The Neoproterozoic Cyanobacteria Have Not Changed Many Large Gaps We Have in Our Morphologically in Over 3 Billion Years

Total Page:16

File Type:pdf, Size:1020Kb

The Neoproterozoic Cyanobacteria Have Not Changed Many Large Gaps We Have in Our Morphologically in Over 3 Billion Years Current Biology Magazine cyanobacteria today? Certainly, it Across these geological timescales, would be diffi cult to assume that it is important to be frank about the The Neoproterozoic cyanobacteria have not changed many large gaps we have in our morphologically in over 3 billion years. understanding of the evolutionary Nicholas J. Butterfi eld Although there are many lines of succession of life. Truly, it is remarkable evidence suggesting that life arose how much we have already been able The Neoproterozoic era was arguably during the Archean, it is important to to piece together through varying fi elds the most revolutionary in Earth history. highlight the uncertainty surrounding spanning biology, paleontology, and Extending from 1000 to 541 million Archean microfossils as evidence of geosciences. The diffi culty in studying years ago, it stands at the intersection early life. these ancient questions should not of the two great tracts of evolutionary Other lines of evidence have stemmed deter us from studying them, but rather time: on the one side, some three from molecular fossils — the presence inspire us to continually fi nd alternative billion years of pervasively microbial and identifi cation of complex organic ways of studying them in order to test ‘Precambrian’ life, and on the other biological molecules (i.e., biomarkers) in prior assumptions about the robustness the modern ‘Phanerozoic’ biosphere sediments, used to date the existence of of previous hypotheses. If anything, with its extraordinary diversity of large certain organisms. Biomarkers make the advances in our understanding of early multicellular organisms. The disturbance assumption that molecules could only life will be interesting in light of newly doesn’t stop here, however: over this have been produced by certain lineages. developed techniques and the growing same stretch of time the planet itself was Ideally, biomarkers would provide the abundance of sequence data to begin in the throes of change. Tectonically, chemical fi ngerprints necessary to testing assumptions we have had with it saw major super-continental identify the microbes living in ancient us for decades. reconfi gurations, climatically its deepest sediments. This assumption has been ever glacial freeze, and geochemically challenged with the gradual acceptance some of the most anomalous of the fact that lateral gene transfer is FURTHER READING perturbations on record. What lies behind nearly ubiquitous across all bacteria. this dramatic convergence of biological Canfi eld, D.E. (2014). Oxygen: A Four Billion Year Correspondingly, some of the most History (Princeton: Princeton University Press). and geological phenomena, and how important cyanobacterial biomarkers Canfi eld, D.E., and Teske, A. (1996). Late exactly did it give rise to the curiously (i.e., 2-methylhopanes) have been Proterozoic rise in atmospheric oxygen complex world that we now inhabit? concentration inferred from phylogenetic and shown to be present in other bacterial sulphur-isotope studies. Nature 382, 127–132. Like all historical reconstructions, phyla. This example highlights how our Dalton, R. (2002). Microfossils: Squaring up over any useful study of the Neoproterozoic ancient life. Nature 417, 782–784. incomplete understanding of extant life Des Marais, D.J. (2000). When did photosynthesis requires a chronological framework can easily alter our interpretations of emerge on earth? Science 289, 1703–1705. to keep things in order (Figure 1). ancient life. Johnston, D.T., Wolfe-Simon, F., Pearson, A., and To a fi rst approximation, the fi rst Knoll, A.H. (2009). Anoxygenic photosynthesis It is impossible to get away from modulated Proterozoic oxygen and sustained half of the era — the Tonian — uncertainty when examining the Earth’s middle age. Proc. Natl. Acad. Sci. USA appears to represent Proterozoic 106, 16925–16929. evidence for early life. This is just the Johnson, J.E., Webb, S.M., Thomas, K., Ono, business as usual, a continuation nature of the subject matter. With this in S., Kirschvink, J.L., and Fischer, W.W. (2013). of the Mesoproterozoic status quo. mind, it becomes even more important Manganese-oxidizing photosynthesis before the Evidence from microfossils (Figure rise of cyanobacteria. Proc. Natl. Acad. Sci. USA to understand the challenges and 110, 11238–11243. 