University of California
Ucmp: Divisions of Precambrian Time
This site provides a brief overview of the Precambrian Era and provides a clickable chart that breaks down this era into five different time frames. A lot of info is provided on each of the five.
Simon Fraser University
Chem1 Virtual Textbook: Formation and Evolution of the Earth
As part of the General Chemistry Virtual Textbook, this site examines a variety of topics related to the Earth. Topics covered in the discussion include formation of the solar system, the planets, the continents, primary differentiation...