Relative dating methods assign an age relative to that of other items, whereas absolute dating determines age in actual years or millions of years. When geologists first embarked on stratigraphic studies, the only means of dating available to them were relative.

Why is stratigraphy relative?

Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence. The method of reading the order is called stratigraphy (layers of rock are called strata). Relative dating does not provide actual numerical dates for the rocks.

What type of dating is stratigraphy?

Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things. Stratigraphy is based on the law of superposition--like a layer cake, the lowest layers must have been formed first.