This figure illustrates how inorganic carbon cycles through the mantle more quickly than organic carbon, which contains very little of the isotope carbon-13. Both inorganic and organic carbon are drawn into Earth's mantle at subduction zones (top left). Due to different chemical behaviors, inorganic carbon tends to return through eruptions at arc volcanoes above the subduction zone (center). Organic carbon follows a longer route, as it is drawn deep into the mantle (bottom) and returns through ocean island volcanos (right). The differences in recycling times, in combination with increased volcanism, can explain isotopic carbon signatures from rocks that are associated with both the Great Oxidation Event, about 2.4 billion years ago, and the Lomagundi Event that followed.