Time (Duration) and Fossil Stumps
The preservation of standing fossil tree stumps has long fascinated scientists because of the implications for rates of burial and age of rock strata surrounding the fossils. In order for a tree stump to be preserved, the time it takes to bury the stump must be faster than the time it takes for the stump to decompose. In modern environments, woody tree stumps rot over a period of decades to centuries (with exceptions), so for a tree stump to be preserved it would have to be buried within that time span. Pennsylvanian lycopod trees were nonwoody plants, so likely would only have lasted decades before completely decomposing. In addition, decomposition tends to be faster in tropical climates, and during the Pennsylvanian Period, what is now Kentucky was close to the equator, and had a tropical climate.
It is important to understand that not all rock layers or beds are deposited in the same amount of time. Some beds are deposited rapidly in short amounts of time. Others require very long periods of sedimentation. The surfaces between two layers or beds also represent varying amounts of time. Some surfaces represent short breaks or changes in sedimentation, whereas others represent long periods of nondeposition or even erosion.