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del Rey Á, Rasmussen CMØ, Calner M, Wu R, Asael D, Dahl TW. Stable ocean redox during the main phase of the Great Ordovician Biodiversification Event. COMMUNICATIONS EARTH & ENVIRONMENT 2022; 3:220. [PMID: 36186548 PMCID: PMC9510202 DOI: 10.1038/s43247-022-00548-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Accepted: 09/05/2022] [Indexed: 06/16/2023]
Abstract
The Great Ordovician Biodiversification Event (GOBE) represents the greatest increase in marine animal biodiversity ever recorded. What caused this transformation is heavily debated. One hypothesis states that rising atmospheric oxygen levels drove the biodiversification based on the premise that animals require oxygen for their metabolism. Here, we present uranium isotope data from a Middle Ordovician marine carbonate succession that shows the steepest rise in generic richness occurred with global marine redox stability. Ocean oxygenation ensued later and could not have driven the biodiversification. Stable marine anoxic zones prevailed during the maximum increase in biodiversity (Dapingian-early Darriwilian) when the life expectancy of evolving genera greatly increased. Subsequently, unstable ocean redox conditions occurred together with a marine carbon cycle disturbance and a decrease in relative diversification rates. Therefore, we propose that oceanic redox stability was a factor in facilitating the establishment of more resilient ecosystems allowing marine animal life to radiate.
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Affiliation(s)
- Álvaro del Rey
- GLOBE Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark
| | | | - Mikael Calner
- Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden
| | - Rongchang Wu
- Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing, 210008 China
| | - Dan Asael
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511 USA
| | - Tais W. Dahl
- GLOBE Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark
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Bobrovskiy I, Hope JM, Golubkova E, Brocks JJ. Food sources for the Ediacara biota communities. Nat Commun 2020; 11:1261. [PMID: 32152319 PMCID: PMC7062841 DOI: 10.1038/s41467-020-15063-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Accepted: 02/13/2020] [Indexed: 12/21/2022] Open
Abstract
The Ediacara biota represents the first complex macroscopic organisms in the geological record, foreshadowing the radiation of eumetazoan animals in the Cambrian explosion. However, little is known about the contingencies that lead to their emergence, including the possible roles of nutrient availability and the quality of food sources. Here we present information on primary producers in the Ediacaran based on biomarker molecules that were extracted from sediments hosting Ediacaran macrofossils. High relative abundances of algal steranes over bacterial hopanes suggest that the Ediacara biota inhabited nutrient replete environments with an abundance of algal food sources comparable to Phanerozoic ecosystems. Thus, organisms of the Ediacara biota inhabited nutrient-rich environments akin to those that later fuelled the Cambrian explosion.
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Affiliation(s)
- Ilya Bobrovskiy
- Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia.
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
| | - Janet M Hope
- Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia
| | - Elena Golubkova
- Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, Russia
| | - Jochen J Brocks
- Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia.
