Knoll, AndrewSperling, Erik A.2015-07-022014Knoll, A. H., and E. A. Sperling. 2014. “Oxygen and Animals in Earth History.” Proceedings of the National Academy of Sciences 111 (11) (March 10): 3907–3908. doi:10.1073/pnas.1401745111. http://dx.doi.org/10.1073/pnas.1401745111.0027-8424http://nrs.harvard.edu/urn-3:HUL.InstRepos:16953023en-USJournal Article2015-07-0210.1073/pnas.1401745111