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CHAPTER 48 



into orbit above our atmosphere. In this 

 position, such telescopes would not be im- 

 peded, as they are now, by the absorption of 

 energy by the contents of our own atmos- 

 phere. Interplanetary research is now in 

 progress to send instruments to or near 

 various planets in the near future. Such 

 missions will be capable of telling us the de- 

 tailed chemistry of any of our neighboring 

 planets, and will, of course, also be designed 

 to detect the presence of organisms and of 

 DNA. We are already sending radio sig- 

 nals into space in an attempt to contact 

 other organisms capable of replying. 



It will become apparent to you that in 

 any space mission it is important to avoid the 

 accidental transplantation of terrestrial geno- 

 types to other planets. For, if a single 

 bacterium, like E. coli, were to be placed on 

 a planet containing a suitable medium, the 

 progeny would occupy a volume the size of 

 the earth in about 48 hours. Such an un- 

 scheduled transplantation would be disas- 

 trous to any plan we would have for a later 

 study either of the preorganismal evolution 

 of organic compounds or of any indigenous 

 organisms. This is why objects sent beyond 

 our atmosphere are carefully sterilized. 



Which heavenly objects, likely to be in- 

 vestigated in the near future, are interesting 

 from the point of view of preorganismal and 

 organismal evolution? We have already 

 mentioned the desirability of exploring Mars. 

 Consider Venus, whose surface is unknown, 

 being hidden completely by an opaque, 

 highly reflecting, cloud layer, containing 

 abundant CO2 and water. While estimates 



of Venus' temperature vary widely, and it 

 is thought that its surface is dry and hot, we 

 cannot assume that organic chemistry or 

 even biological activity is impossible there. 

 After studying its chemistry in sufficient de- 

 tail, it is possible that we might wish to 

 colonize Venus, perhaps first by placing a 

 chlorophyll-containing microorganism in its 

 outer atmosphere. In a very short period, 

 such an organism, by using huge quantities 

 of the atmospheric components for growth 

 and reproduction, might change the entire 

 climate on Venus. Missions to other planets 

 in our solar system would be expected to 

 reveal the kind of chemical evolution which 

 occurs under other environmental conditions. 

 Our own satellite, the moon, has no atmos- 

 phere, and probably no water. Accordingly, 

 the presence there today of earthlike life is 

 out of the question. However, it is possible 

 that the moon is just about as old as the 

 earth and may have had an organic and even 

 a biological evolution similar to our own 

 before it lost its atmosphere. So, it will be 

 interesting to obtain and analyze samples of 

 its surface and, particularly, its subsurface 

 material. It has been suggested that the 

 moon might act as a gravitational trap for 

 fossil spores which may have drifted between 

 planets. Although improbable, the very 

 possibility of an interplanetary gene flow is 

 too important to ignore in our plans to ex- 

 plore and exploit space. Planetary research 

 has many motivations, but the search for 

 evidence of chemical evolution, DNA, or- 

 ganisms, and life would seem to be among 

 the most significant. 



SUMMARY AND CONCLUSIONS 



DNA has been the primary genetic material on earth for about a billion years. During this 

 time DNA together with accessory material has undergone a structural evolution leading 

 to the establishment of chromosomes and of mechanisms for genetic recombination. There 

 has probably been also a functional evolution of genes, which proceeded from those which 

 serve as genes for structure (specifying the organization of nongenic compounds) to those 

 which serve as genes for function (and act as operator genes in operons). 



