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C. Variations of Stable Isotope Ratios in Nature
energy of sunlight is converted into the chemical energy of organic compounds. The reverse reaction is biological oxidation, or respiration, and
the energy thus liberated may appear as heat or work. A fairly close
balance exists between photosynthesis and respiration, although over
the whole of geological time respiration has been exceeded by photosynthesis, and the energy derived from this was stored in coal and petroleum.
Photosynthesis is of great importance in producing isotope fractionations, not only for carbon but also for hydrogen and oxygen. In general,
it is obvious that almost all isotope fractionation due to kinetic effects
occurs in the biosphere, as in the cases of the bacterial sulfate reduction,
photosynthesis, and respiration.
All organic molecules left over from dead organisms can hardly be
preserved without minor or major changes in geological environments.
The transformation of biogenic matter to organic matter in sediments
involves two stages, a biochemical and a geochemical stage. During the
biochemical stage microorganisms are active in reconstituting the organic matter. The biochemical stage is eventually brought to an end when
conditions become unsuitable for bacterial activity. Beyond that stage,
metamorphism, which results from the action of heat and pressure, is
responsible for the further transformation of organic matter.
The origin of coal and petroleum centers around three topics: the
nature and composition of the parent organisms, the mode of accumulation of the organic material, and the reactions whereby it was transformed into the end products.
Coal is fossilized plant matter. Depending upon ecological conditions, different plant tissues are converted into various microscopically
identifiable components of coal. In addition to these tissues, coal also
contains a minor amount of the remains of plant waxes and resins.
Petroleum (frequently also called crude oil) is a naturally occurring
complex mixture, composed mainly of hydrocarbons, but also with varying amounts of heterocompounds containing S, N, 0, and metallo-organic molecules, such as vanadium- and nickel porphyrins. It appears that
most petroleums are similar in their general qualitative compositions
and that the differences observed among them are mainly due to differences in relative amounts of certain components.
Although there are, without any doubt, numerous compounds that
have been formed more or less directly from biologically produced molecules, the majority of petroleum components are of secondary origin,
either decomposition products or products of condensation and polymerization reactions. It should be mentioned that there is strong evidence for the maturation of crude oils, depending on thermal history
and age.
C. Variations of Stable Isotope Ratios in Nature
energy of sunlight is converted into the chemical energy of organic compounds. The reverse reaction is biological oxidation, or respiration, and
the energy thus liberated may appear as heat or work. A fairly close
balance exists between photosynthesis and respiration, although over
the whole of geological time respiration has been exceeded by photosynthesis, and the energy derived from this was stored in coal and petroleum.
Photosynthesis is of great importance in producing isotope fractionations, not only for carbon but also for hydrogen and oxygen. In general,
it is obvious that almost all isotope fractionation due to kinetic effects
occurs in the biosphere, as in the cases of the bacterial sulfate reduction,
photosynthesis, and respiration.
All organic molecules left over from dead organisms can hardly be
preserved without minor or major changes in geological environments.
The transformation of biogenic matter to organic matter in sediments
involves two stages, a biochemical and a geochemical stage. During the
biochemical stage microorganisms are active in reconstituting the organic matter. The biochemical stage is eventually brought to an end when
conditions become unsuitable for bacterial activity. Beyond that stage,
metamorphism, which results from the action of heat and pressure, is
responsible for the further transformation of organic matter.
The origin of coal and petroleum centers around three topics: the
nature and composition of the parent organisms, the mode of accumulation of the organic material, and the reactions whereby it was transformed into the end products.
Coal is fossilized plant matter. Depending upon ecological conditions, different plant tissues are converted into various microscopically
identifiable components of coal. In addition to these tissues, coal also
contains a minor amount of the remains of plant waxes and resins.
Petroleum (frequently also called crude oil) is a naturally occurring
complex mixture, composed mainly of hydrocarbons, but also with varying amounts of heterocompounds containing S, N, 0, and metallo-organic molecules, such as vanadium- and nickel porphyrins. It appears that
most petroleums are similar in their general qualitative compositions
and that the differences observed among them are mainly due to differences in relative amounts of certain components.
Although there are, without any doubt, numerous compounds that
have been formed more or less directly from biologically produced molecules, the majority of petroleum components are of secondary origin,
either decomposition products or products of condensation and polymerization reactions. It should be mentioned that there is strong evidence for the maturation of crude oils, depending on thermal history
and age.