Bertram boltwood radiometric dating
Boltwood joined the faculty at Yale and taught there for the rest of his life, serving from 1910 to 1927 as Professor of Radiochemistry.An expert in laboratory technique and apparatus, he gave much of his energy to planning and supervising the building of the Sloane Physics Laboratory and the Sterling Chemistry Laboratory, both at Yale.It is based on the location of a rock layer in comparison to the location of other rock layers; that is, it is only relative, not absolute, time.In many cases, rock layers are laid down in order, the older layers being below the younger layers.Observing these layers is like taking a trip back in time, with each lower level representing a different time period in the planets history (i Stock).Relative time is a way to establish the relative age of rocks and fossils.Smiths work, combined with the first discoveries of dinosaur fossils in the early 1800s, led to a framework that scientists still use today to divide Earths long history into the geologic time scale, with its various, arbitrary divisions of time including eras, periods, and epochs.
This unambiguously showed that the age of the earth had to be at least 2 billion years, to the considerable relief of evolutionary biologists and most geologists. The uranium mineral boltwoodite was named in his honor in 1956.
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.
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.