International Geologic Time Scale

International Geologic Time Scale
Name	International Geologic Time Scale
Governing body	International Commission on Stratigraphy
Established	1961

International Geologic Time Scale The International Geologic Time Scale provides a standardized chronology for Earth's 4.54-billion-year history, enabling correlation across regional stratigraphy, paleontology, and geochronology. It is used by organizations and institutions to synchronize research in plate tectonics, paleoclimate reconstructions, and planetary geology. Developed and ratified through multinational scientific bodies, the scale underpins studies ranging from the Cambrian explosion to Quaternary glaciations.

Overview and Purpose

The scale defines hierarchical units such as eons, eras, periods, epochs, and ages to coordinate work among entities like the International Union of Geological Sciences, International Commission on Stratigraphy, and national surveys including the United States Geological Survey and the British Geological Survey. It facilitates correlation between datasets produced by laboratories such as the Lawrence Berkeley National Laboratory, the Geological Survey of Canada, and universities like Harvard University and University of Cambridge. The scale aids interpretation of stratigraphic markers used in studies by researchers affiliated with the Smithsonian Institution, the Max Planck Society, and the Scripps Institution of Oceanography.

History of Development and Revisions

Origins trace to stratigraphers and geologists active in forums such as the Geological Society of London and the American Geophysical Union during the 19th and 20th centuries. Key figures associated with stratigraphic standardization appeared in meetings of the Royal Society and congresses organized by the International Geological Congress. Later revisions incorporated dating techniques developed at facilities like Oak Ridge National Laboratory, Lawrence Livermore National Laboratory, and institutions collaborating within the European Geosciences Union. Ratification events have taken place at assemblies convened by the United Nations Educational, Scientific and Cultural Organization and international symposia attended by delegates from the Russian Academy of Sciences, Chinese Academy of Sciences, and Indian National Science Academy.

Time Units and Hierarchy

The hierarchical scheme is formalized through designations comparable to protocols maintained by bodies such as the International Astronomical Union for astronomical timescales. Units include the supereon-level classifications used by commissions at the International Commission on Stratigraphy and operational definitions tested at observatories like the Observatoire de Paris. The framework interfaces with geochronologic standards developed in laboratories including Caltech, Massachusetts Institute of Technology, and the GFZ German Research Centre for Geosciences.

Chronostratigraphy and Geochronology Methods

Establishing boundaries relies on methods promoted by societies such as the European Association of Geochemistry and the Geochemical Society: radiometric dating (e.g., U–Pb zircon analyses performed at ETH Zurich and University of California, Berkeley), biostratigraphy based on fossils curated by the Natural History Museum, London and the American Museum of Natural History, magnetostratigraphy used in cruises organized by the Alfred Wegener Institute, and chemostratigraphy advanced by teams at Woods Hole Oceanographic Institution and Lamont–Doherty Earth Observatory. Analytical advances from collaborations with organizations like the International Atomic Energy Agency and the National Aeronautics and Space Administration have refined boundary placement.

Major Eons, Eras, Periods, and Epochs

The scale segments Earth history into eons recognized in literature from institutions such as the Geological Society of America and the Royal Society of Canada; eras and periods named in syntheses published by scholars associated with the University of Oxford, University of Edinburgh, and the Australian National University. Notable subdivisions used in curricula at universities like Stanford University and Yale University include the Paleozoic, Mesozoic, and Cenozoic eras and periods such as the Jurassic, Cretaceous, and Paleogene. Epochal units like the Holocene and the proposed Anthropocene have been debated at meetings of the International Commission on Stratigraphy and debated in forums hosted by the Royal Geographical Society.

Formalization, Governance, and Ratification

Governance is provided by the International Commission on Stratigraphy under the aegis of the International Union of Geological Sciences with input from national bodies such as the Geological Survey of Japan and the Geological Survey of India. Formal ratification follows procedures similar to those used by the International Organization for Standardization and occurs at congresses like the International Geological Congress. Committees include representatives from academies such as the National Academy of Sciences (US), the Académie des sciences (France), and the Deutsche Forschungsgemeinschaft with liaison from funding agencies like the National Science Foundation.

Applications and Implications in Earth Sciences

The scale supports research programs at centers including the Integrated Ocean Drilling Program, the International Ocean Discovery Program, and the International Continental Scientific Drilling Program. It underlies hazard assessments by agencies such as the United States Geological Survey and climate reconstructions used by the Intergovernmental Panel on Climate Change and the World Meteorological Organization. Applications extend to petroleum exploration guided by firms and institutions interacting with the Society of Petroleum Engineers, as well as planetary comparisons conducted by teams at the Jet Propulsion Laboratory and the European Space Agency.

Category:Geologic time scales