Annual Review of Earth and Planetary Sciences - Volume 41, 2013
Volume 41, 2013
- Preface
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On Escalation
Vol. 41 (2013), pp. 1–19More LessOrganisms have been important agents of selection throughout the history of life. The processes and outcomes of this selection are the subject of this review. Among these, escalation is the most widespread. The primary selective agents are powerful competitors and consumers, which together push many populations toward higher performance in acquiring and defending resources while relegating less competitive species to physiologically marginal settings, where escalation also ensues. The extent to which performance standards rise depends on enabling factors, which control availability of and access to resources. By establishing positive feedbacks between species and enabling factors, effective competitors regulate and enhance resource supply. The pace of escalation toward greater power and reach is dictated by geological factors as well as by growing interdependencies between species and their resources. Evolutionary events on land related to the production of oxygen may have been instrumental in triggering the major episodes of escalation.
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The Meaning of Stromatolites
Vol. 41 (2013), pp. 21–44More LessStromatolites document microbial interactions with sediments and flowing water throughout recorded Earth history and have the potential to illuminate the long-term history of life and environments. Modern stromatolites, however, provide analogs to only a small subset of the structures preserved in Archean and Proterozoic carbonates. Thus, interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian, scale-dependent models of microbial responses to nutrient availability, seawater chemistry, influx of sediment grains, shear, and burial. Models that integrate stromatolite scales, macroscopic organization, and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity. An improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms that contributed to stromatolite growth in early oceans.
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The Anthropocene
Vol. 41 (2013), pp. 45–68More LessThe start of the period of large-scale human effects on this planet (the Anthropocene) is debated. The industrial view holds that most significant impacts have occurred since the early industrial era (∼1850), whereas the early-anthropogenic view recognizes large impacts thousands of years earlier. This review focuses on three indices of global-scale human influence: forest clearance (and related land use), emissions of greenhouse gases (CO2 and CH4), and effects on global temperature. Because reliable, systematic land-use surveys are rare prior to 1950, most reconstructions for early-industrial centuries and prior millennia are hind casts that assume humans have used roughly the same amount of land per person for 7,000 years. But this assumption is incorrect. Historical data and new archeological databases reveal much greater per-capita land use in preindustrial than in recent centuries. This early forest clearance caused much greater preindustrial greenhouse-gas emissions and global temperature changes than those proposed within the industrial paradigm.
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Global Cooling by Grassland Soils of the Geological Past and Near Future
Vol. 41 (2013), pp. 69–86More LessMajor innovations in the evolution of vegetation such as the Devonian origin of forests created new weathering regimes and soils (Alfisols, Histosols) that increased carbon consumption and sequestration and ushered in the Permian-Carboniferous Ice Age. Similarly, global expansion of grasslands and their newly evolved, carbon-rich soils (Mollisols) over the past 40 million years may have induced global cooling and ushered in Pleistocene glaciation. Grassland evolution has been considered a consequence of mountain uplift and tectonic reorganization of ocean currents, but it can also be viewed as a biological force for global change through coevolution of grasses and grazers. Organisms in such coevolutionary trajectories adapt to each other rather than to their environment, and so can be forces for global change. Some past farming practices have aided greenhouse gas release. However, modern grassland agroecosystems are a potential carbon sink already under intensive human management, and carbon farming techniques may be useful in curbing anthropogenic global warming.
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Psychrophiles
Vol. 41 (2013), pp. 87–115More LessPsychrophilic (cold-adapted) microorganisms make a major contribution to Earth's biomass and perform critical roles in global biogeochemical cycles. The vast extent and environmental diversity of Earth's cold biosphere has selected for equally diverse microbial assemblages that can include archaea, bacteria, eucarya, and viruses. Underpinning the important ecological roles of psychrophiles are exquisite mechanisms of physiological adaptation. Evolution has also selected for cold-active traits at the level of molecular adaptation, and enzymes from psychrophiles are characterized by specific structural, functional, and stability properties. These characteristics of enzymes from psychrophiles not only manifest in efficient low-temperature activity, but also result in a flexible protein structure that enables biocatalysis in nonaqueous solvents. In this review, we examine the ecology of Antarctic psychrophiles, physiological adaptation of psychrophiles, and properties of cold-adapted proteins, and we provide a view of how these characteristics inform studies of astrobiology.
