Unknown Earth: Why is Earth's climate so stable?
By Richard Lovett Read all seven of the biggest mysteries about Earth Explore an interactive map of our Unknown Earth Earth wasn’t always the only water-world in the solar system. Mars and Venus also appear to have started out wet but, as conditions changed, they lost their oceans. So how has Earth managed to avoid a similar fate? Our planet’s climate is remarkably stable, and has remained in a narrow, liveable, range for almost 4 billion years. The key appears to lie in the interplay between plate tectonics, carbon dioxide and the oceans (see “The Earth’s thermostat”). The cycle begins with volcanoes spewing CO2 into the atmosphere, which helps keep the planet warm, thanks to the greenhouse effect. This warmth allows seawater to evaporate, forming clouds and rain. As the rain contains dissolved CO2 it is slightly acidic and so it reacts with surface rocks to dissolve carbon-containing minerals into the water. This mixture is then washed out to sea, where the minerals build up and eventually precipitate out to form new carbon-containing rocks on the seabed. Sooner or later, plate tectonics carries these rocks into a subduction zone, where CO2 is baked out of them by heat of the Earth’s interior and later returns to the atmosphere via volcanoes. This cycle turns out to be an extremely effective thermostat. When the planet is warm, rainfall increases, speeding the rate of atmospheric CO2 removal and cooling the planet. When it is cold, rainfall decreases, allowing volcanic gases to build up in the atmosphere,