Beneath our feet, in the oceans and right down to the depths of the Earth’s crust, life accounts for around 550 gigatonnes of carbon – or 550 billion tonnes – according to the global reference assessment published in 2018. Plants, almost all of which are terrestrial, account for nearly 80 per cent of this on their own. The ocean offers a striking contrast: it covers 71 per cent of the Earth’s surface, yet contains only a small fraction of this biomass at any given moment . However, it produces almost as much living matter each year as the continents. How can such a small reserve sustain such high levels of production? The rapid turnover of phytoplankton provides part of the answer. To understand the rest, we need to distinguish between the mass of living organisms, the number of species and annual production. How are these quantities measured? Why is biomass distributed so differently across continents, oceans and deep underground? And how have agriculture, hunting and fishing transformed this distribution?

 

1. Weighing living matter

1.1 Biomass, abundance and production

Biodiversity encompasses the variety of species, their genes, their functions and their interactions (see What is biodiversity?). The Catalogue of Life, [1] – a regularly updated collaborative taxonomic repository – recorded in 2025 more than 2.2 million species described to date; this figure is rising every year (around 49,000 additional species names accepted in 2025, [1]). Biomass measures the quantity of living matter present at a given moment (see focus: Species, individuals and biomass). Abundance counts individuals; species richness counts species. Ants provide an example of this: nearly 20 million billion individuals would represent approximately 0.012 Gt C globally [2]. Production measures the matter formed over time.

To survey groups that are difficult to observe, researchers combine field sampling with analyses of DNA present in water or soil (see DNA barcodes to characterise biodiversity).

Global campaigns, such as Tara Oceans (Figure 1), map marine communities (see When the Tara Oceans expedition explores plankton diversity). On land, forest inventories and field observations complement satellite data.

These methods are used to estimate the biomass of major groups of living organisms. Their accuracy varies depending on the organisms and environments: terrestrial plants are better understood than microorganisms in deep subsoil [3],[4].

Bar-On et al. (2018) [5], followed by Bar-On and Milo (2019) [6] for the ocean, provide the reference assessment illustrated here (see Focus: Estimating the global biomass).

1.2 Why express biomass in terms of carbon?

The mass of an organism depends in part on the water it contains. This can account for around 95 per cent of a jellyfish’s mass and also varies depending on the tissues of a tree (Figure 2). To compare such diverse organisms, researchers estimate their dry mass and then the amount of carbon it contains. As a rough guide, 20 tonnes of dry wood contain around 10 tonnes of carbon, but this proportion varies depending on the tissue.

Global figures are expressed in gigatonnes of carbon (Gt C): 1 Gt C is equivalent to one billion tonnes of carbon. Biomass here refers to the carbon contained in living organisms; it does not include dead organic matter in the soil or carbon in rocks. This unit also enables us to link the study of living organisms to the carbon cycle: photosynthesis incorporates atmospheric carbon (CO₂) into organic matter, whilst respiration and decomposition gradually return it to the atmosphere, thus completing the carbon cycle — with only a tiny fraction escaping this cycle to be stored long-term (see A carbon cycle disrupted by human activities).

2. A biosphere dominated by plants

2.1 The 2018 global assessment

The global inventory published by Bar-On et al. in 2018 [5] estimates the total biomass of living organisms at approximately 550 Gt C (Figure 3). This figure is a reference point, not an exact or timeless measurement: it combines fairly well-known compartments, such as terrestrial plants, with deep-dwelling microorganisms, for which there is much greater uncertainty. The authors also assign an explicit uncertainty factor to each group, which is low for plants (approximately ×1.2) but high for bacteria (approximately ×9): the specific figures given below should therefore be interpreted as orders of magnitude, with varying degrees of precision depending on the group. The estimated distribution is as follows:

• Nearly 80 per cent (≈ 450 Gt C) are plants [7] ;
• ≈13 per cent (≈ 70 Gt C) are bacteria, the second major component of biomass;
• The other groups are fungi (≈ 12 Gt C), archaea (≈ 7 Gt C), protists (≈ 4 Gt C), animals (≈ 2 Gt C) and viruses (≈ 0.2 Gt C). Archaea live in a variety of environments: oceans, soils, sediments and microbiomes, as well as certain extreme environments.

