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Recovery from the greatest mass extinction of all time

Benton M.

School of Earth Sciences, University of Bristol.

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Keywords: end-Permian mass extinction, biotic recovery.

The aftermath of the great end-Permian mass extinction, 252 million years ago, shows how life can recover from the loss of >90% species globally. The initial causes of the catastrophe continued to devastate Early Triassic environments and slowed the biotic recovery. Huge attention is currently focused on the exceptional Permo-Triassic rock successions in China, which document the recovery step-by-step. In addition, novel phylogenetic-macroevolutionary methods are being applied to this greatest-of-all ‘adaptive radiations’. How did the successful post-extinction clades respond to the opportunity, and build up the fundamentals of modern ecosystems?

Benton M.J., Forth J. & Langer M.C. 2014. Models for the rise of the dinosaurs. Current Biology 24, R87-R95, doi:10.1016/j.cub.2013.11.063.
Benton M.J., Zhang Q.Y., Hu S.X., Chen Z.Q., Wen W., Liu J., Huang J.Y., Zhou C.Y., Xie T., Tong J.N. & Choo B. 2013. Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass extinction. Earth-Science Reviews. 123, 199-243, doi:10.1016/j.earscirev.2013.05.014.
Chen Z.Q. & Benton M.J. 2012. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience 5, 375-383, doi:10.1038/ngeo1475. University of Bristol: http://palaeo.gly.bris.ac.uk/PTB/

 


 

 

Atmospheric Oxygen and Biological Evolution

Canfield D.E.

University of Southern Denmark, Department of Biology, Nordic Center for Earth Evolution (NordCEE)

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Keywords: Atmospheric oxygen, biological evolution.

More than any other element, oxygen shapes the current biosphere. It is produced by photosynthesis and it is used to respire most of the organic matter at the Earth surface. However, this is not always been the case. During the first 2 billion years of Earth history, oxygen concentrations were likely over 100,000 times less than present levels. Could an aerobic biosphere have existed with so little oxygen? This question is addressed through growth experiments conducted on E. coli utilizing special oxygen sensors with ultra-low oxygen-detection limits. We find that E. coli can grow and respire oxygen at oxygen concentrations < 2nM which is 100,000 times less than found today in air-saturated water. After about 2.4 billion years ago, oxygen concentrations rose to levels that are uncertain. There is a prevailing view, however, that these levels were insufficient to allow respiration by animals thus preventing their evolution. The minimum levels of oxygen required for animals (as a group), however, is poorly known. We attempt to define the levels required for animal respiration through a variety of respiration and behavior experiments on two different marine sponges. We show that sponges feed and respire at oxygen concentrations ranging between 1 and 4% of present levels. This, therefore, might be viewed as a possible minimum oxygen requirement by early animals. We provide further evidence from the Xiamaling Formation in China to show that atmospheric oxygen may have attained these levels well before animals, implying that other factors controlled the timing of animal evolution.

 


 

 

In memory of Marco Beltrando

Dal Piaz G.V.1 & Manatschal G.2

1. Dipartimento di Geoscienze, Università degli Studi, I-35131 Padova, Italia. 2. Université de Strasbourg/EOST, CNRS, Institut de Physique du Globe de Strasbourg; UMR 7516, F-67084 Strasbourg Cedex, France

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Six months have already passed since December 8th 2015, when, at the age of 36, Marco Beltrando died in an accident in the Western Alps, suddenly leaving his beloved family, relatives and friends. After the tribute to his memory during the EGU Assembly, this SGI Congress reminds us again of Marco Beltrando, addressed in particular to those geologists who did not have the good fortune to know him personally. Time passes quickly, but the memory of such a special young person is still vivid, always cheerful and smiling, although reserved, sincere and generous. Marco was an enthusiastic, curious and brilliant geologist who was especially fascinated by the geological puzzle of the Western Alps and the process required to unravel it back to the complex rifting stage. He also loved the mountains themselves and mountaineering - hiking and climbing during the summer, and cross-country skiing in winter. Marco spent some time as a student at the University of Utrecht, and graduated in Geology at the University of Turin in 2002. He then achieved his PhD at the Research School of Earth Sciences of the Australian National University in Canberra in 2007. On his return to Italy, he worked as a researcher in the Structural Geology Group of the University of Turin, where he taught Structural Geology and Regional Geology of the Alps, and trained many MSc and PhD students working with him. Only four days before his death, Marco had been granted tenure as Associate Professor at the University of Turin (December 4th 2105). He wrote: “My main research focus lies in the field of tectonics, in both convergent and divergent settings. I address large-scale geodynamics through a combination of structural field geology, microstructural analysis, petrography and geochronology. The main questions I am currently addressing range from the tectono-metamorphic evolution of hyper-extended rifted margins, to the influence exerted by rift-inherited hyper-extension on the evolution of orogenic belts”. In particular, he was able to integrate these modern field and laboratory techniques harmoniously in a modern approach, successfully applied to elucidate the paleo-structural setting of a very complex tectono-metamorphic wedge and a fossil subduction zone, including mantle slices within continental to oceanic basement and cover units, and also to develop new ways of thinking about extensional and collisional systems. In both these large fields, he was at the forefront of research, as highlighted by his innovative contributions and many invitations to international conferences. We last saw Marco during his last lecture (recorded), given in Venice at the meeting “Geologia delle Alpi”. In Marco, we do not only lose a great colleague, an outstanding researcher and a very good teacher, but also a dear friend.

