The big cycle is caused by the reaction of magnesium silicate with carbon dioxide. Mg silicate is the chief component of Earth's mantle. As temperature increases, silicate rocks are worn away faster by rain and wind, and absorb more CO2. This CO2 eventually sinks down into the mantle as magnesium carbonate, where it is very slowly re-released by volcanoes (the majority of Earth's carbon is in the mantle). As CO2 is sequestered, the Earth cools, and the weathering of silicate rocks slows, especially when they are covered by glaciers. Then the release of CO2 by volcanoes starts to outpace the absorption by olivine, and the atmosphere warms up again.
Eventually as the Sun gets brighter, the equilibrium amount of CO2 in the atmosphere is expected to drop below the requirements for plant life, and the Earth will die. By heating the atmosphere, we hasten the arrival of the next glacial cycle, but we are (thankfully) at low risk of starving the biosphere.
Eventually as the Sun gets brighter, the equilibrium amount of CO2 in the atmosphere is expected to drop below the requirements for plant life, and the Earth will die. By heating the atmosphere, we hasten the arrival of the next glacial cycle, but we are (thankfully) at low risk of starving the biosphere.