Deep drilling into the ice sheet at Vostok station, Antarctica, was started by specialists of the Leningrad Mining Institute (since 1991, St Petersburg State Mining Institute) in 1970. Five deep holes were cored: hole No. 1 to 952 m; hole No. 2 to 450.4 m; hole No. 3G (3G-1, 3G-2) to 2201.7 m; hole No. 4G (4G-1, 4G-2) to 2546.4 m; and hole No. 5G (5G-1) to 3650.2 m depth. Drilling of hole 5G-1 is not yet complete. The deep drilling at Vostok station has had successes and problems. All the deep holes at Vostok have undergone at least one offset drilling operation because of problems with lost drills. These deviations were made successfully using a thermal drilling technique. Several drilling records have been achieved at Vostok station. The deepest dry hole, No. 1 (952 m), was made during Soviet Antarctic Expedition (SAE) 17 in 1972. The deepest fluid-filled hole, No. 5G-1, made by a thermal drill (TBZS-132), reached 2755 m during SAE 38 in 1993. The deepest fluid-filled hole in ice, No. 5G-1, was drilled with a KEMS-132 electromechanical drill and was stopped above Vostok Subglacial Lake at 3650.2 m depth during Russian Antarctic Expedition (RAE) 51 in 2006.In the summer season of the 15th SAE, the first drilling shelter was constructed on two steel sleds (Fig. 3), providing a work area measuring 15 Â 2.9 Â 2.5 m. A 9.7 m round tower, measured from the top of the hole, was constructed in the center of the work area and wrapped in rubberized cloth for protection ( Fig. 4).

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Many investigators regard Antarctica as a model for solution of such problems as search of life on other planets, the quarantine in planets and at the Earth during interplanetary contacts. It is also a good natural experiment for studying the phenomenon of microbial long-term anabiosis. Remoteness from the regions of intensive anthropogenic effects, low stable temperature and reliable protection of ancient ice horizons against subsequent environmental changes make Antarctic ice sheet an ideal object for methodological works necessary for investigation of various problems of exobiology. Investigations of ice bodies in attempts to fmd there any possible form of life has an advantage over similar studies of other cosmic solids because microorganisms, spores, plant pollen, unicellular algae, and other inclusions rather easily release from the melted ice and their investigation by different methods depends only on the well thought-out techniques. Special techniques of aseptic sampling while drilling at Vostok station and analysis of these samples by different methods have provided evidence for the existence of viable microorganisms in very ancient layers of the ice sheet. The relationship between quantitative distribution of microbes at different horizons of the ice column with the Earth's climate fluctuations at the time ofthese layers formation was also demonstrated.

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The discovery more than 30 years ago of the unique superlong anabiosis phenomenon (deep sleep/dormancy) for ancient microorganisms buried in Antarctic ice deposits created the experimental and theoretical basis for the fields of cryomicrobiology and astrobiology related to searching for life or its evidence in the universe. This discovery is of special interest in light of the upcoming International Polar Year (IPY 2007–2008) and the creation of the U.S. Subglacial Antarctic Lake Environments program (http://salepo.tamu.edu/us_sale). Abysov et al. [1977, 1978] discovered superlong anabiosis for microorganisms in deep Antarctic ice cores above Lake Vostok when his group found and revived ancient microbes frozen for more than 500,000 years (Figure 1). Previously, only science fiction writers had contemplated a deep sleep/dormancy phenomenon that might allow humans to postpone their deaths by freezing and thus travel in time into the future.