 


 

 

Climate change: how can information from the past inform the future?

Masson-Delmotte V.

Laboratoire Des Sciences du Climat et l'Environnement, CEA-CNRS-Université de Versailles Saint-Quentin en Yvelines.

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Keywords: Paleoclimate, Earth's history

During the last decades, curiosity-driven research has continuously explored all dimensions of past climate variations, using a wide variety of natural archives, proxies, methods and models, forming a major collective endeavour. Beyond uncertainties, challenges and unresolved issues, solid knowledge is gradually built about the causes, mechanisms, amplitudes and rates of past natural changes, at regional to global scales, and throughout Earth's history. The study of past climates benefits from modern in situ and remote sensing observations, process studies, and the development of climate models to Earth system models: improved knowledge of present-day climate is crucial to understand the proxies used for paleoclimate reconstructions, and numerical models provide a solid basis to test the plausibility of hypotheses and theories relating potential causes and mechanisms of past changes, and to understand large-scale processes affecting local records. There is no past analogue to the magnitude and rate of human perturbations to the global climate system, and, given the non-linear nature of the climate system, future changes cannot be predicted from an interpolation of recent trends: future changes can only be explored using comprehensive models, based on physical principles, providing ensemble projections of future changes in response to various scenarios of human perturbations. Nevertheless, the same climate system has reacted, in the past, to a variety of natural perturbations of geological or astronomical origin, and has produced internal variability. These past changes can therefore be seen as "natural experiments" on the Earth's system. In this respect, information from the past is first crucial to complement short instrumental or remote sensing records. This is particularly true for difficult-access areas such as polar regions or deep oceans, where paleoclimate records fill modern observational gaps. Long records can inform whether recent changes are part of natural climate variability, or unusual. Moreover, paleoclimate information is crucial to characterize the full range of natural climate variability and associated impacts, including abrupt change, and to assess the magnitude and timescales of response of the climate system to perturbations of the Earth's radiative budget and inform on key issues such as climate sensitivity, or ice sheet vulnerability to polar warming. Finally, information from the past is critical to benchmark climate and Earth system models, which are the only tools that can inform the future. Methodologies are being developed to compare outputs from climate models with paleoclimate data, accounting for uncertainties in model boundary conditions, and uncertainties on magnitude and timing of past changes, sometimes including explicit proxy modelling. While most of these comparisons were so far performed for "steady state", considering the climate response "at equilibrium" (testing whether climate models can produce the right magnitude of responses), new developments are emerging to assess the ability of climate models to resolve the transient aspects of past changes (testing whether climate models can produce the right rate of changes). Given the spread of climate model results for future projections, taking advantage of past climate knowledge may help to identify subsets of models that perform better for a given mechanism, complementing evaluation of models for present-day, and therefore reduce uncertainties on future projected changes. Key questions related to understanding past changes on a variety of timescales are therefore also relevant for future changes and will be illustrated during this presentation.

 


 

 

The Interdependence of Plate Coupling Processes, Subduction Rate, and Asthenospheric Pressure Drop across Subducting Slabs

Royden L.1, Holt A.F.2 & Becker T.W.2

1. Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA. 2. Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA.

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Keywords: plate coupling, astenospheric pressure, subduction rates.

 

One advantage of analytical models, in which analytic expressions are used for the various components of the subduction system, is the efficient exploration of parameter space and identification of the physical mechanisms controlling a wide breadth of slab kinematics. We show that, despite subtle differences in how plate interfaces and boundary conditions are implemented, results for single subduction from a 3-D semi-analytical model for subduction FAST (Royden & Husson, 2006; Jagoutz et al., 2015) and from the numerical finite-element model CitcomCU (Moresi & Gurnis, 1996, Zhong et al., 2006) are in excellent agreement when plate coupling (via shear stress on the plate interface) takes place in the FAST without the development of topographic relief at the plate boundary. Results from the two models are consistent across a variety of geometries, with fixed upper plate, fixed lower plate, and stress-free plate ends. When the analytical model is modified to include the development of topography above the subduction boundary, subduction rates are greatly increased, indicating a strong sensitivity of subduction to the mode of plate coupling. Rates of subduction also correlate strongly with the asthenospheric pressure drop across the subducting slab, which drives toroidal flow of the asthenosphere around the slab. When the lower plate is fixed, subduction is relatively slow and the pressure drop from below to above the slab is large, inhibiting subduction and slab roll-back. When the upper plate is fixed and when the plate ends are stress-free, subduction rates are approximately 50% faster and the corresponding asthenospheric pressure drop from below to above the slab is small, facilitating rapid subduction. This qualitative correlation between plate coupling processes, asthenospheric pressure drop, and rates of subduction can be extended to systems with more than one subduction zone (Holt et al., 2015 AGU Fall Abstract).

