Hydrothermal systems: Doorways to early biosphere evolution

Hydrothermal systems may have provided favorable environments for the prebiotic synthesis of organic compounds necessary for life and may also have been a site for life's origin. They could also have provided a refuge for thermophilic (heat-loving) microorganisms during late, giant-impact events. Phylogenetic information encoded in the genomes of extant thermophiles provides important clues about this early period of biosphere development that are broadly consistent with geological evidence for Archean environments. Hydrothermal environments often exhibit high rates of mineralization, which favors microbial fossilization. Thus, hydrothermal deposits are often rich storehouses of paleobiologic information. This is illustrated by studies of the microbial biosedimentology of hot springs in Yellowstone National Park that provide important constraints for interpreting the fossil record of thermophilic ecosystems. Hydrothermal processes appear to be inextricably linked to planetary formation and evolution and are likely to have existed on other bodies in the solar system. Such environments may have sustained an independent, extraterrestrial origin of life. Thus, hydrothermal systems and their deposits are considered primary targets in the search for fossil evidence of life elsewhere in the solar system.