Miniscule flightless birds have lived in New Zealand’s wetlands for millions of years

February 28, 2018

A tiny extinct rail (30-40g) is overshadowed by a regular duck. Credit: Gavin Mouldey

Fossilized bones of two new species of tiny, flightless extinct birds have been discovered by Australasian scientists in 19 to 16-million-year-old sediments of an ancient lake on the South Island of New Zealand.

The two miniscule species—one barely larger than a sparrow—were members of the rail family, a group of birds common today in wetlands that includes swamphens, moorhens, coots and crakes. Their remains were unearthed near the town of St Bathans in Central Otago.

Many rail species can fly well and have dispersed to far-flung oceanic islands. However, flightlessness has evolved more times in this group of birds that in any other, especially on predator-free islands. The world’s largest rails evolved in New Zealand, notably the flightless takahe and weka.

The study, led by scientists from Flinders University with colleagues from UNSW, Canterbury Museum and the Museum of New Zealand, is published in the Journal of Systematic Palaeontology.

Team member UNSW Professor Mike Archer, says: “This new discovery emphasizes the fact that New Zealand has long been one of the world’s most extraordinary engines driving bird evolution.

“Charting how lineages like these rails have changed through time on an island that has been geographically isolated for more than 80 million years will test basic presumptions made about bird evolution in general,” says Professor Archer of the of the PANGEA Research Centre in the School of Biological, Earth and Environmental Sciences.

Nineteen to 16 million years ago, a 5600 square kilometre megalake dominated the landscape of New Zealand’s South Island. It was surrounded by a subtropical rainforest and plants typical of Australia and long lost from New Zealand, such as eucalypts, casuarinas, palms and cycads, were common there.

“Flightlessness in birds is often associated with an increase in size,” says Ellen Mather, study lead author and Ph.D. student at Flinders University. “The weka, which is in the same family as our fossil birds and lives in New Zealand today, is about the size of a chicken. The Banded Rail, their closest flying relative, is about half that size.”

The most common of the new fossil rails has been named Priscaweka parvales, meaning ancient weka with small wings. It was a mere one twentieth of the weight of a weka and was similar in size to the recently extinct Chatham rail Cabalus modestus.

Small flightless birds only exist in the absence of terrestrial mammalian predators, and New Zealand has long been recognised as the iconic example of a country with an avifauna which evolved in the absence of such predators.

When humans discovered New Zealand, the main islands had many flightless birds including giants within the nine species of moa, several kiwi, two huge geese, two adzebills, even some tiny wrens, and at least five flightless rails.

Team member, Dr. Paul Scofield, a Senior Curator at the Natural History at Canterbury Museum, says: “The new St Bathans’ rails join a host of other fossil birds recovered from these deposits that show New Zealand has long been a land of birds. The discovery of these two miniscule flightless rails raises the question of ‘Where did they come from?'”

The researchers suggest they had ancestors in Australia which flew across the 1500 km ocean to New Zealand in previous millennia. However, the new species are unlike any rail known elsewhere, so their exact origin or closest relatives remain a mystery.

Other than hints of large flightless moa ancestors, these rails are the first flightless birds to be described from this fauna. This is unexpected as the St Bathans Fauna contains small terrestrial mammals, which normally preclude evolution of small flightless species. The tiny flightless rails therefore strongly suggest that the mysterious mammals were not predators of small birds. Flightless birds have been a feature of the New Zealand avifauna for millions of years, much longer than previously thought. They are probably the oldest flightless rails known globally.

“The ongoing research into the fossil birds of New Zealand builds on that begun over 150 years ago. It continues to throw up revelations into the timing and origins of major groups of birds that characterize modern avifaunas” says Associate Professor Trevor Worthy of Flinders University.

Note: The above post is reprinted from materials provided by University of New South Wales.

Volcanic tramping in Eastern Sicily: An old system feeds “young” Etna

February 26, 2018

Mount Etna. Credit: Angelo T. La Spina, Lizenz: CC BY-SA 4.0

Mount Etna in southern Italy is one of the most active volcanoes on Earth, while the Hyblean Volcanoes, located further south, are extinct today. An international team of scientists with the participation of the GFZ searched for the source of magmas of Etna and examined why the ground south of Etna does not emit lava anymore. The results have now been published in the scientific journal Earth & Planetary Science Letters.

Volcanic eruptions and earthquakes most frequently occur alongside of tectonic plate margins. Some volcanoes, however, also arise within a plate; researchers refer to this as “intraplate volcanism”. Well known examples are the chain of islands of Hawaii or the Canary Islands. The volcanoes in Eastern Sicily are of the same type. For about five hundred thousand years now, Etna, a mountain of 3300 meters height, is an active volcano. The Hyblean Volcanoes, however, that were active until about one million years ago, form a mountain range on the southernmost edge of Sicily.

Movements in the deep migrate volcanoes

The scientists modelled the pathways of magma below the Hyblean Volcanoes and Etna, down to the Earth’s crust-mantle boundary in about 30 kilometers depth. The model shows: Magma pathways, also referred to as dikes, both for Etna and the Hyblean Volcanoes all bend to the East and meet with the crust-mantle boundary below the Malta Escarpment. The Malta Escarpment is a system tectonically active now for hundreds of millions of years. It stretches alongside the eastern Sicilian coastline for more than three hundred kilometres, far into the Mediterranean Sea. Often, earthquakes originate in this region. Over the past ten million years, the Earth’s crust in this region was compressed and expanded in different directions again and again.

These movements together with a deepening of the fault scarp led to bent, not vertical, magmatic dikes. Over time, this also resulted in a northwestward migration of active volcanism. Eleonora Rivalta, GFZ section Physics of Earthquakes and Volcanoes, co-author of the study: „Our findings show that Etna and the Hyblean Volcanoes represent eruptions of different ages of the same volcanic system.“ In the future, similar models may be applied to other regions to show where origins of magmas are and how dikes develop over time. (ak)

Reference:
Neri, M., Rivalta, E., Maccaferri, F., Acocella, V., Cirrincione, R., 2018. Etnean and Hyblean volcanism shifted away from the Malta Escarpment by crustal stresses. Earth and Planetary Science Letters, Volume 486, 15-22 pp. DOI: 10.1016/j.epsl.2018.01.006

Note: The above post is reprinted from materials provided by Helmholtz Centre Potsdam/GFZ German Research Centre for Geosciences.

Complete genomes of extinct and living elephants sequenced

February 26, 2018

This is crushed dentine from a Woolly Mammoth for DNA extraction. Credit: JD Howell, McMaster University

An international team of researchers has produced one of the most comprehensive evolutionary pictures to date by looking at one of the world’s most iconic animal families — namely elephants, and their relatives mammoths and mastodons-spanning millions of years.

