||Payne JL et al., Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity. Proc Natl Acad Sci U S A. 2009 Jan 6 106(1):24-7 p.24 left column top paragraph and p.25 fig.1PubMed ID19106296
||Bonner JT (1988) The Evolution of Complexity by Means of Natural Selection (Princeton Univ Press, Princeton).
||Researchers document the evolutionary history of body size on
Earth, focusing on the upper limit to size.
||Ga=billion years ago. (Primary source p.6 bottom paragraph:) "...the 1st organisms observed are bacteria-like and are estimated to be about 3.4 billion years old."