Fossils and Strata; Relative geological time
When one sedimentary layer overlies another, we can be fairly certain that the lowermost is the older of the two. The important step of codifying this relationship in a set of rules was taken up by Nicholas Steno in 1669 (the Law of Superposition). Although fairly obvious now, this was an important intellectual step in understanding what we now call relative time; that things, especially sedimentary strata, are older or younger than other strata. This is the essence of the science we call stratigraphy. Continue reading