For tens of millions of years, what giants have not inhabited the oceans of the Earth: 2,200-kilogram turtles, sea cows the size of a whale, sharks, the size of a bus. But about 2.6 million years ago, they all began to die out en masse. Today this period is described as the extinction of the Pliocene marine megafauna. Then, in a short period, more than a third of animals of incredible size became extinct, including the megalodon - a shark up to 25 meters long. Scientists still cannot understand what caused what happened.
According to the researchers, climate change was definitely one of the main factors. A new ice age has begun. Ice displaced warm water, thereby reducing food reserves for large individuals. However, climate change may not be the only reason for this.
A preprint from arxiv.org for publication in Astrobiology's first issue of 2019 argues that exploding stars are the other major contributing factor to the mass extinction of sea giants.
A group of scientists led by Adrian Melotte, professor of physics and astronomy at the University of Kansas, argues that the beginning of the mass death of marine life on Earth coincides with the period of a supernova, or perhaps even an entire chain of small supernovae nearby. And if these explosions were really strong enough, then they could flood the Earth with their radiation and cause an increasing number of mutations and cancers of the fauna on our planet. Moreover, the process lasted for several hundred years. And the larger the animal was, the researchers say, the worse it was under the influence of so much radiation.
At the heart of the suggestion by Melotte and his colleagues is a 2016 study that found traces of an isotope of iron-60, a radioactive variant of iron with a half-life of approximately 2.6 million years, in ancient seabed sediments. If these radioactive isotopes formed with the Earth, then "they would be gone for a long time," Melotte says. Thus, the only explanation for their presence on the planet is "bombing from the outside" several million years ago.
Scientists, who published their study in 2016, link the discovered isotopes to a series of supernova explosions that occurred 8.7-1.7 million years ago, about 325 light years from Earth. According to Melotte, supernovae exploded far enough to cause significant damage to our planet, but close enough to the Earth that it could be in the path of their residual radioactive radiation.
During stellar explosions, some of the ejected radiation could take the form of muons, which have a similar structure to electrons. However, the difference between them is huge. Muons are two hundred times more massive than electrons and are capable of penetrating deep enough into the Earth for hundreds of kilometers, and, of course, into the very depths of the oceans. Hence the theory arises that after the explosion of a star and after such a flux of muons hit our planet, the marine fauna could unwittingly come into contact with these radioactive particles, which caused mutations and death of animals.
Cosmic radiation, combined with other known factors such as climate change, could be one of the reasons for the change that eventually pulled the sea giants to the bottom. Melotte notes that the evidence for a supernova (or supernovae) near Earth at the time is only "one piece of the puzzle" that will help solve the mystery of the extinction of Earth's sea monsters. We may never know what exactly killed the megalodon, but while scientists are looking into the depths of the sea, it might also be worth turning their eyes to the stars.
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Nikolay Khizhnyak