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palaeontology

Imaggeo on Mondays: An expedition to better understand Antarctic soils

Imaggeo on Mondays: An expedition to better understand Antarctic soils

A dramatic evening sky puts the frame to a photo taken during the Brazilian Antarctic expedition to James Ross Island in 2016. Brazilian palaeontologists and soil scientists together with German soil scientists spent over 40 days on the island to search for fossils and sample soils at various locations of the northern part of the island.

The island was named after Sir James Clark Ross who led the British expedition in 1842, which first charted locations at the eastern part of the island. James Ross Island is part of Graham Land, the northern portion of the Antarctic Peninsula, separated from South America by the stormy Drake sea passage.

Map of the Antarctic Peninsula featuring the James Ross Archipelago (Credit: The Scientific Committee on Antarctic Research, Antarctic Digital Database Map Viewer)

This photo was taken in the northern Ulu Peninsula, which is the northernmost part of the relatively large James Ross Island and the largest ice-free area in the Antarctic Peninsula region. The island’s characteristic appearance is formed by Late Neogene volcanic rocks (3-7 million years old) over fossil rich Late Cretaceous sandstones (66-120 million years old).

In the photo we are looking from a higher marine terrace at the Santa Martha Cove, the ‘home’ to the 2016 Brazilian Antarctic expedition, towards the steep cliffs of Lachman Crags, a characteristic mesa formed by Late Neogene lava flows. The Lachman Crags mesa, the Spanish word for tablelands, dominates the landscape of the northern part of the Ulu Peninsula. Above the cliffs visible in the photo, a glacier covered plateau stretches to the Northwest.

The marine terrace on which the tent is standing is comprised of a flat area that has been ice-free for approximately 6000 years and thus makes for a great model system to study soil development after glacial retreat. The ground is composed of a mixture of volcanic rocks and Cretaceous sandstones rich in all sorts of fossils, from fossilised wood to shark teeth, ammonites and reptile bones.

The strong winds that can start in Antarctica from one moment to the other and the very low precipitation led to the characteristic desert pavement, with stones sorted in a flat arrangement on top of the fine textured, deeply weathered permafrost soils. Although these soils host a surprisingly high number of microorganisms, most terrestrial life is restricted to wetter areas surrounding fresh water lakes and melt water streams. Thus lakes and snow meltwater-fed areas make for higher primary production of algae and mosses, fostering biodiversity and soil development by organic matter input.

As there are no larger bird rookeries on James Ross Island the only way sea-derived nutrients reach the Ulu Peninsula is by a rather grim feature:  dead seal carcasses that lie distributed across the lowlands (< 150 m asl) of the Ulu Peninsula. Carcasses fertilise the soils in their direct vicinity while slowly decomposing over decades, thus feeding small patches of lichens and mosses within the barren cold arid desert. The region is thus an illustration of the harsh Antarctic environment where even Weddell seals, animals that are well adapted for the living in dense pack ice during the polar night, die when losing track on land on the way to the water.

By Carsten Müller, Technical University of Munich Chair of Soil Science, Germany

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: A slice of fossil life

Imaggeo on Mondays: A slice of fossil life

I am a petrographer at the University of Padova, Italy, studying the metamorphic rocks that form the deep Earth’s crust beneath our feet, and what happens when they get so hot to start to melt.

I’ve spent (enjoyed I should say) more than 30 years looking at rocks with an optical microscope. This simple, cheap tool, and more importantly, its skilled use, remain key ingredients for good research in petrology!

I’ve been taught by scientists, like Ron Vernon of Macquarie University in Australia, that a good micrograph is essential to document my research and strengthen my conclusions, and so I’ve always paid particular attention to the quality of photos. In the meanwhile, I have also developed a particular interest in photomicroscopy with an aesthetic purpose, realizing that the cocktail of rocks and polarized light has an extraordinary potential in the ‘sciart’ (Science-and-Art) field.

The digital revolution has marked a turning point in this activity, and 10 years ago I have started my micROCKScopica project to showcase to the public the beauty hidden in the small slices of rock that are thin sections.

When I find a photogenic rock I play with polarizers to get the desired combinations of color, and then I take a photograph. And people can enjoy the images, their colors and shapes, even without knowing the geological history behind them.

This is particularly true for this photograph: it is a thin section of a piece of dinosaur bone but I don’t know much about it (what bone, which dinosaur), only that it had been collected in Utah, in the United States. I received a small sample of the bone by Denise M. Harrison, a friend with whom I collaborated for a book on Lake Superior Agates. She is an award-winning lapidary (someone who cuts, polishes and engraves stones), and makes lovely cabochons with all sort of semiprecious, hard stones. I asked her for some leftovers to make some thin sections, because I wanted to see something new, possibly silicified (impregnated with silica during fossilization) because chalcedony – the very fine-grained variety of common quartz – may be extremely photogenic.

