GSA TODAY • Forests As Carbon Sinks, P
Total Page:16
File Type:pdf, Size:1020Kb
Vol. 8, No. 2 February 1998 INSIDE • G. K. Gilbert, p. 16 GSA TODAY • Forests as Carbon Sinks, p. 22 • Rocky Mountain A Publication of the Geological Society of America Section Meeting, p. 27 The Ediacara Biota: A Terminal Neoproterozoic Experiment in the Evolution of Life Guy M. Narbonne Department of Geological Sciences, A B Queen’s University, Kingston, ON K7L 3N6, Canada, [email protected] ABSTRACT The Ediacara biota is a distinctive assemblage of large, soft-bodied organisms that characterizes terminal Neoproterozoic (latest Precambrian) strata worldwide. Some Ediacaran organisms apparently were the root- stock for the Phanerozoic evolution of animals; other bizarre forms may rep- resent a failed experiment in Precam- brian evolution. The Ediacara biota and its nonactualistic preservation and ecosystem characterized the final 20 m.y. of the Proterozoic, and disap- peared near the beginning of the Cambrian “explosion” of shelly and burrowing animals. Figure 1. Photograph and artist’s reconstruction of the holotype of Swart- puntia germsi from Namibia. For simplic- INTRODUCTION ity, only three petaloids are shown. Met- The terminal Neoproterozoic was a ric scale. After Narbonne et al. (1997, Figs. 6 and 8). period of fundamental change in Earth history. Major changes included the breakup of the supercontinent Rodinia and the subsequent collision of some of the fragments that were to form Gond- wana (Hoffman, 1992; Unrug, 1997), a stone beds (Fig. 1). The Ediacara biota con- Phanerozoic systems (cf. Sepkoski, 1981). succession of at least four global glacia- tains a few forms that might be familiar to Prior to the appearance of the Ediacara tions, and some of the largest known a modern beachcomber, alongside bizarre biota, Mesoproterozoic to mid-Neopro- changes in the oceans and atmosphere taxa whose place in the evolution of mod- terozoic (1600–600 Ma) benthic communi- (Knoll and Walter, 1992). It is against this ern life is uncertain. A few “Ediacaran sur- ties had been dominated by prokaryotic backdrop that we see the appearance of vivors” have been reported from the Cam- microbes along with some sheetlike and abundant, large organisms, including the brian, but most of the archetypical forms ribbonlike algae (Knoll, 1992). Evidence first definite fossil animals in Earth his- disappeared abruptly near the Cambrian from molecular phylogeny suggests that tory, the Ediacara biota. “explosion” (Grotzinger et al., 1995). microscopic animals could have evolved The Ediacara biota typifies terminal The unique biology, ecology, and preser- sometime prior to the appearance of the Neoproterozoic rocks worldwide (Glaess- vational mode of the Ediacara biota effec- Ediacara biota, but the exact timing ner, 1984; Fedonkin, 1992; Jenkins, 1992; tively marks the end of the Proterozoic remains debatable (Wray et al., 1996; Runnegar and Fedonkin, 1992). It was Eon, and may herald the beginning of Conway Morris, 1996). The oldest known first described from Newfoundland and the Phanerozoic. megascopic Ediacara-type remains occur Namibia, but the name is derived from the in the Twitya Formation of northwestern superb assemblages of these fossils discov- EVOLUTIONARY HISTORY Canada (see Fig. 3, locality 22) immedi- ered at Ediacara in the Flinders Ranges of ately below tillites correlated with the The Ediacara biota occupies a pivotal South Australia by Sprigg (1947). In con- Marinoan-Varanger glaciation and position in the evolution of life on Earth, trast with the shelly fossils that character- believed to be about 600 m.y. old (Hof- between the largely microbial (especially ize the Phanerozoic, the Ediacara biota mann et al., 1990). The structures consist stromatolitic) communities that charac- consists almost exclusively of the remains of centimeter-scale rings and discs that are terize the classic “Precambrian” and the of soft-bodied organisms, which are typi- shelly biotas of the Cambrian and younger cally preserved as impressions on sand- Ediacara Biota continued on p. 2 IN THIS ISSUE GSA TODAY February Vol. 8, No. 2 1998 The Ediacara Biota: A Terminal Rock Stars—G. K. Gilbert ............... 16 Neoproterozoic Experiment in the GSAF Update .......................... 18 GSA TODAY (ISSN 1052-5173) is published monthly Evolution of Life ..................... 1 Washington Report .................... 20 by The Geological Society of America, Inc., with offices at 3300 In Memoriam .......................... 2 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box Forests as Carbon Sinks ................ 22 9140, Boulder, CO 80301-9140, U.S.A. Periodicals postage Memorial Preprints ..................... 2 Penrose Conference Reports paid at Boulder, Colorado, and at additional mailing offices. Sarewitz Leaves IEE Post ................ 