Fossil Organic Matter

These materials are chemically very complex and the composition of fossil organic matter depends on the kind of organism from which the deposit has formed [2],... 

Comparable infrared (IR) spectra of complex organic solids such as coals (Fig. 7) 23), cherts, kerogens, humic substances and some natural polymers have been presented in various publications. They show a limited number of rather broad bands which are due to well defined chemical groups and can often be interpreted by comparison to less complicated spectra. The signals commonly observed in fossil organic matter are as follows (Robin et al., 1977 21), Tissot Welte, 1978 24), Rouxhet et al., 1980 22>, Friedel Carlson, 1972 25)) ... 

CH4 and CO, derived mostly from biogenic sources on land, volcanic and diagenetic processes, and a small flux from weathering by atmospheric O2 of fossil organic matter in sedimentary rocks exposed at Earth s surface. 

Once an organism dies and its biochemicals are released into the environment, their chiral purity (and optical activity) may or may not persist depending on the relative chemical stability of the bonds in the vicinity of the chiral center. Various natural chemical processes can lead to racemization, the formation of mixtures of the two enantiomers. While racemization may result in loss or corruption of a biological signature, the rate at which it happens can also have a practical application. The best known example is the dating of fossil organic matter on the basis of the degree of amino acid racemization. 

Our contribution to this project was to find and characterize these PAHs. In themselves, they could be biomarkers of fossilized organic matter of long ago, or they could have come from some nonliving source, such as metal-catalyzed reactions of organics on hot surfaces. If we could establish these PAHs as indigenous to the meteorite, then they would be the first observation of organic molecules found from Mars. 

While some reduced sulfur, either of biogenic or non-biogenic origin, may accumulate in the environment as metal sulfides and elemental sulfur, or be incorporated into fossil organic matter, most is eventually oxidized to sulfate, a process in which microbial activities play a major role. 

Table I. Fossil organic matter reserves of Brazil 03).

Macko S.A., Engel M.H. (1991) Assessment of indigeneity in fossil organic matter, amino acids and stable isotopes. Phil. Tans. Roy. Soc. Lond. B 333, 367—74. 

The Formation of Fossil Organic Matter and its Bulk Composition... 

Fluctuations that have been measured in the 5 G values of sedimentary organic matter over the Earth s history (e g. Schidlowski 1988) can thus be interpreted in terms of the productivity in the water coltrrrm and the availability of DIG in a particular geological time period. In a study of sediments from the central equatorial Pacific Ocean spanning the last 255,000 years it has been demonstrated that the carbon isotopic composition of fossil organic matter depends on the exchange between atmospheric and oceanic GO. Ghanges with time can then be used to estimate past atmospheric carbon dioxide concentratiorrs (Jasper et al. 1994). 

Carbon/nitrogen ratio (C/N) The ratio between carbon and nitrogen in living or fossil organic matter. It is normally calculated from the concentrations of the two elements measured as weight % of the bulk sample, but may also be expressed as an atomic ratio. 

Of the various traits used to address the question of the biogenicity of minute fossil-like objects, three stand out as having proven particularly useful the detailed (micron-scale) morphology of the objects in question the carbon isotopic composition of associated kerogenous matter and the molecular-structural makeup of fossil organic matter. 

At the end of a brief life, the diatom settles to the bottom of the body of water where the organic matter decomposes, leaving the siliceous skeleton. These fossil skeletons, or fmstules, are in the shape of the original diatom plant and have designs as varied and intricate as snowflakes. Examples are shown in Figure 1. 

Our complex modern life style was made possible by the discovery and refining of fossil fuels, fuels that are the result of the decay of organic matter laid down millions of years ago. The natural gas that heats our homes, the gasoline that powers our automobiles, and the coal that provides much of our electrical power are fossil fuels. Vast reserves of petroleum, the source of liquid hydrocarbon fuels such as gasoline and coal, exist in many areas of the world. However, although large, these reserves are limited, and we are using them up at a much faster rate than they can be replaced. 

We have already met carbon dioxide, C02, many times throughout this book. It is formed when organic matter burns in a plentiful supply of air and during animal respiration. It is normally present in the atmosphere but there is widespread and well-founded concern that an increase in atmospheric carbon dioxide due to the combustion of fossil fuels is contributing to global warming (Box 14.2). 

Hare, PE. and von Endt, D. 1990 Variable preservation of organic matter in fossil bone. Annual Report of the Director of the Geophysics Laboratory. Carnegie Institution, Washington. 1989-1990. Washington, D.C., Carnegie Institution ofWashington 115-118. 

Grimalt, J.O., Simoneit, B.R.T. and Hatcher, P.G. (1989). Chemical affinities between the solvent extractable and bulk organic matter of fossil resin associated with an extinct podocarpaceae. Phytochemistry 28 1167-1171. 

---