The explosion of one or more supernovae some 150 light years from Earth, about 2.6 million years ago, would have led to the disappearance of large marine animals such as the megalodon, the largest shark in the world. has never populated the terrestrial oceans.
A strangely bright light appeared in the Pliocene sky and stayed there for weeks or maybe even months, says American astrophysicist Adrian Melott of the University of Kansas.
In the space of a few hundred years, long after the dissipation of this light, a wave of cosmic energy from this explosion of stars reached the Earth and destabilized its atmosphere to the point of causing significant climate change.
Recent papers have revealed the presence of a radioactive isotope of iron in ancient deposits of the seabed; they provide strong evidence of a temporal connection with the explosion of supernovas.
Professor Melott can not say for sure whether the cosmic tsunami is the result of one or more supernovas.
There is a debate as to whether there was only one supernova or rather a chain of supernovas. I prefer to think of a combination of two, one more powerful and closer than the other.
According to the hypothesis of the astrophysicist and Brazilian colleagues, the very architecture of the local Universe of our galaxy, the Milky Way, suggests that it was sculptured following a series of supernovas.
Be that as it may, the Earth has been covered with a layer of iron-60, and particles called muons have joined its surface, causing cancer and mutations, especially in large animals.
We estimated that the cancer rate increased by about 50% for an organism the size of a human being. For an elephant or a whale, the radiation dose increases even more.
The extinction of the Pliocene was concentrated in coastal waters, where the larger organisms received a greater dose of muon radiation.
“The damage caused by the muons extended to organisms living in the first hundreds of meters of the oceans, becoming less serious at greater depths,” say the researchers.
Large marine animals living in shallow waters may have been condemned by supernova radiation.
One of the best-known animal extinctions of this period is the megalodon ( Carcharocles megalodon ), which reached the size of a bus.
We can think that it [the extinction] can be linked to muons. Basically, the larger the creature, the greater the effects of radiation.
The details of this work are published in the journal Astrobiology.