In chronostratigraphy, a stage is a succession of rock strata laid down in an 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. Diagram of geological time scale. ... For other uses, see strata (novel) and strata title. ... Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time. ... Geochronology is the science of determining the age of rocks, fossils, and sediments. ... Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time. ... The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ...

Rock series are divided into stages, just as geological epochs are divided into ages. Stages can be divided into smaller stratigraphic units called chronozones. (See chart at right for full terminology hierarchy.)

The term faunal stage is sometimes used, referring to the fact that the same fauna (animals) are found throughout the layer (by definition). Fauna is a collective term for animal life of any particular region or time. ...

Defining

Stages are primarily defined by a consistent set of fossils (biostratigraphy) or a consistent magnetic polarity (see paleomagnetism) in the rock. 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. This article or section does not cite any references or sources. ... Paleomagnetism refers to the study of the record of the Earths magnetic field preserved in various magnetic minerals through time. ... Index fossils (or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). ...

Thus, for example, in the (still used) local North American subdivision 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. For the robot vacuum cleaner, see Electrolux Trilobite. ...

Stages were very important in the 19th and early 20th century as they were the major tool available for dating rock beds until the development of seismology and radioactive dating in the second half of the 20th Century. Microscopic analysis of the rock (petrology) is also sometimes useful in confirming that a given segment of rock is from a particular age. Seismology (from the Greek seismos(σεισμός) = earthquake and λόγος,logos = knowledge ) is the scientific study of earthquakes and the propagation of elastic waves through the Earth. ... Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ... Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ...

Originally, faunal stages were only defined regionally; however as additional stratigraphic tools, and especially geochonological ones, were developed, stages were defined over broader and broader areas. More recently, the adjective "faunal" has been dropped as regional and global correlations of rock sequences have become relatively certain and there is less need for faunal labels to define the age of formations. A tendency developed to use European and, to a lesser extent, Asian, stage names for the same time period world wide, even though the faunas in other regions often had little in common with the stage as originally defined.

International standardization

Boundaries and names are established by the International Commission on Stratigraphy (ICS) of the International Union of Geological Sciences. As of 2008, the ICS is nearly finished a task begun in 1974, subdividing the Phanerozoic eonothem into internationally accepted stages using two types of benchmark. For younger stages, a Global Boundary Stratotype Section and Point (GSSP), a physical outcrop clearly demonstrates the boundary. For older stages, a Global Standard Stratigraphic Age (GSSA) is an absolute date. The benchmarks will give a much greater certainty that results can be compared with confidence in the date determinations, and such results will have farther scope than any evaluation based solely on local knowledge and conditions. The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... IUGS logo The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ... A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic timescale. ... Outcrop is a geological term referring to the appearance of bedrock exposed at the surface of the Earth. ... A Global Standard Stratigraphic Age, often abbreviated GSSA, is an internationally agreed upon chronological age used to define the boundaries between different periods or epochs on the geologic timescale. ...

In many regions around the world local subdivisions and classification criteria are still used along with the newer internationally coordinated uniform system, but once the research establishes a more complete international system, it is expected that local systems will be abandoned.

Stages and lithostratigraphy

Stages can include many lithostratigraphic units (for example formations, beds, members, etc.) of differing rock types that were being laid down in different environments at the same time. In the same way, a lithostratigraphic unit can include a number of stages or parts of them. Lithostratigraphy is the geological science associated with the study of stratum or rock layers. ... Interstate road cut through limestone and shale strata in eastern Tennessee In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. ... In geology a bed is the smallest division of a geologic formation or stratigraphic rock series marked by well-defined divisional planes (bedding planes) separating it from layers above and below. ... Interstate road cut through limestone and shale strata in eastern Tennessee In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. ...

See also

• Body form
• European Mammal Neogene
• Geologic record
• Geologic time scale
• North American Land Mammal Ages
• Fauna (animals)
• Type locality (geology)
• List of GSSAs
• List of GSSPs

The term body form is used to describe a design of the animal form, a blueprint of life. ... Diagram of geological time scale. ... Fauna is a collective term for animal life. ... In some natural sciences, type locality (Latin locus typicus) is the typical or representative location and is typically the first example of a newly discovered or described object. ...

Notes and references

The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ...

References

• Gehling, James; Jensen, Sören; Droser, Mary; Myrow, Paul; Narbonne, Guy (March 2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine 138 (2): 213–218. doi:10.1017/S001675680100509X. 1. http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=74669. 
• Hedberg, H.D., (editor), International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure, New York, John Wiley and Sons, 1976
• International Stratigraphic Chart from the International Commission on Stratigraphy
• USA National Park Service
• Washington State University
• Web Geological Time Machine
• Eon or Aeon, Math Words - An alphabetical index

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ...

External links

• The Global Boundary Stratotype Section and Point (GSSP): overview
• Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
• Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen (not GSSPs)