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will probably be clarified by the continued cooperative efforts of
scientists such as those in the group that met in Berlin last
September. The staff of Dahlem Konferenzen is responsible for
making the meeting of this group memorably pleasant and pleasantly
mem- orable. Dr. Bernhard's gifts of charm, organizational skill,
and administrative toughness assured that the conference was run
elegantly, smoothly, and decisively, even down to the choice of
editors for this volume. Marie Cervantes-Waldmann performed minor
miracles extracting manuscripts gently but persistently from the
authors and in turning the typescripts into a book. The other staff
members of Dahlem Konferenzen were unfailingly helpful even under
trying circumstances. They will be well rememberedbyall who were
fortunate enough to be asked to Berlin for the first week in
September, 1980. Mineral Deposits and the Evolution of the
Biosphere, eds. H. D. Holland and M. Schidlowski, pp. 5-30. Dahlem
Konferenzen, 1982. Berl in, Heidelberg, New York: Springer-Verlag.
Microbial Processes in the Sulfur Cycle Through Time H. G. TrUper
Institut f. Microbiologie, Rheinische
Friedrich-Wilhelms-Universitat, 5300 Bonn 1, F. R. Germany
Abstract. Two microbial processes are involved in the sulfur cycle
of the earth's biosphere: anoxic dissimilatory sulfur oxidation by
phototrophic bacteria and dissimilatory sulfate reduction by
sulfate-reducing bacteria. In the presence of oxygen at chemoclines
and redoxclines dissimilatory sulfur oxidation by chemolithotrophic
bacteria (Thiobacillus, Beg- giatoa, and others) occurs. In
addition, dissimilatory sulfur reducing bacteria participate in the
sulfur cycle.
3 of the experience of the last few generations. The group of
happily unexperienced events includes large bolide impacts with the
Earth. The evidence for the occurrence of such impacts at intervals
of some tens of millions of years is quite convincing, and Lyell
stands admonished by Hamlet: "There are more things in heaven and
earth, Horatio, than are dreamt of in your philosophy. " The role
of bolide impacts on the history of life during other portions of
the Phanerozoic Eon is less clear (see Raup and Fischer, both this
volume), and catastrophic changes unrelated to extraterrestrial
processes may have been important (see Holser, this volume).
Changes in the later Precambrian biota are still difficult to
interpret, in part because the preservation of soft-bodied animals
from this period of Earth history is so unusual (see Seilacher,
this volume). During the past billion years or so, bolide impacts
have exerted a significant effect on the Earth's surface and its
inhabitants, but not on its interior. The 3800 Ma rocks at Isua in
West Greenland are the oldest terrestrial rocks that are currently
available for inspection (see Dymek, this volume). They contain
abundant evidence for the operation of chemical and physical
processes that are similar to those of the present day. This
situation could not have prevailed during the entire 700 Ma
preceding the formation of the Isua rocks.
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