 By comparing overall formations, geologic structures and local strata, calibrated by those layers which are widespread, a nearly complete geologic record has been constructed since the 17th century.Correcting for discordancies can be done in a number of ways and utilizing a number of technologies or field research results from studies in other disciplines.In this example, the study of layered rocks and the fossils they contain is called biostratigraphy and utilizes amassed geobiology and paleobiological knowledge.