(See chart at right for full terminology hierarchy.) Stages may also be divided into substages or indeed grouped as superstages.
Stages are primarily defined by a consistent set of fossils (biostratigraphy) or a consistent magnetic polarity (see paleomagnetism) in the rock.
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition.
A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.
Microscopic analysis of the rock (petrology) is also sometimes useful in confirming that a given segment of rock is from a particular age.Usually one or more index fossils that are common, found worldwide, easily recognized, and limited to a single, or at most a few, stages are used to define the stage's bottom.Thus, for example in the local North American subdivision, a paleontologist finding fragments of the trilobite Olenellus would identify the beds as being from the Waucoban Stage whereas fragments of a later trilobite such as Elrathia would identify the stage as Albertan.And thanks to Facebook profiles, one day you’re single, and the next you’re suddenly “in a relationship.” But it’s that wide gap between singleness and relationship that is so nebulous, and the cause of so much angst.Lost in all the noise of dating advice is the fact that relationships develop in stages.