High Quality Content by WIKIPEDIA articles! In the stratigraphy sub-discipline of geology, a Global Standard Stratigraphic Age, officially abbreviated GSSA, is a chronological reference point and criterion in the world`s rock records used to define the boundaries (an internationally sanctioned benchmark point) between different geological periods, epochs or ages on the overall geologic time scale in a chronostratigraphically useful rock layer. A worldwide multidisciplinary effort has been ongoing since 1974 to define such important metrics. But such work goes slowly despite a lot of effort, as one criterion is such points and strata need be widespread and contain an identifiable sequence of layers or other unambiguous marker (identifiable or quantifiable) attributes.