The team of scientists-which included researchers from McMaster, the Broad Institute of MIT and Harvard, Harvard Medical School, Uppsala University, and the University of Potsdam-meticulously sequenced 14 genomes from several species: both living and extinct species from Asia and Africa, two American mastodons, a 120,000-year-old straight-tusked elephant, and a Columbian mammoth.

The study, published in the Proceedings of the National Academy of Science, sheds light on what scientists call a very complicated history, characterized by widespread interbreeding. They caution, however, the behaviour has virtually stopped among living elephants, adding to growing fears about the future of the few species that remain on earth.

“Interbreeding may help explain why mammoths were so successful over such diverse environments and for such a long time, importantly this genomic data also tells us that biology is messy and that evolution doesn’t happen in an organized, linear fashion,” says evolutionary geneticist Hendrik Poinar, one of the senior authors on the paper and Director of the McMaster Ancient DNA Centre and principal investigator at the Michael G. DeGroote Institute for Infectious Research.

“The combined analysis of genome-wide data from all these ancient elephants and mastodons has raised the curtain on elephant population history, revealing complexity that we were simply not aware of before,” he says.

A detailed DNA analysis of the ancient straight-tusked elephant, for example, showed that it was a hybrid with portions of its genetic makeup stemming from an ancient African elephant, the woolly mammoth and present-day forest elephants.

“This is one of the oldest high-quality genomes that currently exists for any species,” said Michael Hofreiter at the University of Potsdam in Germany, a co-senior author who led the work on the straight-tusked elephant.

Researchers also found further evidence of interbreeding among the Columbian and woolly mammoths, which was first reported by Poinar and his team in 2011. Despite their vastly different habitats and sizes, researchers believe the woolly mammoths, encountered Columbians mammoths at the boundary of glacial and in the more temperate ecotones of North America.

Strikingly, scientists found no genetic evidence of interbreeding among two of the world’s three remaining species, the forest and savanna elephants, suggesting they have lived in near-complete isolation for the past 500,000 years, despite living in neighbouring habitats.

“There’s been a simmering debate in the conservation communities about whether African savannah and forest elephants are two different species,” said David Reich, another co-senior author at the Broad Institute who is also a professor at the Department of Genetics at Harvard Medical School (HMS) and a Howard Hughes Medical Institute Investigator. “Our data show that these two species have been isolated for long periods of time — making each worthy of independent conservation status.”

Interbreeding among closely related mammals is fairly common, say researchers, who point to examples of brown and polar bears, Sumatran and Bornean orangutans, and the Eurasian gold jackal and grey wolves. A species can be defined as a group of similar animals that can successfully breed and produce fertile offspring.

“This paper, the product of a grand initiative we started more than a decade ago, is far more than just the formal report of the elephant genome. It will be a reference point for understanding how diverse elephants are related to each other and it will be a model for how similar studies can be done in other species groups,” said co-senior author Kerstin Lindblad-Toh, a senior associate member of the Broad Institute and Director of the Science for Life Laboratory at Uppsala University in Sweden.

“The findings were extremely surprising to us,” says Eleftheria Palkopoulou, a post-doctoral scientist in at HMS. “The elephant population relationships could not be explained by simple splits, providing clues for understanding the evolution of these iconic species.”

Researchers suggest that future work should explore whether the introduction of new genetic lineages into elephant populations-both living and ancient-played an important role in their evolution, allowing them to adapt to new habitats and fluctuating climates.

Reference:
Eleftheria Palkopoulou, Mark Lipson, Swapan Mallick, Svend Nielsen, Nadin Rohland, Sina Baleka, Emil Karpinski, Atma M. Ivancevic, Thu-Hien To, R. Daniel Kortschak, Joy M. Raison, Zhipeng Qu, Tat-Jun Chin, Kurt W. Alt, Stefan Claesson, Love Dalén, Ross D. E. MacPhee, Harald Meller, Alfred L. Roca, Oliver A. Ryder, David Heiman, Sarah Young, Matthew Breen, Christina Williams, Bronwen L. Aken, Magali Ruffier, Elinor Karlsson, Jeremy Johnson, Federica Di Palma, Jessica Alfoldi, David L. Adelson, Thomas Mailund, Kasper Munch, Kerstin Lindblad-Toh, Michael Hofreiter, Hendrik Poinar, David Reich. A comprehensive genomic history of extinct and living elephants. Proceedings of the National Academy of Sciences, 2018; 201720554 DOI: 10.1073/pnas.1720554115

Note: The above post is reprinted from materials provided by McMaster University.

Hidden ‘rock moisture’ could be key to understanding forest response to drought

February 26, 2018

Research led by The University of Texas at Austin has found that weathered bedrock can store a significant amount of rock moisture inside its fractures and pores. This moisture in the layer of weathered rock that is commonly located beneath soils is an important part of the water cycle on the local and global level. Tree roots tap into the rock moisture and release it back into the atmosphere as water vapor, and water flows through the fractures and becomes part of the seasonal groundwater storage (blue arrows). Credit: University of Texas at Austin Jackson School of Geosciences.

Research conducted by The University of Texas at Austin and University of California, Berkeley has found that a little-studied, underground layer of rock can hold significant amounts of water that may serve as a vital reservoir for trees, especially in times of drought.

The study, published in the journal PNAS on February 26 looked at the water stored inside the layer of weathered bedrock that commonly lies under soils in mountainous environments.

This transitional zone beneath soils and above groundwater is often overlooked when it comes to studying hydrological processes, but researchers found that the water contained within the fractures and pores of the rock could play an important role in the water cycle at the local and global level.

“There are significant hydrologic dynamics in weathered bedrock environments, but they are not traditionally investigated because they are hard to access,” said lead author Daniella Rempe, an assistant professor in the Department of Geological Sciences at the UT Austin Jackson School of Geosciences. “The study was designed to investigate this region directly.”

Researchers found the water within the bedrock has the ability to sustain trees through droughts even after the soil has become parched. At the field site in Northern California’s Mendocino County, scientists found that up to 27 percent of annual rainfall was stored as “rock moisture,” the water clinging to cracks and pores within the bedrock The impact of rock moisture will vary depending on the region and topography, but researchers said it likely explains how the trees in the study area showed little affect from the severe 2010-2015 drought that killed more than 100 million trees throughout California.

“How trees can survive extended periods of severe drought has been a mystery,” said Richard Yuretich, director of the National Science Foundation’s Critical Zone Observatories program, which funded the research. “This study has revealed a significant reservoir of trapped water that has gone unnoticed in the past. Research of this kind can help greatly in managing natural resources during times of environmental stress.”

