Rock weathering can act as a carbon sink removing CO2 from the atmosphere, but it can also act as a large CO2 source, rivaling that of volcanoes. Currently, this process isn’t included in most natural carbon cycle models. During chemical weathering rocks can suck up CO2 when certain minerals are attacked by the weak acid found in rainwater. But when rocks formed on ancient seafloors (where plants and animals were buried in sediments) are pushed back up to Earth’s surface, the organic carbon in the rocks is exposed to oxygen in the air and water, and it can react and release CO2.
www.ox.ac.uk/news/2023-10-04-new-research-finds-ancient-carbon-rocks-releases-much-carbon-dioxide-worlds