Bremen 2000 – scientific programme
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EP: Extraterrestrische Physik
EP 14: Leben und Lebensbedingungen ausserhalb der Erde II
EP 14.7: Talk
Wednesday, March 22, 2000, 17:15–17:30, N3110
Carbon Isotopes as Recorders of Early Terrestrial Life: Implications for Extraterrestrial Scenarios — •Manfred Schidlowski — Max-Planck-Institut für Chemie, Postfach 3060, D-55020 Mainz
Since the pioneering work by Nier and Gulbransen (1939) it is known that the
incorporation of inorganic carbon into living systems entails sizeable
fractionations of
the stable carbon isotopes. Consequently, it became firmly established that
the
observed bias in favour of the light isotope (12C) characteristic of
biogenic
substances derives, for the most part, from the isotope-discriminating
properties of
the principal carbon-fixing enzyme (ribulose-1,5-bisphosphate carboxylase)
that is
operative in the main chemosynthetic and photosynthetic pathways,
channelling
most of the carbon transfer from the nonliving to the living world. It is
known,
furthermore, that biological carbon isotope fractionations are basically
retained when
organic carbon is incorporated in sediments, the enzymatic isotope effect
thus
having been propagated into the rock section of the carbon cycle over 3.5,
if not 3.8
Ga, of recorded Earth history.
Postulating a universality of biological principles in analogy to the proven
universality
of the laws of physics and chemistry, we may expect enzymatic reactions in
exobiological systems to be beset with similar kinetic fractionation
effects. Hence,
the retrieval from the oldest Martian sediments of isotopic fractionations
between
reduced and oxidized (carbonate) carbon may substantially constrain current
conjectures on the possible existence of former life on Mars.