References

Role of Microorganisms in Wear Down of Rocks and Minerals 65
croorganisms) was first expressed by authors like Paracelsus (see Krumbein
et al. 2003b) and Kant (see Krumbein 1996).
Callendar (1938) suggested that production of carbon dioxide by fossil
fuel combustion, limestone burning and anthropogenic forest fires influences
temperature and climate on the basis of calculated data. The exact
transfer and balances, however, became known when the so-called Keeling
curve was brought to our attention (Callendar 1939, 1958). Fossil fuel burning
can be very clearly calculated from commercial statistics. From this and
fromroughestimatesoftheincreaseofdeforestationforagriculturaluse
(artificial versus natural forest fires), a theoretical increase of carbon dioxide
in the atmosphere can be calculated. The so-called greenhouse effect is
a composite feature that is caused by many gases escaping into the atmosphere.
Carbon dioxide, which makes up about 50 and 75%, seems to stem
from fossil fuel burning. In general, the increase in rain acidity is practically
99% due to carbon dioxide and less than 1% by SO2and NOx. Therefore,
the indirect increase in rock degradation rates through acidity of rain,
runoff water and atmosphere must be attributed mainly to the effects of
carbonic acid and perhaps also additionally to the heavy load of air-borne
anthropogenic organic compounds such as hydrocarbons, sugars, and fatty
acids, which may all be transformed by rock-dwelling microorganisms into
aggressive organic acids.
All major groups of microorganisms, i. e., chemolithotrophic, chemoorganotrophic
and phototrophic bacteria, algae, plants, fungi and protozoa,
have been reported to exist in such subaerial environments and to
contribute to rock wear down. Phototrophic microorganisms like lichens,
algae and cyanobacteria were the first to receive attention. Figure 1 gives
an example of extensive biopitting by desert lichen under relatively dry
and hostile conditions. The idea that heterotrophic life forms rather than
autotrophic ones are the most enduring and important rock dwellers came
up in the last century (Krumbein 1966; Staley et al. 1982; Gorbushina and
Krumbein 1999, 2000). Initially, it was thought that the biological attack
on rocks and minerals is driven either by photosynthesis of algae and
lichen (Sollas 1880; Bachmann 1890), or by chemolithotrophic processes
through nitric or sulfuric acid-producing bacteria (Müntz 1890; Isacenko
1936). However, Bachmann (1916) and Paine et al. (1933) had already hinted
at the chemical attack by heterotrophic fungi and bacteria on rock surfaces.
Fungi have been reported in a wide range of rock types including
limestone, soapstone, marble, granite, sandstone, andesite, basalt, gneiss,
dolerite, amphibolite and quartz, even in the most extreme environments,
e.g., hot and cold deserts (Staley et al. 1982; Sterflinger 2000). Even in
basaltic rocks in Iceland, the increase in porosity flaking and etching in
rocks has been attributed to fungal presence (Etienne and Dupont 2002).
The most obvious subaerial biofilm is the epilithic and endolithic lichen