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The Exceptional Preservation of Interesting and Informative Biomolecules
- Roger E. Summons
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- Journal:
- The Paleontological Society Papers / Volume 20 / October 2014
- Published online by Cambridge University Press:
- 21 July 2017, pp. 217-236
- Print publication:
- October 2014
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Organic carbon compounds record key aspects of the processes of their formation and mechanisms of preservation and are foci for research into the nature of life on the early Earth and the search for life beyond Earth. Prime in this respect are lipids preserved in sediments and sedimentary rocks that reveal much about the evolutionary trajectory of life on our planet. Lipids, predominantly derived from photoautotrophic microbes, dominate hydrocarbon records in the Precambrian. The rise to prominence of the Metazoa in the late Neoproterozoic, metaphytes in the Paleozoic, and modern plankton in the Mesozoic, can also be seen in the occurrences of distinctive molecular fossils. Organic matter of all types is optimally preserved in environments and sediments where radiation (solar and ionizing) and oxygen are excluded. In the marine realm, anoxic water bodies will often become sulfidic (euxinic) due to the activity of sulfate-reducing bacteria. Phototropic sulfur bacteria thrive in such environments, and the presence of their characteristic carotenoid pigments goes hand-in-hand with the enhanced preservation of all organic matter, driven by the reducing power of sulfide. The deleterious effects of radiation and oxygen on the preservation of organic matter are amply demonstrated by the results of ongoing searches for carbon compounds on the surface of Mars. The production of highly oxidizing substances through radical chemistry operating in the Martian atmosphere has resulted in environmental conditions that virtually assure destruction of much of the organic matter produced in situ or carried there on meteorites and interplanetary dust particles.
19 - Composition of Extractable Organic Matter
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- By Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Harald Strauss, Ruhr-Universität Bochum
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 811-820
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Summary
The data presented in this Chapter summarize the available, relevant, organic geochemical parameters for Proterozoic sediments which have, in the course of this project, been studied for their bitumen content and composition.
In Tables 19.1–19.4, “N/A” (not analyzed) indicates that an analysis was not carried out; and “NM” (not measured) indicates that a value for the parameter indicated was not determined, usually because some factor precluded its measurement. Two numbering systems are used here:
(1) Samples included in the PPRG sample collection which were subjected to initial Rock–Eval screening (Chapter 16) are identified by PPRG Sample Number only. Several of these samples, together with others that were acquired late in the project, were re-analyzed at the Bureau of Mineral Resources (BMR), Canberra, Australia, and are therefore denoted by dual PPRG and BMR Sample Numbers. Data regarding the geographic and geologic origin of PPRG samples are included in Chapter 14.
(2) Samples that were collected and analyzed specifically as part of BMR projects are denoted by BMR Sample Numbers only; information about the orgins of these samples is included in BMR publications and unpublished databases.
10 - Biostratigraphy and Paleobiogeography of the Proterozoic
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- By Hans J. Hofmann, University of Montreal, Stefan Bengtson, Uppsala Universitet, J. M. Hayes, Indiana University, Jere H. Lipps, University of California, J. William Schopf, University of California, Harald Strauss, Ruhr-Universität Bochum, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 487-520
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Summary
Biostratigraphy deals with bodies of rock defined or characterized by their fossil content. Biogeography is concerned with the geographic distribution of organisms. The basic biostratigraphic principles and concepts now in use were developed in the early- to mid-nineteenth century by pioneers such as William Smith (1769–1839), Georges Cuvier (1769–1832), Alcide d'Orbigny (1802–1857), and Albert Oppel (1831–1865) who divided the stratigraphic record into successions of distinct faunal assemblages; the fundamental biostratigraphic unit still in use is the biozone, which usually is named after a dominant or a characteristic species. Fossils were unknown in pre-Cambrian rocks in 1835, when Adam Sedgwick introduced the concept of the Cambrian System; in fact, this interval was subsequently given names that referred to the presumed nonexistent or primitive paleontologic record (Agnotozoic, Archeozoic, Azoic, Eozoic, Protozoic, etc.).
Precambrian paleontology started in the 1850s, with the discovery of remains thought to be organic (for an historical summary, see Section 5.2 and Hofmann 1982, pp. 246–247). Although many of the early reported forms later were shown to be pseudofossils, some were true fossils. The number of accepted fossil occurrences increased slowly over the next 100 years, but only after the Second World War did Proterozoic biotic abundance and diversity become established by discoveries in various parts of the world (see Section 5.2). By the late 1950s, data were sufficient to be put to use in subdividing and correlating sequences locally and regionally, principally in the Soviet Union, giving rise to the subdiscipline of Precambrian biostratigraphy.
6 - Modern Mat-Building Microbial Communities: a Key to the Interpretation of Proterozoic Stromatolitic Communities
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- By Beverly K. Pierson, University of Puget Sound, John Bauld, Bureau of Mineral Resources, Richard W. Castenholz, University of Oregon, Elisa D'Amelio, Ames Research Center, David J. Des Marais, Ames Research Center, Jack D. Farmer, University of California, John P. Grotzinger, Massachusetts Institute of Technology, Bo Barker Jørgensen, University of Aarhus, Douglas C. Nelson, University of California, Anna C. Palmisano, Ivorydale Technical Center, J. William Schopf, University of California, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd, David M. Ward, Montana State University
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 245-342
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Summary
Introduction
Modern microbial mats are structurally coherent macroscopic accumulations of microorganisms. Mats are widely distributed on earth. They are found in a surprisingly large number of diverse environments from the equatorial zones to both polar regions. They vary in size from extensive terrestrial and hypersaline mats that cover areas several square kilometers in extent to minute mats only a few square centimeters in area found in small thermal springs. They vary in thickness from massive accumulations measured in meters, such as those in the Persian Gulf and the Red Sea region, to thin films less than a few millimeters in thickness. In addition to being highly varied in size, modern microbial mats are also very diverse in morphology, community structure, and physiological characteristics. What do such mats have in common? Under what conditions do they form? What is the basis of their diversity? What insight do they provide, if any, to the interpretation of the widespread stromatolites of the Proterozoic?
