≥1,000 - 1,000,000 times less than today
||Olivia P. Judson, The energy expansions of evolution, Nature ecology & evolution, 28 April 2017 | Volume: 1 | Article number: 0138 p.1 right column 3rd paragraph
|| Khapercha, Kasting, Siefert, A coupled atmosphere–ecosystem model of the early Archean Earth, Geobiology, April 2005, DOI: 10.1111/j.1472-4669.2005.00049.x  Canfield DE1, Rosing MT, Bjerrum C. Early anaerobic metabolisms. Philos Trans R Soc Lond B Biol Sci. 2006 Oct 29 361(1474):1819-34 DOI: 10.1098/rstb.2006.1906  Sleep, N. H. & Bird, D. K. Niches of the pre-photosynthetic biosphere and geologic preservation of Earth’s earliest ecology. Geobiology 5, 101–117 (2007). DOI: 10.1111/j.1472-4669.2007.00105.xPubMed ID17008221
||P.1 right column 3rd paragraph: "The niches available would have been those near sources of geochemical energy, suggesting a patchy, local distribution of life. Consistent with this, geochemical models (primary sources) suggest that the productivity of the biosphere before it was powered by the sun would have been at least a thousand times less than it is today, and may
have been one million times less."