In 1819, Christian Thomsen developed the three-age system of Stone Age, Bronze Age, and Iron Age while he was trying to organize his museum. He based it on the ideas brought forth in 1813 by the historian Videl-Simonson. The three-age system formed the basis for all Old World archaeology.
This system was initially developed for museum collections with little context, and was based on the hypothesis that prehistoric inhabitants of Europe had passed through three successive stages of technological development, reflected in the production of stone, bronze, and iron tools. Thomson classified collections of artifacts into three groups on the basis of their raw material, which represented the ages of Stone, Bronze, and Iron, then ordered them into a chronological sequence. By the 1840s, Thomson's successor to the directorship of the National Museum of Denmark, J. A. A. Worsaae, conducted excavations finding support for Thomson's theories. Worsaae tested the stratigraphic soundness of the system as well as indicating the widespread validity of the "Three-Age System", and published his results in 1843. Later, the Stone Age was divided into the Paleolithic or Old Stone Age, and the Neolithic or New Stone Age.
The are many people who believe there was a Wood Age but it was not able to be recorded because wood does not last through time as well as the metals do. Stone Age, roughly coinciding with the period of the last Ice Age, was based on the fact that there was a period of time when tools used by early man were made of stone. The Paleolithic or Old Stone Age began 2.5 to 3 million years ago, and is also divided into three subgroupings; Upper, Middle and Lower. The Bronze Age started in the Asian countries and then spread into Europe through trade and exploration. Some areas such as Africa seem to have skipped their Bronze Age and jumped right into the Iron Age.
http://archaeology.about.com/science/archaeology/library/weekly/aa030198.htm?once=true&
http://www.arts.ubc.ca/anso/pokotylo/anth103/chpthree.htm
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http://www.apnet.com/inscight/02271998/iron-ag1.htm
http://ukdb.web.aol.com/hutchinson/encyclopedia/27/M0002927.htm
http://www.gla.ac.uk/Acad/Archaeology/staff/jwh/archcont/whatis.html
Written by Students in an Introduction to Anthropology Class, Minnesota State University, Mankato, Minnesota
Edited by Marcy L. Voelker, 2007