The principles of relative dating for continuous stratigraphic sequences: (as put forth by scientists such as Nicolas Steno): Ice cores are obtained by drilling core samples of ice in glaciated regions, such as near the poles.
Visible light and dark rings can be found in such cores that are then analyzed to determine the age of the ice.
Geologists have divided the Earth's history into Eras -- broad spans based on the general character of life that existed during these times -- and Periods -- shorter spans based partly on evidence of major disturbances of the Earth's crust.
The "relative" positions of layers and fossils to assign estimated dates to strata.
These layers are presumed to be the result of annual fluctuations in climate, and using this method, uniformitarians purport to document ages of over 100,000 years.
Relative dating uses a combination of fossil studies and structural interpretation to draw conclusions about the geological history of an area.
Therefore, the actual length of geologic time represented by any given layer is usually unknown or, at best, a matter of opinion.
William Smith's collecting and cataloging fossil shells from rocks led to the discovery that certain layers contained fossils unlike those in other layers (see: fossil sorting).
It only sequences the age of things or determines if something is older or younger than other things.
Some types of relative dating techniques include climate chronology, dendrochronology, ice core sampling, stratigraphy, and seriation.