2A,F,G), chemical fossils (primarily nuances in interpreting the evidence Mora, C., Tittensor, D.P., Adl, S., Simpson, A.G.B., lipid biomarker molecules) and used in generating further hypotheses and Worm, B. (2011). How many species are sedimentology (stromatolites and other there on Earth and in the ocean? PLoS Biol. 9, on early life. e1001127. microbial mat fabrics) point to on-going Novacek, M.J. (2001). The Biodiversity Crisis: Losing monopolization of marine productivity What Counts (New York: The New Press). Conclusion Planavsky, N.J., Reinhard, C.T., Wang, X., Thomson, by cyanobacteria, while geochemical Phototrophy has sustained life on D., McGoldrick, P., Rainbird, R.H., Johnson, T., proxies document extensively stratifi ed Earth, possibly since the dawn of life. Fischer, W.W., and Lyons, T.W. (2014). Low Mid- oceans with free oxygen limited largely Proterozoic atmospheric oxygen levels and the Archean ecosystems were most likely delayed rise of animals. Science 346, 635–638. to its sun-lit surface layers. Tonian-age sustained by anoxygenic phototrophic Rashby, S.E., Sessions, A.L., Summons, R.E., eukaryotes are recognizable in the form organisms which may have grown in and Newman, D.K. (2007). Biosynthesis of sterane biomarkers and protistan- of 2-methylbacteriohopanepolyols by an stromatolites much like modern day anoxygenic phototroph. Proc. Natl. Acad. Sci. grade microfossils (Figure 2B–D,H,I), microbial mats. With the innovation of USA 104, 15099–15104. but show little inclination to diversify Shih, P.M., and Matzke, N.J. (2013). Primary the oxygen-evolving complex, oxygenic endosymbiosis events date to the later or expand their decidedly marginalized photosynthesis provided the biological Proterozoic with cross-calibrated phylogenetic Mesoproterozoic footprint. There is catalyst to accumulate oxygen in dating of duplicated ATPase proteins. Proc. Natl. no sign of multicellular animals or Acad. Sci. USA 110, 12355–12360. the atmosphere. These metabolic land plants at this stage, and rates of inventions provided profound shifts in evolutionary turnover are fundamentally how once purely abiotic geochemical 1Joint BioEnergy Institute, 5885 Hollis lower than in the subsequent fossil 2 cycles would integrate the evolution St, Emeryville, CA 94608, USA. Physical record. The supercontinent Rodinia Biosciences Division, Lawrence Berkeley of life to ultimately transform into the National Laboratory, One Cyclotron Rd, begins to break up in the middle of the global biogeochemical cycles we Berkeley, CA 94720, USA. Tonian, around 850 million years ago, observe today. E-mail: [email protected] but with little obvious impact to the Current Biology 25, R845–R875, October 5, 2015 ©2015 Elsevier Ltd All rights reserved R859 Current Biology Magazine Bilateria Rodinia Cnidaria Porifera Breakup δ13C Gaskiers Marinoan +5 0 Mesoproterozoic Palaeozoic -5 Sturtian giaciation ? Tonian Cryogenian Ediacaran Cambrian 1000 million years ago 750 635 541 Current Biology Figure 1. The Neoproterozoic. Diagram of the Neoproterozoic Era illustrating the large scale correlation between evolutionary innovation, climate perturbation, and trends in the 13C of marine carbonates (a refl ection of the global carbon cycle). Patterns in the distribution of protistan-grade fossils are depicted below the 13C curve and in- clude pre-Cryogenian ornamented microfossils (orange; typically asymmetrical, moderately large and stratigraphically long-lived), ‘vase-shaped’ microfossils (purple), scale microfossils (green), Ediacaran-age ornamented and ‘embryo’ microfossils (red; typically symmetrical and large, with ‘embryos’ sometimes occurring within the lumen of ornamented forms), Ediacaran macrofossils (grey), and ornamented Cambrian microfossils (dark orange; typically symmetrical and small). Bars above the 13C curve represent molecular clock estimates for the fi rst appearance of major metazoan groups (from Erwin et al. 2011), with white stars marking the fi rst ‘suggestive’ occurrence of corresponding fossils, and red stars indicating fi rst ‘convincing’ occurrence of such fossils. 