Our blue planet ows its habitability to a fascinating feedback mechanism that stabilises greenhouse gas concentrations and hence temperature at its surface at a level that has kept water in the liquid form throughout most of Earth’s history. Weathering
of silicate rocks during the formation of soil consumes the CO2 that is continuously being emitted through volcanic degassing and deposits it as carbonate sediments on the seafloor. Through weathering feedbacks, this “geologic CO2 cycle” has the ability
to accelerate whenever climate gets hotter, withdrawing more CO2, and slowing down if temperatures fall, or if less CO2 is available. Through this “thermostat” weathering stabilises climate over the 100 thousand year time scale. Tectonic activity is also a
key player, as movements between segments of the Earth’s crust creates geomorphic relief that accelerates the formation of soils by weathering. At GFZ we explore these relationships with sophisticated isotope geochemichal methods. We find that weathering and soil formation is subject to strict “limits”, and that at present, Earth’s surface has the right kind of landscapes to make the “thermostat” work. Silicate weathering will, eventually, reduce the anthropogenic CO2 peak to pre-industrial levels. But the time required to do so is some hundred thousand years. The much faster fluxes of carbon into the Earth’s biomass and oceans dominate changes in greenhouse gas concentrations over the human time scale, but they would not do this effectively without the geologic thermostat roughly stabilising temperature in the background.