Question

Why are there periods of the paleozoic and mesozoic subdivided into early middle and late instead of named epochs, as they are in the cenozoic?

Answer 1

The time periods of the Paleozoic and Mesozoic are subdivided into early middle and late instead of named epochs as they are in Cenozoic periods is due to the basis of the occurrence of particular fossils. It is also based upon the absence or appearance of geological horizons.