DOI: 10.1126/science.1106881 , 98 (2005); 308Science et al.Robert Bailis,and Petroleum Energy Futures in AfricaMortality and Greenhouse Gas Impacts of Biomass www.sciencemag.org (this information is current as of August 25, 2007 ):The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/308/5718/98version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/308/5718/98/DC1 can be found at: Supporting Online Material 11 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/collection/atmosAtmospheric Science : subject collectionsThis article appears in the following http://www.sciencemag.org/about/permissions.dtl in whole or in part can be found at: this articlepermission to reproduce of this article or about obtaining reprintsInformation about obtaining registered trademark of AAAS. c 2005 by the American Association for the Advancement of Science; all rights reserved. The title SCIENCE is a CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the on August 25, 2007 www.sciencemag.orgDownloaded fromEthe Wonoka Formation (33)^ and the westernUnited States ERainstorm Member, JohnnieFormation (34)^ but chose to equate it with apostulated Gaskiers-related d13C excursionfrom circa 580 Ma (35). Instead, our dataindicate that this globally correlated negatived13C excursion is not related to any knownglaciation (36). The duration of this excursionis unconstrained; however, given that it iscaptured within over 100 m of section inOman (Fig. 1) combined with approximatesediment accumulation rates calculated withour constraints, we suggest a duration of 91and G10 My.The Doushantuo and correlative stratarecord a fundamental shift from an intervalof large carbon isotopic anomalies corre-sponding to glacial episodes (750 to 580 Ma)to an interval of anomalies unrelated to ob-vious glacial episodes (i.e., the anomalies fromcirca 551 and 542 Ma), as well as subsequentlarge fluctuations in the lower Cambrian.These new geochronological data allow us tocalibrate that shift as being synchronous withthe appearance of larger and more complexmetazoans; this suggests possible feedbackrelationships between evolutionary innovationand seawater chemistry (Fig. 2).Our ages indicate that the DoushantuoFormation spans more than 90% of theEdiacaran Period. These constraints are con-sistent with the upper Doushantuo/Shuram/Kuibis excursion being broadly coincidentwith the first appearance of complex tracefossils and mollusk-like bilaterian Kimberella(37), dated as slightly older than 555.1 T 1.0Ma (24). The advent of large pelagic bi-laterians with unidirectional guts would haveincreased the flux of organic carbon to thedeep ocean (38). Additionally, the radiation ofalgae containing resistant biopolymers in cellwall and cysts (i.e., Miaohe Biota) and theadvent of biomineralization (Namacalathusand Cloudina, 9549 Ma) would have alsoresulted in an increased organic carbon andcarbonate carbon flux (39). These changeswould have resulted in a downward flux oforganic carbon with a possible coupled oxi-dation of the organic reservoir (38, 39)drivingthe negative d13C excursion. This feedbackloopwouldleadtoanincreaseinmarineoxygen levels and stimulate productivity andinferentially predation. It may be no coinci-dence that the first reefs inhabited by abundantweakly calcified and rare fully calcified meta-zoans appeared at about the same time as theisotopic anomaly Ei.e., before 549 Ma inNamibia (6, 40)^.References and Notes1. M. Y. Zhu et al., Prog. Nat. Sci. 13, 951 (2003).2. J. Y. Chen et al., Science 305, 218 (2004).3. S.H.Xiao,Y.Zhang,A.H.Knoll,Nature 391, 553 (1998).4. S. H. Xiao, X. L. Yuan, M. Steiner, A. H. Knoll, J.Paleontol. 76, 347 (2002).5. C. M. Zhou et al., Geology 32, 437 (2004).6. J. P. Grotzinger, S. A. Bowring, B. Z. Saylor, A. J.Kaufman, Science 270, 598 (1995).7. R. J. F. Jenkins, J. A. Cooper, W. Compston, J. Geol.Soc. London 159, 645 (2002).8. G. H. Barfod et al., Earth Planet. Sci. Lett. 201, 203 (2002).9. D. F. Chen, W. Q. Dong, B. Q. Zhu, X. P. Chen,Precambrian Res. 132, 123 (2004).10. Materials and methods are available as supportingmaterial on Science Online.11. Age uncertainties are stated at the 2s level.12. J. D. Yang, W. G. Sun, Z. Z. Wang, Y. S. Xue, X. C. Tao,Precambrian Res. 93, 215 (1999).13. G. Jiang, M. J. Kennedy, N. Christie-Blick, Nature 426,822 (2003).14. M. Macouin et al., Earth Planet. Sci. Lett. 224, 387(2004).15. P. F. Hoffman, D. P. Schrag, Terra Nova 14, 129 (2002).16. This corresponds to approximate sediment accumu-lation rates of about 1.5 to 3 m/My.17. G. P. Halverson, P. F. Hoffman, D. P. Schrag, A. C.Maloof, A. H. N. Rice, Geol. Soc. Am. Bull., in press.18. K.-H. Hoffmann, D. J. Condon, S. A. Bowring, J. L.Crowley, Geology 32, 817 (2004).19. This is the analytical uncertainty on the U-Pb con-cordia age (excluding tracer calibration uncertainty)calculated from Hoffmann et al.(18).20. P. F. Hoffman, A. J. Kaufman, G. P. Halverson, D. P.Schrag, Science 281, 1342 (1998).21. W. Wang et al., Acta Micropalaeontol. Sin. 19, 382(2002).22. S. H. Xiao et al., Precambrian Res. 130, 1 (2004).23. G. M. Narbonne, J. G. Gehling, Geology 31, 27 (2003).24. M. W. Martin et al., Science 288, 841 (2000).25. D. Grazhdankin, Paleobiology 30, 203 (2004).26. S. Bowring, P. Myrow, E. Landing, J. Ramezani, J.Grotzinger, Geophys. Res. Abstr. 5, 13219 (2003).27. The Schwarzrand Subgroup is characterized by a þ2plateau (6,28). In the northern subbasin, the underlyingKuibis Subgroup records a decrease from þ3 down to0 in upper Mooifontein Member with values of –3obtained on carbonates from the underlying MaraMember. In the southern subbasin the Kuibis Subgrouphas values of about 0 at the top that gradually increasetoward the bottom of the section to þ4 and thendecrease down to –1.28. B. Z. Saylor, A. J. Kaufman, J. P. Grotzinger, F. Urban,J. Sediment. Res. 68, 1223 (1998).29. J. E. Amthor et al., Geology 31, 431 (2003).30. S. J. Burns, A. Matter, Eclogae Geol. Helv. 86, 595(1993).31. A. Cozzi, J. P. Grotzinger, P. A. Allen, Geol. Soc. Am.Bull. 116, 1367 (2004).32. P. A. Allen et al.,in16th International Sedimento-logical