The combination of these two types of geologic ages makes a complete record of earth's geologic history in terms of the order of events and in terms of how many years ago each event occurred.Relative geologic age refers to the order in which geologic events occurred.
Crosscutting Relations are those where one rock literally cuts across another, such as for example when igneous dikes and sills are emplaced in fractures within a pile of sedimentary rocks (see picture at left).
Obviously, the sedimentary rocks had to be there prior to emplacement of the igneous rocks, and thus they are older than the igneous rocks.
Geologic time covers the whole sweep of earth's history, from how and when the earth first formed, to everything that has happened on, in, and to the planet since then, right up to now.
Geologists analyze geologic time in two different ways: in terms of relative geologic age, and in terms of absolute (or numeric) geologic age.
Underlying assumptions are 1) that Faunal Succession is based on the observation that animals and animal communities that are preserved in sedimentary rocks change noticeably as geologic time passes (evolution).