How does the modern era differ from the post-classical era?

The modern era is surely after the post-classical era. The post-classical era saw an expansion and growth of civilization into new areas across Asia, Africa, Europe, Mesoamerica, and western South America. The modern era already saw the flourishment of tools, instruments, methods, and the way of living. 

That she has to go to a later concert and tour, but there will be new songs out by billie eilish by then

The answer is cave paintings