MEPhI astrophysicists together with their colleagues from research centres of the USA and Europe have found out that the Earth’s “shooting attack” by supernovae nearly 3,2 and 8,7 million years ago should have affected animals’ “bioclock”, radiating them with rather high radiation dose and accelerating their evolution, says the article, published in Astrophysical Journal Letters.

“I was surprised by how the outbursts have influenced the terrestrial life. I was expecting there to be very little effect at all - 300 light-years is not very close. The big thing turns out to be the cosmic rays. This may have been enough to increase cancer and mutation rates and speed up evolution,” said Adrian Melott from the University of Kansas (the USA).

Melott and his colleagues, including Russian astrophysicist Dmitriy Semikoz of MEPhI, have come up to that conclusion, calculating the consequences of the explosion of 2 supernovae in 300-600 light-years from Earth. Their traces as atoms of depositing 60Fe appearing inside dying stars have been recently found on the bottom of the ocean and in the rocks of the moon soil, delivered to the Earth by the “Apollo” expeditions.

A supernova of Ia kind before the explosion (© Kavli IPMU)

As scientists explain, consequences of the supernova explosion can be divided into two categories – instant and long-lasting ones. The first category comprises the explosion outburst in the optical and X-ray range, and phenomena, connected with it – the destruction of the ozone layer, burns, the change of temperatures and other instant effects.

The influence of the supernova does not end up there – its remains continue to produce a big number of charged particles and atoms, speeded up to the relativistic velocities, for centuries and even millenniums after the explosion. All the supernova traces, as Melott’s team thinks, could “attack” the Earth tens of millenniums after the fading of the explosion.

Calculations, made by the authors of the article, have revealed an unusual picture. Instant effects from the supernovae explosions turned out to be rather weak – they could only affect the animals’ bioclock for several weeks because of the big quantity of the blue light, produced during such outbursts, and would weaken the ozone layer, but wouldn’t cause mass extinctions or cancer epidemics.

On the other hand, long-lasting consequences would be less evident, but more interesting and dangerous for our lives. According to the scientists’ words, a close supernova explosion will enhance nearly 20 times the frequency of the Earth’s “attack” by muons and other particles, as the result of which the radiation load on living organisms will at least triple.

This is a relatively small dose of radiation, even considering the possibility to avoid it, and the enhanced background won’t lead to mass extinctions, but to the growing number of cancer diseases and the acceleration of the evolution on the Earth because of the enhancement of the DNA mutations. The traces of the process, as Melott and his colleagues think, can be found in the microextinction, which happened nearly 2,59 million years ago, which corresponds to the time interval when one of the outbursts happened.

As the Kansas physicist considers, the event could be the reason of the humankind appearance – in his opinion, a sharp climate change and savannas’ appearance in Africa which happened at that time and which is supposedly connected to the evolution of Homo, could be connected with supernovae. The scientist claims that not all of his colleagues share the idea, and it has to be proved. The idea should be checked, measuring the percent of different “cosmic” isotopes, such as beryllium-10 and carbonium-14, in the rocks of that time.