Molecular Decay of Plant Biopolymers - Biopolymers: A Molecular Paleontology Approach - page 3

with seed stock from the Arnold Arboretum of Harvard University, which was
obtained from China in 1947. Samples 1-3 were picked directly from the south side
of the tree to represent samples that were green (sample 1) through those showing
the onset of a change of colour (sample 2) to those turned red (sample 3) during
stages of senescence on the tree. Sample 4 was collected from the ground directly
under the same tree following leaf fall. Samples 5 and 6 were obtained from the lake
under the tree using an environmental dredge. Sample 5 was collected from the
water-sediment interface, whereas sample 6 was obtained from sediments repre-
senting deposition of the previous years. The leaves of sample 5 were lighter in
colour than those of sample 6. Following collection, all samples were divided into
two sets; one was air dried and kept in paper envelopes for morphological investiga-
tion and the other was frozen immediately for chemical analysis. C and N concen-
trations were obtained for sample 1 and 6, the two end members.
Experimental Heating (Maturation)
Modern Metasequoia needles were crushed in liquid N 2 , powdered and heated in
sealed gold cells at 350 °C without any chemical pre-treatment under a confi nement
pressure of 700 bar for 24 h in the absence of water (see Michels et al. 1995 ;
Hautevelle et al. 2006 ; Gupta et al. 2007a ). This technique generates a chemical
composition similar to that of organic fossils, particularly the aliphatic component.
Hence, it can be used to explore how different structural components and biopoly-
mers in plants contribute to the formation of a geopolymer. The temperature chosen
was that at which the most dramatic change in chemical composition was observed
during a previous investigation of arthropod cuticle (Stankiewicz et al. 2000 ; Gupta
et al. 2007a ). These experiments were conducted at the hydrothermal lab of the
Geophysical Lab, Carnegie Institution.
Fossils
Fossil leaves of Metasequoia were collected from sediments of Republic (Eocene,
Washington State, USA), Clarkia (Miocene, Idaho, USA), and Axel Heiberg
(Eocene, Canada).
Analysis
Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) reveals bulk mac-
romolecular information that has been used extensively for the characterization of
insoluble fossil organic matter (Larter and Horsfi eld 1993 ; Logan et al. 1993 ; Gupta