By The Numbers · Nº 01

Underfoot

Six numbers from under your feet.

6 cards · The world, by the numbers.

01 / 06

59 %

the share of all Earth’s species that live in soil — its single most crowded habitat.

Look down. Beneath your feet lies Earth’s most crowded habitat. Nearly three in five of all living species spend their lives inside soil — mostly unnamed, mostly unseen.

Anthony et al., PNAS 2023 (59% ±15%). DOI:10.1073/pnas.2304663120

02 / 06

1,417 Gt

gigatonnes of carbon in just the top metre of soil — two to three times all the air above.

The first metre of soil holds more carbon than every plant and the entire atmosphere combined. The ground is a vast, quiet vault — and we are steadily opening it.

FAO, Global Symposium on Soil Organic Carbon (1,417 Gt top metre; 2–3× atmosphere).

03 / 06

1,000 years

how long nature can take to build a single inch of topsoil (estimates run 500–1,000).

An inch of topsoil can take a thousand years to form and a single season to wash away. What you scuff with a boot is older than most cathedrals.

Columbia Climate School, “Why Soil Matters” (500–1,000 yrs per inch).

04 / 06

15 tonnes

of soil an acre of earthworms hauls to the surface every year — Darwin’s own estimate.

Darwin’s last book was about worms. He calculated they haul tonnes of earth to the surface each year, slowly turning the whole landscape inside out beneath us.

Darwin, 1881, The Formation of Vegetable Mould; via Earthworm Watch (~15 t/acre/yr).

05 / 06

10 billion

microorganisms can live in a single gram of soil — more living things than people on Earth.

Scoop a teaspoon of soil. In your hand are more living organisms than there are people on Earth — an entire civilisation of the invisible, held in a pinch.

Torsvik & Øvreås, Curr. Opin. Microbiol. 2002 (up to 10^10 /g); BioNumbers BNID 110152.

06 / 06

13 Gt

of CO₂ plants pump underground into fungal networks each year — a third of fossil-fuel emissions.

Every year plants pipe billions of tonnes of carbon into fungal threads through the soil — a hidden trade, older than forests, equal to a third of what we burn.

Hawkins et al., Current Biology 2023 (13.12 Gt CO₂e; ≈36% of fossil emissions). DOI:10.1016/j.cub.2023.02.027

Sources

Anthony et al., PNAS 2023 (59% ±15%). DOI:10.1073/pnas.2304663120
FAO, Global Symposium on Soil Organic Carbon (1,417 Gt top metre; 2–3× atmosphere).
Columbia Climate School, “Why Soil Matters” (500–1,000 yrs per inch).
Darwin, 1881, The Formation of Vegetable Mould; via Earthworm Watch (~15 t/acre/yr).
Torsvik & Øvreås, Curr. Opin. Microbiol. 2002 (up to 10^10 /g); BioNumbers BNID 110152.
Hawkins et al., Current Biology 2023 (13.12 Gt CO₂e; ≈36% of fossil emissions). DOI:10.1016/j.cub.2023.02.027