PERENNIALLY ICE COVERED ANTARCTIC LAKES: OASES FOR LIFE AND MODELS FOR OTHER ICY WORLDS

Earth’s biosphere is cold, with 14 % being polar and 90 % (by volume) cold ocean <5 oC (Table 1). More than 70 % of Earth’s freshwater occurs as ice, and a large portion of the soil ecosystem exists as permafrost. Expectations of commercial applications and interest in the early evolution of life have led many researchers to examine microbes in thermal systems. Based on the occurrence of evolutionarily old microbes in extreme thermal systems, in concert with extensive geothermal activity during the early evolution of our planet, it is generally thought that life on Earth evolved in hot environments (Huber et al., 2000; Pederson, 1997). Recent considerations about the evolution of life, however, have suggested that a «hot start » was probably not the only alternative for the origin of life. Though there are strong arguments for a thermal origin of life based on small subunit ribosomal RNA (16S rRNA) phylogenetic relationships, the validity of this relationship is questioned by researchers who believe that phylogenies are strongly biased by the use of just a single gene for the construction of the tree of life. If lateral gene transfer is common among all prokaryotic organisms (Nelson et al., 1999), then