Well, consider the marijuana plant. When the sun disappears, as it will when an asteroid hits the earth, and prays millions of tons of dust into the atmosphere, the marijuana plant panics, thinks it will never find a spouse, and becomes a hermaphrodite in order to have little marijuana plants and save the species.
That's called evolution, and it didn't happen all at once. An asteroid, or a supervolcano, blanked out the sun, and most of these plants died. Then a million years passed, and it happened again. Tens of millions of years passed, producing a small number of events that blocked out the sun.
And eventually- adapting to events that only happen once in ten million years- the marijuana plant became evolved. Turn out the lights for a week and you get hermaphrodite plants.
That's how old the earth is.