Middle to Late Paleozoic Atmospheric CO ₂ Levels from Soil Carbonate and Organic Matter

Abstract

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.