Supernovae Might Have Affected Life On Earth Several Million Years Ago

For years, scientists have been working to understand stellar explosions, also called supernovae, and how they affect everything in their surroundings, including planets. The question has also led many to wonder if the explosions that occurred several million years ago were close enough to trigger mass-extinction events. The exact answer, obviously, remains a mystery, but a new research sheds some light on how these explosions might have affected life on Earth.

The supernovae in question are those that occurred approximately 2.5 and 8 million years ago at a distance ranging between 160 and 320 light years away from Earth. Though previous studies suggest explosions were way beyond the so-called "kill-zone" for a planet, astrophysicist Brian Thomas, the lead author of the latest work, thinks the events might have had a staggering effect on our planet’s atmosphere, which might have had long-term repercussions on all forms of life on Earth.

“We are interested in how exploding stars affect life on Earth, and it turns out a few million years ago there were changes in the things that were living at the time,” Thomas told Astrobiology Magazine. “It might have been connected to this supernova.”

The researcher wanted to understand how the cosmic ray from a supernova that far might have interacted with the atmosphere and finally the surface of our planet and ran a series of models to note the effects on living organisms.

Many think supernova explosions lead to immediate die-offs, but Thomas reiterated cosmic rays spewing from these events hit a particular body over hundreds to thousands of years, with high-energy particles interacting first and low-energy particles coming later. His models revealed the particles from the supernova in question would have depleted the ozone layer, with maximum effect being witnessed about 300 years after the initial particles penetrating our atmosphere.

As the report said, the high-energy particles that zipped earlier would have passed through the stratosphere, having less effect on the ozone, while the less energy materials coming years later would have settled on the stratosphere and depleted the ozone. This would have resulted in an increase in the harmful, genetically altering ultraviolet radiation from the sun.

In the long run, like in about hundreds of years, this could have altered the DNA of several life forms on Earth and made survival of many species impossible. Thomas even noted some of these changes in the fossil record from the same time period.

“There were changes, especially in Africa, which went from being more forested to more grassland.”

Plus, there was also an increase in the global concentration of iron-60 (60Fe), the radioactive isotope produced during a supernova.

In a nutshell, the supernovae that occurred millions of years ago might have triggered processes leading to a change in the abundance of species, with variation in vegetation, more speciation, and an increased rate of extinctions. It is still unclear if processes like these could set off mass extinctions, but as Thomas said, there was a “subtler shift; instead of a ‘wipe-out everything,’ some [organisms] are better off and some are worse off.”