This is "relative dating", but it doesn't give you an exact age.
The age is based on the half-life of the isotopes (their rate of decay over time).
When the age is determined in this manner, it is called the absolute age, from absolute dating techniques.
If the archaeologist finds a sample suitable for carbon dating, then an absolute date may be assigned to an object.
Similarly for paleontologists who find layers of fossils.
The circumstances of the object may allow one to say that one object is older than another without being able to assign a particular age to the objects.
For example: If an archaeologist is studying past civilizations, the archaeologist may be able to say that in a particular location the ruins of once civilization were found to have been build on another and so the layers unearthed in an excavation convey the sequence of historical occupations without revealing the actual dates.
Relative age allows scientists to know whether something is older or younger than something else, while absolute age means that scientists know the exact number in years that have passed since the object was created.
Relative age will require the comparison of two or more objects, whereas absolute age does not.
Geologists deal with the oldest of samples and radiometric dating with uranium is one of the few methods of absolute dating.