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8 Posts tagged with the earth_science_seminars tag

EARTH SCIENCES SEMINAR ROOM Tuesday 8th April - 4.00 pm

Javier Cuadros, Department of Earth Sciences, Natural History Museum, London


Confinement appears to be essential at the mineral-microbial interface and has an effect on both, microbial development and mineral formation. The role of confinement starts before life itself. Prebiotic molecules had to be concentrated from water or gas and "confined", possibly within clay interlayers, where they could react, be protected from adverse physical and chemical conditions, and perhaps also where specific reactions were catalysed.


Microorganisms frequently confine themselves within organic or inorganic walls for a number of reasons such as protection and feeding. They build exopolysaccharide capsules, burrow into mineral grains, etc. Close contact or confinement within mineral grains is arguably the habitat of the largest portion of existing microorganisms.


Microbial confinement has a feed-back effect on minerals. Microbes burrowing into mineral grains contribute to mineral weathering. Confined spaces inhabited by microorganisms, such as burrows, biofilms, exoskeletons of dead microbial algae, have chemical conditions different from the surrounding environment and impact mineral crystallization. For example, glauconite originates largely in connection to biological decay within marine shells.  Microbial activity can thus control to some extent the chemistry, mineralogy and formation rate of the neoformed phases. Clay minerals are obviously affected by microbially-mediated confinement of mineral-solution systems, as they are typically formed in the range of conditions in which these processes take place.


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Fridgeir Grimsson

Department of Palaeontology, University of Vienna


Tuesday 25 March - 4.00 pm

Earth Sciences Seminar Room
(Basement, WEB 05, the previous Mineralogy Seminar Room)
Oldest records of many modern north-temperate woody angiosperm genera are from the Eocene. However, the precise time and place of origin of individual tree genera that play important roles in modern temperate forest ecosystems has largely remained unresolved. One hypothesis about the origin of modern temperate woody elements in the northern hemisphere was proposed in the late 19th century by Adolf Engler, who suggested that many modern temperate tree genera originated in Arctic areas and migrated southwards in the course of the Cenozoic when global climate cooled.


The final objective of the present study is to test the validity of Engler’s (1882) concept of the “arctotertiary element”, that is, to determine whether early Cenozoic high latitude floras were the cradle of a number of tree genera that now dominate north-temperate mid-latitude forests. To achieve this, the systematic affinities of  pollen from Paleocene and Eocene sediments of western Greenland and the Faröe Islands are being assessed using combined light and scanning electron microscopy. Macrofossils from the same areas housed in existing museum and university collections are also under study, and new material has been collected in the field. By combining evidence from the palynofloras and the revised macrofloras, the phylogenetic affinities of the recognized plant taxa are being established in order to determine the proportion of extinct lineages and co-occurring extant genera, representing the “arctotertiary element” in the fossil floras.



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wiltie dacite.jpg


Mixing, mingling and enclave crumbling in the post-Minoan dacitic magmas of Santorini volcano, Greece


Chiara Maria Petrone,

Earth Sciences - Natural History Museum


Tuesday 29th October - 4.00 pm

Earth Sciences seminar room

(Basement, WEB 05, the previous Mineralogy Seminar Room)



The post-caldera islets of Palea- and Nea-Kameni formed as a result of nine eruptive events from A.D. 46-47 to 1950 in the center of the Santorini Minoan caldera. The erupted products are represented by dacitic lava flows and domes hosting basaltic to andesitic mafic enclaves. Dacitic rocks have low porphyritic index that increases with time, whereas their degree of evolution decreases pointing to the composition of the mafic enclaves. Enstatite contents of pyroxene and anorthite contents of plagioclase decrease from mafic enclaves to host lavas. Sr isotopes systematically increase with time and toward the less evolved composition of lavas and mafic enclaves, whereas Nd isotopes decrease. Whole rocks and mineral separates of mafic enclaves from the younger events are more Sr-radiogenic than their host lavas, the opposite occurs in the A.D. 46-47 lavas and enclaves.


