We investigate the long-term co-evolution of the geosphere-biosphere complex from the Archaean up to 1.5 billion years into the planet's future with the help of a conceptual Earth system model. The model focusses on the global carbon cycle as mediated by life and driven by increasing solar luminosity and by decreasing plate tectonics. To calculate the weathering rate we take into account the growth of continental area over geological time scales and extrapolate the present continental growth rate to the future. We determine the "terrestrial life corridor" for the existance of a phototsynthesis-based biosphere in the dependence on the state parameters of the Earth system. For the case of the geostatic approximation we reproduce the results of Caldeira and Kasting (1992) about the life span of the biosphere. The consideration of geodynamics in the new model gives a higher atmospheric carbon content for the past but a much stronger decrease for the future. This leads to a reduction of the life span of the biosphere of up to some hundred million years (Franck et al., 1998).
Caldeira K & Kasting JF, Nature, 360, 721-723, (1992).
Franck S, Kossacki K & Bounama C, PIK Report, 33, 1-20, (1998).
Palaeontologists have long been inclined to take the burgeoning of animal fossils at the transition between the Proterozoic and the Phanerozoic to reflect the true origin and early evolution of animals. Attempts by molecular biologists to date the major divergences within the animal clade have so far not resulted in any precision (Wray et al., 1996; Ayala et al., 1998), but the dates arrived at are older than most palaeontological estimates suggest. This emphasizes the fact that, long or short, there is a period in early animal evolution so far unaccounted for by the fossil record. The major animal lineages may in fact have been in existence for hundreds of millions of years before they began to leave visible remains in rocks. Usually, non-preservation is explained by low potential for fossilization, the animals being too small and/or too soft to leave recognizable fossils. Recent discoveries that non-mineralized larvae and embryos may be preserved in phosphatized carbonates (Zhang & Pratt, 1994; Bengtson & Yue, 1997; Xiao et al., 1998) have made it possible to test such conjectures more critically. However early the animal lineages may have arisen, the 'Cambrian Explosion' remains a real biological event, reflecting one of the most profound reorganizations of the biosphere in the history of the Earth. Animals probably played a crucial role in this reorganization, in that their active modes of life boosted general organismic diversities.
Wray, GA, Levinton, JS & Shapiro, LH., Science, 274, 568-573, (1996).
Ayala, FJ, Rzhetsky, A & Ayala, FJ, Proceedings of the National Academy of Sciences USA, 95, 606-611, (1998).
Zhang X & Pratt, B, Science, 266, 637-639, (1994).
Bengtson, S & Yue Z, Science, 277, 1645-1648, (1997).
Xiao, S, Zhang Y & Knoll, A, Nature, 391, 553-558, (1998).
The diversification of life through geological time indicates a rise from presumably one species to many millions today. The shape of that diversification has been debated, and three main kinds of models have emerged: (1) additive, or straight-line; (2) exponential; and, (3) logistic, or S-shaped.
The first, additive, pattern seems unlikely since it would imply a constantly declining probability of phylogenetic branching through time. The exponential pattern is biologically more likely, since it can be produced by a constant splitting rate. However, such curves imply that there is no upper limit to diversity. Logistic curves begin as exponentials, and then level off as some limiting diversity is approached.
Exponential and logistic curves imply very different understandings of ecology and evolution. An exponential curve implies that diversification is unconstrained so far, that taxa generally do not interact strongly competitively in a way that leads to wholesale extinction, and that new forms can continually evolve into new ecospace. A logistic curve implies that there is more biotic interaction (competition), in which new taxa evolve, but supplant pre-existing taxa, and that there is a fixed number of families (and species) on the earth, which cannot be exceeded.
The reality of exponential and logistic curves in Nature has been debated in the past 40 years. Proponents of both viewpoints have presented strong evidence for the existence of exponential or logistic patterns in their data sets. Perhaps evolution follows either one or the other pattern, or perhaps different major segments of Life have evolved in different ways (Benton, 1995, 1997).
The diversification of marine families in the past 600 million years appears to have followed two or three logistic curves, with equilibrium levels that lasted up to 200 Myr. Continental organisms, however, clearly show an exponential pattern of diversification. It is not clear whether the empirical diversification patterns are real or artefacts of a poor fossil record, although the latter explanation seems unlikely.
The different patterns of diversification of marine and continental organisms could be real. Perhaps marine and continental organisms diversified in different ways, and there are still new sectors of ecospace to be conquered on land, but not in the sea. Or perhaps marine organisms have also diversified exponentially at the specific level, but the appearance of equilibrium patterns are artefacts of taxonomic structures.