To conduct the study, researchers monitored the rock moisture from 2013-2016 at nine wells drilled into the weathered bedrock along a steep forested hillslope. They used a neutron probe, a precision tool that measures the amount of water in a sample area by detecting hydrogen.

They found that the weathered rock layer built up a supply of 4 to 21 inches of rock moisture during the winter wet season, depending on the well. The maximum amount of rock moisture in each well stayed about the same throughout the study period, which included a significant drought year. It’s a major finding that indicates that it doesn’t matter if it rains a little or a lot during the winter dry season—the total rainfall amount does not influence the rock moisture levels.

“It doesn’t matter how much it rains in the winter, rock moisture builds up to the same maximum value,” Rempe said. “That leads to the same amount of water every summer that’s available for use by trees.”

Researchers also found that the average rock moisture at all wells exceeded the average soil moisture measurements at all locations.

“Soils are important, but when it comes to determining if a place is going to experience water stress, it could be the underlying rock that matters most,” Rempe said. “This is the first time this has been demonstrated in a multi-year field study.”

The potential for rock moisture to travel back to the atmosphere via evaporation from tree leaves or to trickle down into groundwater indicates that it could have a broad impact on the environment and climate. Zong-Liang Yang, a professor in the Jackson School’s Department of Geological Sciences who was not involved in the study, said that the research highlights the need to gather data so rock moisture can be incorporated into climate models.

“At present, most, if not all, of global climate and hydrological models neglect moisture stored in rocks,” Yang said. “This study fills a critical gap in our understanding.”

The study provides a glimpse into rock moisture at a small, intensive research site, said co-author William Dietrich, a professor at the University of California, Berkeley. He said the data collected during this study should be a starting point for more research in more places.

“The future paths are many,” Dietrich said. “We have just one site well-studied… A mixture of theory and field studies will need to be developed to provide regional information for climate modelers.”

Reference:
Daniella M. Rempe el al., “Rock moisture: Direct observations of a hidden component of the hydrologic cycle,” PNAS (2018). DOI: 10.1073/pnas.1800141115

Note: The above post is reprinted from materials provided by University of Texas at Austin.

Geological change confirmed as a factor behind the extensive diversity in tropical rainforests

February 26, 2018

Cremastosperma brevipes, French Guiana. Credit: Copyright Paul J. M. Maas

The tropical rainforests of Central and South America are home to the largest diversity of plants on this planet. Nowhere else are there quite so many different plant species in one place. However, the entire region is increasingly threatened by human activity, which is why researchers are stepping up their efforts to record this astonishing biodiversity and find out how it developed. In a project undertaken by Johannes Gutenberg University Mainz (JGU) in collaboration with Dutch research institutions, the causes of this plant diversity were investigated by studying two closely related groups of trees of the Annonaceae family.

The researchers identified three relevant factors: the formation of the Andes mountain range, the disappearance due to natural causes of the extensive Pebas wetlands system that once existed in the Amazon region, and the formation of a land bridge between Central and South America in the form of the Panama Isthmus.

Cremastosperma and Mosannona are two genera of the Annonaceae or custard apple family the habitat of which is neotropical rainforests, where they extend from the lowlands up to elevations of 2,000 meters. They are primarily found in the Andes region of South America, but also as far north as Central America. The team of botanists led by Dr. Michael Pirie, who joined JGU as a researcher in 2013, looked at the distributions of the various species of both genera and their phylogenetic history in order to determine the influence of the geological upheavals on the continent. For this purpose they compiled a time-calibrated phylogenetic tree based on DNA data, using the so-called molecular clock technique which is calibrated using the ages of the available fossils. In total, they analyzed 11 species of the genus Mosannona and 24 species of the genus Cremastosperma.

Table of Contents

Formation of the Andes, the Isthmus of Panama, and the drying-out of the Pebas wetland system all promoted diversification

The research has produced a biogeographical scenario that confirms in this context the significance of the geological history of north-western South America during the late Miocene and early Pliocene periods about 5 to 10 million years ago. “We have actually discovered that the diversification of these two plant genera took place in parallel with major geological events, namely the formation of the Andes, the drying-out of the Pebas system, and the development of a land bridge to Central America,” explained Pirie. Cremastosperma species, for example, were able to spread into what is today the Amazon basin and diversify, once the wetlands had silted up due to the deposition of material from the rising Andes.

One way in which diversification can be stimulated is by migration into a new ecosystem while another is adaptation to new conditions. “Natural changes over longer periods provide plants with a chance to adapt,” added Pirie. On the other hand, rapid changes, such as those that have occurred in the recent past, do not give plants sufficient time to evolve.

While the development of the two genera in line with geological conditions could be said to be more or less as might be expected, the biologists did find one clear difference between them. Although their distribution patterns mostly overlap, Cremastosperma species and Mosannona species to some extent dispersed along differing routes. In the case of Cremastosperma, colonization of an area in what is now Guyana began from north-western South America at a time before the last parts of the Andes developed and could form a barrier. Mosannona, on the other hand, began to spread here at a far later date from its base in the Amazon basin.

Taxonomic update to include five new species

Dr. Michael Pirie will be continuing his research work in 2018 with the aid of a grant from the Heisenberg Program of the German Research Foundation (DFG). This will also involve publication of an extensive monograph in which a total of 34 Cremastosperma species will be described, including five new species that Pirie and his colleagues have recently discovered.

Reference:
Michael D. Pirie, Paul J. M. Maas, Rutger A. Wilschut, Heleen Melchers-Sharrott, Lars W. Chatrou. Parallel diversifications of Cremastosperma and Mosannona (Annonaceae), tropical rainforest trees tracking Neogene upheaval of South America. Royal Society Open Science, 2018; 5 (1): 171561 DOI: 10.1098/rsos.171561

Note: The above post is reprinted from materials provided by Universität Mainz.

Life in world’s driest desert seen as sign of potential life on Mars

February 26, 2018

Hyperarid core of the Atacama Desert. Credit: Dirk Schulze-Makuch

For the first time, researchers have seen life rebounding in the world’s driest desert, demonstrating that it could also be lurking in the soils of Mars.

Led by Washington State University planetary scientist Dirk Schulze-Makuch, an international team studied the driest corner of South America’s Atacama Desert, where decades pass without any rain.

Scientists have long wondered whether microbes in the soil of this hyperarid environment, the most similar place on Earth to the Martian surface, are permanent residents or merely dying vestiges of life, blown in by the weather.

In a new study published in the Proceedings of the National Academy of Sciences, Schulze-Makuch and his collaborators reveal that even the hyper-arid Atacama Desert can provide a habitable environment for microorganisms.

The researchers found that specialized bacteria are able to live in the soil, going dormant for decades, without water and then reactivating and reproducing when it rains.

