Geologic Time Scale Quiz: Test Your Knowledge of Earth's History

Geological Time Scale Summary

The geological time scale (GTS) is a system of chronological dating that uses chronostratigraphy and geochronology to describe the timing and relationships of events in geologic history.
The International Commission on Stratigraphy (ICS) is responsible for defining standardized international units of geologic time.
The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils.
The GTS is divided into chronostratigraphic units and their corresponding geochronologic units, which are represented on the International Chronostratigraphic Chart (ICC).
The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years).
The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships.
The GTS includes eons, eras, periods, epochs, ages, and chronos, with the latter being non-hierarchical formal geochronology units of unspecified rank.
The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the latter.
The names of erathems in the Phanerozoic were chosen to reflect major changes of the history of life on Earth: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (new life).
The establishment of primary principles of stratigraphy is credited to Nicolas Steno, who formulated the principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships.
Over the course of the 18th-century geologists realised that rocks in different regions could be correlated based on their fossil content.
The broader concept that rocks and time are related can be traced back to the philosophers of Ancient Greece, including Xenophanes of Colophon and Aristotle.
The use of regional geologic time scales was replaced by the ICS's standardised globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units.A Brief History of the Geologic Time Scale
Early theories of the Earth's formation included Neptunism and Plutonism, which competed into the early 19th century, with James Hutton's Theory of the Earth and uniformitarianism ultimately prevailing.
William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brongniart pioneered the systematic division of rocks by stratigraphy and fossil assemblages.
Geologists estimated Earth's age based on denudation rates and sedimentary thicknesses or ocean chemistry, while physicists determined ages for the cooling of the Earth or the Sun using basic thermodynamics or orbital physics.
Early attempts at determining ages of uranium minerals and rocks by Ernest Rutherford, Bertram Boltwood, Robert Strutt, and Arthur Holmes culminated in the first international geological time scales by Holmes in 1911 and 1913.
The International Commission on Stratigraphy (ICS) was founded in 1965 and became a member commission of the International Union of Geological Sciences (IUGS) in 1961, with one of its primary objectives being the establishment of the ICS International Chronostratigraphic Chart (ICC).
Several Geologic Time Scale books were published in 1982, 1989, 2004, 2008, 2012, 2016, and 2020. Since 2013, the ICS has taken responsibility for producing and distributing the ICC.
The Anthropocene is a proposed epoch/series for the most recent time in Earth's history, denoting the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact.
Proposals for revisions to the pre-Cryogenian timeline have been made by different groups, including Shields et al. 2021 and Van Kranendonk et al. 2012.
The geologic history of Earth's Moon has been divided into a time scale based on geomorphological markers, namely impact cratering, volcanism, and erosion.
The geological history of Mars has been divided into two alternate time scales, one based on impact crater densities and the other based on mineral alteration observed by the OMEGA spectrometer on-board the Mars Express.
The table of geologic time summarizes the major events and characteristics of the divisions making up the geologic time scale of Earth.
The ICS provides an online interactive version of the ICC, which is based on a service delivering a machine-readable Resource Description Framework/Web Ontology Language representation of the time scale.
Some other planets and satellites in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars, and the Earth's Moon.