Relative age dating principles
For purposes of relative dating this principle is used to identify faults and erosional features within the rock record.Then, by applying the Principle of Cross-Cutting we are able to relatively date those processes.The Principle of Original Horizontality states that due to the influence of gravity all sediment is originally deposited horizontally.In other words, as sediment fills a depositional basins we would expect the upper most surface of the sediment to be parallel to the horizon. Using this principle we can than assume that sedimentary layers which have been deformed/folded must have been deformed after all affected layers have been deposited.The principle of cross-cutting states that any geologic feature that crosses other layers or rock must be younger then the material it cuts across.Using this principle any fault or igneous intrusion must be younger than all material it or layers it crosses.
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.
As sediment weathers and erodes from its source, and as long as it is does not encounter any physical barriers to its movement, the sediment will be deposited in all directions until it thins or fades into a different sediment type.
This concept known as the Principle of Lateral Continuity allows us to assume that similar layers of rock or sediment that are separated by a valley or other erosional feature were once continuos.
Absolute age-dating tells how long ago an event occurred.
Using these methods, geologists have created a geologic time scale for organizing past times in earth’s history.