Geologic time relative dating
For example, the reference to 1809 as Lincoln's birth year is based on the system of time measurement developed in the West, which, in turn, is based on early ideas regarding the date of Christ's birth.
Used, for instance, in archaeological studies, seriation analyzes the abundance of a particular item (for instance, pieces of pottery) and assigns relative dates based on this abundance.
On the other hand, uranium decay takes billions of years, and thus it is used for dating rocks.
Cation-ratio dating, for instance, measures the amount of cations, or positively charged ions, that have formed on an exposed rock surface.
Amino acids exist in two forms, designated L -forms and D -forms, which are stereoisomers, or mirror images of each other.
Virtually all living organisms (except some microbes) incorporate only the L-forms, but once the organism dies the L-amino acids gradually convert to D-amino acids.