el; of Silurian soils as a result of pedoturbat i o~~, effectively mcreasing the average depth of soil CO, proiluction. Our results (Table 1 ) ~m p l y that atmospheric CO-, decllneil 1~y a factor of 10 from the Late S i h r i a n to the Early Permian, closely follow~ng (Fig. 4 ) a decline precllctecl hi; theoretical carbon lnais balance models (1). T h e largest decrease, hetween the Late Sil~lrian a11il Late Devonian. coincides with a of rapid evolution and diversificatlon of the terrestrial

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... cosystem (18). Estimates of atmospheric C02 levels from separated, time-equivalent ~-7aleosols are consistent, suggertlng that a coherent record of changing atlnospheric chem~stry is yreserl-eii In the ancient soil recorJ. REFERENCES AND NOTES 1 R A Berner Science 261, 68 (1 993) At?? J SCI 294 56 (1 994) 2 T J Crowley and G R North, Paleoc!~~rato!ogy (Oxford UI?I\/ Press, Oxford, 1991) 3 R A Berner and R Ralswell, Geochim. Cosmochlm. Acta 47. 855 11983) L R. I<ump and R M Garres At?? J. SCI 286, 377 (1 9861, R A Berner and D E Canfleld A t~i . J. SCI. 289 333 (1 9891; J M Robnson Paiaeogeogr Pa!aeocl~mato! Palaeoecol. 97, 51 (1991) 4 Geocheri~~cal proxies for measuring paleo-CO, are dscussed by J. F. Kastng [~Vature 355, 676 jl992jl and R P Berner [/old 358. 1 14 (1 99211. 5. The s o carbonate paeobarotneter [ I E C e r n g . Am. J. Sci. 291 377 (1 991 )] 1s based on studies of modern sols p E C e r n g Earin Planet Sci Lett.