“It has always fascinated me to go to the places where people don’t think anything could possibly survive and discover that life has somehow found a way to make it work,” Schulze-Makuch said. “Jurassic Park references aside, our research tell us that if life can persist in Earth’s driest environment there is a good chance it could be hanging in there on Mars in a similar fashion.”

Table of Contents

The dry limit of life

When Schulze-Makuch and his collaborators went to the Atacama for the first time in 2015 to study how organisms survive in the soil of Earth’s driest environment, the craziest of things happened.

It rained.

After the extremely rare shower, the researchers detected an explosion of biological activity in the Atacama soil.

They used sterilized spoons and other delicate instrumentation to scoop soil samples from various depths and then performed genomic analyses to identify the different microbial communities that were reproducing in the samples. The researchers found several indigenous species of microbial life that had adapted to live in the harsh environment.

The researchers returned to the Atacama in 2016 and 2017 to follow up on their initial sampling and found that the same microbial communities in the soil were gradually reverting to a dormant state as the moisture went away.

“In the past researchers have found dying organisms near the surface and remnants of DNA but this is really the first time that anyone has been able to identify a persistent form of life living in the soil of the Atacama Desert,” Schulze-Makuch said. “We believe these microbial communities can lay dormant for hundreds or even thousands of years in conditions very similar to what you would find on a planet like Mars and then come back to life when it rains.”

Implications for life on Mars

While life in the driest regions of Earth is tough, the Martian surface is an even harsher environment.

It is akin to a drier and much colder version of the Atacama Desert. However it wasn’t always this way.

Billions of years ago, Mars had small oceans and lakes where early lifeforms may have thrived. As the planet dried up and grew colder, these organisms could have evolved many of the adaptations lifeforms in the Atacama soil use to survive on Earth, Schulze-Makuch said.

“We know there is water frozen in the Martian soil and recent research strongly suggests nightly snowfalls and other increased moisture events near the surface,” he said. “If life ever evolved on Mars, our research suggests it could have found a subsurface niche beneath today’s severely hyper-arid surface.”

Next Steps

On March 15, Schulze-Makuch is returning to the Atacama for two weeks to investigate how the Atacama’s native inhabitants have adapted to survive. He said his research team also would like to look for lifeforms in the Don Juan Pond in Antarctica, a very shallow lake that is so salty it remains liquid even at temperatures as low as -58 degrees Fahrenheit.

“There are only a few places left on Earth to go looking for new lifeforms that survive in the kind of environments you would find on Mars,” Schulze-Makuch said. “Our goal is to understand how they are able to do it so we will know what to look for on the Martian surface.”

Reference:
Dirk Schulze-Makuch el al., “Transitory microbial habitat in the hyperarid Atacama Desert,” PNAS (2018). DOI: 10.1073/pnas.1714341115

Note: The above post is reprinted from materials provided by Washington State University.

Life under extreme drought conditions

February 26, 2018

This is the sampling site Lomas Bayas in the core region of the Atacama. Credit: Dirk Schulze-Makuch, TU Berlin

The core region of the Atacama Desert in South America is one of the most arid places on earth. Sometimes it is raining only once in a decade or even less, the annual precipitation is far less than 20 mm. The dry conditions resulted in high salt concentrations in the soil and low organic matter content. However, scientists have found microorganisms there. But it has remained unclear whether these environments support active microbial growth or whether the observed cells were introduced by wind transport and subsequently degraded. Detailed analyses by an international research team show: Even in the most arid zones of the Atacama a microbial community exists which becomes metabolically active following episodic increase in moisture after rainfalls. The new findings, published in the journal PNAS, are important for evolution of life and landscapes on Earth. Moreover, the results have implications for the prospect of life on other planets – certainly for Mars.

The scientists took soil samples at six different locations in the Atacama Desert between 2015 and 2017. “We have chosen sample locations along a profile of decreasing moisture from the coast up to extreme arid conditions in the core region of the Atacama”, explains first author Dirk Schulze-Makuch from the TU Berlin. “This gradient should be reflected in the life-friendly conditions – we call it habitability – as well as in the number and diversity of the microorganisms.”

To get the whole picture the scientists used a broad range of complementary methods carried out at several geoscientific institutions in Berlin and Potsdam together with international partners. Amongst others the team conducted physico-chemical characterizations of the soil habitability and molecular biological studies. The latter were done mainly at GFZ German Research Centre for Geosciences in Potsdam where intracellular and extracellular DNA was analysed. “With this method we can find out which microorganisms really exist at the different locations in the Atacama probably doing metabolism and which ones are only represented by their naked DNA in the sediment as a signal from the past,” says Dirk Wagner, Head of GFZ-Section for Geomicrobiology and one of the leading authors of the article. “Further investigations like tests on enzymes have shown that the suspected organisms in most cases are in fact metabolically active.”

To scientists it is not only important to know where microbial life exists, it is also relevant to know about changes over time. Here they were lucky: First sampling in April 2015 occurred shortly after an unexpected rain event. The moisture had positive effects on life and activity in the desert. This is documented in samples taken and analysed in the following years in February 2016 and January 2017.

“We can clearly show that some time after a precipitation event, the abundance and biological activity of microorganisms decreases”, says Wagner. But the organisms, which are predominantly bacteria, do not completely die off. According to the authors, single-celled organisms are found mainly in the deeper layers of the Atacama Desert where they have formed active communities for millions of years and have evolved to cope with the harsh conditions.

The findings from the South American desert are very useful for the question of life on other planets, especially in relation to Mars. Martian climate was initially humid, rivers and lakes had existed before the desertification began. No rain can fall from the thin Martian atmosphere today but liquid water can be present near the surface due to nightly snowfall. Additionally, there is fog and on some slopes also salty brines, which sporadically flow down and thus provide fluids. However, the exposure to hard radiation at the surface is much greater than on Earth. Based on the results of the study, the authors come to the conclusion: If life ever evolved on Mars in the past, under better conditions, it could have endured the transition to hyper-arid conditions and perhaps even be found in subsurface niches today.

Reference:
A Transitory Microbial Habitat in the Hyperarid Atacama Desert, Dirk Schulze-Makuch, Dirk Wagner, Samuel Kounaves et al., PNAS, DOI: 10.1073/pnas.1714341115

Note: The above post is reprinted from materials provided by GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre.

Locomotion of bipedal dinosaurs might be predicted from that of ground-running birds

February 22, 2018

Ground-running bird model may predict bipedal dinosaur locomotion. Credit: Peter Bishop, Queensland Museum CC-BY

A new model based on ground-running birds could predict locomotion of bipedal dinosaurs based on their speed and body size, according to a study published February 21, 2018 in the open-access journal PLOS ONE by Peter Bishop from the Queensland Museum, Australia and colleagues.

