Order the units or geologic time from the longest to the shortest: era, period, epoch, eon.

Eon, Era, Period, Epoch

The units of geologic time in order from longest to shortest will be; Eon, Era, period, Epoch. Geologic time scale is the way in which paleontologists divide geologic time based on the life forms. Eon is the longest division of geologic time while Epoch is the shortest division of geologic time and only present in Cenozoic Era, Era is the second longest division of time and is marked by sweeping changes in the fossil record and the Period is the time division which is longer than an epoch but shorter than Era.