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?

Part a: which statement identifies the central idea of the text? a: the north was more powerful than the south and was always going to be the victor of the civil war. b: despite the obvious strength of the north, the outcome of the war was unpredictable at the time. c: the united states underestimated the strength of the south, giving it the upper hand. answer !