Radiogenic dating of meteorites
Stratigraphic Superposition - Because of Earth's gravity, deposition of sediment will occur depositing older layers first followed by successively younger layers.
Age of Earth estimated on the basis of how long it would take the oceans to obtain their present salt content.
The result is the geologic column, which breaks relative geologic time into units of known relative age.
Note that the geologic column was established and fairly well known before geologists had a means of determining absolute ages.
An unconformity is a surface of erosion or non-deposition. Because of the Laws of Stratigraphy, if we see a cross section like this in a road cut or canyon wall where we can recognize an angular unconformity, then we know the geologic history or sequence of events that must have occurred in the area to produce the angular unconformity.
Angular unconformities are easy to recognize in the field because of the angular relationship of layers that were originally deposited horizontally Disconformities (called parallel unconformities in your lab book) are much harder to recognize in the field, because often there is no angular relationship between sets of layers.
The nature of an unconformity can change with distance.