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Initiation and Evolution of Plate Tectonics on Earth: Theories and Observations
Vol. 41 (2013), pp. 117–151More LessThe inception of plate tectonics on Earth and its subsequent evolution are discussed on the basis of theoretical considerations and observational constraints. The likelihood of plate tectonics in the past depends on what mechanism is responsible for the relatively constant surface heat flux that is indicated by the likely thermal history of Earth. The continuous operation of plate tectonics throughout Earth's history is possible if, for example, the strength of convective stress in the mantle is affected by the gradual subduction of surface water. Various geological indicators for the emergence of plate tectonics are evaluated from a geodynamical perspective, and they invariably involve certain implicit assumptions about mantle dynamics, which are either demonstrably wrong or yet to be explored. The history of plate tectonics is suggested to be intrinsically connected to the secular evolution of the atmosphere, through sea-level changes caused by ocean-mantle interaction.
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Experimental Dynamos and the Dynamics of Planetary Cores
Vol. 41 (2013), pp. 153–181More LessLaboratory experiments using liquid metals and nonmetallic liquids reveal a rich set of dynamical processes active in Earth's core and in the cores of other terrestrial planets. These processes include thermochemical convection and a variety of instabilities driven by irregularities in rotation, such as precession, libration, and tides. The spectrum of fluid motions in these experiments ranges from turbulence and inertial wave motions at high frequencies to global-scale zonal flows at low frequencies, and they result from the interplay between buoyant forces, rotational effects, melting and solidification, magnetic fields, and the spherical geometry of the core. This review summarizes strengths and limitations of laboratory fluid experiments for modeling core dynamics, identifies the key physical parameters, and highlights recent advances in understanding the complex flows that control the evolution of the core. Special emphasis is given to ongoing efforts to develop self-sustaining fluid dynamos.
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Extracting Earth's Elastic Wave Response from Noise Measurements
Roel Snieder, and Eric LaroseVol. 41 (2013), pp. 183–206More LessRecent research has shown that noise can be turned from a nuisance into a useful seismic source. In seismology and other fields in science and engineering, the estimation of the system response from noise measurements has proven to be a powerful technique. To convey the essence of the method, we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors. We provide an overview of physics research—dating back more than 100 years—showing that random field fluctuations contain information about the system response. This principle has found extensive use in surface-wave seismology but can also be applied to the estimation of body waves. Because noise provides continuous illumination of the subsurface, the extracted response is ideally suited for time-lapse monitoring. We present examples of time-lapse monitoring as applied to the softening of soil after the 2011 Tohoku-oki earthquake, the detection of a precursor to a landslide, and temporal changes in the lunar soil.
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Miller-Urey and Beyond: What Have We Learned About Prebiotic Organic Synthesis Reactions in the Past 60 Years?
Vol. 41 (2013), pp. 207–229More LessThe synthesis of amino acids in the Miller-Urey spark-discharge experiments in the early 1950s inspired a strong interest in experimental studies of prebiotic organic chemistry that continues today. Over the years, many of the basic building blocks of life as we know it have been synthesized in the laboratory from simple ingredients, including amino acids, sugars, nucleobases, and membrane-forming lipids. Questions remain, however, concerning whether the conditions that allow synthesis of these compounds in the laboratory accurately simulate those that might have been present on the early Earth, and a closer convergence between plausible prebiotic conditions and laboratory simulations remains a challenge for experimentalists.
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The Science of Geoengineering
Vol. 41 (2013), pp. 231–256More LessCarbon dioxide emissions from the burning of coal, oil, and gas are increasing atmospheric carbon dioxide concentrations. These increased concentrations cause additional energy to be retained in Earth's climate system, thus increasing Earth's temperature. Various methods have been proposed to prevent this temperature increase either by reflecting to space sunlight that would otherwise warm Earth or by removing carbon dioxide from the atmosphere. Such intentional alteration of planetary-scale processes has been termed geoengineering. The first category of geoengineering method, solar geoengineering (also known as solar radiation management, or SRM), raises novel global-scale governance and environmental issues. Some SRM approaches are thought to be low in cost, so the scale of SRM deployment will likely depend primarily on considerations of risk. The second category of geoengineering method, carbon dioxide removal (CDR), raises issues related primarily to scale, cost, effectiveness, and local environmental consequences. The scale of CDR deployment will likely depend primarily on cost.
