The ices of Earth’s polar regions and high mountains, once seen as sterile, harsh environments too poor in nutrients and liquid water to sustain life, are now known to harbor rich, complex microbial communities in the ice ecosystems of alpine and polar lakes, sea ice, glacier ice, and even ice of supercooled cloud droplets. The combination of dust, water, organic matter, sunlight, and life results in a tiny microcosm that derives liquid water and usable energy from the Sun, accumulations known as cryoconites. Cryoconite assemblages and their icy habitat have been proposed as a model system for understanding the challenges microbial life would face on Earth or other planets early in their evolution. (To learn more about microbial life in Antarctica, please read the complete article).