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V. POSSIBILITY OF AN INDIGENOUS LUNAR PARABIOLOGY Because of its great potential importance, the admittedly very speculative possibility must be raised that, at some time in the remote past, life arose on the Moon. Conditions on the Moon while it still retained its secondary reducing atmosphere some 4 or 5 x 10' years ago were probably not very different from conditions on the Earth during the same epoch. Organic matter was being produced, bodies of liquid water probably abounded, and energy was available for higher order syntheses. How these conditions might lead to the origin of life has been described elsewhere (v., e.g., Oparin, 1957; Sagan, 1957). Recent thinking is increasingly inclined towards a very rapid origin of the first self-reproducing system on this planet. If a similar event also occurred on the Moon, natural selection may be expected to have kept pace with the increasingly more severe lunar environment, at least for some period of time. As the lunar atmosphere escaped to space, surface temperatures and radiation fluxes became more extreme, and meteoritic debris began covering the synthesized organic matter, it is only reasonable to anticipate that any indigenous organisms took to a subsurface existence. It is remarkable that the depth at which surviving lunar organic matter is expected to be localized (sectionn) is just the depth at which temperatures appear to be optimum for familiar organisms (section IV). At such temperatures and depths, some moisture should be expected, arising from meteoritic and organic bound water. Watson, Murray and Brown (1961) have recently pointed out that ice could have been retained on permanently shaded areas of the Moon. These circumstances provide all the survival requirements of many terrestrial organismsâwater and other metabolites, appropriate temperature, and negligible radia- tion. That autochthons evolving with the changing environment could also survive under these conditions is far from inconceivable. A somewhat analogous case is the anaerobic microflora which in- habit terrestrial petroleum deposits (v., e. g., Davis and Updegraff, 1954; ZoBell, 1950). It follows that the possibility of an extant lunar parabiology must not be dismissed in as cavalier a manner as it has been in the past. As we shall see in section VI, it is likely that relics of past lunar organisms, if any, could be pre- served indefinitely if sequestered well beneath the protective cover 24
of the upper lunar surface material. Thus, neither should the possibility of lunar paleontology be overlooked. It is probably unnecessary to remark that the study of any extraterrestrial organism will have the deepest influence on the fundamental prob- lems of biology. Even if the chances of success are small, at- tempts should be made to detect lunar subsurface autochthons, both living and dead. 25