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The geochemical carbon cycle as interpreted by the GEOCARB model. Fm is weathering flux of carbonates, Fmc the degassing flux from thermal carbonate decomposition, Fwg the weathering flux of organic matter, Fmg the degassing flux from thermal organic matter decomposition, Fic the burial flux of carbonates in sediments, and Fbg the burial flux of organic matter in sediments. A steady state, required over a multimillion year time scale gives Fwc + F^ + Fwg + F^ = Fic + Fig (after Bemer l"5a).

For the next decade, BLAG evolved with greater complexity, extending the time period back over the whole of Phanerozoic time (Berner and Barron 1984; Berner 1990a, 1991, 1994; for a popularization, see Berner and Lasaga 1989). The latest version is GEOCARB II (Berner 1994, 1995a; see figure 3-3). Innovations included mathematical simplification, incorporation of variation of solar luminosity (which has changed about 6% over Phanero-zoic time), different assumed feedbacks for carbonate and silicate weathering, updating based on new data on subduction and seafloor spreading over the past 150 million years, changes in the assumed activation energy of chemical weathering of silicates and global runoff, and the inclusion of explicit biological effects on weathering rates (i.e., fertilization of land plants by atmospheric pCO2 levels, difference in weathering from angiosperms and gym-nosperm cover, etc.; more on this in chapter 4).

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