Middle to Late Paleozoic Atmospheric CO_2 Levels from Soil Carbonate and Organic Matter

The stable carbon isotope compositions of ancient soil carbonate and coexisting soil organic matter indicate that atmospheric CO_2 levels decreased by a factor of 10 during the middle to late Paleozoic era. Proxy measurements of CO_2 were made by application of a soil carbonate CO_2 paleobarometer to a suite of paleosols that share key physical and chemical characteristics. The estimates agree with theoretical models that imply that a decrease in Paleozoic atmospheric CO_2 levels was associated with afforestation of the land surface by terrestrial plants and with global climate change leading to the extensive Permo-Carboniferous glaciation.