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Proceedings of the NATIONAL ACADEMY of SCIENCES Proceedings of the NATIONAL ACADEMY OF SCIENCES Volume 47 - Number 11 November 15, 1961 WOODRING CONFERENCE ON MAJOR BIOLOGIC INNOVATIONS AND THE GEOLOGIC RECORD BY P. E. CLOUD, JR., AND P. H. ABELSON DEPARTMENT OF GEOLOGY, UNIVERSITY OF MINNESOTA, AND GEOPHYSICAL LABORATORY, CARNEGIE INSTITUTION OF WASHINGTON Communicated September 29, 1961 The problem of correlating biochemical and phenotypical evolution was raised by W. P. Woodring6l at the spring meeting of the Academy in 1951. This led to the organization of a highly productive conference on biochemistry, paleoecology, and evolution, held at Shelter Island in June, 1953.62 Early in 1961 several of the participants in that conference decided that it was time for a new multi-disciplinary consideration of major biological innovations in the context of the geologic record, and with emphasis on the nature, manifestations, and timing of events leading to the first Metazoa. P. H. Abelson, W. H. Bradley, P. E. Cloud, Jr., Sterling Hendricks, K. E. Lohman, and W. W. Rubey constituted an organizing committee whose activities were sponsored by the National Academy of Sciences and the Carnegie Institution of Washington, with funds from the National Science Foundation. The conference was named in recognition of its ancestry and in appreciation of Woodring's outstanding contributions to science. The Woodring Conference was held at Big Meadows Lodge, Skyline Drive, Virginia, June 14-16, 1961. It was attended by twenty-three biochemists, biolo- gists, biophysicists, geologists, paleontologists, and geochemists: P. H. Abelson, C. B. Anfinsen, Elso Barghoorn, David Bonner, W. H. Bradley, M. N. Bramlette, Melvin Calvin, P. E. Cloud, Jr., Marcel Florkin, S. W. Fox, R. M. Garrels, S. B. Hendricks, T. C. Hoering, H. D. Holland, M. K. Hubbert, H. L. James, K. E. Lohman, H. A. Lowenstam, N. W. Pirie, D. L. Ray, Roger Stanier, J. R. Vallentyne, and W. P. Woodring. The Paleontologic Record.-The conference began with a review by Cloud of some of the major problems and their current status. What were the great pre-metazoan events? What kind of a fossil record have they left? What might have been the geochemical consequences of events for which we have as yet no record and how might these consequences be identified in the rocks? How did each step reflect and precondition those that preceded and followed it? Given autotrophic life to start with, the advent of photosynthesis stands as the crucial biologic innovation. Com- plexly patterned and laminated limestone structures whose relationship to radio- genically dated intrusives is interpreted as indicating an age greater than 2.7 billion years28,41, 42, 63 closely resemble structures of known algal origin, are associated 1705 Downloaded by guest on October 6, 2021 1706 GEOLOGY: NATIONAL ACADEMY OF SCIENCES CONFERENCE PROC. N. A. S. with sediments that denote deposition in shallow well-aerated water, and evidently carried on metabolic activities that were capable of bringing about precipitation of CaCO3 (presumably by CO2 assimilation). It remains to be unequivocally demon- strated that photosynthesis was already operative at this early time, but im- portant elements of the mechanism were evidently there. As to the origin of the Metazoa, Cloud reported that critical review of reported Precambrian occurrences in all instances had raised doubt either as to their metazoan nature or their Pre- cambrian age save possibly for the Porifera. The most likely record, the diversi- fied Ediacaran fauna of South Australia,'9 54 is at its oldest very late Precambrian29 and may well be Early Cambrian.25 Interpreted at face value, available evidence suggests first appearance of the Metazoa essentially coincidental with the transition from Precambrian to Cambrian about 0.6 billion years ago; then rapid diversifica- tion to fill a range of previously unoccupied ecologic niches.12 Discussion focussed on the validity of the evidence and the adequacy of the record. Micropaleontological studies currently in progress on Precambrian coal and chert from northern Michigan were described by Barghoorn.58 59 These rocks are correlated with others having a radiogenically estimated age of metamorphism of about 1.7 billion years20 and, therefore, are presumed to be more than 1.7 billion years old. Myriads of morphologically distinctive, minute, brown-translucent to black, ovoid and actiniform bodies and meshwork filaments are found in stromato- litic portions of the chert (known as the Gunflint chert). Photomicrographs of these were exhibited and discussed, but their taxonomic position was not agreed upon. A biological organization, however, is supported by geochemical evidence. Re- duced carbon and pyrite are associated with these structures. The