Scientists Say the Cause of Mass Extinctions May Be Even Older Than Humanity
Apart from black holes, supernovae are one of the most destructive forces in the universe. If our Sun decided to suddenly explode, it would boil away half the Earth with the shockwave alone. Even if a supernova occurred 30 light-years away, it would still spell doom for most of life on Earth.
So what about two supernovae 163 and 326 light-years away?
This is where things get interesting... because they've already happened.
Astrophysicist Dr. Brian Thomas from Washburn University in Kansas found that radiation from two supernovae, exploding about 2.5 and 8 million years ago, may have had enough power to not only reach Earth but degrade the ozone layer at key points in Earth's history.
Interestingly, the degradation wouldn't have been instant and dramatic—it would have happened in waves, as higher energy particles reached Earth, then low-energy ones.
According to Thomas: "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. It might have been connected to this supernova."
The ozone depletion from the supernovae probably didn't result in mass extinctions, but Thomas' research shows that increased UV radiation did cause damage to organisms in a wide variety of ways, including skin cancer, cataracts, and plant damage.
In addition to UV radiation increasing during these periods, "There were changes, especially in Africa, which went from being more forested to more grassland," according to Thomas.
This means that supernovae may not always be detrimental to Earth's biosphere, at least not when they're far away. "There is a subtler shift; instead of a 'wipe-out everything', some [organisms] are better off and some are worse off," says Thomas.
The next step for Thomas' research? Finding out how supernovae affected the evolution of humans.