This category provides a listing of all Encyclopedia articles that reference various Ages of history, as defined by various sources.
In general, an Age is a period of history used to measure time from one dramatic, or broad spectrum change to another. Most sources define an Age as beginning with some major, sweeping change that has a dramatic affect on the environs, and ending when another such change takes place following that. These changes are usually on the level of sweeping changes in geology, ecology, or biology; dramatic shifts in the evolution of a planet, rise of new species, or the gaining of dominance by a new species are typical examples.
As Ages vary in their origin and definition, so they vary in their exactness depending on their source and use. Defined Ages may utilize specific events or conditions that can be isolated to specific points in time to mark their beginning or end, or they may have very generalized or vague beginning and ending points. Various Ages may also overlap as their focus or definition is based on other conditions or circumstances, or the markers used to distinguish the age may be broader, slowly changing factors that had a period of transition that could span centuries.
It should be noted, this reference does not use a definitive set of Ages, as defined by a single source, but documents various Ages, as tracked or defined by multiple sources. As a result, many will overlap, contradict, or be totally unrelated to one another in focus and/or setting.
See individual entries for more detail on the defining principles used for specific Ages.