ENVIRONMENTAL BIOPHYSICS AND MICROBIAL UBIQUITY 



J. R. Vallentyne 

 Department of Zoology, Cornell University, Ithaca, N.Y. 



Since the downfall of the near-collision theory of the origin of the solar sys- 

 tem and the revival of the dust cloud hypothesis it has generally been assumed 

 that planetary systems must be common in the universe. There has also been 

 a strong tendency to regard the formation of life within a planetary system as 

 the probable outcome of a series of nonbiological events operating within a re- 

 stricted range of physicochemical conditions. These points of view contrast 

 markedly with those held even as little as 30 years ago. Few persons today 

 would attempt to maintain that Earth is the sole place in the universe where 

 life resides. 



In spite of this drastic change in attitude and the recent reports of organized 

 matter in carbonaceous chondrites (Nagy et al., 1961; Claus and Nagy, 1961), 

 there are still many who hesitate to beUeve that life within the solar system can 

 exist beyond the confines of Earth. In relation to the cjuestion of life on Mars, 

 for example, it is customary to tmd opinions clouded in a mass of delicately 

 phrased intellectual jargon that is designed to be all inclusive and noncommit- 

 tal. Much of the criticism levelled against the notion of life on Mars is made 

 from what the self styled Soviet astrobotanist, G. A. Tikhov (1955), would 

 term a geocentric point of view. Thus, it is often questioned whether organ- 

 isms could survive the rigors of a Martian climate: an average temperature 

 50° C. below that of the earth; daily temperature fluctuations of about 60° C. 

 at the equator; an atmosphere richer in CO2 , and decidedly lower in O2 and 

 total pressure than that characteristic of Earth; an environment in which water 

 is scarce and in which the level of ultraviolet radiation may reach "lethal" 

 proportions. 



This, however, is absolutely the wrong approach to the question. The whole ap- 

 proach assumes a curious lack of adaptation on the part of the presumed Mar- 

 tian organisms, almost forcing them to adapt to terrestrial conditions in a 

 Martian locality. At least two assumptions seem to be involved in the reason- 

 ing: (1) that a complete body of information exists defining the environmental 

 limits beyond which life, as known on Earth, is impossible; and (2) that these 

 geoenvironmental limits of life are not exceeded on a cosmic scale. The first 

 of these assumptions is clearly erroneous as the present paper will show, and 

 the second seems rather questionable. 



My main purpose here is to summarize current knowledge and ignorance re- 

 garding the environmental boundaries that delimit the "stability field" of liv- 

 ing matter. The problem is approached purely on an empirical basis. Most 

 of the discussion is limited to conditions that permit growth and reproduction 

 because this is the central cjuestion that has to be faced; however, some remarks 

 are made concerning survival because of its pertinence to life in fluctuating 

 environments. The review is not intended to be exhaustive, nor comprehen- 

 sive in anything other than a qualitative sense; only to serve as a reminder of 

 forgotten or little known facts concerning some of the extreme types of environ- 

 ment inhabited by living organisms. Attention is focussed on microorganisms 



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