13C data taken primarily from Halverson et al. (2010) and Lenton et al. (2014), with early Tonian data from Xiao S. et al. (2014) Biostratigraphic and chemostratigraphic constraints on the age of early Neoproterozoic carbonate successions in North China. Precambrian Res. 246, 208–225. Note that there are substantial dif- ferences of opinion over the stratigraphic correlation of much of the data depicted here, particularly with respect to the age-range of Ediacaran microfossils and the relationship between the Gaskiers glaciation and carbon isotope excursions. The boundary between the Tonian and the Cryogenian has yet to be formally defi ned. The dashed line at ~530 million years ago marks the onset of rapid evolutionary change, and regime shift into recognizably Phanerozoic style ecological and evolutionary dynamics, the ‘Cambrian Explosion’, as well as return to the relatively equable 13C expression of the early Tonian. The end of the Neoproterozoic Era (and Proterozoic Eon) is coincident with the beginning of the Palaeozoic Era (and Phanerozoic Eon). system beyond increased variability in ice-sheets repeatedly
Recommended publications
  • Experimental Taphonomy Shows the Feasibility of Fossil Embryos
    Experimental taphonomy shows the feasibility of fossil embryos Elizabeth C. Raff*, Jeffrey T. Villinski*, F. Rudolf Turner*, Philip C. J. Donoghue†, and Rudolf A. Raff*‡ *Department of Biology and Indiana Molecular Biology Institute, Indiana University, Myers Hall 150, 915 East Third Street, Bloomington, IN 47405; and †Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom Communicated by James W. Valentine, University of California, Berkeley, CA, February 23, 2006 (received for review November 9, 2005) The recent discovery of apparent fossils of embryos contempora- external egg envelope within 15–36 days, but no preservation or neous with the earliest animal remains may provide vital insights mineralization of the embryos within was observed (18). into the metazoan radiation. However, although the putative fossil Anyone who works with marine embryos would consider remains are similar to modern marine animal embryos or larvae, preservation for sufficient time for mineralization via phospha- their simple geometric forms also resemble other organic and tization unlikely, given the seeming fragility of such embryos. inorganic structures. The potential for fossilization of animals at Freshly killed marine embryos in normal seawater decompose such developmental stages and the taphonomic processes that within a few hours. We carried out taphonomy experiments might affect preservation before mineralization have not been designed to uncover the impact of the mode of death and examined. Here, we report experimental taphonomy of marine postdeath environment on the preservational potential of ma- embryos and larvae similar in size and inferred cleavage mode to rine embryos and larvae. presumptive fossil embryos.
    [Show full text]
  • Neoproterozoic Glaciations in a Revised Global Palaeogeography from the Breakup of Rodinia to the Assembly of Gondwanaland
    Sedimentary Geology 294 (2013) 219–232 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo Invited review Neoproterozoic glaciations in a revised global palaeogeography from the breakup of Rodinia to the assembly of Gondwanaland Zheng-Xiang Li a,b,⁎, David A.D. Evans b, Galen P. Halverson c,d a ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia b Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA c Earth & Planetary Sciences/GEOTOP, McGill University, 3450 University St., Montreal, Quebec H3A0E8, Canada d Tectonics, Resources and Exploration (TRaX), School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia article info abstract Article history: This review paper presents a set of revised global palaeogeographic maps for the 825–540 Ma interval using Received 6 January 2013 the latest palaeomagnetic data, along with lithological information for Neoproterozoic sedimentary basins. Received in revised form 24 May 2013 These maps form the basis for an examination of the relationships between known glacial deposits, Accepted 28 May 2013 palaeolatitude, positions of continental rifting, relative sea-level changes, and major global tectonic events Available online 5 June 2013 such as supercontinent assembly, breakup and superplume events. This analysis reveals several fundamental ’ Editor: J. Knight palaeogeographic features that will help inform and constrain models for Earth s climatic and geodynamic evolution during the Neoproterozoic. First, glacial deposits at or near sea level appear to extend from high Keywords: latitudes into the deep tropics for all three Neoproterozoic ice ages (Sturtian, Marinoan and Gaskiers), al- Neoproterozoic though the Gaskiers interval remains very poorly constrained in both palaeomagnetic data and global Rodinia lithostratigraphic correlations.