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Zhang S, Wang X, Wang H, Bjerrum CJ, Hammarlund EU, Haxen ER, Wen H, Ye Y, Canfield DE. Paleoenvironmental proxies and what the Xiamaling Formation tells us about the mid-Proterozoic ocean. GEOBIOLOGY 2019; 17:225-246. [PMID: 30839152 DOI: 10.1111/gbi.12337] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 01/17/2019] [Accepted: 01/29/2019] [Indexed: 06/09/2023]
Abstract
The Mesoproterozoic Era (1,600-1,000 million years ago, Ma) geochemical record is sparse, but, nevertheless, critical in untangling relationships between the evolution of eukaryotic ecosystems and the evolution of Earth-surface chemistry. The ca. 1,400 Ma Xiamaling Formation has experienced only very low-grade thermal maturity and has emerged as a promising geochemical archive informing on the interplay between climate, ecosystem organization, and the chemistry of the atmosphere and oceans. Indeed, the geochemical record of portions of the Xiamaling Formation has been used to place minimum constraints on concentrations of atmospheric oxygen as well as possible influences of climate and climate change on water chemistry and sedimentation dynamics. A recent study has argued, however, that some portions of the Xiamaling Formation deposited in a highly restricted environment with only limited value as a geochemical archive. In this contribution, we fully explore these arguments as well as the underlying assumptions surrounding the use of many proxies used for paleo-environmental reconstructions. In doing so, we pay particular attention to deep-water oxygen-minimum zone environments and show that these generate unique geochemical signals that have been underappreciated. These signals, however, are compatible with the geochemical record of those parts of the Xiamaling Formation interpreted as most restricted. Overall, we conclude that the Xiamaling Formation was most likely open to the global ocean throughout its depositional history. More broadly, we show that proper paleo-environmental reconstructions require an understanding of the biogeochemical signals generated in all relevant modern analogue depositional environments. We also evaluate new data on the δ98 Mo of Xiamaling Formation shales, revealing possible unknown pathways of molybdenum sequestration into sediments and concluding, finally, that seawater at that time likely had a δ98 Mo value of about 1.1‰.
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Affiliation(s)
- Shuichang Zhang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing, China
| | - Xiaomei Wang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing, China
| | - Huajian Wang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing, China
| | - Christian J Bjerrum
- Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen K, Denmark
| | - Emma U Hammarlund
- Nordcee, Institute of Biology, University of Southern Denmark, Odense M, Denmark
- Translational Cancer Research, Lund University, Lund, Sweden
| | - Emma R Haxen
- Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen K, Denmark
| | - Hanjie Wen
- State Key Laboratory of Ore Deposit Geochemistry (SKLODG), Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
| | - Yuntao Ye
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing, China
| | - Donald E Canfield
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing, China
- Nordcee, Institute of Biology, University of Southern Denmark, Odense M, Denmark
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Canfield DE, Zhang S, Frank AB, Wang X, Wang H, Su J, Ye Y, Frei R. Highly fractionated chromium isotopes in Mesoproterozoic-aged shales and atmospheric oxygen. Nat Commun 2018; 9:2871. [PMID: 30030422 PMCID: PMC6054612 DOI: 10.1038/s41467-018-05263-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 06/15/2018] [Indexed: 11/28/2022] Open
Abstract
The history of atmospheric oxygen through the Mesoproterozoic Era is uncertain, but may have played a role in the timing of major evolutionary developments among eukaryotes. Previous work using chromium isotopes in sedimentary rocks has suggested that Mesoproterozoic Era atmospheric oxygen levels were too low in concentration (<0.1% of present-day levels (PAL)) for the expansion of eukaryotic algae and for the evolution of crown-group animals that occurred later in the Neoproterozoic Era. In contrast, our new results on chromium isotopes from Mesoproterozoic-aged sedimentary rocks from the Shennongjia Group from South China is consistent with atmospheric oxygen concentrations of >1% PAL and thus the possibility that a permissive environment existed long before the expansion of various eukaryotic clades. There is a long standing debate whether low atmospheric oxygen levels during the Mesoproterozoic Era hindered the evolution of crown-group animals. Here, the authors show with shale-hosted chromium isotopes that sufficient atmospheric oxygen for crown-group animals likely predated their evolution by over 400 million years.
