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Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life Author(S): J

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Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life Author(S): J Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life Author(s): J. William Schopf Reviewed work(s): Source: Science, New Series, Vol. 260, No. 5108 (Apr. 30, 1993), pp. 640-646 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/2881249 . Accessed: 07/04/2012 21:09 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve and extend access to Science. http://www.jstor.org REFERENCESAND NOTES 9. Y. Hiwatari,in Molecular Dynamics Simulations, F. (World Scientific, Singapore, 1988), vol. 1, p. Yonezawa, Ed., vol. 113 of Springer Series in 247. 1. H. Takayama, News Letter No. 1 (Research Group Solid State Sciences (Springer-Verlag, Heidel- 23. F. Yonezawa, S. Sakamoto, M. Hori, J. Non-Ctyst. on a new project, "Computational Physics as a berg, 1992), p. 32. Solids 137, 135 (1991). New Frontier in Condensed Matter Research" 10. S. Fujiwara and F. Yonezawa, in preparation. 24. F. Yonezawa and S. Sakamoto, Optoelectronics- under the support of the Grant-in-Aidfor Scientific 11. S. Chandrasekhar, Contemp. Phys. 29, 527 Devices Technol. 7, 117 (1992). Research on Priority Areas from the Ministry of (1988). 25. R. Car and M. Parrinello, Phys. Rev. Lett. 55, 2471 Education, Science, and Culture of Japan, Tokyo, 12. K. M. Aoki and F. Yonezawa, Phys. Rev. A 46, (1985). 1991). 6541 (1992). 26. ,_ ibid. 60, 204 (1988); G. Galli, R. M. Martin, 2. N. Metropolis, A. Rosenbluth, M. Rosenbluth, A. 13. K. Omata, K. M. Aoki, F. Yonezawa, in prepara- R. Car, M. Parrinello, ibid. 62, 555 (1989); ibid. 63, Teller, E. Teller, J. Chem. Phys. 21 1087 (1953). tion. 988 (1989); 1. Stich, R. Car, M. Parrinello, ibid., p. 3. F. Yonezawa, Ed., Molecular Dynamics Simula- 14. M. Cheng, J. T. Hsi, R. Pindak, Phys. Rev. Lett. 61, 2243; G. Seifert, G. Pastore, R. Car, J. Phys. tions, vol. 103 of the Springer Series in Solid 550 (1988). Condens. Matter 4, L179 (1992); P. Ballone, W. State Sciences (Springer-Verlag, Heidelberg, 15. B. I. Halperin and D. R. Nelson, ibid. 41, 121 Andreoni, R. Car, M. Parrinello, Phys. Rev. Lett. 1992). (1978). 60, 271 (1988). 4. S. Nos6, Ed., Prog. Theor. Phys. Suppl. 103, 1 16. R. J. Birgeneau and J. D. Lister, J. Phys. Paris 39, 27. T. Oguchi and T. Sasaki, Prog. Theor. Phys. (1991). L399 (1978). Suppl. 103, 93 (1991). 5. F. Yonezawa, in Solid State Physics, H. Ehren- 17. R. Pindak, D. E. Moncton, S. C. Davey, J. S. 28. Y. Morikawa, K. Kobayashi, K. Terakura, S. reich and D. Turnbull,Eds. (Academic Press, New Goodby, Phys. Rev. Lett. 46, 1135 (1981). Blugerl, Phys. Rev. B44, 3459 (1991). York, 1990), vol. 45, p. 179. 18. R. Geer et al., Nature 355, 152 (1992). 29. M. Tsukada, K. Kobayashi, N. Isshiki, H. 6. _ , S. Nos6, S. Sakamoto, Neue Folge 156, 19. W. E. Spear and P. G. LeComber, Solid State Kageshima, Surf. Sci. Rep. 13, 265 (1991). 77 (1988). Commun. 17, 1193 (1975). 30. W. Kohn and L. J. Sham, Phys. Rev. 140, 1133 7. F. C. Frank, Proc. R. Soc. London Ser. A 215, 43 20. D. L. Staebler and C. R. Wronski, Appl. Phys. Lett. (1965). (1952). 31, 292 (1977). 31. G. B. Bachelet, D. R. Hamann, M. Schluter, Phys. 8. J.-L. Barrat, J.-N. Roux, J.-P. Hansen, Chem. 21. K. Morigaki, Jpn. J. Appl. Phys. 27, 163 (1988). Rev. B26, 4199 (1982). Phys. 149,198 (1990); J.-L. Barratand M. L. Klein, 22. W. B. Jackson and J. Kakalios, in Amorphous 32. I thank my students S. Sakamoto, K. M. Aoki, S. Annu. Rev. Phys. Chem. 42, 23 (1991). Silicon and Related Materials, H. Fritzsche, Ed. Fujiwara, and K. Omata for collaboration. understandingof the evolutionarystatus of early evolving microorganisms,and suggest that cyanobacterialoxygen-producing pho- tosynthesizersmay have alreadybeen extant Microfossils of the Early Archean this earlyin Earthhistory. The Archean fossil record. Unlike that Apex Chert: New Evidence of the of the laterPrecambrian Proterozoic (5), the fossil recordof the Archean is minuscule; few fossils have been detected and their Antiquity of Life studyhas been plaguedby misinterpretation and questionableresults (4). In order to J. William Schopf establishthe authenticityof Archeanmicro- fossils,five principalcriteria must be satisfied Eleven taxa (including eight heretofore undescribed species) of cellularly preserved fila- (3). The putativemicrofossils must (i) occur mentous microbes, among the oldest fossils known, have been discovered in a bedded in rocks of known provenanceand (ii) es- chert unit of the Early Archean Apex Basalt of northwestern Western Australia. This tablishedArchean age; (iii) be demonstrably prokaryotic assemblage establishes that trichomic cyanobacterium-like microorganisms indigenousto and (iv) syngeneticwith the were extant and morphologically diverse at least as early as -3465 million years ago and primarydeposition of the