The rock fossils depict the history of life because they consist of several deposits of old age fossil in different layers of rock strata. The layer of rock strata which lies at the bottom of any rock deposits is the oldest layer. By examining this oldest layer one can determine the prevailing atmospheric condition at the time of its formation. Also, examining the remains of fossil can help us to understand the forms of life existing during that time.
In this way all the layer of rock strata can be examined one by one from bottom (oldest) to top (youngest). This shall also allow us to understand the pattern of evolution of biological species with time.