A Terminology
Microbial mats are accretionary cohesive microbial communities which are often laminated and found growing at the sediment-water (occasionally sediment-air) interface. Most mats stabilize unconsolidated sediment. The mats are comprised of the various microorganisms that accumulate along with their metabolic products. The most conspicuous of these products is usually a copious amount of extracellular polysaccharide which helps hold the cells together to form a cohesive structure.
18 - Procedures for Analysis of Extactable Organic Matter
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- By Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Harald Strauss, Ruhr-Universität Bochum
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 799-810
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Summary
As is discussed in Section 3.1.1, great care must be exercised to avoid contamination of extractable hydrocarbon samples by extraneous bitumens, particularly if the TOC (total organic carbon) content is low or if the amount of sample is small. In this study, sediment cores and outcrop samples were pre-rinsed with CH2C12 and dried to remove external contaminants. Where sample size permitted, external surfaces were removed by cutting with a diamond saw. Samples were then hammered to chips which were subsequently crushed to less than 200 mesh in a ring crusher. Rock powders were stored in clean glass containers. Lids were lined with pre-baked aluminium foil. All items used to handle the samples were scrupulously washed with hot water, and then distilled solvent, between each use.
TOC determination and Rock–Eval pyrolysis analysis were found to be particularly informative screening techniques. Samples with less than 0.2% TOC (i.e., <2mgC/g) were generally considered unsuitable for comprehensive hydrocarbon analysis because of the problems of contamination, although elemental and carbon isotopic analyses of their kerogens were parameters which could be reliably established at this low level of organic carbon. Samples with >0.2% TOC were usually assessed using Rock–Eval pyrolysis and the results interpreted using guidelines discussed by Espitalié et al. 1977. The relative proportions of bitumen (the Rock–Eval S1 peak in kg/tonne) and kerogen (S2 peak in kg/tonne), the pyrolysis temperature Tmax (°C), and the overall appearance of the pyrograms all provided useful information.
3 - Proterozoic Biogeochemistry
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- By J. M. Hayes, Indiana University, David J. Des Marais, Ames Research Center, Ian B. Lambert, Resource Assessment Commission, Australia, Harald Strauss, Ruhr-Universität Bochum, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
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- 04 April 2011
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- 26 June 1992, pp 81-134
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Summary
Biogeochemistry encompasses the study of chemical fossils. It includes and draws on knowledge of the biochemical activities of contemporary organisms in modern sedimentary environments, including their roles in the biogeochemical cycling and isotopic fractionation of important elements such as carbon, oxygen, sulfur, and nitrogen, and their production of taxonomically distinctive organic compounds. This Section deals with the chemical entities preserved in the Proterozoic sedimentary record that may carry information about the biology and evolution of early life.
Chemical fossils can be discerned at the atomic level, in the occurrence of anomalous concentrations of a particular element or an isotope; at a molecular level, in the structure and stereochemistry of hydrocarbons derived from membrane lipids or pigments; and at a macromolecular level by way of the preservation of detailed chemical structures in kerogen and morphologically distinct microfossils. Paleobiochemical information is encoded in the nucleic acids of extant organisms and in their comparative biochemistry; this topic is treated in Chapter 9. Here we examine and discuss the occurrence of isotopic and molecular fossils. A considerable and consistent body of information derived, in part, from techniques developed during exploration for petroleum and minerals is now available. Rapid expansion of this knowledge is presently taking place, particularly with regard to chemical processes in early preservation of organic matter, structures of kerogen, isotopic composition of individual biomarkers, and global secular variations in organic and inorganic isotopic abundances.
16 - Procedures of Whole Rock and Kerogen Analysis
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- By Harald Strauss, Ruhr-Universität Bochum, David J. Des Marais, Ames Research Center, J. M. Hayes, Indiana University, Ian B. Lambert, Resource Assessment Commission, Australia, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 699-708
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Biomarkers: Molecular Fossils
- Roger E. Summons
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- Journal:
- Short Courses in Paleontology / Volume 1 / 1988
- Published online by Cambridge University Press:
- 17 July 2017, pp. 98-113
- Print publication:
- 1988
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Curiosity about the history of life on our planet is a major motivational force for earth scientists. Fossil organic compounds, the components of petroleum and sedimentary organic matter, record aspects of the evolution of the biosphere from as far back as 1.8 billion years and perhaps longer. Elucidation of this record is continually advancing as a result of the concerted interests and efforts of geologists, biologists and chemists. It is also aided by advances in technique and instrumentation. Fascinating new developments and insights abound. In this paper I review some early landmarks and discuss the recent progress made in organic geochemistry, particularly as it applies to biomarker research. The examples of recent work are heavily biased toward my own interests and are not intended to be comprehensive. Because the literature citations are also selective and rely heavily on reviews, readers are advised to seek out the primary literature for accurate detail of specific subjects.