Previous research has investigated the biomechanics of ground-dwelling birds to better understand the how bipedal non-avian dinosaurs moved, but it has not previously been possible to empirically predict the locomotive forces that extinct dinosaurs experienced, especially those species that were much larger than living birds. Bishop and colleagues examined locomotion in 12 species of ground-dwelling birds, ranging in body mass from 45g to 80kg, as the birds moved at various speeds along enclosed racetracks while cameras recorded their movements and forceplates measured the forces their feet exerted upon the ground.

The researchers found that many physical aspects of bird locomotion change continuously as speed increases. This supports previous evidence that unlike humans, who have distinct “walking” and “running” gaits, birds move in a continuum from “walking” to “running.” The authors additionally observed consistent differences in gait and posture between small and large birds.

The researchers used their data to construct the biomechanically informative, regression-derived statistical (BIRDS) Model, which requires just two inputs — body mass and speed — to predict basic features of bird locomotion, including stride length and force exerted per step. The model performed well when tested against known data. While more data are needed to improve the model, and it is unclear if it can be extrapolated to animals of much larger body mass, the researchers hope that it might help predict features of non-avian dinosaur locomotion using data from fossils and footprints.

Reference:
Bishop PJ, Graham DF, Lamas LP, Hutchinson JR, Rubenson J, Hancock JA, et al. The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs. PLOS ONE, 2018 DOI: 10.1371/journal.pone.0192172

Note: The above post is reprinted from materials provided by PLOS.

Stable gas hydrates can trigger landslides

February 22, 2018

Schematic evolution of retrogressive slope failure due to overpressured gas below the gas haydrate stability zone (GHSZ): a submarine slope with gas hydrate-bearing sediments and overpressured gas (bright area) at the bottom of the GHSZ induces pipe generation into the GHSZ, the conduit encounters a permeable layer; gas enters and leads to overpressure transfer from the bottom of the GHSZ to the shallow subsurface, and finally overpessured gas causes shear banding in the weak layer and generates retrogressive slope failure. Credit: Helmholtz Association of German Research Centres

Like avalanches onshore, there are different processes that cause submarine landslides. One very widespread assumption is that they are associated with dissociating gas hydrates in the seafloor. However, scientists at GEOMAR Helmholtz Centre for Ocean Research Kiel have now found evidence that the context could be quite different. Their study has been published in Nature Communications.

In the mid-1990s, German scientists, among others, were able to prove that the continental slopes at ocean margins contain large amounts of gas hydrates. These solid, ice-like compounds of water and gas are often considered a kind of cement, which stabilizes the slopes. Since gas hydrates are only stable at high pressure and low temperature, rising water temperatures can cause gas hydrates to dissociate, or ‘melt’, in simple terms. It has been suggested previously that large-scale gas hydrate dissociation could cause submarine landslides that could in turn trigger tsunamis. The fact that many fossil landslides correlate spatially with sediments containing gas hydrates seems to strengthen this argument.

Now, researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel, together with colleagues from Kiel University and the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, have found evidence that gas hydrates and submarine landslides are indeed linked — but in a quite different way than previously thought. “Our data show that stable gas hydrates can indirectly destabilize the sediment above,” says Dr. Judith Elger from GEOMAR. She is the lead author of the study, which has been published in the international journal Nature Communications.

An inconsistency in the previous theory, which focused on melting gas hydrates as the cause of submarine landslides, was the starting point of the new research. “The water depths did not match. With rising water temperatures or decreasing sea levels, gas hydrate melting would be initiated around the upper parts of continental slopes. However, most known fossil submarine landslides were triggered in greater depths,” explains Dr. Elger.

To resolve this contradiction, the geophysicist examined seismic data from the area of the Hinlopen Slide, which occurred about 30,000 years ago north of Svalbard in 750 to 2,200 meters water depth. The team used the seismic data to simulate new processes with a computer model.

It turned out that gas hydrates can form a solid, impermeable layer beneath the seafloor. Free gas and other fluids can accumulate below this layer. Over time they create overpressure. Eventually, gas hydrates and sediments no longer withstand this elevated pore pressure and hydro fractures form in the sediments. These fractures form conduits that transfer overpressure to shallower coarse-grained sediments and thereby trigger shallow slope failure. In the case of the Hinlopen Slide, these fluid conduits are still visible in the seismic data.

“We were able to show that this process is a realistic alternative to other triggering processes for the Hinlopen Slide, and it is completely independent of climatic changes. However, important information about the properties of gas hydrate-bearing sediments is still lacking to improve our models,” says Dr. Elger.

In any case, the study shows a new causal process that has not been considered so far in the search for causes of submarine landslides. “Further studies that combine seismic data and geotechnical laboratory experiments must now show whether similar fractures can be detected beneath the seafloor on other historical landslides and whether this is a common phenomenon,§ Dr. Elger concludes.

Reference:
Judith Elger, Christian Berndt, Lars Rüpke, Sebastian Krastel, Felix Gross, Wolfram H. Geissler. Submarine slope failures due to pipe structure formation. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-03176-1

Note: The above post is reprinted from materials provided by Helmholtz Centre for Ocean Research Kiel (GEOMAR).

New insight into how magma feeds volcanic eruptions

February 22, 2018

Teide volcano in Tenerife. Credit: Dr Janine Kavanagh, University of Liverpool

A novel research study by scientists at the University of Liverpool has provided new insights into how molten rock (magma) moves through the Earth’s crust to feed volcanic eruptions.

Using laboratory experiments involving water, jelly and laser imaging, researchers were able to demonstrate how magma flows through the Earth’s crust to the surface through magma-filled cracks called dykes.

This new approach to studying magma flow revealed that prior to a volcanic eruption there was recirculation of the fluid in the dyke and instability in the flow, details which had previously not been documented before.

Nearly all volcanic eruptions are fed by dykes that transport magma from its source to the surface. Understanding how magma travels through these dykes to the surface is central to forecasting the style, longevity and climatic impact of volcanic eruptions.

Researchers created a scaled-down model of an active volcanic plumbing system using a perspex tank filled with gelatine, representing the Earth’s crust, and then injected this with dyed water, representing the magma.

They applied cutting-edge laser imaging techniques to look inside the model. Passive-tracer particles added to the fluid glowed in a laser sheet to allow the flow of the model magma to be mapped as the dyke grew.

Digital cameras recorded changes in the shape of the model volcanic plumbing system over time and the changes to the surface of the crust was recorded using an overhead laser scanner. Polarized light allowed subsurface stress patterns that would result in rock fracturing in nature to be observed as the dyke grew.

This novel experimental setup allowed, for the first time, the simultaneous measurement of fluid flow, sub-surface and surface deformation during the magma ascent through magma-filled fractures.