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Affiliation(s)
- Donald E Canfield
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China. .,Nordcee, Institute of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
| | - Shuichang Zhang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China
| | - Anja B Frank
- Department of Geoscience and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350, Copenhagen K, Denmark
| | - Xiaomei Wang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China
| | - Huajian Wang
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China
| | - Jin Su
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China
| | - Yuntao Ye
- Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, 100083, Beijing, China
| | - Robert Frei
- Department of Geoscience and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350, Copenhagen K, Denmark
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Abstract
Long thought to be inaccessible to empirical inquiry, Earth's early biosphere has in recent decades become a central focus of evolutionary and paleobiological research. Knowledge of Precambrian ecosystems comes from three principal sources. The conventional fossil record consists of the compressed and permineralized remains of cyanobacteria, protists and other microorganisms (e.g., Knoll, 1996), complemented by stromatolites and oncolites, the accretionary trace fossils of microbial mat communities (Walter, 1976). Independent inferences about early evolution can be drawn from molecular phylogenies (Pace, 1997). The third principal source of information comprises biogeochemical signatures encrypted in the chemistry of ancient sedimentary rocks. Biomarker molecular fossils and distinctive isotopic compositions record the metabolic activities of organisms not necessarily preserved morphologically (Summons and Walter, 1990). In this paper, we review the inferences about early life and environments that can be drawn from the isotopic records of carbon and sulfur.
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Biologically induced initiation of Neoproterozoic snowball-Earth events. Proc Natl Acad Sci U S A 2011; 108:15091-6. [PMID: 21825156 DOI: 10.1073/pnas.1016361108] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The glaciations of the Neoproterozoic Era (1,000 to 542 MyBP) were preceded by dramatically light C isotopic excursions preserved in preglacial deposits. Standard explanations of these excursions involve remineralization of isotopically light organic matter and imply strong enhancement of atmospheric CO(2) greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We examine a scenario in which the isotopic signal, as well as the global glaciation, result from enhanced export of organic matter from the upper ocean into anoxic subsurface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate- or iron-reducing bacteria. In both cases, this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric CO(2) concentration, possibly plunging Earth into an ice age. This scenario predicts enhanced deposition of calcium carbonate, the formation of siderite, and an increase in ocean pH, all of which are consistent with recent observations. Late Neoproterozoic diversification of marine eukaryotes may have facilitated the episodic enhancement of export of organic matter from the upper ocean, by causing a greater proportion of organic matter to be partitioned as particulate aggregates that can sink more efficiently, via increased cell size, biomineralization or increased CN of eukaryotic phytoplankton. The scenario explains isotopic excursions that are correlated or uncorrelated with snowball initiation, and suggests that increasing atmospheric oxygen concentrations and a progressive oxygenation of the subsurface ocean helped to prevent snowball glaciation on the Phanerozoic Earth.
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Abstract
Recent data imply that for much of the Proterozoic Eon (2500 to 543 million years ago), Earth's oceans were moderately oxic at the surface and sulfidic at depth. Under these conditions, biologically important trace metals would have been scarce in most marine environments, potentially restricting the nitrogen cycle, affecting primary productivity, and limiting the ecological distribution of eukaryotic algae. Oceanic redox conditions and their bioinorganic consequences may thus help to explain observed patterns of Proterozoic evolution.
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Affiliation(s)
- A D Anbar
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA.
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Chandler MA, Sohl LE. Climate forcings and the initiation of low-latitude ice sheets during the Neoproterozoic Varanger glacial interval. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jd900221] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Canfield DE, Habicht KS, Thamdrup B. The Archean sulfur cycle and the early history of atmospheric oxygen. Science 2000; 288:658-61. [PMID: 10784446 DOI: 10.1126/science.288.5466.658] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The isotope record of sedimentary sulfides can help resolve the history of oxygen accumulation into the atmosphere. We measured sulfur isotopic fractionation during microbial sulfate reduction up to 88 degrees C and show how sulfate reduction rate influences the preservation of biological fractionations in sediments. The sedimentary sulfur isotope record suggests low concentrations of seawater sulfate and atmospheric oxygen in the early Archean (3.4 to 2.8 billion years ago). The accumulation of oxygen and sulfate began later, in the early Proterozoic (2.5 to 0.54 billion years ago).
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Affiliation(s)
- D E Canfield
- Danish Center for Earth System Science (DCESS) and Institute of Biology, Odense University, SDU, Campusvej 55, 5230 Odense M, Denmark.
