Additional reading:
Library research

http://www.carleton.edu/campus/library/reference/coursepages/GEOL/GEOL110bh.html

Geologic Time:

http://www.ucmp.berkeley.edu/help/timeform.html

http://www.ucmp.berkeley.edu/exhibit/geology.html

The Smithsonian Institution Human Origins Program

National Geographic

Nature

The Leakey Foundation

Natural History Museum

Indiana University-Human Origins

Washington State University-Human Prehistory

Talk Origins Archive (Links Section)

The Stone Age Institute