    [Show full text]
  • Integrative and Comparative Biology Integrative and Comparative Biology, Volume 58, Number 4, Pp
    Integrative and Comparative Biology Integrative and Comparative Biology, volume 58, number 4, pp. 605–622 doi:10.1093/icb/icy088 Society for Integrative and Comparative Biology SYMPOSIUM INTRODUCTION The Temporal and Environmental Context of Early Animal Evolution: Considering All the Ingredients of an “Explosion” Downloaded from https://academic.oup.com/icb/article-abstract/58/4/605/5056706 by Stanford Medical Center user on 15 October 2018 Erik A. Sperling1 and Richard G. Stockey Department of Geological Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305, USA From the symposium “From Small and Squishy to Big and Armored: Genomic, Ecological and Paleontological Insights into the Early Evolution of Animals” presented at the annual meeting of the Society for Integrative and Comparative Biology, January 3–7, 2018 at San Francisco, California. 1E-mail: [email protected] Synopsis Animals originated and evolved during a unique time in Earth history—the Neoproterozoic Era. This paper aims to discuss (1) when landmark events in early animal evolution occurred, and (2) the environmental context of these evolutionary milestones, and how such factors may have affected ecosystems and body plans. With respect to timing, molecular clock studies—utilizing a diversity of methodologies—agree that animal multicellularity had arisen by 800 million years ago (Ma) (Tonian period), the bilaterian body plan by 650 Ma (Cryogenian), and divergences between sister phyla occurred 560–540 Ma (late Ediacaran). Most purported Tonian and Cryogenian animal body fossils are unlikely to be correctly identified, but independent support for the presence of pre-Ediacaran animals is recorded by organic geochemical biomarkers produced by demosponges.
    [Show full text]
  • 1 Eric Davidson and Deep Time Douglas H. Erwin Department Of
    Eric Davidson and Deep Time Douglas H. Erwin Department of Paleobiology, MRC-121 National Museum of Natural History Washington, DC 20013-7012 E-mail: [email protected] Abstract Eric Davidson had a deep and abiding interest in the role developmental mechanisms played in the generating evolutionary patterns documented in deep time, from the origin of the euechinoids to the processes responsible for the morphological architectures of major animal clades. Although not an evolutionary biologist, Davidson’s interests long preceded the current excitement over comparative evolutionary developmental biology. Here I discuss three aspects at the intersection between his research and evolutionary patterns in deep time: First, understanding the mechanisms of body plan formation, particularly those associated with the early diversification of major metazoan clades. Second, a critique of early claims about ancestral metazoans based on the discoveries of highly conserved genes across bilaterian animals. Third, Davidson’s own involvement in paleontology through a collaborative study of the fossil embryos from the Ediacaran Doushantuo Formation in south China. Keywords Eric Davidson – Evolution – Gene regulatory networks – Bodyplan – Cambrian Radiation – Echinoderms 1 Introduction Eric Davidson was a developmental biologist, not an evolutionary biologist or paleobiologist. He was driven to understand the mechanisms of gene regulatory control and how they controlled development, but this focus was deeply embedded within concerns about the relationship between development and evolution. Questions about the origin of major metazoan architectures or body plans were central to Eric’s concerns since at least the late 1960s. His 1971 paper with Roy Britten includes a section on “The Evolutionary Growth of the Genome” illustrated with a figure depicting variations in genome size in major animal groups and a metazoan phylogeny (Britten and Davidson 1971).
    [Show full text]
  • 1 Kon-Tiki Experiments Penultimate Version, Forthcoming in Philosophy
    Kon-Tiki Experiments Penultimate Version, forthcoming in Philosophy of Science Aaron Novick Department of Philosophy Purdue University [email protected] Adrian M. Currie Department of Sociology, Philosophy, and Anthropology University of Exeter [email protected] Eden W. McQueen Department of Biological Sciences University of Pittsburgh [email protected] Nathan L. Brouwer Department of Biological Sciences University of Pittsburgh [email protected] Acknowledgments For comments on drafts and presentations, the authors are grateful to Joseph McCaffrey, Raphael Scholl, Nora Boyd, Joshua Eisenthal, three anonymous reviewers for Philosophy of Science, members of a 2016 seminar at the University of Pittsburgh, and an audience at Vrije Universiteit Brussel. AC’s research was funded by a generous grant from the Templeton World Charity Foundation (no. 222637). 1 Kon-Tiki Experiments Abstract We identify a species of experiment—Kon-Tiki experiments—used to demonstrate the com- petence of a cause to produce a certain effect, and we examine their role in the historical sci- ences. We argue Kon-Tiki experiments are used to test middle-range theory, to test assump- tions within historical narratives, and to open new avenues of inquiry. We show how the re- sults of Kon-Tiki experiments are involved in projective (rather than consequentialist) infer- ences, and we argue (against Kyle Stanford) that reliance on projective inferences does not provide historical scientists with any special protection against the problem of unconceived alternatives. 2 1. The Voyage of Kon-Tiki In 1947, Thor Heyerdahl and a small crew set sail from Peru on a balsa raft, hoping to reach Rapa Nui (Easter Island).
