510 Annals New York Academy of Sciences 



criteria for a biological origin seems to hold for these particles. They do not 

 fluoresce and they do not take biological stains in a manner that will distinguish 

 them from irregular silicate fragments in Orgueil and in kimberlite. Because 

 they disappear after treatment with acids, we believe that they are most Ukey 

 grains of minerals, although they are classilied as organized elements by Nagy 

 et al. The 2 particles remaining in our sample after HF-HCl treatment re- 

 semble terrestrial contaminants. Moreover, it must be emphasized that only 

 2 were seen where several thousand should have been found. 



Even if organic particles should be found, a biological origin need not be 

 inferred. Both the polypeptide particles of Fox'* and the hydrocarbon poly- 

 mer particles of Wilson'^ have an appearance at least as organized as the less 

 structured organized elements. These materials are produced in vitro, by dry 

 polymerization of amino acids,^* and the Miller-Urey type synthesis,'*'''^ re- 

 spectively. In FIGURE 11 is illustrated a preparation obtained through the 

 courtesy of Wilson in which most of the polymer occurred in the form of sheets 

 containing thickened, round spots about 10 /x in diameter. Much of the ma- 

 terial was fluorescent, but some of the larger spots were not. 



It may well be that life did exist in meteorites, but we feel that the present 

 evidence is not adequate to suggest an extraterrestrial biological origin for the 

 particles found in the carbonaceous chondrites. 



Criteria for Identification of Life Forms 



If the present data are inadequate, what kind of information is needed to 

 decide whether or not a particle is, in fact, a life form? This requires an initial 

 definition of life. Life has three essential qualities. Life requires reproduc- 

 tion of itself with the possibility of mutations developing along the way. Regu- 

 lated and integrated anabolical and catabolical chemical processes are a second 

 feature of life. Structural organization at the molecular and supramolecular 

 levels is a third feature. Probably for simple, small organisms, it is necessary 

 to demonstrate all of these features — reproduction, metabolism, and organiza- 

 tion — to establish the presence of life. 



What is needed to establish that life had been present at some time in the 

 past? Ideally, remnants of all these features should be found. In reproduc- 

 tion of all terrestrial forms, nucleic acids carry information from one genera- 

 tion to the next. Nucleic acids or breakdown products from them may remain 

 after life has ceased. Evidence of metabolic processes frequently remains. 

 Many carbohydrates and lipids are rather resistant and persist for long periods. 



Persistence of the organization of any organism forms the basis for terrestrial 

 paleontology. This morphology may be the result of partial or complete 

 replacement of biological materials with nonbiogenic compounds. If replace- 

 ment has been complete, probably one can never be entirely certain that a 

 given structure was originally of biological origin. In terrestrial materials, 

 this is occasionally an important question but it is never a critical one. For 

 nonterrestrial materials it is a critical question. 



If "fossilization" or replacement has been incomplete, then metabolical 

 products of various sorts will remain. In pre-Cambrian rocks containing ap- 

 parent fossil forms, there are, in fact, substances that resist the acid treatments 

 used to remove the mineral materials.'" With cytochemical as well as other 