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Abstract
Negative carbon isotope anomalies in carbonate rocks bracketing Neoproterozoic glacial deposits in Namibia, combined with estimates of thermal subsidence history, suggest that biological productivity in the surface ocean collapsed for millions of years. This collapse can be explained by a global glaciation (that is, a snowball Earth), which ended abruptly when subaerial volcanic outgassing raised atmospheric carbon dioxide to about 350 times the modern level. The rapid termination would have resulted in a warming of the snowball Earth to extreme greenhouse conditions. The transfer of atmospheric carbon dioxide to the ocean would result in the rapid precipitation of calcium carbonate in warm surface waters, producing the cap carbonate rocks observed globally.
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Affiliation(s)
- PF Hoffman
- P. F. Hoffman, G. P. Halverson, D. P. Schrag, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA. A. J. Kaufman, Department of Geology, University of Maryland, College Park, MD 20742, USA
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Kaufman AJ, Knoll AH, Narbonne GM. Isotopes, ice ages, and terminal Proterozoic earth history. Proc Natl Acad Sci U S A 1997; 94:6600-5. [PMID: 11038552 PMCID: PMC21204 DOI: 10.1073/pnas.94.13.6600] [Citation(s) in RCA: 364] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Detailed correlations of ancient glacial deposits, based on temporal records of carbon and strontium isotopes in seawater, indicate four (and perhaps five) discrete ice ages in the terminal Proterozoic Eon. The close and repeated stratigraphic relationship between C-isotopic excursions and glaciogenic rocks suggests that unusually high rates of organic carbon burial facilitated glaciation by reducing atmospheric greenhouse capacity. The emerging framework of time and environmental change contributes to the improved resolution of stratigraphic and evolutionary pattern in the early fossil record of animals.
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Affiliation(s)
- A J Kaufman
- Botanical Museum, Harvard University, Cambridge, MA 02138, USA
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Canfield DE, Teske A. Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies. Nature 1996; 382:127-32. [PMID: 11536736 DOI: 10.1038/382127a0] [Citation(s) in RCA: 168] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The evolution of non-photosynthetic sulphide-oxidizing bacteria was contemporaneous with a large shift in the isotopic composition of biogenic sedimentary sulphides between 0.64 and 1.05 billion years ago. Both events were probably driven by a rise in atmospheric oxygen concentrations to greater than 5-18% of present levels--a change that may also have triggered the evolution of animals.
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Affiliation(s)
- D E Canfield
- Max Planck Institute for Marine Microbiology, Bremen, Germany
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Abstract
Truth, goes an old proverb, is the daughter of time. Fifty years ago, G. G. Simpson (1944) brought paleontology into the Neodarwinian fold, arguing that evolutionary tempo can be documented in the geological record and used to inform debate about evolutionary mode. Today, increasingly sophisticated paleontological investigations of rate—be it diversification, extinction, migration, morphological change, or divergence in macromolecular sequence—require calibration of the geological time scale with a precision far greater than Simpson could have anticipated. Expanding research on the relationships between environmental history and evolution also requires unprecedented resolution in correlation and geochronometry.
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Affiliation(s)
- A H Knoll
- Botanical Museum, Harvard University, Cambridge, Massachusetts 02138, USA
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Logan GA, Hayes JM, Hieshima GB, Summons RE. Terminal Proterozoic reorganization of biogeochemical cycles. Nature 1995; 376:53-6. [PMID: 11536694 DOI: 10.1038/376053a0] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Proterozoic aeon (2,500-540 million years ago) saw episodic increases in atmospheric oxygen content, the evolution of multicellular life and, at its close, an enormous radiation of animal diversity. These profound biological and environmental changes must have been linked, but the underlying mechanisms have been obscure. Here we show that hydrocarbons extracted from Proterozoic sediments in several locations worldwide are derived mainly from bacteria or other heterotrophs rather than from photosynthetic organisms. Biodegradation of algal products in sedimenting matter was therefore unusually complete, indicating that organic material was extensively reworked as it sank slowly through the water column. We propose that a significant proportion of this reworking will have been mediated by sulphate-reducing bacteria, forming sulphide. The production of sulphide and consumption of oxygen near the ocean surface will have inhibited transport of O2 to the deep ocean. We find that preservation of algal-lipid skeletons improves at the beginning of the Cambrian, reflecting the increase in transport by rapidly sinking faecal pellets. We suggest that this rapid removal of organic matter will have increased oxygenation of surface waters, leading to a descent of the O2-sulphide interface to the sea floor and to marked changes in the marine environment, ultimately contributing to the Cambrian radiation.
