The Effects of Cosmic Rays

Cosmic radiations permeate everything around us at all times of the day. Some of them are generated near us, on a radius of a few thousand light-years, while some only reach our planet after a ten- to 11-billion-year journey. They are unnoticeable to humans, but some researchers believe they may have played a crucial role in the development of life on Earth, and maybe even in some extinction events. The truth is that most of these issues are opened for debate, Space reports.

However, astronomers almost unanimously agree that, if a supernova was to explode within a few light-years from our solar system, then the amount of emitted radiation would be enough to wipe out, directly or indirectly, a significant number of species. “There may have been nearby astronomical goings-on that drastically increased the radiation on Earth,” University of Illinois expert Brian Fields explains. However, he concedes, “Just finding dead beasties is not proof of a nearby supernova.”

Cosmic radiation is made up of high-energy protons, which are mostly generated by supernova explosions and the ensuing shock waves. There is, at this point, no clear way of finding out where they came from, mostly because they are prone to the influence of magnetic fields. This means that they “bounce” inside the galaxy for up to a few million years, before finally making their way to Earth. Still, once here, they usually don't reach the surface. They collide with ions (electrically charged atoms) in the upper atmosphere, and break up into a shower of “secondary” particles, which are harmless.

“Every square centimeter on the top of the Earth's atmosphere is hit by several cosmic rays per second. This is forever going on,” Fields explains. Still, a supernova going off just 30 light-years away from the Earth would generate cosmic radiation of sufficient intensity to break through the planet's defenses, and reach the surface, where it would wreak havoc among all living things, from bacteria to humans.

Some theories hold that muons, some of the secondary particles created by broken cosmic radiation, may have played an important part in the evolution of life on Earth. At this point in time, we are subjected to roughly the equivalent of ten chest X-rays of radiation from these fast-traveling particles alone. They can rip ions out of our bodies, which can lead to genetic mutations. “It is very likely that organisms of early Earth possessed DNA that was unstable and could easily mutate under external agents, more so, perhaps, than the DNA of present-day bacteria,” the authors of a new study on the issue, published in a recent edition of the journal Astrobiology, say.