Benton, M. J., Science, 268, 52-58, (1995).
Benton, M. J., Trends Ecol. Evol, 12, 490-495, (1997).
Physical changes in the marine environment caused by the evolutionary diversification of some widely-distributed organismal lineages can provide opportunities and exert constraints on the macroevolutionary paths available to a wide variety of other unrelated and ecologically distinct organismal lineages. One of the best examples of this phenomenon is the correspondence between patterns of diversification in Mesozoic plankton and a variety of contemporaneous marine benthic clades. The diversification of plankton (especially foraminiferal & coccolithophores) in the Jurassic altered the nature of deep-sea sedimentation patterns with respect to the surface-to-deep transport of organic carbon. In response to the provision of this new resource, evolutionary diversification took place in a number of deep-sea benthic clades that changed the nature of biotic activity on the marine sea floor. Subsequent alterations on planktonic biodiversity in the upper Maastrichtian (brought about as a result of climatic change) also appear to have elicited a benthic response as these clades adjusted their morphologies and life-history strategies to an interval of diminished and/or fluctuating resource availability. Comparative historical studies of evolutionary dynamics between planktonic and benthic clades can reveal the nature of selection pressures that control both microevolutionary and macroevolutionary regimes and be used to probe the causes and timing of major biotic turnover events.
The basic units of biotic diversity reconstructions are species richness and species evenness. Species richness is the result of past differences in speciation and extinction rates. Species evenness is likely the result of environmental variability. But in all paleontological examples major uncertainties remain because of taphonomic biases and the dearth of studies establishing a link between living and fossil assemblages. The basic conceptual models, which are used by biologists (ecologists) and paleontologists to explain diversity changes, are very similar, but a major difference lies in the time-scales considered.
Using calcareous nannofossils as an example, attempts to "integrate ... diversity into Earth system history" will be discussed. The success of these attempts crucially depends on our ability to (1) find or develop adequate methods to describe and quantify biotic diversity, (2) determine the diversity patterns today and in the past, (3) identify the likely factors influencing diversity of living taxa, and (4) transpose this knowledge to situations in the geological past, or (5) invoke extraordinary processes or rare events in the past that may not be observable in our present-day world.
For the living plankton, attempts to quantify the extent of physical forcing through correlations between species abundance and abiotic environmental parameter variability, have been reasonably successful in a few case studies. In the case of the terminal Cretaceous mass-extinctions, the direct effects of known past changes in the physical environment on oceanic plankton populations have been demonstrated and accepted by a majority of paleontologists. For other periods of known environmental change, however, such links are much more uncertain.
Several examples exist of dramatic past changes in the species evenness of plankton populations - especially coccolithophores. None of these have been convincingly linked to known environmental changes yet and none of these seem to have affected the rest of the assemblages. Geographically widespread dominance intervals of single taxa of coccolithophores, lasting from as little as a few thousand up to hundreds of thousands of years, have occurred since the late Jurassic. Should they not be prime examples for "life as a strong forcing factor for the evolution of the system Earth"?
Organisms evolve towards a form that is optimal in the pertaining conditions. Fluctuating environments, for example in temperate climatic zones or tidally influenced marine habitats, constitute a moving target to organisms that inhabit them. Sheldon's (1996) "Plus ça change" hypothesis proposes that evolutionary stasis with punctuation will tend to occur under these circumstances, and gradual evolution will tend to occur in stable environments: this creates a compromise between hypotheses of gradual and punctuated modes. A simple genetic algorithm model has been designed to investigate the dynamics of an evolving population in response to varying degrees of fluctuation of a target. In the model, simulated populations are seen to evolve slower towards a mean optimum if the optimum fluctuates. If the fluctuation of the target is large relative to the change in the mean, then the sequence is indistinguishable from stasis or a random walk. This can be explained in terms of the shape of the function relating rate of evolution to amount of disequilibrium. Although the details of this function are dependent on various assumptions about the population frequency distribution and intensity of selective pressure, the important properties of the result are unaffected. The result is also the same regardless of the nature of the fluctuation: random or cyclic. Evolutionary case studies from the Quaternary are currently being analysed to assess the validity of the model. As a consequence of slow evolution towards a mean optimum, the model predicts that, in a changing environment where fluctuation is superimposed on a systematic trend, a population will eventually subsist at the limits of the viable range of variation. This has implications regarding the viability of populations in temperate, shallow marine and other variable environments during global warming.
Sheldon PR, Palaeogeography, Palaeoclimatology, Palaeoecology, 127, 209-227, (1996).