    [Show full text]
  • (Silurian) Anoxic Palaeo-Depressions at the Western Margin of the Murzuq Basin (Southwest Libya), Based on Gamma-Ray Spectrometry in Surface Exposures
    GeoArabia, Vol. 11, No. 3, 2006 Gulf PetroLink, Bahrain Identification of early Llandovery (Silurian) anoxic palaeo-depressions at the western margin of the Murzuq Basin (southwest Libya), based on gamma-ray spectrometry in surface exposures Nuri Fello, Sebastian Lüning, Petr Štorch and Jonathan Redfern ABSTRACT Following the melting of the Gondwanan icecap and the resulting postglacial sea- level rise, organic-rich shales were deposited in shelfal palaeo-depressions across North Africa and Arabia during the latest Ordovician to earliest Silurian. The unit is absent on palaeohighs that were flooded only later when the anoxic event had already ended. The regional distribution of the Silurian black shale is now well-known for the subsurface of the central parts of the Murzuq Basin, in Libya, where many exploration wells have been drilled and where the shale represents the main hydrocarbon source rock. On well logs, the Silurian black shale is easily recognisable due to increased uranium concentrations and, therefore, elevated gamma-ray values. The uranium in the shales “precipitated” under oxygen- reduced conditions and generally a linear relationship between uranium and organic content is developed. The distribution of the Silurian organic-rich shales in the outcrop belts surrounding the Murzuq Basin has been long unknown because Saharan surface weathering has commonly destroyed the organic matter and black colour of the shales, making it complicated to identify the previously organic-rich unit in the field. In an attempt to distinguish (previously) organic-rich from organically lean shales at outcrop, seven sections that straddle the Ordovician-Silurian boundary were measured by portable gamma-ray spectrometer along the outcrops of the western margin of the Murzuq Basin.
    [Show full text]
  • A Fundamental Precambrian–Phanerozoic Shift in Earth's Glacial
    Tectonophysics 375 (2003) 353–385 www.elsevier.com/locate/tecto A fundamental Precambrian–Phanerozoic shift in earth’s glacial style? D.A.D. Evans* Department of Geology and Geophysics, Yale University, P.O. Box 208109, 210 Whitney Avenue, New Haven, CT 06520-8109, USA Received 24 May 2002; received in revised form 25 March 2003; accepted 5 June 2003 Abstract It has recently been found that Neoproterozoic glaciogenic sediments were deposited mainly at low paleolatitudes, in marked qualitative contrast to their Pleistocene counterparts. Several competing models vie for explanation of this unusual paleoclimatic record, most notably the high-obliquity hypothesis and varying degrees of the snowball Earth scenario. The present study quantitatively compiles the global distributions of Miocene–Pleistocene glaciogenic deposits and paleomagnetically derived paleolatitudes for Late Devonian–Permian, Ordovician–Silurian, Neoproterozoic, and Paleoproterozoic glaciogenic rocks. Whereas high depositional latitudes dominate all Phanerozoic ice ages, exclusively low paleolatitudes characterize both of the major Precambrian glacial epochs. Transition between these modes occurred within a 100-My interval, precisely coeval with the Neoproterozoic–Cambrian ‘‘explosion’’ of metazoan diversity. Glaciation is much more common since 750 Ma than in the preceding sedimentary record, an observation that cannot be ascribed merely to preservation. These patterns suggest an overall cooling of Earth’s longterm climate, superimposed by developing regulatory feedbacks
    [Show full text]
  • 1. TITLE of CONSTITUENT BODY International Commission on Stratigraphy (ICS) 2. OVERALL OBJECTIVES, and FIT WITHIN IUGS SCIENCE P
    1 INTERNATIONAL UNION OF GEOLOGICAL SCIENCES Chair INTERNATIONAL COMMISSION ON STRATIGRAPHY Chair Prof. Stanley FINNEY, Department of Geological Sciences, California State University at Long Beach, Long Beach, CA 90840, USA TEL: 1-562-985-8637 (office); FAX: 1-562-985-8638; E-mail: [email protected] Vice Chair Prof. Shanchi PENG, Nanjing Institute of Geology & Palaeontology, Chinese Academy of Sciences, 39 East Beijing St., Nanjing 210008, China TEL and FAX: 86-25-8328 2135; E-mail: [email protected] Secretary General Dr. Paul R. BOWN, Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK TEL: 44-0-20-7504-2431 office; FAX 44-0-20-7388-7614; E-mail: [email protected] 1. TITLE OF CONSTITUENT BODY International Commission on Stratigraphy (ICS) Summary and compilation of subcommission reports submitted jointly by: Chair: Prof. Stanley C Finney Department of Geological Sciences, California State University at Long Beach, Long Beach, CA 90840, USA Tel: 1-562-985-8637; Fax: 1-562-985-8638; E-mail: [email protected] Secretary General: Dr. Paul R Bown Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK Tel: +44(0)20-7679-2431; E-mail: [email protected] 2. OVERALL OBJECTIVES, AND FIT WITHIN IUGS SCIENCE POLICY Objectives The International Commission on Stratigraphy (ICS) is a body of expert stratigraphers founded for the purpose of promoting and coordinating long-term international cooperation and establishing standards in stratigraphy. Its principal objectives are: (a) Establishment and publication of a standard global stratigraphic time scale and the preparation and publication of global correlation charts, with explanatory notes.
