Meinschein et al. : Evidence in Meteorites of Former Life 555 



carbonaceous chondrites may be minerals or sulfur droplets; whereas Briggs 

 and Kitto" conclude that the "complex organic microstructures" in the Mokoia 

 meteorite may be either of biogenic or abiogenic origin. It remains to be 

 demonstrated, however, that these abiotic products can duplicate the fluores- 

 cence, size, and numerical distributions, structural details, biological stain 

 acceptance, and behavior during palynological treatment which have been 

 reported'^ '^ for the microfossil-like "organized elements" in meteorites. In 

 the opinion of Nagy el al.,~^ no organic particles have yet been prepared that 

 possess all the properties of "organized elements" or cell remnants. Bernal-^ 

 states, "the question of whether the objects admittedly composed of sulfur or 

 mineral fragments are or are not identical with the 'organized elements' . . . 

 clearly requires for its resolution careful comparisons by a panel of impartial 

 experts." Urey^^ feels that "although the present evidence is not conclusive, 

 there are good reasons for exploring possible origins of lifelike forms in the 

 carbonaceous chondrites other than contamination after their arrival on earth." 



Biological Indicators 



Living things may be grossly regarded as unique assemblages of parts or 

 molecules that possess efficient means of synthesizing, using highly select 

 arrays of complex molecules, and of reproducing their specie. Plants can con- 

 vert several per cents of the solar energy that they receive into molecular 

 energy or food. Compounds which form a major portion of the constituent 

 parts of organisms comprise an exceedingly small fraction of the compounds 

 which theoretically can be made by abiotic reactions. Sagan'''^ reports "the 

 most optimistic extrapolation from existing laboratory ultraviolet experimental 

 data" for the quantum yield of organic molecules by Miller-Urey-*^ type syn- 

 theses is 1 part in 1()(),()()0 parts, and the products of these syntheses are neither 

 solely nor entirely the compounds made by living things. Organisms are 

 apparently in excess of a thousand times more efficient than abiotic reactions 

 which may have occurred in a primordial environment.-^ 



Although some nonbiological process under some presently undelinable 

 conditions may duplicate the productive capacities of living cells, available 

 data support the view that detectable concentrations of complex molecular 

 mixtures composed of compounds resembling those in living cells are products 

 of life.'-^ 



Because organisms are efficient and apparently unique producers of certain 

 arrays of molecules, plant and animal matter has probably exerted a major 

 control on the compositions of many carbonaceous substances in terrestrial 

 sediments for the last 2 or more billion years.-^ Either the preserved or the 

 altered biosynthetic products in Earth's sediments may provide a valuable, 

 legible record of prehistorical life and its evolution. Analyses of extracts of 

 terrestrial sediments indicate that ancient plants and animals have left evidence 

 of their existence and that some extractable substances of natural samples 

 may be used as biological indicators. 



In this investigation, the compositions of the benzene extracts of soils and 

 marine sediments froni various regions on earth have been used as references. 

 It is postulated that the terrestrial extracts retain evidence of biological activity, 

 and it is assumed that similarities between terrestrial and meteoric extracts 