Mixing and mingling processes between dacitic and mafic magmas, along with crumbling of the mafic enclaves in the host lavas are responsible for the observed textural and geochemical characteristics of the dacitic host lavas. The variations of Sr-Nd isotopes with time in the enclave magmas seem to indicate assimilation of limestone from the basement by the most mafic magmas; this process is associated to new mafic magma inputs and femic phase crystallization. A shallow layered reservoir with dacitic magmas overlaying lower mafic magmas is supported by our data. Crystal fractionation and cumulitic processes affect the lower part of the plumbing system allowing further layering of the mafic magmas, generating the variable and complex textures shown by the mafic enclaves. Different portions of the layered reservoir were frequently and variably sampled during time, as testified by variable types, compositions and distributions of mafic enclaves in the different eruptions. All this allows us to suggest periodic arrivals of mafic magmas in the post-Minoan plumbing system of Santorini, also implying for a still active magmatic system whose behaviour needs to be fully evaluated, also in the light of the 2011-2012 unrest.  


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On the nature & causes of volcanism in the Galápagos archipelago


Tuesday 21st May - 4.00 pm - Mineralogy seminar room


Dr Sally A Gibson, Department of Earth Sciences, University of Cambridge, UK.


Diversity appears to be key to understanding natural phenomena in the Galápagos archipelago. Whilst most associate this with the unusual creatures that inhabit the islands it is also true of their volcanic nature.

Historical perspective: The volcanic nature of Galápagos was based on reports of pirates, buccaneers and naval admirals until 1835, when Charles Darwin visited the archipelago during the Beagle voyage. Although widely regarded as a zoologist, Darwin was first and foremost a geologist and especially interested in the formation of volcanic islands. Whilst in Galápagos, most of his time was spent on James Island (now known as Santiago) and here he made a crucial observation regarding the occurrence of different volcanic rock types; he realised that confinement of low-density trachytes to elevated parts and higher-density basalts to lower slopes of the same volcano meant that different types of magma could form in ‘the body of a volcanic mountain’ by sinking of crystals. In this regard he was the first scientist to link the diversity of volcanic rock types to what we now refer to as crystal settling. Darwin’s theory of crystal sinking was published in 1844 but not widely accepted at the time.


21st Century importance: The Galápagos archipelago is a natural laboratory for Earth Scientists and provides a unique opportunity to test models of mantle melting. It is one of the world’s most volcanically active regions with eruptions of predominantly basaltic lavas occurring every 3 to 5 years. Galápagos is located above a mantle plume and adjacent to an oceanic spreading centre. Whilst the greatest volumes of melt occur in the west of the archipelago, close to the postulated axis of the plume, volcanism is widespread. There are no age-progressive linear relationships between activity and distance from the location of the present-day hotspot and no temporal variation in magma type as there is for example at Hawaii. The large geochemical dataset for recently erupted basalts and high-resolution seismic database allow greater constraints to be imposed on the causes of volcanism than for any other archipelago. Melt generation occurs both in the region of active mantle upwelling, which has a radius of ~100 km, and also where plume mantle is being dispersed laterally towards the adjacent spreading centre. The composition of erupted basalts is closely linked to the thickness of the underlying lithosphere: numerical modelling of geochemical and geophysical datasets has revealed that this is relatively thin (45 km) beneath the NE of the archipelago and allows the generation of tholeiitic basalts. Above the current zone of active plume upwelling the lithosphere is thicker (60 km) such that the amount of melting is lower and alkali basalts are generated. Isla Santiago is located in central Galápagos above the margin of the zone of active upwelling and also on the edge of the zone of thin lithosphere. The island is unique in that it has experienced recent eruptions of basaltic melts with extremely varied major- and trace-element and also isotopic compositions. This diversity is a manifestation of both complex physical processes and compositional variations in the underlying mantle plume.

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Tuesday 7th May - 4.00 pm

Mineralogy seminar room


Another point of view on sexual selection in prehistoric animals

Dr Rob Knell, Senior Lecturer at Queen Mary University of London.