This finding will help inform the interpretation of data from field studies and geophysical surveys, which will ultimately improve our ability to understand if an eruption is likely to happen.

Liverpool volcanologist, Dr Janine Kavanagh, who heads up the University’s specialist MAGMA laboratory, said “For the first time, using innovative laboratory experiments that combined our knowledge of volcanic plumbing systems with engineering expertise, we have managed to see how magma flows through the Earth’s crust to the surface through dykes.

“Our experiments, the first to use laser imaging technology in this way, revealed a strong coupling between surface deformation patterns and subsurface processes.

“This indicates that it is both the magma properties and the host rock properties that controls how the dyke ascends, which is a brand new finding and challenges our existing thinking on magma flow through rocks.

“As it’s not possible to always successfully predict volcanic events due to the lack of complete knowledge of the signals leading to catastrophes, these results are an important new finding and ultimately we hope they will contribute to our understanding of where and when the next volcanic eruption will be.”

With more than 800 million people worldwide living near a volcano at risk of eruptive activity, understanding the triggers for volcanic eruptions is vital for forecasting efforts, hazard assessment, and risk mitigation.

The paper ‘Challenging dyke ascent models using novel laboratory experiments: Implications for reinterpreting evidence of magma ascent and volcanism’ is published in the Journal of Volcanology and Geothermal Research.

Reference:
Janine L. Kavanagh et al, Challenging dyke ascent models using novel laboratory experiments: Implications for reinterpreting evidence of magma ascent and volcanism, Journal of Volcanology and Geothermal Research (2018). DOI: 10.1016/j.jvolgeores.2018.01.002

Note: The above post is reprinted from materials provided by University of Liverpool.

Extinct lakes of the American desert west

February 22, 2018

Erosional Pleistocene shorelines in Surprise Valley, California, USA. Credit: Anne Egger

The vestiges of lakes long extinct dot the landscape of the American desert west. These fossilized landforms provide clues of how dynamic climate has been over the past few million years.

Identification of ancient lake shoreline features began with early explorers of the continent. The first detailed studies were conducted by pioneering American geologists such as G.K. Gilbert and I.C. Russell in the late 1800s, who studied Lake Bonneville, now the remnant Great Salt Lake in Utah, and Lake Lahonton, located in northwestern Nevada.

Through this long history of studying fossil shorelines and lake sediments, we know that these lakes existed during two periods with distinct environmental conditions during the geologically recent past. The first was during ice age maxima, such as the last ice age, 14 to 30 thousand years ago, when global temperatures were 4 to 6 degrees colder and continental ice sheets expanded into the continental United States.

The second time period was about three million years ago during the middle of the Pliocene epoch—a global climate characterized by warmer temperatures and atmospheric CO2 levels roughly equivalent to today’s values, which has led many scientists to view the Pliocene as a potential analogue for future climate change.

These observations lead to an important question, says the study’s lead author, Daniel Ibarra, “Why are there lake systems under both colder and warmer climates, but not today?” Of particular interest, he says, is the presence of lakes under warmer conditions, which, under a “wet gets wetter, dry gets drier” paradigm, goes against projections of future warming.

To answer this question, Ibarra and colleagues looked at the competing influences of temperature and precipitation, and how they combine to allow for the existence of lakes under these dual climate states.

The authors compiled evidence for, and created models of, lakes during both colder and warmer than modern periods of the Pliocene-Pleistocene (the last 5 million years). During colder glacial periods, they found that increased precipitation and decreased evaporation combined to form large lakes that occupied the inward draining basins in the western United States, particularly in northern Nevada and Utah.

Increased precipitation also drove the formation of lakes, particularly in southern Nevada and southern California during the warmer middle Pliocene, outpacing higher temperatures and evaporation rates during that time. This increase in precipitation during the middle Pliocene and dominantly southwestern distribution of lake deposits is similar to the pattern of precipitation during modern El Niño years, corroborating previous hypotheses for mean “El Niño-like” conditions during the mid-Pliocene.

The team’s interdisciplinary approach explains the conditions driving lake systems in mid-latitude regions today and over the geologic past. Further, notes Ibarra, “This work illustrates the importance of understanding how the El Niño Southern Oscillation drives precipitation patterns in arid regions, which is important for future water resources planning for the western United States.”

Reference:
Gilbert G. K., 1884, The topographic features of lake shores. United States Geological Survey, Fifth Annual Report, 69–123.
DE Ibarra, AE Egger, KL Weaver, CR Harris, K Maher, 2014, Rise and fall of late Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence from Lake Surprise, California, Geological Society of America Bulletin, 126 (11-12), 1387-1415. DOI: 10.1130/G39962.1

Note: The above post is reprinted from materials provided by Geological Society of America.

Continental interiors may not be as tectonically stable as geologists think

February 20, 2018

Cratonic lithosphere with a high-density root undergoes delamination when perturbed by mantle plumes from beneath. The removed cratonic root then thermally grows back, with its rock fabrics preserving recent mantle deformation. Credit: Lijun Liu

A University of Illinois-led team has identified unexpected geophysical signals underneath tectonically stable interiors of South America and Africa. The data suggest that geologic activity within stable portions of Earth’s uppermost layer may have occurred more recently than previously believed. The findings, published in Nature Geoscience, challenge some of today’s leading theories regarding plate tectonics.

The most ancient rocks on Earth are located within continental interiors, far from active tectonic boundaries where rocks recycle back into the planet’s interior. These strong, buoyant and deeply rooted blocks of Earth, called cratons, have been drifting on the surface for billions of years, seemingly undisturbed. They occasionally join and break apart along their edges in a dance called the supercontinent cycle.

“We usually think of cratons as being cold, stable and low-elevation,” said professor of geology and study co-author Lijun Liu. “Cold because the rocks are far above the hot mantle layers, stable because their crusts have not been disturbed significantly by faulting or deformation, and their low elevation is because they have been sitting there, eroding down for billions of years.”

However, there are places where cratons don’t follow these rules.

“For example, there are regions of high topography within the cratons of South America and Africa,” said graduate student and lead author Jiashun Hu.

The researchers processed geophysical data with the Blue Waters supercomputer at the National Center for Supercomputing Applications at Illinois hoping to better understand these high-elevation regions. The thick roots of cratons have been thought to be buoyant due to their low-density mineral content, allowing them to float on top of the hot underlying mantle. However, the new data indicate that the cold mantle that lies below these regions in South America and Africa – once joined as part of the supercontinent Pangea – has a layered structure and that the lower layer was more dense in the past than it is today, Liu said.

This density difference could be the result of a process called mantle delamination. During delamination, the denser lower mantle layer peels away from the buoyant upper layer under the crust of the craton after interacting with hot magma from mantle plumes, the researchers said.