Terrestrial plants, particularly vascular plants, dominate plant biomass [8]. In the context of Bar-On’s assessment, the ‘plants’ group also includes green and red algae, but not brown algae, which are classified as protists. Around 70 per cent of plant biomass is found in the stems and trunks of trees, which are slow to regenerate [8]. Leaves and fine roots generally regenerate more quickly than trunks and large roots [9].

Bacteria and archaea in the soil and subsoil constitute another form of biomass, distinct from roots and dead organic matter. In deep subsoil, certain microorganisms regenerate very slowly, sometimes over years or longer. A large biomass stock therefore does not necessarily imply rapid production (see Focus: Biomass of soil organisms).

A reassessment by Magnabosco et al. (2018) [10] puts the global biomass of prokaryotes at around 23 to 31 Gt C, compared with approximately 78 Gt C for bacteria and archaea in the assessment by Bar-On et al. [5]. These estimates are based on different methods and extrapolations. The discrepancy between them highlights the uncertainty that surrounds microorganisms in deep environments in particular.

3. Continents, oceans and deep subsurface

3.1 Highly uneven carbon stocks

Excluding deep subsurface reservoirs, the 2018 inventory [5] attributes approximately 470 Gt C to terrestrial environments, compared with approximately 6 Gt C to marine environments: nearly eighty times more on the continents (Figure 4 and Table 1). Yet the ocean covers 71 per cent of the Earth’s surface. This comparison relates to stocks present at a given point in time, rather than annual production.

• Plants are almost entirely terrestrial; green and red algae and seagrass beds account for only a small fraction of the marine stock of the ‘plants’ group as defined in the 2018 assessment [5].
• Conversely, a large proportion of animal biomass is marine: arthropods, fish, molluscs and annelids contribute to this. Small deep-sea fish and crustaceans remain difficult to count accurately.
• Bacteria and archaea also inhabit the deep subsoil of continents and oceans. A distinction must be made between surface soils, marine sediments and the oceanic crust: estimates for these are neither interchangeable nor equally reliable.

Figure 4B contains significant uncertainties, particularly regarding terrestrial protists, marine fungi and deep-sea environments (see Focus: Estimating the global biomass). Parasites represent another gap: their global biomass remains poorly assessed, despite their presence in many groups of living organisms.

Table 1. Approximate biomasses, expressed in gigatonnes of carbon (Gt C). Totals are rounded; some breakdowns by environment, particularly in deep subsoil, are highly uncertain. [Table based on data from Bar-On et al., ref. [5]; Open-access article distributed under a CC BY-NC-ND 4.0 licence]

3.2 What does marine biomass represent?

In the 2019 ocean budget, animals, protists and bacteria together account for nearly 80 per cent of the estimated marine biomass (Figure 5) [6]. Animals include, in particular, crustaceans – such as copepods and krill – as well as fish. The Antarctic krill species Euphausia superba alone was estimated at around 0.05 Gt C in the 2018 balance [5], a magnitude of order close to that of the entire human population (see focus: Species, individuals and biomass). This example illustrates just how concentrated biomass can be within a single abundant species. However, the biomass of certain deep-sea groups remains difficult to assess.

Protists include, in particular, diatoms, coccolithophores, dinoflagellates and brown algae, including kelp. In the classification adopted for this assessment, green and red algae belong to the plant group, along with the flowering plants of seagrass beds. Bacteria include photosynthetic cyanobacteria, such as Prochlorococcus and Synechococcus.

Archaea are also present in the ocean and its sediments. Fungi are found throughout the marine environment, from coastal waters to great depths, but their biomass remains poorly understood. Finally, marine viruses, particularly phages, cause the lysis of their hosts and thus contribute to the recycling of matter. Despite their abundance, they account for only a small proportion of the carbon stock considered in this assessment (see focus: Phytoplankton: a small stock, immense production and focus: Ocean viruses). [11]

This breakdown describes stocks, not the production of the various groups. A modest stock can therefore support high production if it is rapidly replenished (see focus: Species, individuals and biomass). A large proportion of marine biomass is planktonic, carried by currents; nekton swim independently of them. Other organisms live on the seabed, where habitats remain unevenly studied.

