Fossil assemblage is representative of the death assemblage and has not been biased or contaminated. Fossil remains can be identified to a sufficiently low taxonomic level to enable uniformatarianism principles to apply. Pollen and spores are produced in great abundance by plants. Pollen and spores preserved when processes of biological decomposition are inhibited by lack of oxygen. This occurs in bogs, lakes, fens, and ocean floor.
Pollen is well mixed by atmospheric turbulence, which results in a more or less uniform pollen rain.
Proportion of each pollen type related to number of parent plants. Therefore, pollen is a function of the composition of the vegetation. A pollen sample is an index of the vegetation at a point in space and time. If a sample of pollen rain is examined from a peat or mud of known age, the pollen spectrum is an index of vegetation surrounding that place at a point in time in the past. Pollen spectra from several levels of sediment provide a picture of vegetation and its development at that place through the length of time represented by the sediments.