Data from the great Permo-Triassic biotic crisis are restricted to a limited number of geological sections, often characterized by an unconformity within continental platform successions (Wignall et al.; 1996). In order to solve this problem (global regression event), the study of oceanic successions emerges as one alternative. Recent attempts confirm this potential: for instance, pelagites of the Mino-Tamba terrane from Japan include the boundary within a 15 m interval of black shales intercalated within radiolarian chert of respectively late Permian (Changxingian) and early Triassic (Dienerian) ages (Isozaki; 1997). This succession has been interpreted as recording a significant decrease of siliceous bioproductivity in the late Permian, predating a major anoxia event around the boundary, followed by progressive recovery of siliceous planktic productivity in the early Triassic (Isozaki, ibid.). Present debate also includes the patterns of selectivity of extinctions and the search for suitable paleooceanographic causes (Knoll et al.; 1996) as well as mechanisms of survival and recovery specific to each faunal group. For planktic and nektonic organisms around the P-T boundary, these mechanisms are not always well documented.
In this perspective, we thought of testing the quality of the sedimentary record from various oceanic successions, as well as investigate the paleogeographic range and timing of this anoxia on a global scale. For this purpose, we selected two domains: the Oman Mountains and the North American Cordillera, identified as two complementary areas from two major domains of the world ocean at the end of the Permian: Tethys and Panthalassa. Our multidisciplinary approach is based on: (1) biochronologic, paleobiogeographic and evolutionary study of radiolarian, conodont, ostracod, ammonite and pseudoplanktic bivalve faunas; (2) facies analysis and stable isotopes geochemistry. We identified and sampled several Permo-Triassic oceanic successions of the Hawasina series (Oman), the Candelaria flysch and the Black Rock terrane (Nevada), and the Cache Creek terrane (British Columbia). Four preliminary observations can be drawn from our first phase of field work: (1) most localities display radiolarian chert as the dominant type strata in the late Permian; (2) up section, successions grade into "boundary shales" and/or black shales or various thicknesses devoid of apparent unconformities; (3) earliest Triassic successions usually consist of shales and/or platy carbonates; (4) siliceous sedimentation reappears progressively up section. This typology is consistent from one locality to another, along with close lithologic resemblance between remote localities, for instance the Hawasina series (Oman) and the Black Rock terrane (Nevada). Differences of sedimentation rates related to the amount of carbonate input within starved basins seems a significant factor for some local variations. Biochronology and geochemistry in progress will be critical in support of these preliminary correlations.
Isozaki, Y., Science, 276, 235-238, (1997).
Knoll AH, Bambach RK, Canfield DE & Grotzinger JP, Science, 273, 453-457, (1996).
Wignall PB, Kozur, H, & Hallam, A, Historical Biology, 12, 39-62, (1996).
There is an opinion assuming the origin of the genus Tyrrhenocythere from the genus Hemicytheria Pokorny (1955) (Ostracoda, Crustacea). This assumption is documented by not only morphological valve resemblance, but also by existence of the species with transitiv structures of the marginal pore canals (MPC). The MPC evolution is observed from straight and narrow forms (Hemicytheria omphalodes, H. loerentheyi, H. reniformis) through the forms with partly connecting canals (H. biornata, H. major, H. marginata, T. transitivum, n.sp.) to the polyfurcate canal types (T. pezinokensis, T. astislavensis, n.sp., T. sp.). Described phenomenon can be detected on the same time level. The changes started before the upper pannonian (upper tortonian). An ascendent of T. pezinokensis seems to be H. omphalodes or H. loerentheyi, which have a lot of correlated morphological structures. Its strong ornamented and thick shell affects very ancient in a contrast with light shell features of T. transitivum, n.sp, T. rastislavensis, n.sp., T. sp. It evokes an idea that T. pezinokensis is an independent evolution branch which rose by a phyletic transformation process and lived together with the T. species transforming themselves from the other Hemicytheria species. It's well known that a salinity decreasing and the fresh-water conditions took place on the Central Paratethys area during a time span (end of badenian--mesinian crisis) and in the coursefrom N to S. The first Hemicytheria species are known from sarmatian (serravalian, 3 species) Their amount increased during the lower and middle pannonian (serbian) in the Pannonian lake to the number of the 7 species. Their boom set in upper pannonian (serbian), when the 17 species survivedin the basins. The cause of their population explosion is the raising of the water area (max. flooding surface). Greater living area led to the raising of the population and it caused a higher evolution change frequency. The great decline on the pannonian/pontian boundary is a result of a regresion. The genus was formed by 6 species in lower and 4 in the upper pontian age. The new transgresion and the changed ecological conditions didn't enable their next development. Tyrrhenocythere occupies more and more significante role in the ecosystem. It's possible that its ecological and food relations were very similar to Hemicytheria, but Tyrrhenocythere replaced it due to the progressive genetic and functional qualities. Up to the present, the genus T. has not been found in the older sediments that pontian and only in the Mediterranean and Paratethys region. The discovery of T. pezinokensis, T.transitivum, n.sp., T.rastislavensis, n.sp. and T. sp. in the pannonian layers of the Danube basin makes a possibility to say that their descendents migrated from the Danube basin to the south parts of the Pannonian lake and across the Dacian basin they passed up to the East Paratethys and Mediterranean sea.
