Andean high life

Natural History, Dec, 2008 by Harvey Leifert

The Puca Glacier, perched above 16,000 feet in the Peruvian Andes, is retreating by seventy feet per year. Its withdrawal is exposing some of the driest, most barren terrain on Earth for the first time in at least 700 years. The soil, nearly devoid of organic carbon and nitrogen, seems a poor home for life of any kind.

Yet large communities of microbes known as cyanobacteria spring up immediately in the glacier's wake, says Steven K. Schmidt of the University of Colorado at Boulder. With ten colleagues, he catalogued microbial DNA at various distances from the glacier and analyzed chemical and structural changes to the soil caused by cyanobacteria over a five-year study period.

As the glacier vanishes, cyanobacteria riding in icebound soil pockets drop onto the dry ground, the team found. The cyanobacteria quickly improve the soil by fixing carbon (through photosynthesis) and nitrogen from the air, as well as by leaving behind rich remains at death. Other cyanobacteria, borne in by the wind, can then establish themselves, and within just four years, colonies of increasingly complex microbes take hold. Soil exposed seventy-nine years ago now supports lichens and other plant life.

The Puca Glacier is subjected to intense ultraviolet radiation, extreme daily temperature variations, and a lack of rain. Scientists looking for evidence that life might once have existed on Mars may find clues by studying the microbes that inhabit such harsh Earthly environments, says Schmidt. (Proceedings of the Royal Society B)