570 Annals New York Academy of Sciences 



hydrocarbons from prehistoric Hfe have been preserved for geological periods 

 of time in nature, and these compounds may be used to define and study the 

 existence of ancient organisms. 



It has been suggested that saturated isoprenoid type hydrocarbons synthe- 

 sized either by living things*-'^* or from sterol and isoprenol remnants of 

 organisms^'* •^^•^^•"■^'^ are major sources of naturally occurring alkane hydro- 

 carbons. Disagreement on the origin of terrestrial alkanes centers about the 

 issue of whether living things*""^^'^^ or chemical reactions acting on plant and 

 animal remains'*^ ■^''•^''•^'^''^"'®^ make most of the saturated hydrocarbons in 

 nature. Either of these sources would yield biosynthetically controlled prod- 

 ucts which could serve as reliable biological indicators. 



Similarities and differences in the benzene and analogous extracts of terrestrial 

 sediments may be generally summarized and partially explained. An average 

 sediment contains between 20 and 80 parts per million of Cm and larger hydro- 

 carbons.^' ■■*" •'*^ ■** These hydrocarbons usually comprise between 10 and 30 

 per cent of most extracts, and the hydrocarbons can be separated chromato- 

 graphically from the organic oxygen, nitrogen, and sulfur containing molecules 

 which make up 70 to 90 per cent of the extract.^' ■^"•^^ Hydrocarbons are 

 eluted primarily in the w-heptane, carbon tetrachloride, and benzene eluates; 

 whereas the organic nonhydrocarbons appear chiefly in the methanol eluates 

 from silica gel chromatographic cokmns. 



The extractable organic nonhydrocarbon fractions from sediments normally 

 show hydroxyl or amino (2.9 to 3.0 fx), carbon-hydrogen (3.3 to 3.5 m), carbonyl 

 (5.7 to 5.9 fx) and broad absorptions in the 7 to 15 /jl regions of the infrared. 

 Saturated and aromatic hydrocarbons from sedimental extracts show the 

 usual carbon-hydrogen absorptions in the 3.3 to 3.5 n and 7.2 to 7.8 m regions. 

 In addition, the saturated hydrocarbons in most cases absorb at the carbon 

 chain frequency near 13.9 n which is indicative of //-paraffins, and aromatics 

 generally absorb at the "oil band" frequencies of 12.4 and 13.4 fx. 



Nonlinear polyring aromatics are dominant in sedimental hydrocarbon 

 mixtures. Phenanthrenes, chrysenes, pyrenes, and perylenes appear with and 

 without alkyl and cycloalkyl substituents in many soils and marine sediments. 

 Anthracenes, naphthacenes, and larger linear polyring aromatics have not been 

 identified in extracts of soils or marine sediments. Carruthers^'' has isolated 

 some alkylanthracenes from crude oils; but in petroleum also, phenanthrenes 

 are much more abundant than anthracenes.^^ 



Sedimental extracts can be divided into two broad classes: (1) soil or aerobic, 

 and (2) marine sediment or anaerobic. Overlaps do exist. Anaerobes and 

 aerobes both live in soils and marine sediments, but aerobes appear dominant 

 in most soils. Soil extracts normally contain more wax-esters and less free 

 sulfur and aromatic hydrocarbons than do extracts of marine sediments.^' •''^ 

 Although the same molecular structures appear to be present^^'^^'*^ in sedi- 

 mental hydrocarbons, the ratio of saturated to aromatic hydrocarbons is 

 usually greater in soils than in marine sediments.'*' •^'*'^"''*^ 



Apparently, the compositions of sedimental extracts can be grossly explained 

 on the basis of the stabilities of plant and animal constituents in different 

 natural environments. Chemically and/or biochemically active carbohy- 

 drates, proteins, fats, oils, and porphyrins (hemin, etc.) comprise all but a 



