Absolute and relative dating of rock
However, carbon dating is an absolute dating technique that can give an estimate of the actual age of an artifact and thus an estimate of the age of other objects in the same layer.
Carbon dating is one example of radiometric dating.
The radiometric techniques that give absolute dating estimates are based on radioactive decay of elements such as uranium. Looking at how rock formations are structured, a geologist may be able to say which rock was developed in which layer in a particular order but not be able to determine that actual geologic age of the layers.
Geologists also have radiometric methods for absolute dating based on radioactive decay of certain elements.
Short Answer: The term relative dating is distinguished from absolute dating to make it clear that one does not get a specific estimate of the age of an object from relative dating, but one does get such an estimate of true age from absolute dating.
By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change.
Very often historical evidence is found in layers and older layers are further down that the top layers.
For example: If an archaeologist is studying past civilizations, the archaeologist may be able to say that in a particular location the ruins of one civilization were found to have been built on another and so the layers unearthed in an excavation convey the sequence of historical occupations without revealing the actual dates.
All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.
Additionally, elements may exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.
Before radiometric dating (or other methods of absolute dating like counting tree rings) it was difficult to determine the actual age of an object.