Dendrochronology relative dating method
Each year a tree adds a layer of wood to its trunk and branches thus creating the annual rings we see when viewing a cross section.
Wide rings are produced during wet years and narrow rings during dry seasons.
Visible light and dark rings can be found in such cores that are then analyzed to determine the age of the ice.
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.
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).
Using these key or index fossils as markers, geologists began to identify a particular layer of rock wherever it was exposed.
This technique does not give specific ages to items.
Dendrochronology is a technique of dating past climatic changes through a study of tree ring growth.
However, unlike tree-ring dating -- in which each ring is a measure of 1 year's growth -- no precise rate of deposition can be determined for most of the rock layers.
Therefore, the actual length of geologic time represented by any given layer is usually unknown or, at best, a matter of opinion.