This just blew me away: (Science via Ars Technica)
[A] team of scientists has taken a closer look at the particulates that cause snow to form, and it seems that most of them are... alive.
Ice formation in the troposphere doesn't tend to happen on its own if the temperatures are higher than -40˚C (coincidentally -40˚F), but biological particulates can catalyze ice formation at higher temperatures by acting as a nucleus.
DNA-stained cells of P. syringae (green dots) frozen within individual ice crystals. Image courtesy of Shawn Doyle and Brent Christner, Louisiana State University
forming rain or snow [may be] part of the bacterial life cycle; "We think if (the bacteria) couldn't cause ice to form, they couldn't get back down to the ground," Sands said. "As long as it rains, the bacteria grow."
Sands suggests that changing bacterial populations may affect rainfall; for example, overgrazing during a summer could reduce the bacterial population, resulting in lower raindrop formation.
I'm looking up at the sky, full of unseen clouds of tiny life that I didn't even know existed. It floats around higher than jets fly just to boldly go where no Pseudomonas has gone before, and changes our climate while it's at it without us suspecting a thing.
(Did I mention that I'm boggled?)