The absolute dating method first appeared in 1907 with Lord Rutherford and Professor Boltwood at Yale University, but wasn’t accepted until the 1950s.
The first method was based on radioactive elements whose property of decay occurs at a constant rate, known as the half-life of the isotope.
Carbon-14, or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide.
Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies.
Based on a discipline of geology called stratigraphy, rock layers are used to decipher the sequence of historical geological events.
Relative techniques can determine the sequence of events but not the precise date of an event, making these methods unreliable.
Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon-14 content.
Aerial Photography - The various techniques of taking photographs of natural or cultural features from the air, using balloons, airplanes, satellites, and other sources, in order to study the features in their entirety from a top-down (bird's eye) view.
Aerial Reconnaissance - The technique of searching for sites and features, both cultural and natural, from the air, often using aerial photography or the human eye.
This also works with stone tools which are found abundantly at different sites and across long periods of time.
Stratigraphic dating is based on the principle of depositional superposition of layers of sediments called strata.
Cultural seriations are based on typologies, in which artifacts that are numerous across a wide variety of sites and over time, like pottery or stone tools.