The story of this great change in the conception of the history of Earth is not a simple one.
The chronicle of this great change can be broken into five periods; ran from AD 1600-1700.
Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.
There are over forty such techniques, each using a different radioactive element or a different way of measuring them.
Despite this, the momentum gained in the two decades prior to 1972 has made 4.5 b.y.