Ages epochs and other geological timescales go hand in hand with the stratigraphy. There's generally a stratigraphic rationale for making any of the divisions, and it is something like "this index fossil appears starting here and stops there" which easily identifies across the world what the time period is. If there's nothing that easily identifies the differences, then is there really a difference?
Another thing to illustrate the point is the cretaceous ends at the dust layer from the meteorite impact. Didn't change anything about geological processes except that there's a world wide layer that's easily identifiable and is our bookmark for 66mya.
