Short Answer:

In many instances, absolute dating is considered more accurate than relative dating because it gives a specific time or age to an event or object but with an accuracy that varies with the particular technique and particular object. Relative dating gives one the ordering of events or gives one the relative ages, i.e. object A is older than object B without saying the actual age of either.

Long Answer:

Asking if one approach is more accurate than another is not a well defined question. These techniques are not used separately and the value of each is enhanced by the other. Further, neither of them is a single technique. Dating with uranium isotopes is different than counting tree rings. There are no less than a dozen different radiometric techniques and these are but one area of the more general class of methods referred to as absolute dating.

The value of each depends on the question. If I want to know whether or not the dinosaurs were made extinct by the collision of an asteroid or comet with Earth 65 million years ago, the question can not be answered by radiometric dating. The question first asks whether one event occurred before another, i.e. comet/asteroid before extinction. If radiometric dating says the dinosaurs went extinct 62 to 66 million years ago and a collision occurred 60 to65 million years ago, one can not answer the original question. Causality is a separate question not addressed by either technique. Relative dating may collect information about other related events, i.e. absence of other species in the fossil records after the iridium layer which indicate environmental catastrophe and that is not something you get from radiometric dating. If relative dating shows lots of dinosaurs before the iridium layer and none after, then relative dating has given information that radiometric dating could not.

So, the real answer to the question is that the two approaches, relative age dating and absolute dating, are able to answer different questions and depending on the question, one approach may be more appropriate than another and when they can be used together that brings added value.

More Background:

Sciences such as geology, paleontology and archeology are very interested in identifying the age of objects found and these scientists sometimes use either relative dating or absolute dating to characterize the age of the objects they study.

Before radiometric dating it was difficult to determine the actual age of an object. Few things other than tree rings actually count the passing of years. Radiometric dating, based on known rates of decay of radioactive isotopes in objects, allows a specific age of an object to be determined to some degree of accuracy.

Relative dating is a scientific process of evaluation used to determine the relative order of past events, but does not determine the absolute age of an object. 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. 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. By deducing which fossils are formed in the sequence of time, the periods when the particular fossilized entities existed can be arranged in order without the actual dates of when the fossils were laid down. Radioactive isotopes can also be used by a paleontologists to assign an age to a fossil in some cases and that is an example of absolute dating with radiometric methods.

For geologists, it is similar. 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 deal with the oldest of samples and radiometric dating with uranium is one of the few methods of absolute dating.

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