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Shock Events in the Solar System: The Message from Minerals in Terrestrial Planets and Asteroids
Vol. 41 (2013), pp. 257–285More LessImpacts are central to the origin and evolution of planets of the Solar System. The shapes of craters, which can reach up to 1,000 km in diameter on the Moon, provide critical information on the large-scale dynamics of the impact and related shock. Minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale, typically from a few micrometers to a few millimeters. Local flaws in rocks, such as voids and mineral interfaces, are the preferential sites for the formation of high-pressure melts and minerals. Calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration, transient pressure, and prevailing temperature conditions of shock events. Case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration. Many of the high-pressure mineral phases of olivine, pyroxenes, feldspars, silica, phosphates, titanium oxide, and carbon have been discovered in these heavily shocked rocks and provide unique opportunities to study the high-pressure minerals that exist in the deep Earth.
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The Fossil Record of Plant-Insect Dynamics
Vol. 41 (2013), pp. 287–311More LessProgress toward understanding the dynamics of ancient plant-insect associations has addressed major patterns in the ecology and evolution of herbivory and pollination. This advancement involves development of more analytical ways of describing plant-insect associational patterns in time and space and an assessment of the role that the environment and internal biological processes have in their control. Current issues include the deep origins of terrestrial herbivory, the spread of herbivory across late Paleozoic landscapes, recoveries from sudden major crises, reaction to and accommodation of protracted environmental perturbations, and the nature of herbivory and pollination before the appearance of angiosperms during the mid-Mesozoic. These and other exploratory research themes provide a more complete account of a great nexus of ecological activity that has been wedged between the two most diverse organismic groups on land for the past 410 million years.
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The Betic-Rif Arc and Its Orogenic Hinterland: A Review
Vol. 41 (2013), pp. 313–357More LessThe Betic-Rif arc is one of the smallest and tightest orogenic arcs on Earth, and together with its extensional hinterland, the Alborán Domain, it formed between two colliding continents. The region provides examples of a range of tectonic processes that are not predictable from the rules of rigid-plate tectonics. The Alborán Domain reveals two stages of subduction and accretion, with different thermal histories and mechanisms of exhumation. The external Betic-Rif thrust belt illustrates four processes that create an arcuate orogen and a strongly divergent pattern of slip vectors: (a) the interaction between the westward moving Alborán Domain and the converging African and Iberian margins, (b) divergence in relative motion due to extension within the Alborán Domain, (c) slip partitioning onto strike-slip faults within the arc, and (d) vertical-axis rotations resulting from oblique convergence on the limbs of the arc.
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Assessing the Use of Archaeal Lipids as Marine Environmental Proxies
Vol. 41 (2013), pp. 359–384More LessArchaea are abundant in marine and terrestrial aquatic environments, sediments, and soils. They inhabit at least an 85°C temperature range from the polar ocean to hydrothermal springs. Many Archaea produce membrane lipids called glycerol dialkyl glycerol tetraethers (GDGTs). Experiments on pure and enrichment cultures as well as an empirical correlation for marine sediments (the TEX86 index) together show positive relationships between temperature and the number of cyclopentane or cyclohexane rings in GDGTs. The resulting TEX86 paleotemperature proxy has been applied across a wide range of geologic history and depositional settings. The exact relationship between TEX86 and temperature, however, remains poorly understood. Environmental systems and cultures have different temperature dependencies, and the ecological niche(s) of aquatic Archaea are still a subject of active investigation. Here we review some of the remaining questions about GDGT paleotemperature proxies. Better answers to these challenging problems will help refine future paleoceanographic applications.
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Heat Flow, Heat Generation, and the Thermal State of the Lithosphere
Vol. 41 (2013), pp. 385–410More LessThe thermal structure of the lithosphere controls many properties and processes of Earth's crust. The total ∼47-TW heat loss of Earth is key to understanding and modeling this thermal structure, as is partitioning the various sources of that heat into heat entering the base of the lithosphere, heat generated within the lithosphere by radioactive decay (primarily within the continental crust), and secular cooling of the mantle lithosphere (primarily in oceanic lithosphere). A set of framework geotherms for the continental lithosphere explains deep crustal melting in high heat flow regions, metamorphic pressure-temperature (P-T) space in the crust, partial melting at the base of the lithosphere to produce an S-wave low-velocity zone in Phanerozoic and younger terranes, and the P-T fields inferred from mantle xenoliths. Important perturbations to a standard thermal state are produced by orogenic overprints, transient thermal regimes, and exhumation.
