Cambrian Explosion FAQ: This site is still under construction, but for now, here's a list of references, and their links.

Andrew H. Knoll and Sean B. Carroll 1999. Early Animal Evolution: Emerging Views from Comparative Biology and Geology. Science 284: 2129-2137 (link)

James L. Cornette, Bruce S. Lieberman, and Robert H. Goldstein. 2002. Documenting a significant relationship between macroevolutionary origination rates and Phanerozoic pCO2 levels. Proc. Natl. Acad. Sci. USA, Vol. 99, Issue 12, 7832-7835, June 11, 2002 (abstract)

Susumu Ohno 1996. The notion of the Cambrian pananimalia genome. Vol. 93, Issue 16, 8475-8478, August 6, 1996 (PNAS)

Nicole King and Sean B. Carroll 2001. A receptor tyrosine kinase from choanoflagellates: Molecular insights into early animal evolution. Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 26, 15032-15037, December 18, 2001 (PNAS).

Joseph L. Kirschvink, Eric J. Gaidos, L. Elizabeth Bertani, Nicholas J. Beukes, Jens Gutzmer, Linda N. Maepa, and Rachel E. Steinberger. 2000. Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences. Vol. 97, Issue 4, 1400-1405, February 15, 2000 (PNAS)

Simon Conway Morris 2000. The Cambrian "explosion": Slow-fuse or megatonnage?   Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 9, 4426-4429, April 25, 2000 (PNAS)

Kevin J. Peterson and Eric H. Davidson 2000. Regulatory evolution and the origin of the bilaterians. Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 9, 4430-4433, April 25, 2000 (PNAS)

Shuhai Xiao, Xunlai Yuan, and Andrew H. Knoll 2000. Eumetazoan fossils in terminal Proterozoic phosphorites?  Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 25, 13684-13689, December 5, 2000 (PNAS)

Anatoliy B. Kudryavtsev, J. William Schopf, David G. Agresti, and Thomas J. Wdowiak 2001. In situ laser-Raman imagery of Precambrian microscopic fossils. Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 3, 823-826, January 30, 2001 (PNAS)

Jun-Yuan Chen, Paola Oliveri, Chia-Wei Li, Gui-Qing Zhou, Feng Gao, James W. Hagadorn, Kevin J. Peterson, and Eric H. Davidson 2000. Precambrian animal diversity: Putative phosphatized embryos from the Doushantuo Formation of China. Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 9, 4457-4462, April 25, 2000 (PNAS)

Shozo Yokoyama, Huan Zhang, F. Bernhard Radlwimmer, and Nathan S. Blow 1999. Adaptive evolution of color vision of the Comoran coelacanth (Latimeria chalumnae). Vol. 96, Issue 11, 6279-6284, May 25, 1999 (PNAS)

The Precambrian to Cambrian Fossil Record and Transitional Forms by Keith B. Miller

A Review of The Evidence For Trilobite Predecessors in the Fossil Record

http://www.science.uwaterloo.ca/earth/waton/F975.html

http://www.science.uwaterloo.ca/earth/waton/S985.html

http://geol.queensu.ca/museum/exhibits/ediac/ediac.html

http://www.geo.wvu.edu/~kammer/g231/PrecambrianFossils/

http://www.dc.peachnet.edu/~pgore/geology/geo102/precamb.htm

http://www.ucmp.berkeley.edu/vendian/mistaken.html

http://biocrs.biomed.brown.edu/Books/Chapters/Ch%2019/Fossil-Embryos/NYtimes-microfossils.html

http://www.cals.ncsu.edu/course/zo402/Early_Fossils/earlfosl.html

http://www.unisa.edu.au/search/search_phone.asp

http://www-geology.ucdavis.edu:8000/~gel3/slushball.html

http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

Still, here's a thought. Hard parts in invertebrates, which is what most of those early fossils are, are the product of polyphenoloxidase. Or catecholoxidase -- I've done a lot of research on these. This results in the tanning and hardening of invertebrate cuticles. These enzymes depend on iron  and copper, which would in turn depend on ocean chemistry. Similar enzymes are involved in neurochemistry. I suspect these enzymes are very early developers, and may well have been involved in the Cambrian explosion. Polyphenoloxidases work much more effectively in alkaline environments.