Research+bibliography

Works Cited "Cambrian Period." //Paleo-Portal//. Web. Dec. 2011. .

Krause, David W. //History of Life//. Peterborough, NH: Cobblestone Pub., 2000. Print.

Levin, Harold L. //Life through Time//. [Dubuque, Iowa]: W.C. Brown, 1975. Print.

"UMCp Web Time Machine." Umcp.berkely.edu, 2004. Web. 2011. .