enclosing rock; suggests that oxygen-producing photoautotrophy may have already evolved by this early and (v) be of assuredbiological origin. All stage in biotic history. but a few of the microfossil-likeobjects reported from Archean sediments have failedto meet one or moreof these require- ments (3, 4). Among recent such examples When life originatedand the rate of evo- severelyaltered by metamorphism(1). The wasthe discoveryof authenticmicrofossils in lution and diversificationof the earlybiota most promisingterrain for such studies is rocks evidently belonging to the Early continue to be fascinatingquestions. Simi- that of the PilbaraBlock of northwestern Archean WarrawoonaGroup of Australia larly, it is unclearwhen a physiologically WesternAustralia, a region underlainby a (6), a reportunconfirmed because it has not modem ecosystembased on oxygen-produc- 30-km-thicksequence of relativelywell-pre- proved possible to relocate the geologic ing photosynthesisbecame established. The servedsedimentary and volcanic rocksthat sourceof the fossiliferoussamples (3). Sim- sole source of direct evidence relevant to are -3000 to -3500 millionyears old (Fig. ilarly, becauseof their simple morphology, such questionsis the paleobiologicrecord 1). From this region, I describea diverse solitaryunicell-like spheroids reported from contained in rocks deposited during the assemblageof filamentousmicrobial fossils severalArchean units (7, 8) arebest consid- ArcheanEon of Earthhistory [>2500 mil- detectedin the EarlyArchean (-3465 mil- ered to be possibly rather than assuredly lion years ago (Ma)]. The search for lion yearsold) Apex chert, cellularprokary- biogenic (3, 4). Other than the filamentous Archean fossils, however, is fraughtwith otes morethan 1300million years older than Apex fossilsdiscussed below, the relatively difficulty:Few Archean sedimentaryrocks any comparablesuite of fossils previously well-establishedArchean microfossil record have survivedto the present,and paleobio- reportedfrom the geologicrecord. Microfos- consistsof two typesof cyanobacterium-like logic evidencein most such units has been sils were first discoveredin this deposit in filamentsfrom the -2750-million-year-old 1986 (2); in a preliminaryaccount, three TumbianaFormation of WesternAustralia The author is in the Center for the Study of Evolution taxawere identified (3). The eight addition- (4); sheath-enclosedcolonial unicells oc- and the Origin of Life, Institute of Geophysics and al species describedhere demonstratethat curring in -3465-million-year-old sedi- Planetary Physics, the Department of Earth and Space Sciences, and the Molecular Biology Institute, Univer- the EarlyArchean biota was more diverse mentary rocks of the Towers Formation, sity of California, Los Angeles, CA 90024. than previouslyknown (3, 4), providenew also of Western Australia(2); and narrow 640 SCIENCE * VOL. 260 * 30 APRIL 1993 nonseptate bacterium-likefilaments from mapped in detail (13). Studies of petro- mineralizedin subangularto roundedsili- -3450-million-year-oldunits of the Swazi- graphicthin sections demonstratethat the ceous sedimentaryclasts less than 1 mm to land Supergroupof South Africa (3, 8, 9). three-dimensionalfossils are cellularlyper- a few millimetersin diameter(Fig. 3, A and Although stromatolites (finely layered mound-shapedsedimentary structures pro- Fig. 1. Stratigraphiccolumn (13, duced by microbial communities) have Pilbara 15), distributionof reportedstro- been reportedfrom more than 20 Archean Supergroup I (Gad 313C(per mil) matolites and microfossils (3), ap- geologic units (10), including the Tumbi- 30 WHIMCREEK 3.0 -30 -20 -10 0 GGROUP proximateages (15, 40), and car- ana, Towers, and Swazilanddeposits ( 1), 0 =Organic carbon 1 bon isotopic data (14) for geolog- their putative biological origin has been 25- * =Carbonatecarbon J ic units of the Pilbara Supergroup questioned(12). GORGE of northwesternWestern Austra- Geologicsetting. The microfossilassem- CREEK g H/C=0.09(N=1) lia. GROUP blage that I describeis foundin a sedimen- 20- tarychert unit of the Apex Basalt,a 1.5- to E 00 2.0-km-thick formationconsisting of tho- e) 15- WYMANFM 1 -3.3 leiitic pillow lava, high-magnesiumbasalt, c and komatiite interbedded with minor Yd CL EURO BASALT . PANORAMAFM -3.4C chert members that immediatelyoverlies - CYT APEX BASALT GD0 0 the TowersFormation in the lowerthird of 10 C- OWER M _ (3(D 0 <DUFFERUFFE _ O* the LowerArchean PilbaraSupergroup of 3.4 TOWERSH/C=0.25 o FORMATION northwesternWestern Australia (Fig. 1) ~~(0. 5- 3~~~~~~: 30 to 0.16, N=3) (13). Kerogensisolated from Towers For- <1: MOUNTADA 0 BASALT mation sediments have H/C ratios from < McPHEEFM _ 3.5 3'NORTHSTAR-3 -2 -1 0 0.30 to 0.16 (Fig. 1) (14), consistentwith 0 3 BASALT _ _ -1_0-30 -20 minerologicdata indicating that these units have been metamorphosedto prehnite- pumpellyiteand lowergreenschist facies (1, I- Fig.
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