AP BIOLOGY

Detailed explanation-1: -In formal usage, eons are the longest portions of geologic time (eras are the second-longest).

Detailed explanation-2: -eon = The largest unit of time. era = A unit of time shorter than an eon but longer than a period. period = A unit of time shorter than an era but longer than epoch. epoch = A unit of time shorter than a period but longer than an age.

Detailed explanation-3: -The largest defined unit of time in geological scale is the supereon which is composed of eons. Each eon is made up of around a billion years, and is divided into eras.

Detailed explanation-4: -The longest timeframe officially designated as an era is the Paleoproterozoic, which lasted 900 million years from 2, 500-1, 600 mya. The largest subunit of geologic time is the Precambrian Supereon that lasted almost 4.2 billion years from the formation of the planet to around 252 million years ago.