Geological Time Scale
   time measurements can be used to calibrate the relative time scale,
   producing an integrated geologic or "geochronologic" time scale.
   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
   entire scale rather than its individual subdivisions).
   constructing this geological time scale.
   This gelogical time scale is based upon Harland et al., 1990, but with
   The time scale is depicted in its traditional form with oldest at the
   in scale, the younger intervals have been successively expanded to the
   [1][time_scale.gif] geological time scale
   and Smith, D.G., 1990. A geologic time scale, 1989 edition. Cambridge
   more recent compilations of the entire geologic time scale.]
   geochronologic time scale.]
   Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E.
   [Proposes revisions to the Cretaceous time scale at the resolution of