“From several types of seismic imaging data, we can see what we think are delaminated mantle slabs sinking into the hot, viscous deep mantle,” Liu said.

“The material that subsequently grows back at the roots of the cratons after delamination, due to cooling from above, is probably compositionally much less dense than what was there before,” said geology professor Craig Lundstrom. “That adds buoyancy, and that force from buoyancy could be what forms the anomalously high topography.”

This multidisciplinary study is beginning to give the team a very logical – albeit complicated – update on the story of Earth’s tectonic history, the researchers said.

“The high topography of Africa and South America is only part of the story,” Hu said. “There are many geologic phenomena such as the location of hotspot trajectories, continental volcanism, surface uplift and erosion, as well as seismically imaged deformation within the craton roots that all seem to correlate well with the proposed delamination event, implying a potential causal relationship.”

There is also evidence to support other locations of craton-plume interaction during other times in Earth’s history.

“The rock record shows that uplift and erosion events have taken place during previous supercontinent cycles,” said geology professor and School of Earth, Society and Environment director Stephen Marshak. “A related study discusses what might be a similar event, namely continental uplift possibly related to delamination of cratonic lithosphere that caused the period of global erosion resulting in the Great Unconformity, which is the contact between Precambrian basement rock and Paleozoic sedimentary strata.”

For now, it is not clear if and how craton-plume interaction may affect modern-day earthquake activity and volcanism in areas thought of as geologically inactive. However, the study marks new thinking in how geologists may understand the so-called stable cratons.

Reference:
Jiashun Hu et al. Modification of the Western Gondwana craton by plume–lithosphere interaction, Nature Geoscience (2018). DOI: 10.1038/s41561-018-0064-1

Note: The above post is reprinted from materials provided by University of Illinois at Urbana-Champaign.

Plants colonized Earth 100 million years earlier than previously thought

February 20, 2018

Rhynia gwynne-vaughanii -- 400 million-year-old fossil plant stem from Aberdeenshire, Scotland. — Rhynia gwynne-vaughanii — 400 million-year-old fossil plant stem from Aberdeenshire, Scotland. Credit: The Natural History Museum, London.

For the first four billion years of Earth’s history, our planet’s continents would have been devoid of all life except microbes.

All of this changed with the origin of land plants from their pond scum relatives, greening the continents and creating habitats that animals would later invade.

The timing of this episode has previously relied on the oldest fossil plants which are about 420 million years old.

New research, published today in the journal Proceedings of the National Academy of Sciences, indicates that these events actually occurred a hundred million years earlier, changing perceptions of the evolution of the Earth’s biosphere.

Plants are major contributors to the chemical weathering of continental rocks, a key process in the carbon cycle that regulates Earth’s atmosphere and climate over millions of years.

The team used ‘molecular clock’ methodology, which combined evidence on the genetic differences between living species and fossil constraints on the age of their shared ancestors, to establish an evolutionary timescale that sees through the gaps in the fossil record.

Dr Jennifer Morris, from the University of Bristol’s School of Earth Sciences and co-lead author on the study, explained: “The global spread of plants and their adaptations to life on land, led to an increase in continental weathering rates that ultimately resulted in a dramatic decrease the levels of the ‘greenhouse gas’ carbon dioxide in the atmosphere and global cooling.

“Previous attempts to model these changes in the atmosphere have accepted the plant fossil record at face value — our research shows that these fossil ages underestimate the origins of land plants, and so these models need to be revised.”

Co-lead author Mark Puttick described the team’s approach to produce the timescale. He said: “The fossil record is too sparse and incomplete to be a reliable guide to date the origin of land plants. Instead of relying on the fossil record alone, we used a ‘molecular clock’ approach to compare differences in the make-up of genes of living species — these relative genetic differences were then converted into ages by using the fossil ages as a loose framework.

“Our results show the ancestor of land plants was alive in the middle Cambrian Period, which was similar to the age for the first known terrestrial animals.”

One difficulty in the study is that the relationships between the earliest land plants are not known. Therefore the team, which also includes members from Cardiff University and the Natural History Museum, London, explored if different relationships changed the estimated origin time for land plants.

Leaders of the overall study, Professor Philip Donoghue and Harald Schneider added: “We used different assumptions on the relationships between land plants and found this did not impact the age of the earliest land plants.

“Any future attempts to model atmospheric changes in deep-time must incorporate the full range of uncertainties we have used here.”

Reference:
JL Morris, MN Puttick, J Clark, D Edwards, P Kenrick, S Pressel, CH Wellman, Z Yang, H Schneider and PCJ Donoghue. Timescale of early land plant evolution. Proceedings of the National Academy of Sciences, 2018. DOI: 10.1073/pnas.1719588115

Note: The above post is reprinted from materials provided by University of Bristol.

Earthquakes follow wastewater disposal patterns in southern Kansas

February 20, 2018

Wastewater created during oil and gas production and disposed of by deep injection into underlying rock layers is the probable cause for a surge in earthquakes in southern Kansas since 2013, a new report in the Bulletin of the Seismological Society of America concludes.

Until 2013, earthquakes were nearly unheard of in Harper and Sumner counties, the site of recent intensive oil and gas production. But between 2013 and 2016, 127 earthquakes of magnitude 3 or greater occurred in Kansas, with 115 of them taking place in Harper and Sumner counties. Prior to 1973, there were no felt earthquakes reported in the area, and only one magnitude 2.0 earthquake between 1973 and 2012.

Using data collected by a network of seismic stations installed by the U.S. Geological Survey, lead researcher Justin Rubinstein and his colleagues analyzed 6,845 earthquakes that occurred in the counties between March 2014 and December 2016.

They found that the dramatic uptick in seismicity correlated in time and location with increases in wastewater disposal that began in 2012 — and that decreases in seismicity during that time also corresponded to decreases in disposal rates.

Between 1974 and 2012, there were no magnitude 4 or greater earthquakes in the study area. Between 2012 and 2016, six such earthquakes occurred. “The probability of this rate change occurring randomly is approximately 0.16%,” Rubinstein and colleagues write in the BSSA study.

Kansas had the second-highest statewide earthquake rate in the central United States between 2013 and 2016, coming in behind Oklahoma, where a similar dramatic increase in seismicity also has been linked to wastewater injection.

In the southern Kansas study area, wastewater injection decreased significantly in 2015, falling from an average of 5 million barrels a month from July to December 2014 to 3.8 million barrels per month in March 2015. This decrease was likely due in part to a drop in oil and gas production as the prices for those commodities dropped, the researchers said, noting that the price of a barrel of oil fell by half between August 2014 and January 2015.

