Carbonization, also known as distillation, is one process that preserves fossils of soft-bodied animals and leaves and stems of plants. Carbonization chemically alters the proteins and cellulose of tissues through degradation by bacteria, by chemical action, and by pressure and heat, until only carbon films remain. Other organic materials are dissipated as gases — carbon dioxide, methane, hydrogen sulfide, and water vapor. For example, a thick, fleshy fern leaf of Pennsylvanian times falls into mud. Hundreds of millions of years later a paper-thin black carbon copy of the leaf is found, perfectly preserving its details in shale. Coal is formed in the same way, but on a much larger scale. Carbonized plants are common in the shale overlying coal seams.
Carbonization preserved specimens of the Silurian worm Lecthyalus gregarius which wriggled about Chicago seas 400 million years ago. Carbonized fossils are by no means confined to such ancient rocks. The Cretaceous and younger formations of Tennessee contain plant leaves of this type, and so do the ash beds at Florissant, Colorado, the shales at Green River, Wyoming, and the Latah formations near Spokane, Washington. More commonly, however, Cenozoic plants exist as impressions.
The original plant material of this fern has been reduced to a carbon film. This is typical of plant fossils found near coal seams. Pennsylvanian period; Terre Haute, Indiana.
Soft-bodied animals, such as this worm, are rarely preserved except as a carbon film. Parts of this Silurian annelid, Lecthyalus gregarius, found near Chicago, are still attached to the mold in the limestone.
Was this article helpful?