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The Isotopic Anatomies of Molecules and Minerals
Vol. 41 (2013), pp. 411–441More LessMost natural compounds are composed of diverse isotopologues that differ in the number and/or symmetrically unique atomic locations of isotopic substitutions. Little of this isotopic diversity is observed by conventional methods of stable isotope geochemistry, which generally measure concentrations of rare isotopes without constraining differences in isotopic composition between different atomic sites or nonrandom probabilities of multiple isotopic substitutions in the same molecule. Recent advances in analytical instrumentation and methodology have created a set of geochemical tools—geothermometers, biosynthetic signatures, forensic fingerprints—based on these position-specific isotope effects and multiply substituted isotopologues. This progress suggests we are entering a period in which many new geochemical tools of this type will be created. This review describes the principles, background, analytical methods, existing applied tools, and likely future progress of this emerging field.
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The Behavior of the Lithosphere on Seismic to Geologic Timescales
A.B. Watts, S.J. Zhong, and J. HunterVol. 41 (2013), pp. 443–468More LessThe strength of the lithosphere and how it responds to loading and unloading are fundamental problems with wide implications. Flexure studies suggest that the elastic thickness, a proxy for the strength of the lithosphere, increases with plate age but decreases with load age. The elastic thickness is significantly less than the seismic thickness of the lithosphere, as indicated by the depth to the low-velocity zone, suggesting that the lithosphere is a strong structure at short seismic timescales and a weak one at long timescales. The mechanism controlling this weakening is not known, but it probably involves some form of load-induced stress relaxation. Despite weakening, the lithosphere is capable of retaining its strength and supporting loads such as volcanoes and sediments for long periods of geological time. Lithosphere relaxation should be included in geodynamical models, especially as it has impacts on stratigraphy, sea-level change, and dynamic topography.
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The Formation and Dynamics of Super-Earth Planets
Vol. 41 (2013), pp. 469–495More LessSuper-Earths, objects slightly larger than Earth and slightly smaller than Uranus, have found a special place in exoplanetary science. As a new class of planetary bodies, these objects have challenged models of planet formation at both ends of the spectrum and have triggered a great deal of research on the composition and interior dynamics of rocky planets in connection to their masses and radii. Being relatively easier to detect than an Earth-sized planet at 1 AU around a G star, super-Earths have become the focus of worldwide observational campaigns to search for habitable planets. With a range of masses that allows these objects to retain moderate atmospheres and perhaps even plate tectonics, super-Earths may be habitable if they maintain long-term orbits in the habitable zones of their host stars. Given that in the past two years a few such potentially habitable super-Earths have in fact been discovered, it is necessary to develop a deep understanding of the formation and dynamical evolution of these objects. This article reviews the current state of research on the formation of super-Earths and discusses different models of their formation and dynamical evolution.
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Kimberlite Volcanism
Vol. 41 (2013), pp. 497–528More LessKimberlite magmas are volatile-rich, silica-poor ultrabasic magmas originating as small-degree mantle melts at depths of 150 km or greater. Alteration and entrained xenoliths obscure their original magma chemistry and properties. Kimberlite magmas decrease temperature by a few hundred degrees during ascent. Changes of melt composition can result as a function of assimilation. Stalling of kimberlite can result in fractional crystallization, loss of xenocrysts, and loss of volatiles. Multiple pulses of kimberlite magmas form several distinct geological units in the same pipe or intrusion. Kimberlite pipes form by explosive disruption and deformation of country rocks. Confinement in a pipe introduces new processes such as fluidization, dynamic sintering, and intense mixing between volcanic jets and concentrated trapped mixtures. Occurrences of extravent and crater-fill lithofacies indicate that kimberlite eruptions generate eruptive products that are similar to those produced by common magma types. Alteration is largely attributed to hydrothermal systems, diagenesis, and weathering involving external water.
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Differentiated Planetesimals and the Parent Bodies of Chondrites
Vol. 41 (2013), pp. 529–560More LessMeteorites are samples of dozens of small planetary bodies that formed in the early Solar System. They exhibit great petrologic diversity, ranging from primordial accretional aggregates (chondrites), to partially melted residues (primitive achondrites), to once fully molten magmas (achondrites). It has long been thought that no single parent body could be the source of more than one of these three meteorite lithologies. This view is now being challenged by a variety of new measurements and theoretical models, including the discovery of primitive achondrites, paleomagnetic analyses of chondrites, thermal modeling of planetesimals, the discoveries of new metamorphosed chondrites and achondrites with affinities to some chondrite groups, and the possible identification of extant partially differentiated asteroids. These developments collectively suggest that some chondrites could in fact be samples of the outer, unmelted crusts of otherwise differentiated planetesimals with silicate mantles and metallic cores. This may have major implications for the origin of meteorite groups, the meaning of meteorite paleomagnetism, the rates and onset times of accretion, and the interior structures and histories of asteroids.
