Chronozone
（重定向自Chron）
A chronozone or chron is a slice of time that begins at a given identifiable event and ends at another. Such tracer events are usually keyed to the disappearance (extinction) of fossils of a widely distributed and rapidly changing species or the appearance of such a species in the geological record. Researchers use chronozones or chrons especially frequently in the various disciplines related to geology, notably in stratigraphy where they contribute to relative dating.