Relative dating geologic events
Our editors will review what you’ve submitted and determine whether to revise the article.
Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!
Episodes of global volcanic activity, rifting of continents, folding, and metamorphism are defined by absolute ages.
The need to correlate over the rest of geologic time, to correlate nonfossiliferous units, and to calibrate the fossil time scale has led to the development of a specialized field that makes use of natural radioactive isotopes in order to calculate absolute isotopes has been improved to the point that for rocks 3 billion years old geologically meaningful errors of less than ±1 million years can be obtained.
Relative dating is the process of determining the age of an artifact, a layer of rock, a fossil, or something else by using the position of that item in relation to other surrounding rock layers and items.
(Remember, we are only able to determine whether something is older or younger compared to something else.) See this link for a thorough review of how relative dating is done.
The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere.
Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.