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Splendid and Seldom Isolated: The Paleobiogeography of Patagonia
Vol. 41 (2013), pp. 561–603More LessThe idea that South America was an island continent over most of the Cenozoic, during which its unusual mammalian faunas evolved in isolation, is outstandingly influential in biogeography. Although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified, it is still repeated in much current literature. The persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals, reptiles, and plants from the Jurassic to the Paleogene of Patagonia, which has by far the richest fossil record on the continent. All three groups show distribution patterns that are broadly consistent with South America's long separation history, first from Laurasia by the Late Jurassic, then from Africa and India-Madagascar during the late Early Cretaceous, and finally from Antarctica and Australia during the early-middle Eocene, after which “isolation” finally commenced. We highlight areas of promising future research and provide an updated view of South American isolation.
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Electrical Conductivity of Mantle Minerals: Role of Water in Conductivity Anomalies
Vol. 41 (2013), pp. 605–628More LessThe electrical conductivity of Earth's mantle has recently become an interesting topic across diverse Earth science communities. Many electrical conductivity data of mantle phases have been accumulated through the development of high-pressure experiments. These data will provide information on valence states, water concentration, Fe concentration, oxygen fugacity, and the connectivity of the conductive phase in geological materials such as minerals, melts, and rocks. Although several groups have measured the electrical conductivity of mantle materials at high pressure, they have provided inconsistent results, especially with regard to the effect of water. Thus, it is timely to review the problems underlying experimental techniques. We discuss the current understanding of the effect of water on the electrical conductivity of nominally anhydrous mantle minerals, with some speculation on the form of volatile components in Earth's interior. Finally, we consider the role of water in major conductivity anomalies observed in the upper mantle and transition zone.
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The Late Paleozoic Ice Age: An Evolving Paradigm
Vol. 41 (2013), pp. 629–656More LessThe late Paleozoic icehouse was the longest-lived ice age of the Phanerozoic, and its demise constitutes the only recorded turnover to a greenhouse state. This review summarizes evidence for the timing, extent, and behavior of continental ice on Pangea in addition to the climate and ecosystem response to repeated transitions between glacial and interglacial conditions. Combined empirical and climate modeling studies argue for a dynamic ice age characterized by discrete periods of glaciation separated by periods of ice contraction during intermittent warmings, moderate-size ice sheets emanating from multiple ice centers throughout southern Gondwana, possible glaciation of the Northern Hemisphere, and atmospheric CO2 as a primary driver of both ice sheet and climate variability. The glacioeustatic response to fluctuations of these smaller ice sheets was likely less extreme than previously suggested. Modeling studies, stratigraphic relationships, and changes in both the geographic patterns and community compositions of marine fauna and terrestrial flora indicate the potential for strong responses to high-latitude glacial conditions in both ocean circulation and low-latitude climate. The forcings and feedbacks of these linkages, as well as existing climate paradoxes, define research targets for future studies of the late Paleozoic.
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Composition and State of the Core
Vol. 41 (2013), pp. 657–691More LessThe composition and state of Earth's core, located deeper than 2,900 km from the surface, remain largely uncertain. Recent static experiments on iron and alloys performed up to inner core pressure and temperature conditions have revealed phase relations and properties of core materials. These mineral physics constraints, combined with theoretical calculations, continue to improve our understanding of the core, in particular the crystal structure of the inner core and the chemical composition, thermal structure and evolution, and possible stratification of the outer core.
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Enceladus: An Active Ice World in the Saturn System
Vol. 41 (2013), pp. 693–717More LessEnceladus, one of the mid-sized icy moons of Saturn, has an importance to planetary science far greater than its modest 504-km diameter would suggest. Intensive exploration of Enceladus by the Cassini Saturn orbiter has revealed that it is the only known icy world in the solar system with ongoing deep-seated geological activity. Active tectonic fractures at Enceladus's south pole, dubbed “tiger stripes,” warmed by internal tidally generated heat, spew supersonic jets of water vapor, other gases, and ice particles into circum-Saturnian space. A subsurface saltwater sea probably exists under the south pole, between the ice shell and the silicate core. Because of evidence that liquid water is probably present at the jet sources, Enceladus is also of great astrobiological interest as a potential habitat for life.