    [Show full text]
  • Oxygenation History of the Neoproterozoic to Early Phanerozoic and the Rise of Land Plants ∗ Malcolm W
    Earth and Planetary Science Letters 466 (2017) 12–19 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants ∗ Malcolm W. Wallace a, , Ashleigh vS. Hood a,b, Alice Shuster a, Alan Greig a, Noah J. Planavsky b, Christopher P. Reed a,c a School of Earth Sciences, University of Melbourne, Parkville, Vic. 3010, Australia b Department of Geology and Geophysics, Yale University, 201 Whitney Ave., New Haven, CT 06511, USA c Teck Resources Chile Ltda., Avenida Isidora Goyenechea N° 2800, Oficina 802, piso 8, Las Condes, Santiago, Chile a r t i c l e i n f o a b s t r a c t Article history: There has been extensive debate about the history of Earth’s oxygenation and the role that land plant Received 1 December 2016 evolution played in shaping Earth’s ocean–atmosphere system. Here we use the rare earth element Received in revised form 20 February 2017 patterns in marine carbonates to monitor the structure of the marine redox landscape through the Accepted 26 February 2017 rise and diversification of animals and early land plants. In particular, we use the relative abundance of Available online xxxx cerium (Ce ), the only redox-sensitive rare earth element, in well-preserved marine cements and other Editor: M. Frank anom marine precipitates to track seawater oxygen levels. Our results indicate that there was only a moderate Keywords: increase in oceanic oxygenation during the Ediacaran (average Cryogenian Ceanom = 1.1, average Ediacaran ocean oxygenation Ceanom = 0.62), followed by a decrease in oxygen levels during the early Cambrian (average Cryogenian carbonate geochemistry Ceanom = 0.90), with significant ocean anoxia persisting through the early and mid Paleozoic (average Devonian Early Cambrian–Early Devonian Ceanom = 0.84).
    [Show full text]
  • Proterozoic Ocean Chemistry and Evolution: a Bioinorganic Bridge? A
    S CIENCE’ S C OMPASS ● REVIEW REVIEW: GEOCHEMISTRY Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge? A. D. Anbar1* and A. H. Knoll2 contrast, weathering under a moderately oxidiz- Recent data imply that for much of the Proterozoic Eon (2500 to 543 million years ing mid-Proterozoic atmosphere would have 2– ago), Earth’s oceans were moderately oxic at the surface and sulfidic at depth. Under enhanced the delivery of SO4 to the anoxic these conditions, biologically important trace metals would have been scarce in most depths. Assuming biologically productive marine environments, potentially restricting the nitrogen cycle, affecting primary oceans, the result would have been higher H2S productivity, and limiting the ecological distribution of eukaryotic algae. Oceanic concentrations during this period than either redox conditions and their bioinorganic consequences may thus help to explain before or since (8). observed patterns of Proterozoic evolution. Is there any evidence for such a world? Canfield and his colleagues have developed an argument based on the S isotopic compo- n the present-day Earth, O2 is abun- es and forms insoluble Fe-oxyhydroxides, sition of biogenic sedimentary sulfides, 2– dant from the upper atmosphere to thus removing Fe and precluding BIF forma- which reflect SO4 availability and redox the bottoms of ocean basins. When tion. This reading of the stratigraphic record conditions at their time of formation (16–18). O 2– life began, however, O2 was at best a trace made sense because independent geochemi- When the availability of SO4 is strongly 2– Ͻϳ constituent of the surface environment. The cal evidence indicates that the partial pressure limited (SO4 concentration 1 mM, ϳ intervening history of ocean redox has been of atmospheric oxygen (PO2) rose substan- 4% of that in present-day seawater), H2S interpreted in terms of two long-lasting tially about 2400 to 2000 Ma (4–7).
