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.For example, if an area used for trash has modern refuse in it such as CDs and computers, and the layer underneath has cans made of tin, then it is safe to say the layer of tin cans have a greater relative age than the layer with modern refuse.However, this does not say anything about the absolute age of the layers.That is, scientists cannot tell exactly how old the layers are in years to the present date, only which is older than the other.
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.
For a determination in the field, geologists attempt to date a rock or fossil based on its relative age, which is usually determined by the presence of a trace fossil, or the position of the rock layer in relation to a layer of rock with a known age.
Continue Reading Relative age comes up often in various fields, such as archeology.
If archaeologists find a site with layers in it, they can make assumptions about the relative age based on the composition of materials in each layer.