I had no idea of how a bone could look like under the microscope, and the first sight left me speechless! The porous structure, and the patterns of the radiating textures in the chalcedony fillings are extraordinary, and provide a wealth of possibilities for nice images.

In this shot, that I replicated in red and blue, a larger hole had been filled with a fine-grained quartz sand – the dark moon shape on top left – somehow interrupting the regular pattern of the bone tissue, that to someone may recall Australian Aboriginal artwork.

Curiously, this anatomically-related image made me quite popular among pathologists and other medical doctors, who find many analogies with their subjects of research. The ages of the specimens are some hundred million years apart, though…

By Bernardo Cesare, University of Padova, Italy

www.microckscopica.org

Editor’s note: The fossil sample featured in this photo was collected and distributed legally from Utah.

If you pre-register for the 2019 General Assembly (Vienna, 07–12 April), you can take part in our annual photo competition! From 15 January until 15 February, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Nummulites, the living lentils

Imaggeo on Mondays: Nummulites, the living lentils

This photograph depicts a close-up of Eocene limestones from the Sardinero Formation in Cantabria (Northern Spain). The limestone is rich with foraminifera shells, most of them from the Nummulitidae family. These organisms once lived in a very shallow sea that separated Europe from Iberia in the late Mesozoic and early Cenozoic era. Later the sea basin’s  closure led to the formation of the Pyrenees.

The remarkable abundance of these Paleogene and Eocene fossils around the globe led Eugène Renevier, a Swiss geologist from the 19th century, to propose merging the two Epochs into the Nummulitic Period, a suggestion that did not succeed.

Nummulitidae were also some of the first microfossils recognized in literature. Their features were described in Book XVII of Geography, written by the Greek geographer and historian Strabo around the beginning of the 1st century. In this passage Strabo finds the Nummulitidae fossils embedded in the rocks used to build Egyptian pyramids, however he mistakes the shells for lentils dropped by rushed workers. It reads below:

One of the marvellous things I saw at the pyramids should not be omitted: there are heaps of stone-chips lying in front of the pyramids; and among these are found chips that are like lentils both in form and size; and under some of the heaps lie winnowings, as it were, as of half-peeled grains. They say that what was left of the food of the workmen has petrified; and this is not improbable.

Indeed, in my home-country, in a plain, there is a long hill which is full of lentil-shaped pebbles of porous stone; and the pebbles both of the seas and of the rivers present about the same puzzling question; but while these latter find an explanation in the motion caused by the current of water, the speculation in that other case is more puzzling.

It has been stated elsewhere that in the neighbourhood of the quarry of the stones from which the pyramids are built, which is called “Trojan”, and that there are caves at the foot of it, and a village near both these and the river which is called Troy, being an ancient settlement of the captive Trojans who accompanied Meneläus but stayed there.

Despite this initial description referring to lentil-sized Nummulitidae, the size of these fossils varies considerably among different species, and can reach up to 12 cm, some of which have been found in Cenozoic rocks in the same area where the photograph was taken. Such a size is remarkable, considering the fact that Nummulitidae are unicellular organisms.

There are lots of genera within the Nummulitidae family, the most common of which are Assilina and Nummulites. The fossils in the photograph are about 1 cm in length and pertain to the Nummulites genus. Nonetheless, more elongated and white fossils from the Discocyclinidae family are also present in the limestone; one of them can be found right below the crawling snail.

While taking some pictures of the outcrop, I noticed the snail in the lower part of the frame, slowly crawling towards the top of it. To my surprise, it chose to follow the path drawn by two large Discocyclinidae shells, and I rushed to take this photograph. Two living beings together but separated by 50 million years, embodying a sort of spacetime paradox.

By Manuel de Paz Álvarez, the University of Oviedo

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submittheir photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

How certain plants survive mass extinction events: study

How certain plants survive mass extinction events: study

We often read about Earth’s mass extinction events and how they wiped out vast numbers of animal species, leaving survivors to evolve and repopulate the planet. But it’s rarer to hear about how plants managed these catastrophes.

A new study published last month by a team at University College Dublin, Ireland, in the journal Nature Plants shows how plants with thicker, heavier leaves were more likely to survive the Triassic-Jurassic mass extinction caused by an episode of global warming 200 million years ago – around the time when dinosaurs came to dominate the planet. The extinction event is known to have had a massive impact on life, both on land and in the oceans, with an estimated half of species on Earth going extinct at the time.

“Previously we knew a bit about plant survival in terms of their abundance – whether they are present or absent in fossil record,” says the study’s lead author Wuu Kuang Soh, of University College Dublin, “but we didn’t know how they survived or the intrinsic factors of plants that contributed to their survival.”

