Speed and Conditions of Fossilization

Bonnie Blackwell

Tom Holtz referred the person who asked about fossilization processes to any elementary textbook on geology or paleontology to answer this question. I have found, however, that these books have one glaring error: the speed at which they assume these processes occur. My research has shown that secondary mineralization, remineralization, leaching of bone mineral, and biologically-induced mineralization begin very rapidly after the bone is exposed to the environment. If the bone is not buried or underwater within 1-2 years of defleshing, it will literally become dust in the wind. The bone fragments may persist for several more years, but they are unrecognizable as to species. If the bone is buried or underwater, diagenetic processes begin rapidly. A bone can be completely remineralized within 5-10 years. Secondary mineralization can fill all the porosity elements within a few months in some environments. These are the environments which preserve bone the best.

Hypersaline environments in which carbonates are precipitating favor bone remineralization and secondary mineralization. Saline environments also are good, but there the processes are slower. Caves may offer excellent preservation over the short term, but karst processes may attack the bone later destroying it along with the cave.

Soil is not a favorable environment generally because the bone mineral will tend to dissolve in the acidic conditions that occur in many soils, carbonate-rich soils of arid zones being the exceptions. It is the requirement of rapid burial/submergence that ensures that few vertebrates become fossilized.