Absolute chronometric dating methods is ben barnes dating anyone
Because of the vast difference in scale, the younger intervals have been successively expanded to the right to show some of these finer subdivisions.
In addition, like any good scientific measurement, every dated boundary has an uncertainty associated with it, expressed as "+- X millions of years".
These can not be included in the diagram for practical reasons, but can be found in Harland , 1990, along with a detailed description of the history of earlier-proposed time scales and the terminology, methodology and data involved in constructing this geological time scale.
It is important to realize that with new information about subdivision or correlation of relative time, or new measurements of absolute time, the dates applied to the time scale can and do change.
Revisions to the relative time scale have occurred since the late 1700s.
The numerically calibrated geologic time scale has been continuously refined since approximately the 1930s (e.g., Holmes, 1937), although the amount of change with each revision has become smaller over the decades (see fig.1.5 and 1.6 of Harland ) and a few numerical estimates were available previously (but often for the duration of the entire scale rather than its individual subdivisions).