Origin Story: A Big History of Everything

by David Christian

Of course, if too much carbon dioxide was buried in this way, Earth would freeze. That was prevented (most of the time) by the second feature of the geological thermostat. Driven by plate tectonics (a mechanism that is probably not working on icy Mars), carbon dioxide can return to the atmosphere at divergent zones, where material from the mantle, including buried carbon dioxide, rises to the surface through volcanoes.6 There is a balance between the two halves of this mechanism because higher temperatures generate more rainfall, which accelerates erosion, moving more carbon back into the mantle. But if the Earth cools too much, rainfall will dwindle, less carbon dioxide will be buried, carbon dioxide levels will build up as it is pumped up through volcanoes, and that will warm things up again. The geological thermostat has been adjusting to the increasing warmth of our sun over four billion years.