3.3 Producers, consumers and renewal

Figure 6 compares the biomass stocks of producers and consumers in terrestrial and marine environments, based on the 2018 and 2019 balances [5],[6]. On the continents, plants dominate by a wide margin, accounting for 450 Gt C, whilst all consumers combined account for 20 Gt C. In the ocean, heterotrophic organisms may, at any given time, represent a stock greater than that of photosynthetic producers. In the marine balance sheet by Bar-On and Milo (2019) [8], heterotrophs account for approximately 5 Gt C, compared with approximately 1.3 Gt C for marine producers.

Annual production tells a different story. According to Field et al. (1998) [12], primary production is estimated at around 56 Gt C per year on the continents and 49 Gt C per year in the ocean. The ocean therefore contributes almost as much as the continents to global primary production, despite its much smaller stock of producers. These figures describe carbon fluxes, not the biomass present at any given moment.

The rapid turnover of phytoplankton helps to explain this contrast. Based on nearly 100,000 profiles collected by BGC-Argo floats, Stoer and Fennel (2024) [13] estimate its stock in the open ocean at around 0.3 Gt C; nearly half of this is located below the layer directly observed by satellites. This figure relates to phytoplankton in the open ocean, whilst the 1.3 Gt C in the 2019 balance [6] also includes other marine producers, notably macroalgae and seagrass beds. The two estimates therefore do not refer to the same set of organisms.

On a global ocean scale, the stock of consumers may exceed that of photosynthetic producers, although this comparison does not allow us to conclude that the former produce more. Phytoplankton is consumed and replenished rapidly: this reversal in stock levels depends on the groups, environments and time periods under consideration. It is therefore neither universal nor permanent (see focus: Phytoplankton: a small stock, immense production).

4. A biosphere reshaped by humanity

Agriculture, domestication, hunting and changes in land use have altered the distribution of biomass. Their impact is evident in mammals, birds and plants alike.

4.1 The biomass of wild mammals

Greenspoon et al. (2023) [14] provide a global assessment of mammalian biomass. For wild terrestrial mammals, they have global population estimates for 392 species and extrapolate for species lacking such data: their calculation thus covers 4,805 species. The fresh biomass of all mammals included in the study totals approximately 1,080 million tonnes (Mt), of which some 20 Mt is accounted for by wild terrestrial mammals and 40 Mt by wild marine mammals (Figure 7). The marine estimate is based on population data collected separately. The composition of the two wild groups differs significantly.

On the continents, artiodactyls – which include deer, gazelles and wild boar – constitute the largest group in terms of biomass, ahead of rodents. Elephants also contribute significantly due to their large individual mass. The number of species, the number of individuals and biomass therefore provide different perspectives on the world of mammals (see focus: Species, individuals and biomass).

In the oceans, baleen whales account for more than half of the biomass of wild mammals. The marine inset in Figure 7 also distinguishes between sperm whales, other toothed whales, seals, dolphins and porpoises (see focus: Species, individuals and biomass).

4.2 The role of humans and domestic animals

In the same assessment, humans account for approximately 390 Mt of fresh biomass and domestic mammals for approximately 630 Mt, mainly cattle. Together, they make up nearly 94 per cent of the current mammalian biomass estimated in this assessment; wild mammals, both terrestrial and marine, combined, account for only about 6 per cent [14].

A similar contrast is observed among birds (Figure 8): the assessment by Bar-On et al. (2018) [5] attributes approximately 0.005 Gt C to domestic poultry, compared with 0.002 Gt C to wild birds. The values in the two figures use different units: fresh biomass for Figure 7, and carbon for Figure 8.

4.3 From historical losses to recent changes

Figures 7 and 8 describe current stocks, but do not show how they have changed over time. Bar-On et al. (2018) [5] compare these with highly uncertain historical reconstructions: the biomass of wild terrestrial mammals is thought to have fallen from around 0.02 to 0.003 Gt C since the major Quaternary extinctions, a reduction by a factor of nearly seven. Their estimate of the past is based in particular on Barnosky (2008) [15].