    [Show full text]
  • Experimental Taphonomy Shows the Feasibility of Fossil Embryos
    Experimental taphonomy shows the feasibility of fossil embryos Elizabeth C. Raff*, Jeffrey T. Villinski*, F. Rudolf Turner*, Philip C. J. Donoghue†, and Rudolf A. Raff*‡ *Department of Biology and Indiana Molecular Biology Institute, Indiana University, Myers Hall 150, 915 East Third Street, Bloomington, IN 47405; and †Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom Communicated by James W. Valentine, University of California, Berkeley, CA, February 23, 2006 (received for review November 9, 2005) The recent discovery of apparent fossils of embryos contempora- external egg envelope within 15–36 days, but no preservation or neous with the earliest animal remains may provide vital insights mineralization of the embryos within was observed (18). into the metazoan radiation. However, although the putative fossil Anyone who works with marine embryos would consider remains are similar to modern marine animal embryos or larvae, preservation for sufficient time for mineralization via phospha- their simple geometric forms also resemble other organic and tization unlikely, given the seeming fragility of such embryos. inorganic structures. The potential for fossilization of animals at Freshly killed marine embryos in normal seawater decompose such developmental stages and the taphonomic processes that within a few hours. We carried out taphonomy experiments might affect preservation before mineralization have not been designed to uncover the impact of the mode of death and examined. Here, we report experimental taphonomy of marine postdeath environment on the preservational potential of ma- embryos and larvae similar in size and inferred cleavage mode to rine embryos and larvae. presumptive fossil embryos.
    [Show full text]
  • Francis A. Macdonald
    Francis A. Macdonald Professor of Geology Department of Earth Sciences 2111 Webb Hall University of California at Santa Barbara Santa Barbara, CA 93106 (857) 998-9993 [email protected] Education Ph.D. Earth and Planetary Sciences, Harvard University, Cambridge, MA, 2009. B.S. Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 2001. Experience § Professor of Geology, University of California, Santa Barbara, CA, 2018-present. § Professor of Earth and Planetary Sciences, Harvard University, Cambridge, MA, 2017- 2018. § John L. Loeb Associate Professor of the Natural Sciences, Harvard University, Cambridge, MA, 2014-2017. § Associate Professor, Harvard University, Cambridge, MA, 2013-2014. § Assistant Professor, Harvard University, Cambridge, MA, 2009-2013. § Research Assistant, USGS Astrogeology, Flagstaff, AZ, 2004. § Lab Manager, Paleomagnetics Laboratory, Caltech, Pasadena, CA, 2002-2004. § Field Technician, Aguoron Paleoproterozoic Drilling Project, South Africa, 2002-2003. § Field Technician, Geophysical cruise ship, South Pacific, 2000-2001. § Research Assistant, Caltech, 1999-2000. Awards § Macelwene Medal (American Geophysical Union Early Career Award), 2019. § Reviewer Award, Geology, for consistently prompt, insightful, meticulous, and tactful reviews, 2015. § Donath Medal (Geological Society of America Young Scientist Award), 2014. § Star Family Prize for Excellence in Advising Award, Harvard College, 2012. § Ian Hamilton Golden Brunton Award, for excellence in field mapping, Caltech, 2001. Grants & Fellowships § NSF Frontier Research in Earth Systems: Do arc-continent collisions in the tropics set global climate state? 2019-present § NSF Sedimentary Geology and Paleontology: Collaborative Research: Did the formation of the Great Unconformity trigger oxygenation and the Cambrian explosion? 2018- present. § Inter-Continental Drilling Program (ICDP): Geological Research through Integrated Neoproterozoic Drilling, Ediacaran-Cambrian transition (GRIND-ECT) for scientific drilling in Brazil, Namibia, and South China.
    [Show full text]