References

Role of Microorganisms in Wear Down of Rocks and Minerals 77
the needed time scales and speed because the reactive reservoir of rocks is
large enough to adsorb the carbon dioxide passing annually into the atmosphere
by a considerable increase in biotic weathering or rock wear down.
The latter is probably driven by a heterotrophic flora fed by organic compounds
supplied mainly by the atmosphere (Krumbein and Gorbushina
1996; Gonzales-del Valle et al. 2003; Gorbushina et al. 2001, 2003a). This
flora is creating its own niche for life on and within rock materials. They
createcavitiesanddwellingplacesnotunlikethosecreatedbyanyanimal
searching for a safe place to live and care for its offspring. Figures 2–4
illustrate the enormous potential of rock carving and cavity production of
some heterotrophic and phototrophic organisms.
Natural fossil fuel burning as well as natural biological oxidation of
hydrocarbons has been documented for many periods of Earth’s history.
Thunderstorms and volcanism have not only regularly set forests on fire,
but also peat, lignite, coal, oil deposits and oil shale. The best-studied example
is an oil shale between Jerusalem and Jericho, which was set on
fire in the Tertiary and produced temperatures high enough to initiate a
“natural” Portland cement oven with its typical minerals from the carbonate/shale
content of the rock in question, which contained “only” about
2–5% petroleum. The biological oxidation of hydrocarbons is witnessed by
petroleum seeps at 2000–3000 m water depth in the Atlantic Ocean of South
America, where a dense microbial population creates an organic matter
oxidation oasis comparable to the chemolithotrophic black smoker environments
of the Deep Sea. Certainly, the anthropogenic dimension of fossil
fuelburningandcementindustrymaybemoreseverethantheseaccidental
forest fires by lightning or the coal and petroleum deposits seeping out and
being set on fire in the geological past. These processes, however, must have
occurred at a very high frequency. Overproduction of organic matter under
optimal conditions for photosynthesis and simultaneous overproduction
of oxygen in the atmosphere may have occurred many times in the geological
record. This, in turn, caused even wet leaves to burn when natural
firesoccurred.Furthermore,itcannotbeunderestimatedthathumanfossil
fuel burning affects less than 0.1% of the total organic matter embedded
in the sedimentary rocks. In the geological past and today, 99.5–99.9% of
the reduced organic matter rising to the Earth’s surface was and is oxidized
in a slower way by natural biological or physical processes than described
before. The total mass oxidized at these natural rates is considerably larger.
Therefore, it seems that fossil fuel burning is only a minor factor in the
total release of carbon dioxide from fossil-reduced carbon deposits. The
presently observed disequilibrium of carbon dioxide levels in the atmospheremaythushaveverylittletodowithanthropogenicactivities.Itmay
be just a response pattern to other geophysiological constraints and reactions
that have happened in the past and will happen in the future even