The Goldilocks Planet? How Silicate Weathering Maintains Earth “Just Right”

Earth’s climate is buffered over long timescales by a negative feedback between atmospheric CO2 level and surface temperature. The rate of silicate weathering slows as the climate cools, causing CO2 to increase and warming the surface through the greenhouse effect. This buffering system has kept liquid water stable at Earth’s surface, except perhaps during certain ‘Snowball Earth’ episodes at the beginning and end of the Proterozoic. A similar stabilizing feedback is predicted to occur on rocky planets orbiting other stars if they share analogous properties with Earth, most importantly an adequate (but not overly large) abundance of water and a mechanism for recycling carbonate rocks into CO2. Periodic oscillations between globally glaciated and ice-free climates may occur on planets with weak stellar insolation and/or slow volcanic outgassing rates. Most silicate weathering is thought to occur on the continents today, but seafloor weathering (and reverse weathering) may have been equally important earlier in Earth’s history.