Here are some of the most common radiometric methods: Radiocarbon dating: Sometimes called carbon-14 dating, this method works on organic material.Both plants and animals exchange carbon with their environment until they die.Tephrochronology: Within hours or days of a volcanic eruption, tephra — fragments of rock and other material hurled into the atmosphere by the event — is deposited in a single layer with a unique geochemical fingerprint.Researchers can first apply an absolute dating method to the layer.In a steady effort ongoing since 1974, the International Commission on Stratigraphy has been working to correlate the world's local stratigraphic record into one uniform planet-wide benchmarked system.American geologists have long considered the Mississippian and Pennsylvanian to be periods in their own right though the ICS now recognises them both as 'subperiods' of the Carboniferous Period recognised by European geologists.This family of dating methods, some more than a century old, takes advantage of the environment’s natural radioactivity.Certain unstable isotopes of trace radioactive elements in both organic and inorganic materials decay into stable isotopes. By measuring the proportion of different isotopes present, researchers can figure out how old the material is.
Paleomagnetism: Earth’s magnetic polarity flip-flops about every 100,000 to 600,000 years.
These methods — some of which are still used today — provide only an approximate spot within a previously established sequence: Think of it as ordering rather than dating.
Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.
Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.
Unlike observation-based relative dating, most absolute methods require some of the find to be destroyed by heat or other means.
The following table includes all currently recognized periods.