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geologic time
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A detailed geologic time scale chart displaying Earth's history from the Hadean Eon over 4.5 billion years ago to the present, organized by eons, eras, periods, epochs, and ages with color-coded columns and corresponding dates in millions of years. Vertical timeline illustration showing major events in Earth's history, from the planet's fiery formation and moon creation, through ancient rocks and early life such as blue-green algae, to the rise of atmospheric oxygen, ice ages, and the evolution of hard-shelled animals, dinosaurs, mammals, and humans, with labeled graphics and a geologic time scale on the right. Cutaway diagram of a Grand Canyon wall showing layered sedimentary rocks-limestone, shale, sandstone, and composite rocks-with labels indicating Paleozoic rocks (about 252-541 million years old) above older Precambrian rocks, which include Proterozoic (541 million to 2.5 billion years old) and Archean (over 2.5 billion years old) layers. The Colorado River is shown at the base. Line graph showing the number of marine animal families from the Precambrian era to the present, with illustrations of key groups such as trilobites, ammonoids, marine reptiles, and diatoms. The graph highlights major extinction events and a rise to 1,900 living families today. Plumb the depths of geologic time. A vertical geologic time scale chart spanning from 650 million years ago to the present, with colored bands for each era and period. Illustrations and labels highlight key evolutionary events such as the appearance of skeletal elements, first fishes, land plants, amphibians, reptiles, dinosaurs, mammals, and humans.
Quizzes
Cross section of Earth showing the core, mantle, and crust
Everything Earth
Pangaea (Pangea) was a supercontinent 225 million years ago formed by plate tectonics and continental drift.
Name That Geologic Interval
Encyclopaedia Britannica thistle graphic to be used with a Mendel/Consumer quiz in place of a photograph.
36 Questions from Britannica’s Most Popular Science Quizzes

geologic time: References & Edit History

Article Contributors

Primary Contributors

  • The Editors of Encyclopaedia Britannica
    Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.

Other Contributors

  • Rasoul Shiri

Other Encyclopedia Britannica Contributors

Article History

Type Description Contributor Date
Modified link of Web site: National Park Service - Geology - Geologic Time Scale. Sep 26, 2026
Add new Web site: Open Education Alberta - A Practical Guide to Introductory Geology - Geological Time. Dec 01, 2025
Add new Web site: University of Minnesota - College of Science and Engineering - Minnesota Geological Survey - Geologic Time. Aug 29, 2025
Add new Web site: Tulane University - Geologic Time. Mar 27, 2025
Add new Web site: Pressbooks at Virginia Tech - Introduction to Earth Science - Geologic Time. Nov 19, 2024
Add new Web site: Paleontological Research Institution - Digital Atlas of Ancient Life - Geological time scale. Sep 13, 2024
Add new Web site: USGS Publications Warehouse - Geologic Time. Jul 30, 2024
Add new Web site: University of Notre Dame - Geologic Time Scale. May 28, 2024
Added interactive. Apr 05, 2024
Add new Web site: Academia - The significance of Geological Time. Feb 16, 2024
Add new Web site: University of Houston Libraries - Geologic Time. Nov 05, 2023
Add new Web site: British Geological Survey - Geological timechart. Jun 27, 2023
Add new Web site: Geology.com - Geologic Time Scale. May 20, 2023
Add new Web site: Geosciences LibreTexts - The Geologic Time Scale. Nov 13, 2022
Added an illustration of rock layering in the Grand Canyon. Jun 02, 2020
Added material about the role of fossil species in defining geologic time. Apr 15, 2020
Added illustration of significant moments in Earth's geologic history. Apr 15, 2020
Add new Web site: National Park Service - Geology - Geologic Time Scale. Mar 12, 2019
Added a chart that tracks the diversity of marine life through geologic time. Mar 22, 2018
Added text describing the purpose of the International Chronostratigraphic Chart. Mar 22, 2018
Add new Web site: HyperPhysics - Geological time scale. Sep 02, 2016
Cross-references added. Sep 09, 2015
Text added noting that geologic time began with Earth's formation some 4.6 billion years ago. Sep 09, 2015
Add new Web site: Fact Monster - World - Aceh, Indonesia. Sep 01, 2011
Added new Web site: National Aeronautics and Space Administration - Geologic Time. Apr 02, 2008
Added new Web site: Ecotao Enterprises cc - Table of the Geological Time Scale. Apr 02, 2008
Added new Web site: Humboldt State University - Natural History Museum - Geological Time. Apr 02, 2008
Added new Web site: Smithsonian National Museum of Natural History - The Geologic Timescale. Apr 02, 2008
Added new Web site: Museum Victoria Australia - The geological time scale. Apr 02, 2008
Added new Web site: New Georgia Encyclopedia - Science and Medicine - Geologic History of Georgia. Apr 02, 2008
Added new Web site: Kansas Geological Survey - Geologic Time. Apr 02, 2008
Article revised and updated. Nov 16, 2007
Added new Web site: USGS Publications Warehouse - Geologic Time. Apr 26, 2007
Added new Web site: Exploring the Environment - Geologic Time. Jan 08, 2007
Added new Web site: USGS Publications Warehouse - Geologic Time. Jan 08, 2007
Added new Web site: None. Jul 10, 2006
Added new Web site: University of California Museum of Paleontology - Geologic time scale. Jun 27, 2006
Added new Web site: Enchanted Learning - Geologic Time Scale. May 17, 2006
Article added to new online database. Jul 20, 1998
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