LAUSR

Enhanced weathering of uplifted rocks in the tropics may have driven past glaciations Over the past 541 million years (the Phanerozoic eon), Earth's climate has been relatively stable compared to preceding eons. However, there have been periods of longer glaciations, which have been attributed to changes in the balance between CO2 sources and sinks. The major CO2 sources are thought to be mantle degassing at hotspot volcanoes, mid-ocean ridges, and rifts; subduction zone volcanoes; metamorphosis of carbonate rocks into silicate rocks; and oxidative weathering (see the figure) (1). The main CO2 sink is chemical weathering and the subsequent transfer of carbon to the ocean, where carbonate sediments lock up CO2 for long periods of time. During arc-continent collisions, rocks from volcanic arcs are accreted to continents. On page 181 of this issue, Macdonald et al. (2) propose that weathering can rise after the accreted rocks are exposed at Earth's surface. This mechanism may explain the glaciations seen during the Phanerozoic.