Scientists have long been trying to uncover the secrets of the extinction of this or that animal population. Many of them are explained by terrestrial factors, but the event that killed 36 percent of the living creatures in the ocean 2.6 million years ago in the Pliocene, including the giant shark megalodon, could have happened outside the Earth.
“I studied this issue for 15 years, and each time my work was based on the usual knowledge of how these supernovae were supposed to affect the Earth at one time or another. However, this time it's different. We have evidence of events that took place not far from us at a certain time. We know the distance at which they traveled, so we can calculate exactly how it affected the Earth and compare it with the available knowledge,”says University of Kansas researcher Adrian Melott.
The scientist talks about deposits of iron-60 isotopes found on the seabed. A related study was published in the journal Astrobiology.
Iron-60 is a radioactive substance with a half-life of about 2.6 million years. This means that any iron-60 that could have formed on Earth 4.54 billion years ago would have disintegrated long ago. The fact that iron-60 remains on the planet today means it must have come from somewhere else: scientists speculate that this is due to a supernova explosion in space, just 150 light-years from our planet.
Radioactive isotopes are relatively easy to study, so we roughly know their age. According to Melotte, the big splash occurred about 2.6 million years ago, and some minor events began about 10 million years ago.
According to the researchers, this is confirmed by the presence of the Local Bubble - a region of rarefied hot gas of an irregular shape, extending for 300 light years, through which the solar system is now moving. Melotte claims that with a high degree of probability it was created as a result of a series of supernova explosions, which fits well with the hypotheses of scientists.
The idea that supernovae could cause mass extinction of life on Earth is not new. For a long time, it was believed that a gamma-ray burst that occurs in a supernova could have caused the disappearance of the Ordovician 450 million years ago. According to the work of Melotte and his team, a completely different mechanism was behind the disappearance of the Pliocene marine megafauna. Instead of gamma-ray bursts, it was a type of cosmic ray elementary particle called muons - a bit like an electron, but with more mass and energy.
“These particles are very penetrating. About one fifth of our radiation dose comes from muons, but this is almost harmless. However, multiply these muons by a few hundred - when their number is so huge and the energy is so high, you get an increased risk of mutation and cancer as the main biological effects. We calculated that the incidence of cancer would increase by about 50 percent for a living being the size of a human - and the larger the organism, the worse the consequences. For an elephant or a whale, the radiation dose is significantly increased,”explains the scientist.
And since muons are able to penetrate quite deeply, they could enter the ocean, affecting its inhabitants and - most of all - creatures of enormous size, for example, the megalodon. The deeper the habitat, the less penetration the muons will have, which is confirmed by the data on the mass extinction of species, since the shallower, coastal waters experienced this event much more deplorable.