Relative dating is the science of determining the relative order of past events without necessarily determining their absolute age. It is used in geology to correlate one stratigraphic column with another using rocks, superficial deposits, fossils, and lithologies. Prior to the discovery of radiometric dating, archaeologists and geologists used relative dating to determine the ages of materials. Relative dating can only determine the sequential order in which a series of events occurred, not when they occurred.
Some key principles of relative dating include:
- Law of Superposition: This states that older layers will be deeper in a site than more recent layers.
- Principle of Original Horizontality: This states that layers of sediment are generally deposited in a horizontal position.
- Principle of Cross-Cutting Relationships: This states that a rock or fault is younger than any rock or fault through which it cuts.
Relative dating is used to arrange geological events and the rocks they leave behind in a sequence. It does not provide actual numerical dates for the rocks. Fossils can help match rocks of the same age, even when they are found far apart. This matching process is called correlation, which has been an important process in constructing geological timescales. Correlation can involve matching an undated rock with a dated one at another location.
Relative dating is a useful technique in paleontology and is, in some respects, more accurate than other methods. It is also used to determine the order of events on Solar System objects other than Earth.