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Affiliation(s)
- G A Logan
- Departments of Geological Sciences and of Chemistry, Indiana University, Bloomington 47405-1403, USA
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Kaufman AJ, Hayes JM, Knoll AH, Germs GJ. Isotopic compositions of carbonates and organic carbon from upper Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism. PRECAMBRIAN RESEARCH 1991; 49:301-327. [PMID: 11538647 DOI: 10.1016/0301-9268(91)90039-d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The carbon isotope geochemistry of carbonates and organic carbon in the late Proterozoic Damara Supergroup of Namibia, including the Nama, Witvlei, and Gariep groups on the Kalahari Craton and the Mulden and Otavi groups on the Congo Craton, has been investigated as an extension of previous studies of secular variations in the isotopic composition of late Proterozoic seawater. Subsamples of microspar and dolomicrospar were determined, through petrographic and cathodoluminescence examination, to represent the "least-altered" portions of the rock. Carbon-isotopic abundances in these phases are nearly equal to those in total carbonate, suggesting that 13C abundances of late Proterozoic fine-grained carbonates have not been significantly altered by meteoric diagenesis, although 18O abundances often differ significantly. Reduced and variable carbon-isotopic differences between carbonates and organic carbon in these sediments indicate that isotopic compositions of organic carbon have been altered significantly by thermal and deformational processes, likely associated with the Pan-African Orogeny. Distinctive stratigraphic patterns of secular variation, similar to those noted in other, widely separated late Proterozoic basins, are found in carbon-isotopic compositions of carbonates from the Nama and Otavi groups. For example, in Nama Group carbonates delta 13C values rise dramatically from -4 to +5% within a short stratigraphic interval. This excursion suggests correlation with similar excursions noted in Ediacaran-aged successions of Siberia, India, and China. Enrichment of 13C (delta 13C> +5%) in Otavi Group carbonates reflects those in Upper Riphean successions of the Akademikerbreen Group, Svalbard, its correlatives in East Greenland, and the Shaler Group, northwest Canada. The widespread distribution of successions with comparable isotopic signatures supports hypotheses that variations in delta 13C reflect global changes in the isotopic composition of late Proterozoic seawater. Within the Damara basin, carbon-isotopic compositions of carbonates provide a potentially useful tool for the correlation of units between the Kalahari and Congo cratons. Carbonates depleted in 13C were deposited during and immediately following three separate glacial episodes in Namibia. The correspondence between ice ages and negative delta 13C excursions may reflect the effects of lowered sea levels; enhanced circulation of deep, cold, O2-rich seawater; and/or the upwelling of 13C-depleted deep water. Iron-formation is additionally associated with one of the glacial horizons, the Chuos tillite. Carbon-13 enriched isotopic abundances in immediately pre-glacial carbonates suggest that oceanographic conditions favored high rates of organic burial. It is likely that marine waters were stratified, with deep waters anoxic. A prolonged period of ocean stratification would permit the build-up of ferrous iron, probably from hydrothermal sources. At the onset of glaciation, upwelling would have brought 13C-depleted and iron-rich deep water onto shallow shelves where contact with cold, oxygenated surface waters led to the precipitation of ferric iron.
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Affiliation(s)
- A J Kaufman
- Department of Geology, Indiana University, Bloomington 47405-5101, USA
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