evolved by ∼3,500 - 3,400Mya: biovolume of ∼3.4×10^−6mm^3
||Smith et al., Body size evolution across the Geozoic, Annual Review of Earth and Planetary Sciences, Vol. 44 :523-553, 2016 DOI: 10.1146/annurev-earth-060115-012147 link p.528 bottom paragraph
||Schopf JW. 2006. The first billion years: When did life emerge? Elements 2: 229–33 DOI: 10.2113/gselements.2.4.229 link AND Payne JL, Boyer AG, Brown JH, Finnegan S, Kowalewski M, et al. 2009. Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity. PNAS 106: 24–27 doi: 10.1073/pnas.0806314106. PubMed ID19106296
||P.528 bottom paragraph: "The when and why of how life evolved are still open questions, there remains a lively debate about the validity of the oldest fossils (Schopf 1993, Brasier et al. 2002, Marshall et al. 2011). Because the earliest life forms were very small, differentiating putative fossils from abiotic look-alikes involves determining whether they were biogenic and whether they are clearly indigenous to rocks of known provenance and well-defined Archean age. Regardless of the ultimate status of these fossils, microscopic cyanobacteria-like organisms had likely evolved by ∼3.5 to 3.4 Ga (primary source Schopf 2006). These were very small, with biovolumes of only ∼3.4×10^−6 mm^3 (primary source Payne et al. 2009). Over the next 3.5 Ga, the range of body size occupied by life on the planet increased by another ∼18 orders of magnitude (Figure 2), to include not only these simple microscopic cells but also giant sauropods, blue whales, and sequoia trees (BNID 113313)."