Jagoutz O., Royden L., Holt A. & Becker T.W., 2015. Anomalously fast convergence of India and Eurasia caused by double subduction. Nature Geoscience 8, 475-478, doi:10.1038/NGEO2418.

Moresi L.N. & Gurnis M. 1996. Constraints on the lateral strength of slabs from three-dimensional dynamic flow models. Earth and Planetary Science Letters 138, 15-28.

Royden L.H. & Husson L. 2006. Trench motion, slab geometry and viscous stresses in subduction systems. Geophysical Journal International 167, 881-905.

Zhong S. 2006. Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature. Journal of Geophysical Research, 111, doi: 10.1029/2005JB003972.

 


 

 

Tra Scilla e Cariddi: communicating geology to the public

Stewart I.

Plymouth University, School of Geography, Earth and Environmental Sciences, Faculty of Science and Engineering.Questo indirizzo email è protetto dagli spambots. È necessario abilitare JavaScript per vederlo.">

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Keywords: public communication, geoscience.

Geoscientific knowledge and understanding lies at the heart of many of the most critical societal issues that face us in the 21st century. The pressing human challenges of natural disaster reduction, energy supply and security, and mineral and water resource management, rest on geological foundations. And yet, outside of the academic and industrial geoscience community there is a limited appreciation of Earth Science, especially among policy makers. Geology, it seems, lies out of sight and out of mind. For that reason, geologists are increasingly being encouraged to communicate more broadly what they do and what they know. Yet how can we do that when, for most people, geology is about 'stones' and stones are 'boring'! It is a problem compounded by the fact that many of our most acute geo-issues are rooted in the unfamiliar realm of the ‘deep’ subsurface. This talk will use the experience of popularising geoscience for mainstream television to explore ways in which geologists can make our research connect better with the dissonant public, and in doing so forge more effective strategies for public communication.

 


 

 

Changes in River Network Geometry and Implications for Landscape Evolution over Geologic Timescales

Willett S.

Department of Earth Sciences, ETH Zurich.

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Keywords: river networks, tectonic processes, geomorphic processes.

The map pattern of river networks has always held great promise for providing information about tectonic and geomorphic processes on the Earth’s surface, but we have never had the tools or the conceptional framework to exploit this information. One of the fundamental characteristics of river networks, potentially serving as the basis for an interpretative framework, is the observation that drainage area and channel slope tend to scale at all points in a river network. If this condition represents an equilibrium state of a river network, deviations from this state can be interpreted in terms of tectonic or climatic perturbations. This is easier to visualize through the integral form of this relationship, which predicts a linear relationship between elevation of a point in a channel network and the downstream integral of the drainage area, a quantity now commonly referred to as x. A spatial map of x quickly and clearly shows patterns that can be interpreted in terms of landscape disequilibrium, demonstrating where and how the geometry and topology of a river network is adjusting through divide migration or river capture. Maps of x are easily constructed using modern GIS methods and commonly available digital elevation models. I present several examples in this talk of mountain belt or continental-scale river reorganization on-going in response to tectonic forcing. The first example is the Danube river basin in central Europe. The Danube represents the last vestiges of the Tethys Ocean, north of the Alps, and its successor, the North Alpine foreland basin. The closure of the Tethys is continuing into the modern era with the drainage basin of the Danube showing collapse and loss of drainage area with advance of the water divides from the Rhine and Adriatic drainages into the Danube. We interpret this as the natural response to ocean closure and isostatic rebound of the foredeep, as well as retreat of baselevel for the Alpine rivers from the former marine foredeep to the modern Black Sea. A second example is presented from the Great Plains of North America, where the subduction-related, mid-continent seaway retreated at the end of the Cretaceous leaving the Mississippi river basin between the Rockies and the Appalachian mountains. In the late Miocene, the Rockies experienced a period of dynamic uplift related to the motion of North America over a mantle upwelling north of the East Pacific Rise. This renewed sedimentation into the Rockies foreland with the deposition of the Ogallala group, which served to completely resurface the High Plains physiographic province and, at its peak extent, covered more than half a million square kilometers. Today we are witnessing the establishment of a new river network incising into the Miocene alluvial fan surface. This is evident in the dissection of the Ogallala units, with isolated erosional remnants being consumed by surrounding rivers as they integrate parallel, fan-face channels into dendritic basins. Finally, I present an example from the active orogenic belt of Taiwan, where rapid uplift has produced short, steep catchments in uniform lithology competing laterally for drainage area. I present evidence for various modes of catchment area exchange, including river capture, tributary stripping and steady divide migration. Processes are confirmed by differential erosion rates measured with concentrations of cosmogenic 10Be.