Future of Earth the ozone layer that protects the surface from ultraviolet (UV) radiation from the Sun. An increase in UV-B radiation of only 10–30% is sufficient to cause a significant impact to life; particularly to the phytoplankton that form the base of the oceanic food chain. A supernova explosion at a distance of 26 light years will reduce the ozone column density by half. On average, a supernova explosion occurs within 32 light years once every few hundred million years, resulting in a depletion of the ozone layer lasting several centuries. Over the next two billion years, there will be about 20
Exposing Microorganisms in the Stratosphere stratosphere (31 km above sea level), 99.9% of the entire population was destroyed. According to the researchers, "most terrestrial bacteria would be inactivated within the first [day] on Mars if contaminated spacecraft surfaces receive direct sunlight." Of the 40 million spores exposed to the stratosphere, only 267 spores (or 0.0007%) remained viable. Extrapolating this, no viable spores would remain if flight samples had an additional 150 minutes of Sun exposure in the stratosphere (630 min total time). The survivors showed three single nucleotide (base pair) substitutions compared to unexposed controls kept on the ground. These three coding regions are associated