Ducksters
Ducksters: Chemistry for Kids: Isotopes
Study the science of isotopes in chemistry including naming isotopes, hydrogen, examples, fun facts, unstable, and stable on this site.
Idaho State University
Radioactivity in Nature
Interesting information including: average annual dosage, radioactivity in space, in the human body, and in the oceans.
US Geological Survey
The Numeric Time Scale
This is a good source for getting an in-depth description of using radioactive decay to measure the ages of rocks. In addition to describing the process of radiometric dating, this resource also includes a geologic time scale and four...