Relative dating is a method of determination of age, in which one object or organism is compared with the other object or organism found in the heap of strata. It is a method for determining the relative order of the past events, without stating the absolute age.
Stratigraphy is a branch of geology that studies the relative position of the sediments and rocks in the strata with respect to the geological timescale. Biostratigraphy is the branch of stratigraphy which deals with the relative aging of fossils with respect to the strata in which these are found defining a particular period of geological time scale.
Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
