Geologic Time and Dating
Geologic Time Scale: Eons and Eras
The three eons and ten eras of the official geologic time scale.
Geologic Time Scale: Eons, Eras and Periods
This shows all the geologic time units of period rank.
Geologic Time Scale: Precambrian Time
Geologic time units from the first nine-tenths of geologic history.
Geologic Time Scale: The Phanerozoic Eon
Eras, periods and epochs of geologic time after the Precambrian.
Geologic Time Scale: The Paleozoic Era
Ages, epochs and periods of the Paleozoic Era, the earliest part of the Phanerozoic.
Geologic Time Scale: The Mesozoic Era
Ages, epochs and periods of the Mesozoic Era, the middle part of the Phanerozoic.
Geologic Time Scale: The Cenozoic Era
Ages, epochs and periods of the Cenozoic Era, the latest part of the Phanerozoic.
The Rise and Fall of the Tertiary and Quaternary
These two geologic time terms share a deep history.
The Quaternary Refuses to Die
The time period encompassing the most recent past was (temporarily) erased by a bureacratic bulldozer.
An exploration of this important idea.
Introducing the Anthropocene
A brand-new name for the current time period, the Anthropocene Epoch, might get some currency.
How to Visualize Geologic Time
People tell their tricks and tips for grasping millions of years.
Mapping Deep Time
How we learned to keep track of geologic time without using clocks or numbers.
Global Boundary Stratotypes and Sections are the absolute boundaries of the geologic time scale.
About Isotopic Dating: Measuring Deep Time
Explaining the isotopic dating method in terms of your backyard barbecue.
Uranium-lead method is the oldest and, when done carefully, the most reliable isotopic dating method.
Potassium-Argon Dating Methods
Potassium-argon isotopic dating is especially useful for determining the age of lavas.
Radioisotopes from Space
Closing in on radiocarbon discrepancies through the space program pays off in knowledge about the Earth.
Radioisotopes that are useful in studying short-lived geologic processes.
Paleoclimate indicators that are as accurate as calendars, good to the nearest year.
Geo-Quiz Number 23: Geologic Time
Who wants to be a geo-whiz? The trivia game: GEOLOGIC TIME
How we track Earth's magnetism back in geologic time and use it to tell us when we are.
Provincial Time Terms
Not all of the geologic time units are settled and universal.
Geologic Time: The Story of a Changing Earth
This online exhibit lets you zoom in and out of the billions of years of Earth history and includes some good supporting material.
"How Old Is the Earth? Why Should We Care?"
A commentary by Marli Miller of the University of Oregon gives the answer to the question, and the reasons, in a lucid and commonsense way.
Geological Time Machine
Click on any of the geologic ages, eras, and epochs to learn more about that part of ancient time, from the University of California Berkeley.
Dr. Bob's Geologic Time Page
Geo-time mnemonics, or handy ways to keep all the geologic time units straight, from Eastern Illinois University.
GSA Geologic Time Scale
This Geological Society of America time scale closely follows the international standard; click through for the PDF. Earlier versions are available here too.
This cooperative effort to intercalibrate and improve the world's age dating methods is the cutting edge of geochronology.
The Ancient Bristlecone Pine
A lovely site by Leonard Miller about the oldest trees on Earth, including a section on dendrochronology.
Accelerator Mass Spectrometry
An introduction from the Purdue Rare Isotope Measurement (PRIME) Lab.
An introductory page from the Research Laboratory for Archaeology and the History of Art, Oxford University.
The flagship journal of carbon-14 studies (and other cosmogenic isotopes) has contents, abstracts, and some sample articles online for nonsubscribers.
Radiometric Dating: A Christian Perspective
Roger Wiens, an Earth scientist who is a Christian, wrote this article to combat common misunderstandings among creationists about the tools of geologic dating.
Radiogenic Isotopes and the Eastern Mineral Resources Program
Robert Ayuso of the U.S. Geological Survey describes exactly how radiometric dating studies are being used on real practical problems.
A brief version from Pamela Gore's Geology 102 course notes at Georgia Geoscience Online.
Radiometric Time Scale
From the U.S. Geological Survey's pamphlet "Geologic Time" comes this basic explanation of isotope geochronology.
The Sclerosponge Home Page
It's a bit sketchy, but it's the best place to learn about these hard white "corals" that I think of as the bristlecone pines of the sea.
Stable Carbon Isotopes in Paleoceanography
Ellen Thomas, at Wesleyan University, posted this in-depth look at carbon isotopics and their use in studying ancient climate.
Table of the Nuclides
Every isotope known to science is displayed here. Click on any one for a bunch of basic physical data.
TIMS Sample Loading Tour
Cornell University's geology lab hosts this trip through its Thermal Ionization Mass Spectrometer. See exactly how radiometric dating is done!