carbon was found by Hoering to possess a 5C'3 of about -32 per mil relative to Solenhofen limestone, an isotopic composition common in living matter. The prospect of preserving even minute biologic details in suitable geologically ancient sediments was illustrated by Bradley by means of a Spirogyra filament con- taining a chloroplast which he recently discovered in the 60-million-year-old middle Eocene Green River shale of Wyoming. Vallentyne discussed the possible significance in the geologic record of pyrite (FeS2) spherules44 53 which, in some instances, may replace microorganisms.32 39 He concluded that their biologic affinities were in doubt. Reference was also made to recent Russian and French work on minute sporelike bodies as well as on pre- sumably algal stromatolites from the Precambrian of Russia, Scandinavia, France, and West Africa.2' 22, 30, 36, 37, 45, 52, 56, 57 Stratigraphy and Geochemistry.-Evidence relating to the composition of the early atmosphere was summarized by James and Holland. James emphasized the similarity of even the oldest Precambrian sedimentary deposits to younger rocks and sediments and discussed the characteristics and oxidation states of "iron forma- tion" rocks (see also Eskola,'4 Geijer,'8 James,33' 34 Macgregor40). Holland ad- vanced detailed arguments for a three-stage evolution of the atmosphere based on equilibrium, relations and the composition of volcanic gases. He also reasoned from the evidence of unoxidized and supposedly detrital uraninite in metasediments hav- ing radiogenic ages as young as 1.8 billion years that reducing conditions of his second stage prevailed at least until then.26 27, 50, Hubbert reported analyses by his colleagues of hydrocarbons obtained from F. Downloaded by guest on October 6, 2021 VOL. 47, 1961 GEOLOGY: NATIONAL ACADEMY OF SCIENCES CONFERENCE 1707 M. Swain55 and extracted from Minnesota rocks having radiogenic ages greater than 1.7 billion years. One of these samples was found to contain normal paraffins with a definite excess of odd over even numbers of carbon atoms per molecule in the C25 to C30 range, implying derivation from living matter.6 He recognized the possibility of migration from younger sedimentary rocks, although the hydrocar- bons actually considered appear to be indigenous. The significance of mineral equilibria for the Precambrian record was reviewed by Garrels and Holland. They pointed out that the common oxide minerals- hematite, for example-can be formed in equilibrium at partial pressures of oxygen far below that of the modern atmosphere. The use of minerals as environmental indicators for the Precambrian, however, is handicapped by the fact that one can rarely be sure that minerals from rocks this old are primary. Lowenstam reviewed the significance of isotope ratios for paleoecology and evolution (see also Ault and Kulp,5 Craig"3) and Lohman and Bramlette discussed the possible biologic significance of siliceous organic sediments. It is not under- stood why diatoms, whose opaline tests are abundant and diversified in many late Mesozoic and younger sediments, seem to disappear abruptly downward in the geologic sequence; whereas radiolarian tests of apparently identical composition extend downward throughout the Paleozoic and doubtfully into the Precambrian. The possible biologic significance of Precambrian bedded cherts remains a problem. Organic Synthesis and Biologic Innovation.-The significance of studies on the laboratory synthesis of organic molecules was discussed by Abelson, Calvin, Hendricks, and Fox (see also Abelson,' Calvin,7 8Fox 17 Goldschmidt,2' Grundland,23 Haldane,24 Miller and Urey,43 and Pirie48 49). Abelson reviewed the synthesis of amino acids from inorganic substances as revealed in a number of different mixtures exposed to electric discharge or ultraviolet radiation. Two- and three-carbon amino acids greatly predominate as products. Experiments involving reasonable starting materials have produced no detectable arginine, histidine, isoleucine, leucine, or valine. Moreover, simple carbohydrates and amino acids react chemically and hence could not simultaneously be present in the widely assumed "thick soup." Many of the components of living matter such as fats and porphyrins would be in- soluble in an aqueous environment. Thus both laboratory and environmental con- siderations suggest that first life may have been built from a few components which, once combined, held the capacity for biochemical innovation and synthesis. Calvin also favored the idea of starting with something simple and building up, but Hendricks presented the case for complexity. Hendricks also suggested that too much emphasis might have been placed on the need for an ozone screen to re- duce the destructive effects of ultraviolet radiation as early
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