When looking at the Earth’s vast carbon stores, we need need to use units of Petaton – a billion billion tons. There are some 7’500 to 40’000 Petatons tons of carbon on Earth. The above table gives the estimated mass and % range for the total carbon on earth – in earth’s core, mantle, lithospheric mantle, and curst (deep carbon), as well as in oceans, land, and air (surface carbon). The most obvious observation is that as part of the total, the terrestrial carbon is less than the size of a rounding error.

The most important carbon store is in earth’s core. Whilst the exact numeric estimates vary, the liquid iron-nickel core is likely to contain a number of lighter elements and its carbon content is estimated to vary between 0.1-1.0 wt %. Either way, this makes earth’s core by far the largest carbon repository, holding between 70 to 95 % of the total. ¹

Whilst the massive core carbon is quite well isolated and locked in, even the remaining some 2000 Petatons of deep carbon dwarf the surface carbon stores by a factor of some 40’000.²

Furthermore, as this carbon form mantle and lithosphere actively interacts with atmospheric carbon, with its magnitude of size difference, the Deep Carbon cycle is the key determinant of earth’s climate over the VERY long – million year – time scales.

1. (Fisher et al 2021) ↩︎
2. In order of size, the second largest carbon deposit is in the Lower Mantle, which contains two to three times more carbon than the depleted Upper Mantle and Lithosphere. Earth’s crust (the thick outer shell of rock) is less than one percent of the planet’s radius and volume. ↩︎