These must be corrected for degassing of carbon and other elements. Įstimates of the carbon content in the upper mantle come from measurements of the chemistry of mid-ocean ridge basalts (MORBs). Even at the lower concentration, this would account for half Earth's carbon. Depending on the model, carbon is predicted to contribute between 0.2 and 1 percent by weight in the core. Some of this carbon may have ended up in the core. Even accounting for evaporation, however, the silicates making up the crust and mantle of the Earth have a carbon concentration that is five to ten times less than in CI chondrites, a form of meteor that is believed to represent the composition of the solar nebula before the planets formed. The Earth likely started with a similar ratio but lost a lot of it to evaporation as it accreted. In the photosphere of the Sun, carbon is the fourth most abundant element. Over 90% may reside in the core, most of the rest being in the crust and mantle. Large as this quantity is, it only amounts to a small fraction of one percent of Earth's carbon. A gigatonne is one billion metric tonnes, equivalent to the mass of water in over 400,000 Olympic-size swimming pools. There are about 44,000 gigatonnes of carbon in the atmosphere and oceans. Studies of the composition of basaltic magma and the flux of carbon dioxide out of volcanoes reveals that the amount of carbon in the mantle is greater than that on the Earth's surface by a factor of one thousand. Furthermore, techniques like seismology have led to greater understanding of the potential presence of carbon in the Earth's core. Nonetheless, several pieces of evidence-many of which come from laboratory simulations of deep Earth conditions-have indicated mechanisms for the element's movement down into the lower mantle, as well as the forms that carbon takes at the extreme temperatures and pressures of this layer. īecause the deep Earth is inaccessible to drilling, not much is conclusively known about the role of carbon in it. Without it, carbon would accumulate in the atmosphere, reaching extremely high concentrations over long periods of time. By returning carbon to the deep Earth, it plays a critical role in maintaining the terrestrial conditions necessary for life to exist. It forms part of the carbon cycle and is intimately connected to the movement of carbon in the Earth's surface and atmosphere.
The deep carbon cycle is geochemical cycle (movement) of carbon through the Earth's mantle and core.