by these high-energy muons and died, according to the researchers.

It struck whales, seabirds, turtles and the famous giant shark Carcharocles megalodon: About 2.6 million years ago, a mass extinction brought about a third of all large marine animals there. However, what was the cause of this death of the marine megafauna is puzzling. Some researchers see the climatic changes of the beginning ice age as a trigger, others the changes of the global ocean currents by the closing land bridge of Panama.

Starburst as a Deathbringer?

But there is an alternative explanation, as demonstrated by Adrian Melott of the University of Kansas in their study. They have investigated whether perhaps a close supernova could have caused the death of so many great sea creatures. It is known, among other things, that the high-energy radiation released in such stellar explosions can damage the ozone layer - and thus the most important UV protection of the earth.

The explosion of the muons - heavier relatives of the electrons - can also penetrate to the surface of the earth and even into the sea and cause there serious cell damage, as the researchers explain. Unlike other radiation, these elementary particles can easily penetrate even water and the bodies of living things.

Supernova 2.6 million years ago

But before 2.6 million there was a supernova near the earth? Initial evidence for this has been provided some time ago elevated levels of the isotope iron-60 in well two million years old deposits and fossils. Because this radioactive atomic variant of iron on Earth is rare and also disintegrates within a few million years, this iron-60 must come from space - from a starburst. display

In the meantime, the indications of one or possibly even several supernovae have risen about 2.6 million years ago: "The strongest signal comes from an event about 2.5 million years ago, which coincided well with time the mass extinction on the Pliocene-Pleistocene border ", the researchers report. It is commonly believed that this stellar explosion took place some 150 light-years away, and thus relatively close to cosmic standards.

One hundredfold increased muon dose

Whether the radiation released by this supernova could actually have had catastrophic consequences, at least for some animals, has now been examined more closely. "We know how far away the supernova was and can calculate how it must have affected the Earth, " Melott says. According to the supernova, the radiation exposure of muons may have increased by a factor of one hundred.

Was the supernova also to blame for the extinction of the giant shark Megalodon? Karen Carr / CC-by-sa 3.0

Due to the great energy of the muons, a large part of them could even penetrate several hundred meters into the oceans. The sea dwellers of the coastal areas, in particular, would have suffered a considerable radiation shower. "We estimate that it would increase the cancer rate for a human being by 50 percent, " Melott said. "The bigger you are, the worse it gets."

Cause of death also for basking shark Megalodon?

According to the researchers, this could well be enough to explain the mass extinction of the marine megafauna 2.6 million years ago. "So far, there has been no really good explanation for this extinction, " says Melott. "This could be one." One of the victims of this primeval stellar explosion could have been the giant shark Carcharocles megalodon. "These sharks disappeared just at the time of the supernova that could be the fault of the muons, " said the researcher. Other scientists have so far seen more shortage and competition than causes.

Whether the scientists are right with their scenario must now be shown in further studies. If, however, the supernova confirms itself as the cause of the mass extinction, this would be the second event, which goes back to cosmic "death-bringer". The asteroid impact, which fell victim to the dinosaurs some 65 million years ago, was the first. (Astrobiology, 2018; doi: 10.1089 / ast.2018.1902)

Source: University of Kansas

- Nadja Podbregar