Introduction

Because Earth is the only place where we are certain that life exists, the characteristics of terrestrial life underpin our search for life elsewhere. In essence, the search for extraterrestrial life begins here on Earth. In the mid-twentieth century, early astrobiologists had recognized this reality and began studying life in remote and extreme environments that could be considered as analogues to places on Mars or elsewhere (e.g. Kooistra et al., 1958; Cameron, 1963; Briot et al., 2004). Early work by NASA and the Jet Propulsion Laboratory included studies of arid-soil microbiology in various locations, including the Atacama Desert and the Antarctic Dry Valleys (Cameron et al., 1966; Cameron, 1969; Horowitz et al., 1969; Cameron et al., 1970). Testing of NASA's earliest life-detection instruments also took place at these and other extreme environments (Levin et al., 1962; Levin and Heim, 1965). In parallel, microbiologists were also studying experimentally the survivability and adaptation of microorganisms isolated from desert soils and exposed to Lunar and Martian conditions in the context of forward contamination of the Moon and Mars, as well as towards the possibility of the existence of extraterrestrial life (e.g. Fulton, 1958; Kooistra et al., 1958; Davis and Fulton, 1959; Packer et al., 1963).

In recent years, Earth-based microbiological research, especially in harsh or extreme environments, has greatly expanded our understanding of the nature and limits of life (e.g. Rothschild and Mancinelli, 2001; Steven et al., 2006; Pikuta et al., 2007; Southam et al., 2007).