Sexual selection is one of the most important driving forces in evolution and is responsible for a tremendous amount of the morphological diversity that we see today. Many of the most charismatic prehistoric animals also appear to carry traits that could be explained as the result of sexual selection: horns, crests, plates, sails and many others. Nonetheless, palaeontologists have traditionally avoided using sexual selection as an explanation for these features and have preferred mechanical, thermoregulatory or species-recognition based interpretations, probably because it is very hard to produce testable hypotheses about the behavioural significance of such traits when we are unable to observe an animal's behaviour. This conservative approach is likely to lead to a significant degree of misinterpretation - sexual selection is a ubiquitous and powerful force and there is no reason to discount it as an explanation for morphological diversity in the fossil record. I will examine the problem of how we can detect sexual selection in the fossil record and discuss issues such as sexual dimorphism, allometry and how it changes with sexual maturity, apparent cost and diversity as potentially helpful indicators of sexually selected features in extinct animals.



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Studying new minerals: the nature and value of novelty - Dr Mark Welch (NHM).  Tuesday 26th March 2013, 1600h, Earth Sciences Seminar Room


The geological history of the Earth over the past 4.5 billion years has seen immense diversity in the physical and chemical conditions in the crust.  In these various conditions, different minerals form and for many years a significant part of Museum research undertaken by the Department of Earth Sciences has been the identification and characterisation of minerals new to science. Characterisation of minerals involves a comprehensive determination of atomic-scale structure, composition and diagnostic physical properties using both traditional techniques and advanced analytical equipment.


Apart from their novelty, new minerals offer the chance to develop models of structural hierarchies in which major building principles are uncovered by relating these minerals to others. Time and again new minerals provide insights into perplexing mineralogical problems that often bear upon wider geological or technological issues, such as the possibilities for effective storage or immobilisation of toxic elements, transformations between environmentally radical and benign minerals, or new directions for preparing new synthetic analogues of technological materials such as nanoporous and microporous catalysts and molecular sieves.


In this talk an outline of the new-mineral research currently undertaken will be given, describing the experimental techniques involved in characterising new minerals. A few examples illustrating how the study of new minerals has provided fertile ground for wider scientific research will be described.


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Sexual selection in prehistoric animals: misidentifications and false positives


Prof Kevin Padian, Department of Integrative Biology & Museum of Paleontology, University of California, Berkeley


Tuesday 11th December 2012
Neil Chalmers Seminar Room, DC2, NHM, 1330


Darwin acknowledged that the roles of some morphological structures are difficult to determine.  But he was clear about what sexual selection is, and the role of sexual dimorphism in it.  Because Darwin invented sexual selection, and based it on observations that have never been falsified, his definition cannot be wrong.  It has three components: (1) it explains why sexual dimorphism exists, and its central role in sexual selection; (2) the dimorphic structures or behaviours are used by one gender to attract mates or repel rivals for mates; and (3) these structures and behaviours help the bearer gain access to mates.  Strangely, palaeontologists and neontologists have largely ignored him.  Assertions of sexual selection/dimorphism in the fossil record suffer from a lack of statistical rigor and an unwillingness to test hypotheses through independent lines of evidence.  No such study has had any independent assessment of the chronological age or stage of its individuals, although such information is frequently available.  We show why much alleged sexual dimorphism in fossil tetrapods is more likely simply ontogenetic change, and why both a statistically significant population sample and an independent assessment of age of specimens are needed before the hypothesis of sexual dimorphism can be tested.



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Fungal-plant associations in Palaeozoic-Mesozoic times

Dr Christine Strullu-Derrien, Department of Earth Sciences, NHM

Thursday 15th November
Neil Chalmers Seminar Room, DC2, NHM 15:00



A fungal mode of life (mycelial growth and mode of nutrition) is shared by several living groups of organisms, notably Fungi (Eumycota) and Oomycetes (Stramenopila). Originally, a lot of these groups were called fungi, but now we know that they have quite diverse relationships among eukaryotes. These organisms are known to have coexisted with plants since the dawn of life on land, but their role in plant evolution is still poorly understood.


Recent research based on historic collections of petrified plants is opening up a rich new source of information for the study of fungal-plant associations. Dr Strullu-Derrien will present an overview of recent findings including fossil evidence for fungi and fungi-like symbionts in Palaeozoic and Mesozoic ecosystems.



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