For marine mammals, the same article by Bar-On et al. (2018) [5] estimates a decline in biomass from approximately 0.02 to 0.004 Gt C – a five-fold reduction – linked primarily to whaling and the exploitation of other marine mammals. This comparison draws in particular on the population reconstructions by Christensen (2006) [16]. These historical values are reconstructed orders of magnitude rather than direct measurements; they are not shown in Figures 7 and 8. The growth of human and domesticated mammal populations has, however, increased the total biomass of mammals.

4.4 Vegetation and materials produced by humankind

The most significant change concerns plants. Deforestation, forest management and the expansion of cropland and pasture have reduced vegetation stock relative to the estimated potential in the absence of human use (see Impacts of agriculture on biodiversity and ecosystem functioning). According to reconstruction assumptions, the shortfall amounts to around half of this potential [8].

Figure 9 illustrates the contrast between an ancient forest (the world’s oldest tropical rainforest to have survived uninterrupted) and agricultural land that was ‘cleared from the wilderness’ (forests, swamps), etc., at the beginning of the 20^th century.

Cultivated plants account for around 10 Gt C, or nearly 2 per cent of global plant biomass in the 2018 assessment [5]. This small proportion measures a stock at a given point in time: crops are harvested and rapidly replenished. Replacing a forest with a field therefore does not preserve the same standing biomass.

Increases in vegetation cover are observed in some regions, whilst others are losing it. An increase in biomass does not necessarily mean the return of the species, habitats and carbon stocks of the lost ecosystem.

The transformation of living matter is accompanied by an accumulation of materials produced by humankind. Their dry mass has reached a similar order of magnitude to that of all living biomass; Elhacham et al. (2020) [17] estimate that the two masses crossed round 2020, with an uncertainty of ± 6 years. This comparison is based on dry masses, not gigatonnes of carbon.

5. Messages to remember

• The global biomass of living organisms is estimated at around 550 Gt C. Plants account for nearly 80 per cent of this, but the various groups are not known with the same degree of precision.
• Biomass, number of individuals, number of species and annual production describe different aspects of living organisms. A group that is very abundant in terms of individuals may represent little carbon.
• The continents contain much more biomass than the ocean. Yet marine primary production is almost as significant as that of the continents: phytoplankton forms a small stock that is rapidly replenished.
• Humans and domesticated mammals now account for the bulk of mammalian biomass. This dominance masks the historical decline of many wild mammals, both on land and at sea.
• Agriculture and land management have profoundly altered plant biomass. A cultivated field can produce a great deal each year whilst, at any given moment, containing far less biomass than a forest.
• These estimates provide orders of magnitude rather than a definitive inventory: microorganisms in deep-sea environments and several marine groups remain particularly difficult to estimate.

 

The assessments by Bar-On et al. (2018) [5], Bar-On and Milo (2019) [6] and Greenspoon et al. (2023) [14] serve as the references for the distribution figures presented here. The articles are published as ‘open access’ and distributed under a Creative Commons licence (CC BY-NC-ND 4.0):

• Bar-On Y.M., Phillips R. & Milo R. (2018) The biomass distribution on Earth. Proc. Nat. Acad. Sci. U.S.A. 115:6506-6511 ; https://www.pnas.org/doi/10.1073/pnas.1711842115. The data have been deposited in GitLab (https://github.com/milo-lab/biomass_distribution).
• Bar-On Y.M. & Milo R. (2019) The biomass composition of the oceans: A blueprint of our blue planet, Cell, 179 :1451–1454 ; https://doi.org/10.1016/j.cell.2019.11.018. The data have been deposited in (github.com/milo-lab/ocean_biomass)
• Greenspoon L., Krieger E., Sender R., Rosenberg Y., Bar-On Y.M., Moran U., Antman T., Meiri S., Roll U., Noor E., & Milo R. (2023), The global biomass of wild mammals, Proc. Natl. Acad. Sci. U.S.A. 120 (10) e2204892120, https://doi.org/10.1073/pnas.2204892120. The data have been deposited in (https://gitlab.com/milo-lab-public/mammal_biomass/)

 

 

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Notes and references

Cover image. A certain idea of biomass: Zebra (Equus zebra) and wildebeest (Connochaetes taurinus) in the African savannah, Masai Mara National Reserve, Kenya. [Source: photo © Jacques Joyard]

