Pearson Comments: Mark Goodwin is right, of course, that we cannot guarantee, on textural evidence alone, that any given fossil is chemically pristine. In our studies of the calcite shells of marine microfossils, we have combined detailed morphological study with a range of chemical and isotopic analyses. We find that texturally pristine fossils always have a wider range of interspecies isotopic differences than more recrystallized ones, and infer that the data more nearly reflect differences in the original chemistry at the time the various organisms lived. However, we can never rule out the possibility of secondary alteration.
Bone is especially problematic because its porous and intricately sculpted apatite structure makes it prone to rapid recrystallization. Bone quickly acquires a chemical signal from its environment after burial. 1 In our foraminifer shells, recrystallization is undoubtedly slower, and by focusing our studies on carbon and oxygen isotopes (major constituents of calcium carbonate), we are less apt to isolate a secondary signal than we would be if, for example, we analyzed just the trace elements that are abundant in the surrounding sediment.
