A supernova explosion triggered a surge of viruses in Africa.

Back in 2004, astronomers became intrigued by a discovery in sedimentary rocks raised from the depths of the Pacific Ocean: they contained iron-60 — a radioactive isotope with a half-life of about 2.6 million years. It is known for its extraterrestrial origin — such atoms are formed in the ejected material of a “dying” star, known as a supernova. In fact, it can be said that nearly a third of everything listed in the periodic table is a product of these cosmic events.

Subsequently, scientists concluded that approximately 2.7 million years ago, another supernova erupted somewhere relatively close to the Solar System, and the radioactive dust it scattered bombarded our planet for hundreds of thousands of years. It’s worth noting that a supernova explosion involves a sudden shedding of the outer layers of a massive star that has exhausted its thermonuclear fuel, thus completing its primary “life” cycle.

In the center of the explosion's cloud, the former stellar core collapses to a minuscule size of just a few tens of kilometers. Depending on the original mass of the star, this core either collapses into a state of ultra-dense clump of subatomic particles, becoming a neutron star, or it “falls” into the fabric of space-time — turning into a black hole. According to rough estimates from astronomers, such occurrences happen somewhere in our Galaxy approximately every 50 years.

Things became particularly interesting after analyzing ancient rocks from the bottom of Lake Tanganyika in Africa — one of the largest and deepest lakes on the planet. For the continent's inhabitants, it has always been a vital source of fresh water and food. It was discovered that around 2.5 million years ago, the body of water suffered an epidemiological disaster — there was a sharp increase in the diversity of fish-infecting viruses.

Experts suggest that this was the result of mutations caused by cosmic radiation. Moreover, preserved “imprints” both at the bottom of the lake and in the oceanic crust indicate that the radioactive variant of iron reached Earth even before the presumed supernova explosion — approximately six or six and a half million years ago.

Recently, astrophysicists from the University of California, Santa Cruz (USA) correlated all this information. In a paper published in the journal The Astrophysical Journal Letters, they explained that these are the inevitable features of “life in a bubble.”

Approximately six and a half million years ago, the Solar System found itself within a vast, sparse cloud of interstellar material, which extended over 900 light-years and is known as the Local Bubble. This cloud is the result of a whole series of supernovae that exploded one after another. Thus, the bubble is composed of the material of burnt-out stars.

Scientists believe that at the moment Earth entered this bubble, our biosphere received its “first batch” of radioactive iron, and 2.5 million years ago, apparently, another star indeed exploded somewhere nearby. Astronomers even have suspicions about where exactly — in one of the two closest stellar associations: either in the OB association of Scorpius-Centaurus, approximately 450 light-years away from us, or in the Tucana-Horologium Association, which is located half as far.

Researchers lean towards the first option. They even have a candidate for the “culprit” of the damage inflicted on Earth's nature — a pulsar (that is, a neutron star) currently located just over a thousand light-years away from us, PSR J1932+1059. According to calculations, it formed from the explosion of its parent star approximately three million years ago, which means it is of the right age to be considered a “suspect.”

By the way, this is a so-called runaway star — it has accelerated to “turbo speeds,” enabling it to overcome the galaxy's gravitational pull and escape from it. The pulsar's trajectory indicates that its parent star once belonged to a binary system with another “runaway” — Zeta Ophiuchi. According to scientists, both stars were propelled away during the supernova explosion.

Notably, during that time, at the turn of the Neogene and Quaternary periods, significant changes occurred on Earth: the ice age began, sea levels dropped, forest areas shrank, and many mammals went extinct in the tropics. However, all this proved beneficial for the first representatives of the genus Homo, the ancestors of humans, as they gained more freedom to move across open spaces.