https://phys.org/news/2018-05-stratospheric-life-possibility-extreme-worlds.html

You might not realize it when you're staring out a plane window (we fly through the lowest levels of the stratosphere when we're cruising over 35,000 feet), but there are all kinds of microorganisms out there, according to Professor Shiladitya DasSarma, who is a microbiologist at the University of Maryland School of Medicine, USA , and a co-author on the new study, which is published in the journal Current Opinion in Microbiology.

"Generally, people don't think of microbes being airborne," he tells Astrobiology Magazine. "But there's a saying in microbiology: Everything is everywhere."