...exactly what qualifies as an "era" or an "eon" depends on upon who you talk to...
Essentially, the words era and eon are suffixes that designate how old a particular rock layer, or one of its subdivisions
called stages, might be.
The prefix on front of the name of one of the six major layers of rock tell whether that sub-layer is on the very bottom or
Look for the same name of the major layer to follow each suffix, except for the case of the Hadean Eon.
Notice that the classification of the rock layers is done in two different ways.
One is concerned with the age,
or "chronological" dating of the layers, noting that catastrophic geological events punctuate the separation into six major
The other table of organization is concerned with "the strata" of all the rocks, as if each Stage is a unit
of division from the others, in general.
This often confuses the
issue of noting that there are only six actual separate and distinct layers.
The distinction of six chronological
layers rests upon the catastrophic events which separated these layers, one from the other.