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Understanding the processes of fossilization is vital to the
interpretation of fossils themselves, especially of geochemical fossils. The
search for past life on other planets will likely be the search for such
biosignatures or, at best, morphologically intact fossil “microbes”.
However, the interpretation of ancient microfossils found even in
terrestrial sediments has been hotly debated for years. It is for this
reason that new techniques and approaches to organic chemical
characterization of morphological fossils and geochemical biosignatures
must be developed.

Laser-Raman spectroscopy, nuclear magnetic resonance spectroscopy,
and pyrolysis-gas chromatography/mass spectrometry are three such
techniques. This study involves the use of these three techniques to analyze
the structural chemistry of a modern fern (Dennstaedtia cicutaria) and its
Eocene-aged three dimensionally permineralized fossil analogue
(Dennstaedtiopsis aerenchymata) as well as representative individual
structural biochemicals of fern cell walls. Specimens of the modern fern and
aliquots of the biochemicals have been anoxically thermally degraded to
simulate the alteration that occurs during diagenesis and resultant
fossilization.

Results thus far are promising. The analyses show that there is a
wealth of chemical information preserved in the fossil organic matter that
is of sufficient quality to be informative about its original composition.
Moreover, the heating experiments show that the organic matter of the modern
fern can be converted into carbonaceous matter that closely resembles that
of the fossil fern, providing new insight into the processes and products of
geochemical maturation. The three analytical techniques investigated, useful
for analyzing fossil terrestrial organic matter, hold promise for studies of
extraterrestrial materials as well.