A frozen home
Glaciers are essentially huge blocks of ice, frigid and foreboding, and we once thought of them as simply too extreme to harbor life. Now, however, we know they're not only habitable, but possibly one of the major ecosystems on Earth, considering they cover 11% of the Earth's land area. It's just that their denizens are tiny microbes.
New microbes may arrive at the glacier blown in by the wind or riding on dust particles or precipitation such as snowflakes. Over the slow march of time, natural selection and the extreme conditions will shape these new residents of the glacier to better fit their now home.