Final answer:
An eon represents the longest span of time in geologic terms, followed by an era, period, and then epoch.
Step-by-step explanation:
The segment that represents the longest span of time in geologic terms is an eon. Geologic time is divided into four major subdivisions: eons, eras, periods, and epochs. Specifically, geologic time starts with eons which are the largest; these include the Hadean, Archean, Proterozoic, and Phanerozoic. The first three eons combined are sometimes referred to as the Precambrian, a "super" eon. Eons are further divided into eras, which are subdivided into periods, then into epochs, and eventually into ages.
For instance, the Phanerozoic eon is divided into the Paleozoic, Mesozoic, and Cenozoic eras. Each era is further divided into periods such as the Cambrian, Jurassic, or Cretaceous, and each period is further divided into epochs. The longer the geological time division, the broader the extent of geological events and changes it encompasses.