Presumably if all the world’s outcrops were integrated, sediments representing all of geologic time would be available for examination.
This optimistic hope, however, must be tempered by the realization that much of the record—older than 541 million years—is missing.
Highland County igneous rock intrudes sedimentary rock (Photograph by Stan Johnson) This light-colored Highland County igneous intrusion cuts through the darker sedimentary rock.
Stratigraphy is a branch of geology that studies rock strata with an emphasis on distribution, deposition, age and evidence of past life.
This section discusses the methods geologists use to determine how old a fossil or rock is. Therefore, the sedimentary rock must be older than the intrusion.
The most useful indication of time equivalence is similar fossil content, provided of course that such remains are present.
The age of formations is marked on a geologic calendar known as the geologic time scale.
Development of the geologic time scale and dating of formations and rocks relies upon two fundamentally different ways of telling time: relative and absolute.
Once Steno recognized that the fossils he was contemplating (sharks teeth and sea shells) were formed in the sediments of oceans he was able to work out the basic rules of stratigraphy.
Steno formalized the laws of superposition, original horizontality, original continuity and inclusions in his publication entitled states that any inclusion is older than the rock that contains it.