1. Britt, Robert Roy. 2004. "Survival of the Smallest: Mini-microbes Redefine Extreme Living" in space.com (May 26), online at http://www.space.com/ scienceastronomy/microbe_limits_040526.html (accessed February 15, 2008).
2. Carson, Rachel. 1962. Silent Spring. Boston: Houghton Mifflin.
3. Center for Astrobiology at the University of Colorado, online at http://lasp .colorado.edu/life/ (accessed February 20, 2008).
4. Center for Space Exploration and Policy Research Bibliography, online at http:// www.boulder.swri.edu/CSEPR/projects/biblio.htm (accessed February 20, 2008).
5. Methodological and Epistemic Differences between Historical Science and Experimental Science