environment given that rates of evolution tend to be slow under conditions of low temperature (Gillooly et al. 2005) and low productivity (Horner-Devine et al. 2003).

If the source population of microbial communities in subglacial aquatic environments is derived from the overlying glacial ice, these populations have been isolated for at least 1 million years, which is the age of the oldest Antarctic ice. Against the backdrop of 3.7 billion years during which microbes have been present on Earth, 1 million years is not a long time in terms of evolution. In the case of Lake Vostok, rates of evolution are likely to slow under the conditions of low temperature and low microbial productivity. The result is likely to be that the metabolically active and growing microorganisms present in these communities should represent those better adapted to the ambient conditions but will still be related to microorganisms found in other environments today.

A much longer time for evolution may have occurred if, however, the original inoculum to Lake Vostok dates back to the time of the isolation of the lake from the overlying atmosphere more than 15 million years before the present. This time of isolation could be even longer if the founding populations were derived from rocks or sediments. In this latter case, the microbial populations could have been isolated from the surface approximately 35 million to 40 million years ago, prior to the formation of the lake.

Samples of microbes from water and sediment are the only way to answer these questions of the uniqueness of microbial life in subglacial aquatic systems. Although the effect of the extreme conditions is unknown, there is a chance that the microbes have been isolated long enough that significant genetic divergence of microbial lineages has occurred.