[1] Catalogue of Life (2025), accessed at catalogueoflife.org

[2] Schultheiss P. et al. (2022), The abundance, biomass, and distribution of ants on Earth, Proc. Natl. Acad. Sci. U.S.A. 119, e2201550119, https://www.pnas.org/doi/10.1073/pnas.2201550119

[3] Carvalhais N. et al. (2014) Global covariation of carbon turnover times with climate in terrestrial ecosystems. Nature 514:213–217. https://www.nature.com/articles/nature13731

[4] Quere C.L. et al. (2005) Ecosystem dynamics based on plankton functional types for global ocean biogeochemistry models. Glob. Change Biol. 11:2016–2040. https://research-portal.uea.ac.uk/en/publications/ecosystem-dynamics-based-on-plankton-functional-types-for-global-/

[5] Bar-On Y.M., Phillips R. & Milo R. (2018) The biomass distribution on Earth. Proc. Nat. Acad. Sci. U.S.A. 115:6506-6511, https://www.pnas.org/doi/10.1073/pnas.1711842115

[6] Bar-On, Y.M. & Milo R. (2019) The biomass composition of the oceans: A blueprint of our blue planet, Cell, 179 :1451–1454 ; https://doi.org/10.1016/j.cell.2019.11.018

[7] What Bar-On et al. [5] define as plants are all embryophytes (commonly known as land plants), green algae and red algae. For French-speaking authors (Romaric Forêt and his *Dictionnaire de sciences de la vie*, Le Guyader & Lecointre and their *Classification phylogénétique du vivant*), the term ‘plants’ is synonymous with ‘embryophytes’. For Wikipedia, the term ‘plants’ is synonymous with ‘Archaeoplastida’ (green lineage).

[8] Erb K.-H. et al. (2018) Unexpectedly large impact of forest management and grazing on global vegetation biomass. Nature 553:73–76. https://pmc.ncbi.nlm.nih.gov/articles/PMC5756473/

[9] Yizhao, C., Jianyang, X., Zhengguo, S. et al. (2015). The role of residence time in diagnostic models of global carbon storage capacity: model decomposition based on a traceable scheme. Sci Rep 5, 16155. https://doi.org/10.1038/srep16155

[10] Magnabosco C. et al. (2018), The biomass and biodiversity of the continental subsurface, Nature Geoscience 11, 707–717, https://cris.vtt.fi/en/publications/the-biomass-and-biodiversity-of-the-continental-subsurface/

[11] The ratio of ten viruses to one microbial cell, long used as a general guideline, does not apply uniformly to marine environments: this ratio varies depending on location and microbial density. Wigington C.H. et al. (2016), ‘Re-examination of the relationship between marine virus and microbial cell abundances’, Nature Microbiology, 1, 15024, article corrected in 2017 https://pubmed.ncbi.nlm.nih.gov/28974689/

[12] Field C.B. et al. (1998), Primary production of the biosphere: integrating terrestrial and oceanic components, Science 281, 237–240, https://pubmed.ncbi.nlm.nih.gov/9657713/

[13] Stoer A.C. & Fennel K. (2024), Carbon-centric dynamics of Earth’s marine phytoplankton, Proc. Natl. Acad. Sci. U.S.A. 121, https://www.pnas.org/doi/10.1073/pnas.2405354121

[14] Greenspoon L. et al. (2023), The global biomass of wild mammals, Proc. Natl. Acad. Sci. U.S.A. 120, e2204892120, https://www.pnas.org/doi/10.1073/pnas.2204892120

[15] Barnosky A.D. (2008) Colloquium paper: Megafauna biomass tradeoff as a driver of Quaternary and future extinctions. Proc. Natl. Acad. Sci. 105:11543–11548. https://www.pnas.org/doi/10.1073/pnas.0801918105.

[16] Christensen L.B. (2006) Marine Mammal Populations: Reconstructing historical abundances at the global scale. Fisheries Centre Research Reports 14(9). Fisheries Centre, University of British Columbia, Vancouver. 161 p.

[17] Elhacham E. et al. (2020), Global human-made mass exceeds all living biomass, Nature 588, 442–444, https://www.nature.com/articles/s41586-020-3010-5