8 Postmaster: Send address changes to GSA Today, Member- Tectonics of Interiors ................. 23 ship Services, P.O. Box 9140, Boulder, CO 80301-9140. GSA Summer Internships ............... 8 Faults and Subsurface Flow ........... 25 Copyright © 1998, The Geological Society of America, Inc. SAGE Remarks ......................... 9 Rocky Mountain Section Meeting ....... 27 (GSA). All rights reserved. Copyright not claimed on content Call for Nominations—Biggs Award .... 12 Calendar .............................. 32 prepared wholly by U.S. Government employees within the scope of their employment. Permission is granted to individ- Letters ................................ 13 GSA Meetings ......................... 33 uals to photocopy freely all items other than the science arti- Bulletin and Geology Contents .......... 34 cles to further science and education. Individual scientists are GSA on the Web ....................... 14 hereby granted permission, without royalties or further 1998 Division Officers .................. 15 Classifieds ............................. 35 requests, to make unlimited photocopies of the science arti- cles for use in classrooms to further education and science, About People .......................... 15 1998 GeoVentures ..................... 36 and to make up to five copies for distribution to associates in Award Nominations .................... 15 the furtherance of science; permission is granted to make more than five photocopies for other noncommercial, non- profit purposes furthering science and education upon pay- ment of a fee ($0.25 per page-copy) directly to the Copy- right Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA, phone (508) 750-8400; when paying, reference In Memoriam GSA Today, ISSN 1052-5173. Written permission is required from GSA for all other forms of capture, reproduction, Rudolph W. Edmund James G. Osborne, Jr. and/or distribution of any item in this publication by any Cockeysville, Maryland Lander, Wyoming means, including posting on authors’ or organizational Web sites, except that permission is granted to authors to post November 20, 1997 September 20, 1997 the abstracts only of their science articles on their own or their organization’s Web site providing the posting includes Frank A. Exum Cleone M. Rotan this reference: “The full paper was published in the Geologi- Denver, Colorado West Columbia, South Carolina cal Society of America’s newsmagazine, GSA Today, [include August 26, 1997 April 2, 1997 year, month, and page number if known, where article appears or will appear].” GSA provides this and other forums Jacob E. Gair Norman R. Tilford for the presentation of diverse opinions and positions by sci- entists worldwide, regardless of their race, citizenship, gen- Kensington, Maryland College Station, Texas der, religion, or political viewpoint. Opinions presented in January 1, 1998 November 13, 1997 this publication do not reflect official positions of the Society. Robert C. Lafferty SUBSCRIPTIONS for 1998 calendar year: Society Eau Gallie, Florida Members: GSA Today is provided as part of membership dues. Contact Membership Services at (800) 472-1988, December 1997 (303) 447-2020 or [email protected] for member- ship information. Nonmembers & Institutions: Free with paid subscription to both GSA Bulletin and Geology, otherwise $50 for U.S., Canada, and Mexico; $60 else- where. Contact Subscription Services. Single copies may Memorial Preprints be requested from Publication Sales. Also available on an annual CD-ROM, (together with GSA Bulletin, Geology, GSA Data Repository, and an Electronic Retrospective Index to The following memorial preprints are now available, free of charge, by writing journal articles from 1972); $89 to GSA Members, others call GSA Subscription Services for prices and details. Claims: to GSA, P.O. Box 9140, Boulder, CO 80301. For nonreceipt or for damaged copies, members contact Membership Services; all others contact Subscription Ser- Robert E. Bergstrom John “Benny” Joseph DeBenedetti vices. Claims are honored for one year; please allow suffi- Morris W. Leighton with contributions George B. Pichel cient delivery time for overseas copies, up to six months. from Margaret (Carlson) Bergstrom and George Edmund Peter Eastwood Jack A. Simon STAFF: Prepared from contributions from the GSA staff Neil Church and membership. James Robert Butler Executive Director: Donald M. Davidson, Jr. Dorothy Jung Echols Science Editors: Suzanne M. Kay, Department of Daniel A. Textoris Geological Sciences, Cornell University, Ithaca, NY 14853; L. Greer Price Molly F. Miller, Department of Geology, Box 117-B, Vanderbilt Robert J. Cordell Gus H. Goudarzi University, Nashville, TN 37235. Lewis S. Pittman and James Gibbs