By looking at fossilized leaves of two plant groups uncovered in Greenland, the authors suggest that the reason for some plants’ survival is that those with heavier leaves were more resilient to environmental stressors such as high air temperature and rising carbon dioxide.

According to Barry Lomax, a lecturer in Environmental Science at the University of Nottingham, UK, who was not involved in the research, “being able to establish that different plant groups respond differently to stress, and that their capacity to adapt to this stress is reflected in their propensity for survival, is a great piece of detective work.”

New proxy development

The work presented in this study – a joint research effort by University College Dublin and Macquarie University, Australia – relied heavily on the development of a new proxy i.e. a physical characteristic which is used to infer details about some related, but immeasurable, trait. By showing how the thickness of a plant’s leaf cuticle (the protective layer covering a leaf) is related to the leaf mass per unit area (LMA) in modern leaves, the team were able to use their fossils to identify how heavy the paleo leaves were for their size.

Macrofossil of 200 million years old Triassic ginkgo, Sphenobaiera spectabilis. Used with permission of the study authors (Credit: Mark Wildham).

For some scientists, this development itself is the study’s highlight. “I think the key finding of the work is that it gives us another set of tools to unpick how plants have responded to large scale perturbations in the carbon cycle which have influenced climate,” says Lomax.

By using the new proxy for LMA the authors were able to look at changes in two plant groups – Ginkoales (an gymnosperm order – see image) and Bennettitales (a now extinct order of seed plant)– across the Triassic-Jurassic mass extinction, and discover their opposing fates; the former flourishing and the latter experiencing sharp ecological decline.

“We found that plants with higher LMA had a higher chance of survival than plants with lower LMA during this global warming induced mass extinction event” says lead author Soh.

Commenting on the study, Charilaos Yiotis, a plant physiologist at University College Dublin who did not participate in the research, says that “under the greenhouse conditions of the Triassic-Jurassic Boundary – or, may I add, under near-future greenhouse conditions – plants with fast leaf turnover rates (low LMA) are outcompeted by those adopting more “conservative” strategies like robust, low turnover leaves (high LMA).” The turnover rate Yiotis refers to is the time taken for leaves to be produced and then fall.

“The spectrum describes how “fast” or “slow” the plant is turning over its nutrient resources,” adds Dana Royer, a paleobotanist at Weslayan University, Connecticut, who peer-reviewed the paper for Nature. “At the fast-return end (low LMA), plants have high photosynthetic rates, high nutrient contents, short-lived (deciduous, for example) and cheaply built leaves. This is the live-fast-die-young strategy. At the slow-return end (high LMA), plants show the reverse.”

The current mass extinction

The study’s findings are important in relation to the sixth mass extinction event which is currently underway. Scientists believe that a similar extinction process to those in the past is now taking place, as the variety of life on land gives way to the seemingly unstoppable human developments of agriculture, industry, and urbanisation. By looking at the paleo-evidence the authors tentatively suggest that today’s plant communities which host thicker, heavier leaves (high LMA) may be better adapted to deal with the current episode of anthropogenic warming, and therefore have a better chance of future ecological success than plants with lighter leaves (low LMA).

“More specifically, plants that can have leaves with both low and high LMA appear to do well after surviving a catastrophic mass extinction episode,” says Soh. “Our finding is important because it means that plants with flexibility in LMA will be the favourite to flourish during future global warming.”

“A shift to higher LMA is common for plants when they are exposed to high CO2” says Royer, “so the fact that the authors are finding the same response in a “natural” experiment – albeit 200 million years ago – lends support to the idea that we should expect a similar response in our own future.”

Further looking to the future, University College Dublin’s Charilaos Yiotis finds it alarming that most plants of economic importance today would probably never have made it through the Triassic-Jurassic Boundary.

“At a time where humanity’s biggest challenge is to feed an ever-growing human population,” he says, “this study should make us think again about how big a threat climate change is to future food security.”

By Conor Purcell, a Science & Nature Writer with a PhD in Earth Science.

Conor has previously worked with the authors of this paper, but not on the project itself. He can be found on twitter @ConorPPurcell and some of his other articles at cppurcell.tumblr.com.

References

Soh, W.K., Wright, K.L, Bacon, T.I., et al., Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event, Nature Plants, 3, doi:10.1038/nplants.2017.104, 2017.

Editor’s note: This blog post provides a summary to a research paper that is paywalled, unlike other scientific articles featured on GeoLog. The EGU supports and promotes open access, publishing 17 open access journals and having endorsed Open Access 2020, an initiative to promote the large-scale transition to open access publishing. Since research in the realm of palaeontology and evolutionary biology is rarely featured on GeoLog, an exception was made on this occasion to publish a story on a scientific paper not accessible to all. The lead author of the study is happy to be contacted with questions about the research; if you’d like to find out more please email Wuu Kuang Soh (wuukuang@gmail.com).