Secondly, annual rainfall is a regional climatic event, and so tree ring dates for the southwest are of no use in other regions of the world.
It is certainly no exaggeration to call the invention of radiocarbon dating a revolution.
Each tree then, contains a record of rainfall for the length of its life, expressed in density, trace element content, stable isotope composition, and intra-annual growth ring width.
Using local pine trees, Douglass built a 450 year record of the tree ring variability.
Since the turn of the century, several methods to measure elapsed time have been discovered.
The first and simplest method of absolute dating is using objects with dates inscribed on them, such as coins, or objects associated with historical events or documents.
Until the 20th century, with its multiple developments, only relative dates could be determined with any confidence.
And, outside of certain periods in our past, there simply were no chronologically dated objects, or the necessary depth and detail of history that would assist in chronologically dating civilizations.
Without those, the archaeologists were in the dark as to the age of various societies. The use of tree ring data to determine chronological dates, dendrochronology, was first developed in the American southwest by astronomer Andrew Ellicott Douglass.
There are dendrochronological records for Europe and the Aegean, and the International Tree Ring Database has contributions from 21 different countries.
The main drawback to dendrochronology is its reliance on the existence of relatively long-lived vegetation with annual growth rings.
Search for method dating:
The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.