≈7 gigatons of carbon (Gt C)
||Bar-On YM, Phillips R, Milo R. The biomass distribution on Earth. Proc Natl Acad Sci U S A. 2018 Jun 19 115(25):6506-6511. doi: 10.1073/pnas.1711842115 abstract, p.2 table 1PubMed ID29784790
||P.1 right column 3rd paragraph: "The Biomass Distribution of the Biosphere by Kingdom: In Fig. 1 and Table 1, [investigators] report [their] best estimates for the biomass of each taxon analyzed. [They] use biomass as a measure of abundance, which allows [them] to compare taxa whose members are of very different sizes. Biomass is also a useful metric for quantifying stocks of elements sequestered in living organisms. [They] report biomass using the mass of carbon, as this measure is independent of water content and has been used extensively in the literature (refs 6, 16, 17)." P.4 right column 3rd paragraph: "In Table 1, [investigators] detail the relevant supplementary table that summarizes the steps for arriving at each estimate. All of the data used to generate [their] estimates, as well as the code used for analysis, are open-sourced and available at link ."
||Abstract: "Here, [investigators] assemble the overall biomass composition of the biosphere, establishing a census of the ≈550 gigatons of carbon (Gt C) of biomass distributed among all of the kingdoms of life. [They] find that the kingdoms of life concentrate at different locations on the planet: plants (≈450 Gt C, the dominant kingdom) are primarily terrestrial, whereas animals (≈2 Gt C) are mainly marine, and bacteria (≈70 Gt C) and archaea (≈7 Gt C) are predominantly located in deep subsurface environments."