Relative geologic age refers to the order in which geologic events occurred.
Relative geologic age is established, based on such evidence as the order in which layers of sediment are stacked, with the younger layer originally on top.
Although the types of trash in each pit is quite variable, each layer has a distinctive kind of trash that distinguishes it from other layers in the pits. Stratigraphy = the study of strata (layers) in the Earth's crust.
Laws of Stratigraphy Original Horizontality - sedimentary strata are deposited in layers that are horizontal or nearly horizontal, parallel to or nearly parallel to the Earth's surface.
By using the principles of relative geologic age, the sequence of geologic events -- what happened first, what happened next, what happened last -- can be established.
Absolute geologic age refers to how long ago a geologic event occurred or a rock formed, in numeric terms, such as 65.5 million years ago.
Revisions to the relative time scale have occurred since the late 1700s.Within the context of the Phanerozoic Eon, geologists beginning in the late 1700's recognized that fossils appeared in an orderly fashion in stratigraphic units.Moreover, these geologists recognized that the fossilized biota demonstrated rather large changes in overall composition and showed both similarities with, and differences from living taxonomic groups.In the Geologic Time Scale, time is generally divided on the basis of the earth's biotic composition, with the Phanerozoic Eon (i.e.the Paleozoic, Mesozoic and Cenozoic Eras) representing the period of Earth's history with advanced life forms, and the Pre Cambrian (or Proterozoic and Hadean Eras) representing the period before advanced life.