Chapter 3: Geologic Time and Earth History

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Time, Space, and Earth Processes

Earth Systems and Cycles. Has an excellent paragraph on uniformitarianism and catastrophism.

An article on Leonardo da Vinci's early observations and work on fossils.

An article on William Smith and his discovery of the principle of faunal succession.

USGS article on the relative time scale. Includes links to excellent diagrams of geologic sections and index fossils.

Absolute Geologic Time

USGS article on radiometric dating. Includes a table of materials that have been dated by radiometric methods. Also has a link to a chart showing, for a hypothetical example, how the age of a sample is related to the radiometric time scale by bracketing it within time zones that are determined by dating appropriately selected igneous rocks.

Answers to frequently asked questions about radon hazards.

An interactive geologic time scale with clickable links to exhibits for many of the subdivisions. (The exhibits for some of the time periods are "under construction.") The exhibits include information on stratigraphy, ancient life, and localities.

A simple color diagram of the geologic time scale.

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