Now, because we've already established that this cake is pure insanity, you're going to cut out a big hole in the middle that pierces all 3 layers and stick in some new feature. This exact same concept can be applied to layers of rock underneath the surface.
We know that we can relatively date layers of rock by knowing that the layers on bottom are older than the layers on top.
Metamorphic rocks may also be radiometrically dated.
However, radiometric dating generally yields the age of metamorphism, not the age of the original rock.
Most ancient sedimentary rocks cannot be dated radiometrically, but the laws of superposition and crosscutting relationships can be used to place absolute time limits on layers of sedimentary rocks crosscut or bounded by radiometrically dated igneous rocks.
Crosscutting Relationships: Relative ages of rocks and events may also be determined using the law of crosscutting relationships, which states that geologic features such as igneous intrusions or faults are younger than the units they cut across.
Gaps in the geologic record, called unconformities, are common where deposition stopped and erosion removed the previously deposited material.
Fortunately, distinctive features such as index fossils can aid in matching, or correlating, rocks and formations from several incomplete areas to create a more complete geologic record for relative dating.
For example, shells, wood, and other material found in the shoreline deposits of Utah’s prehistoric Lake Bonneville have yielded absolute dates using this method.
These distinct shorelines also make excellent relative dating tools.