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The arc exhumation hypothesis states that new basalt-rich sources lifted during arc-continent collisions cause atmospheric PCO2 drawdown and global cooling. Drawdown lags the early release of CO2 and Os from uplifted continental margin sediments. It generally precedes release of Sr from continental crust exhumed later. During the Miocene, Australia collided with New Guinea, lifting up a composite arc terrane around 15 Ma. Benthic foraminiferal usd\delta\spusdO values increased from 1 to 2usd\perthoususd in response to polar cooling between 14.8 and 12.8 Ma. Marine Os/Os ratios began to increase at 0.1/my while the rate of change of Sr/Sr ratios decreased at 16 Ma. Bulk carbonate usd\delta\spusdC values began to decrease at 0.3usd\perthoususd/my after 14 Ma. A new coupled C-Os-Sr isotopic mass balance model calculates atmospheric PCO2 from the Sr/Sr ratio of weathered silicates (following a large correction for weathering of intermediate and radiogenic carbonates) based on the lithology-dependent time constant associated with Ca and Mg release. Seafloor-spreading rate constrains the metamorphic carbon fluxes, and the riverine flux of Os, associated with organic matter, constrains the weathering of sedimentary carbon. Model atmospheric PCO2 mimics the proxy for climate (inverse benthic foraminiferal usd\delta\spusdO values). The rate of change of basalt weathering generally increases at times expected from independent records of basalt exhumation. Calculated organic C burial accelerates at 16 Ma, perhaps triggered by high rates of sedimentation of fine-grained material from Indonesia, and the organic C cycle is a net CO2 sink (1-2 ocean reservoirs of C). Carbonate burial results, which decrease from 20 to 15 Ma and then increase, resemble the time evolution of the CCD. Arc exhumation operated at other times of global cooling, including the Pliocene (northern Andes and central America?), middle Miocene (Indonesia), Eo-Oligocene (proto-Himalayas), Permo-Carboniferous (Urals-Varisco-Hercynides), late Ordovician (Taconics), and late Precambrian (early Pan-African). Related organic C burial events may explain biologically important steps in the evolution of atmospheric PO2. During exhumational events, especially in the Archean, silicate weathering must have fractionated accreted mafic terranes, with the sialic by-products contributing to growth of andesitic continental crust.
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