Dendrochronology, or tree-ring dating, provides absolute dates in two different ways: directly, and by calibrating radiocarbon results.
Direct Dating of Wood Cross-dating determines the age of undated wood by directly matching ring patterns with trees of known age.
Unfortunately there are no affordable direct methods for dating pigments, except in some cases as we will see later.
When plants are alive the carbon-14 to carbon-12 ratio remains constant, but after they die the ratio begins to decline.
A measurement of the ratio, therefore, provides a way to estimate how much time has elapsed since the plant was alive.
Radiocarbon, or Carbon-14, dating is probably one of the most widely used and best known absolute dating methods. Radiocarbon dating relies on a simple natural phenomenon.
This allowed for the establishment of world-wide chronologies.
This process of ingesting C-14 continues as long as the plant or animal remains alive.
The C-14 within an organism is continually decaying into stable carbon isotopes, but since the organism is absorbing more C-14 during its life, the ratio of C-14 to C-12 remains about the same as the ratio in the atmosphere.Greatly simplified, the process samples living and dead trees in a given area.The tree-ring patterns are matched, and laid down in series, building a continuous timeline of known dates.The Miyake events stand out amongst the normal carbon-14 levels detected in the atmosphere and can be dated because the tree-rings retain the carbon-14 level from the year in which they grew.Archives mapping out the growth year of every tree-ring are known, making the Miyake events in tree-rings time markers.As the Earth's upper atmosphere is bombarded by cosmic radiation, atmospheric nitrogen is broken down into an unstable isotope of carbon - carbon 14 (C-14).