Bertram boltwood radiometric dating
The eon represents the longest geologic unit on the scale; an era is a division of time smaller than the eon, and is normally subdivided into two or more periods.
An epoch is a subdivision of a period; a stage is a subdivision of an epoch.
Geologic time is the immense span of time that has elapsed since Earth first formed almost 4.5 billion years ago to recent times.
In 1815, he published a map of England and Wales geology, establishing a practical system of stratigraphy, or the study of geologic history layer-by-layer.The geologic time scale is not an arbitrary listing of Earths natural history, nor are the divisions merely fanciful.Each boundary between divisions represents a change or an event that delineates it from the other divisions.He did important research on radioactive elements (he discovered ionium, an isotope of thorium, but believed it to be a new element) and pioneered in the radioactive dating of geological strata.Boltwood was the first person to use the U/Pb method of dating uranium-bearing minerals.