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Earth's Background Free Oscillations
Vol. 41 (2013), pp. 719–740More LessEarth's background free oscillations, known as Earth's hum, were discovered in 1998. Excited modes of the oscillations are almost exclusively fundamental spheroidal and toroidal modes from 2 to 20 mHz. Seasonal variations in the source distribution suggest that the dominant sources are ocean infragravity waves in the shallow and deep oceans. A probable excitation mechanism is random shear traction acting on the sea bottom owing to linear topographic coupling of the infragravity waves. Excitation by pressure sources on Earth's surface is also significant for a frequency below 5 mHz. A possible pressure source is atmospheric turbulence, which can cause observed resonant oscillations between the solid modes and atmospheric acoustic modes.
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Global Warming and Neotropical Rainforests: A Historical Perspective
Vol. 41 (2013), pp. 741–766More LessThere is concern over the future of the tropical rainforest (TRF) in the face of global warming. Will TRFs collapse? The fossil record can inform us about that. Our compilation of 5,998 empirical estimates of temperature over the past 120 Ma indicates that tropics have warmed as much as 7°C during both the mid-Cretaceous and the Paleogene. We analyzed the paleobotanical record of South America during the Paleogene and found that the TRF did not expand toward temperate latitudes during global warm events, even though temperatures were appropriate for doing so, suggesting that solar insolation can be a constraint on the distribution of the tropical biome. Rather, a novel biome, adapted to temperate latitudes with warm winters, developed south of the tropical zone. The TRF did not collapse during past warmings; on the contrary, its diversity increased. The increase in temperature seems to be a major driver in promoting diversity.
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The Scotia Arc: Genesis, Evolution, Global Significance
Vol. 41 (2013), pp. 767–793More LessThe Scotia arc is the eastward-closing loop of mountains and locally emergent submarine ridges extending from the southernmost Andes through the active South Sandwich volcanic arc to the Antarctic Peninsula. Its origins lie in the Jurassic initial fragmentation of Gondwana. This fragmentation involved extreme intercratonic extension, Pacificward translation of rotating crustal blocks, and an ignimbrite flare-up. Relative motion between South America, Africa, and East Antarctica during the opening of the southern ocean basins resulted in mid-Cretaceous uplift of the Pacific margin cordillera and translation of elevated crustal blocks eastward to form the North and South Scotia Ridges. The South Sandwich volcanic arc system originated in Neogene westward-directed subduction beneath oceanic crust formed between South America and Antarctica and serves as an excellent tectonic laboratory. The physiography of the entire Scotia arc region has profoundly influenced the onset and development of the Antarctic Circumpolar Current and migration of marine and terrestrial biota.
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Previous Volumes
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Volume 51 (2023)
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Volume 50 (2022)
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Volume 49 (2021)
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Volume 48 (2020)
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Volume 47 (2019)
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Volume 46 (2018)
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Volume 45 (2017)
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Volume 44 (2016)
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Volume 43 (2015)
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Volume 42 (2014)
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Volume 41 (2013)
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Volume 40 (2012)
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Volume 39 (2011)
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Volume 38 (2010)
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Volume 37 (2009)
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Volume 36 (2008)
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Volume 35 (2007)
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Volume 34 (2006)
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Volume 33 (2005)
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Volume 32 (2004)
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Volume 31 (2003)
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Volume 30 (2002)
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Volume 29 (2001)
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Volume 28 (2000)
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Volume 27 (1999)
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Volume 26 (1998)
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Volume 25 (1997)
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Volume 24 (1996)
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Volume 23 (1995)
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Volume 22 (1994)
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Volume 21 (1993)
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Volume 20 (1992)
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Volume 19 (1991)
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Volume 18 (1990)
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Volume 17 (1989)
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Volume 16 (1988)
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Volume 15 (1987)
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Volume 14 (1986)
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Volume 13 (1985)
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Volume 12 (1984)
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Volume 11 (1983)
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Volume 10 (1982)
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Volume 9 (1981)
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Volume 8 (1980)
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Volume 7 (1979)
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Volume 6 (1978)
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Volume 5 (1977)
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Volume 4 (1976)
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Volume 3 (1975)
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Volume 2 (1974)
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Volume 1 (1973)
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Volume 0 (1932)