University of California
Ucmp: A Relative Dating Activity
An learning activity to help learners grasp the concept of relative dating and geologic time.
Other
University of Waikato: Science Learning Hub: Absolute Dating
Explains what absolute dating is as compared to relative dating and how they can work together. The characteristics of several different radiometric methods are compared. Includes three short videos and an interactive where students...
Smithsonian Institution
National Museum of Natural History: Paleobiology: Absolute Dating
An explanation of radiometric or absolute dating of geological formations based on using the half-life of radioactive elements to figure out how old given rock layers are. A link on the left provides information about relative dating as...
Other
Planetary Society: Relative and Absolute Ages in Histories of Earth and the Moon
A lengthy scholarly article that discusses the geologic time scale, its history of development, age-dating events that occurred in different eras, and how absolute and relative dating are used to assess the ages of the Earth and Moon....
US Geological Survey
Relative Time Scale
This is a good resource for anyone who wants to understand the historical development that led to our understanding of relative dating. This site also has links to index fossils and a table of geologic time.
Other
Utah Geological Survey: How Do Geologists Know How Old a Rock Is?
Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, that it is found in. The age of formations is marked on a geologic calendar known as the geologic time scale. Development of the...
US Geological Survey
U.s. Geological Survey: Geologic Time
A discussion of geologic time, how scientists use the concept, and how they have determined its span.