Which of the following has the longest duration?

If you have been asked “ Which of the following has the longest duration?” and you have been given 4 options out of which you have to choose one. For example, the four options could be Era, Period, Epoch, and Eon. So, which one is the correct option? Let us discuss the answer to this question. The correct answer is Eon. Eon is the longest duration in geological time. There are mainly four recognized eon and they are phanerozoic eon, the proterozoic eon, and the archean eon. From among these four eons, the shortest eon is Phanerozoic eon. EON Actually refers to a span of 1 billion years in science.