The main purpose of this paper is to estimate the biological life changes coursed by the variability of small atmosphere compound connected with the natural and anthropogenic sources. Modern level of biological life on the Earth is determined by the UV-radiation balance depending on the solar radiation flux at the atmosphere top and the atmosphere composition. The main role in the radiation extinction is plaid by aerosols and ozone contents. There are a lot of natural and anthropogenic processes leading to the changes of radiation-active atmosphere components. They are the solar activity changes, volcanic eruptions, global atmosphere circulation changes. But the most important problem in environment protection is the estimation of different anthropogenic impacts on the atmosphere leading to its composition changes: emission of ozone-destructing chemical compounds like freons, development of subsound (tropospheric) and supersound (stratospheric) aviation, fires etc. On the basis of the developed by authors flux and brightness atmosphere models with altitude and spectral super-resolution the fields of direct, upward, downward and actinic UV-fluxes were calculated for different scenarios of atmosphere composition violations. Dynamic of UV-radiation behavior on the Earth's surface after El-Chichon and Penatubo eruptions is analyzed. The features of regional formation of erithemical irradiation connected with the local «ozone holes» above Antarctica and Eastern Siberia with searched. The estimation of possible impact of atmosphere pollution by the stratospheric aviation exhausts leading to ozone destruction (about 1-2% of full content to 2015 year) on the UV-radiation regime were made and harm to the environment was analyzed.
Coccolithophorids are a major phytoplankton group with important impact on global change processes, especially the carbon cycle, and an outstanding fossil record. As a result they have attracted multi-disciplinary research interest. CODENET is a recently established network research project funded by the EC Training and Mobility of Researchers program (TMR). This network brings together eight research groups with diverse interests in coccolithophorids - The Natural History Museum London, ETH-Zurich, Free University Amsterdam, Netherlands Institute for Sea Research (NIOZ), Alfred Wegener Institute Bremerhaven (AWI), Instituto de Ciencias del Mar, Barcelona (CSIC-ICM), University of Caen, and University of Lisbon. These include geological, marine biological, molecular genetic and organic geochemical research groups. In addition to these, core-funded, teams many other groups are participating in various ways, including geological teams from Bremen, Milan, Firenze and University College London. Each of these teams has been using coccolithophorids as test organisms within their different fields of study. By combining our endeavours we are able to work more efficiently and effectively, to produce an excellent training opportunity and to study larger scale problems. Our research is focused on six carefully selected taxa. Each of these will be studied in culture to obtain a well constrained overview of diversity in the coccolithophorids as a whole in the following key areas - life cycles; cytology; lipid biochemistry; coccolith ultrastructure; and molecular genetics. Complimenting these studies of high level variation will be fine scale study of variation at the species level and of microevolutionary processes based on a combination of culture studies of inter-strain variability, biogeographic studies and geological study of their evolutionary record. We hope this project can provide a model for a new type of approach to the integration of multidisciplinary studies needed to investigate the interaction of biota and environment. Extended information on the project is available at:
http://www.nhm.ac.uk/hosted_sites/ina/CODENET/ details.html
Meaningful integration of palaeobiology into study, and especially modelling, of global change requires detailed understanding of the ecology of key organisms. As part of the CODENET (Coccolithophorid evolutionary biodiversity and ecology network) project we are investigating the prime constraints on coccolithophorid ecology and the ecological significance of biodiversity within the coccolithophorids. Our study will provide a multiple approach analysis of the ecology of six key coccolithophorid species, including comparison and synthesis of information from physiological studies, biogeography, seasonal succession, and palaeontological response to global change. This is intended both to maximise the palaeoeological information retrieval from these species and to enhance understanding of the ecology of the coccolithophorids as a group. This will allow critical interpretation of the coccolith record and modelling of the role of coccolithophorids within the global carbon cycle.
We will present here a revision for the Atlantic Ocean of the available data on three of the CODENET taxa (Helicosphaera carteri, Umbilicosphaera sibogae and Syracosphaera pulchra). based on data from plankton samples, sediment traps and surface sediment samples.
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