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Re: A couple of questions



Randy King wrote:

>1)  When a bone fossilizes, is there any organic material left?  What minerals
>replace what?

"Bones are chemically unstabe when exposed to surface conditions an begin
changing soon after death. Organic matter (Approx. 20%) decomposes and
crystallites of calcium phosphate "ripen" by changing in size and
composition. Trace elements may be absorbed during early crystal changes or
permineralization, changing the original composition of the bone. Under
favourable postburial chemical conditions, CaCO3, Fe2O3, and/or SiO2
gradually penetrate bones replacing the original materials and/or infilling
cavities left by decaying organic matter." Behrensmeyer (1991)

Recalcitrant organic matter can persist for quite some time, and is used to
date bones up to 40,000 years old via C14 dating. Modern techiques only
need micrograms of sample. Previously, several grams was needed, which led
to contamination and resulted in mammoth dates of only 2-3000 years. This
was brought about partly because it was thought that the white areas in
bone represented unaltered material, when in fact it represented late stage
addition of CaCO3.

Behrensmeyer, A.K. (1991) Terrestrial vertebrate accumulations. In
Taphonomy: Releasing the Data Locked in the Fossil Record, P.A. Allison &
D.E.G. Briggs (eds). pp 291-335. Plenum Press, New York.

Chris
Geology & Geophysics
University of Adelaide

cnedin@geology.adelaide.edu.au