During the same time, the Kansas Corporation Commission developed rules to limit wastewater injection in the study area, with the rules going into full effect in July 2015. Since then, wastewater injection in the study area has dropped by almost 50 percent.

There is a corresponding decrease in seismicity in 2015, but Rubinstein said it is difficult to tell how much economic shifts or new regulation contributed to that trend. “We can’t fully disentangle it. But there’s no question that economics plays a role here because injection started to drop off before the new rules went into place. ”

“It certainly seems probable that regulations have an effect,” he said, “but we would need to speak to individual [oil and gas] operators to determine the extent of that effect.”

The researchers say that fluids injected into the crystalline rock basement below the Kansas oil and gas sites increased pressures in the rock pores and reduced friction along faults to trigger these induced earthquakes. Not all wastewater injection disposal sites have earthquakes associated with them, Rubinstein noted. In some cases, the fluid pressures may not be able to get to depths where earthquakes occur, or there may be some places in the rock basement that are more susceptible than others to fluid effects.

It’s also difficult to know how long these stresses might continue to produce earthquakes, he added. Seismicity related to an injection well in Youngstown, Ohio in 2013 lasted only a few weeks, while fluid injection at Rocky Mountain Arsenal in Colorado stopped in 1966 but significant seismicity continued in the area until the 1980s.

“It’s hard to say how long it’s going to last given that what we’re looking at in Kansas is a much higher rate of injection than in the places where seismicity slowed quickly, and many, many more wells,” said Rubinstein. “If they shut off all the injection, the decay could still take years, just because there’s been such a dramatic change in the regional pressure field.”

Rubinstein will continue to work in Kansas to learn more about whether seismologists can consistently see foreshocks and earthquake swarms in the seismic record. “We have an incredible network there, and one of the best documented cases of induced seismicity with publicly available seismic data,” he said.

Reference:
Justin L. Rubinstein, William L. Ellsworth, Sara L. Dougherty. The 2013–2016 Induced Earthquakes in Harper and Sumner Counties, Southern Kansas. Bulletin of the Seismological Society of America, 2018; DOI: 10.1785/0120170209

Note: The above post is reprinted from materials provided by Seismological Society of America.

Analysis of major earthquakes supports stress reduction assumptions

February 17, 2018

This schematic illustration of the 2014 Iquique earthquake off the coast of Chile (magnitude 8.1) shows the locations of foreshocks (blue) and aftershocks (red) relative to the area of large slip on the fault (contour lines). The mainshock involved thrust faulting on the plate boundary between the underthrusting Nazca and the overriding South American plates. Credit: Wetzler et al., Science Advances, Feb-2018

A comprehensive analysis of 101 major earthquakes around the Pacific ring of fire between 1990 and 2016 shows that most of the aftershock activity occurred on the margins of the areas where the faults slipped a lot during the main earthquakes. The findings support the idea that the area of large slip during a major earthquake is unlikely to rupture again for a substantial time.

The idea that earthquakes relieve stress on faults in the Earth’s crust makes intuitive sense and underlies the common assumption that the portion of a fault that has just experienced an earthquake is relatively safe for some time. But not all studies have supported this, according to Thorne Lay, professor of Earth and planetary sciences at UC Santa Cruz.

“This intuition has been challenged by statistical treatments of seismic data that indicate that, based on the clustering of earthquakes in space and time, the area that has just slipped is actually more likely to have another failure,” Lay said. “The truth appears to be more nuanced. Yes, the area that slipped a lot is unlikely to slip again, as the residual stress on the fault has been lowered to well below the failure level, but the surrounding areas have been pushed toward failure in many cases, giving rise to aftershocks and the possibility of an adjacent large rupture sooner rather than later.”

In the new study, published February 14 in Science Advances, Lay and other seismologists at UC Santa Cruz and Caltech took advantage of advanced slip-imaging methods applied to recent earthquakes of magnitude 7 or greater. When they examined the locations of aftershocks with respect to the slip during the mainshock, they found that very few aftershocks occur in the regions of a fault that had a large amount of slip, and aftershocks that do occur in the slip zone tend to be weak, with negligible additional slip. Most aftershock activity occurs on the margins of the area that slipped in the mainshock.

“This produces a halo of aftershocks surrounding the rupture and indicates that the large-slip zone is not likely to have immediate rerupture,” Lay said.

These findings indicate that the stress reduction during a major earthquake is large and pervasive over the ruptured surface of the fault. Stress will eventually build up again on that portion of the fault through frictional resistance to the gradual motions of the tectonic plates of Earth’s crust, but that’s a very slow process. Although immediate rerupture of the large-slip zone is unlikely, regional clustering of earthquakes is likely to occur due to the increased stress outside the main slip zone.

The findings also suggest that if unusually intense aftershock activity is observed within the high-slip zone, a larger earthquake in the immediate vicinity of the first event might still be possible. The authors noted that earthquake sequences are highly complex and involve variable amounts of slip and stress reduction.

Reference:
“Systematic deficiency of aftershocks in areas of high coseismic slip for large subduction zone earthquakes” Science Advances (2018). DOI: 10.1126/sciadv.aao3225

Note: The above post is reprinted from materials provided by University of California – Santa Cruz.

How seafloor weathering drives the slow carbon cycle

February 16, 2018

The oceanic slow carbon cycle. Credit: Adriana Dutkiewicz

A previously unknown connection between geological atmospheric carbon dioxide cycles and the fluctuating capacity of the ocean crust to store carbon dioxide has been uncovered by two geoscientists from the University of Sydney.

Prof Dietmar Müller and Dr Adriana Dutkiewicz from the Sydney Informatics Hub and the School of Geosciences report their discovery in the journal Science Advances.

Many of us are familiar with the Slow Movement philosophy, which includes slow living, slow cooking, slow fashion, and even slow TV. But most of us would not have heard of the slow carbon cycle, which is about the slow movement of carbon between the solid Earth and the atmosphere.

The slow carbon cycle predates humans and takes place over tens of millions of years, driven by a series of chemical reactions and tectonic activity. The slow carbon cycle is part of Earth’s life insurance, as it has maintained the planet’s habitability throughout a series of hothouse climates punctuated by ice ages.

One idea is that when atmospheric carbon dioxide rises, the weathering of continental rock exposed to the atmosphere increases, eventually drawing down carbon dioxide and cooling the Earth again.

Less well-known is that weathering exists in the deep oceans too. Young, hot, volcanic ocean crust is subject to weathering from the circulation of seawater through cracks and open spaces in the crust. Minerals such as calcite, which capture carbon in their structure, gradually form within the crust from the seawater.

Recent work has shown that the efficiency of this seafloor weathering process depends on the temperature of the water at the bottom of the ocean—the hotter it is, the more carbon dioxide gets stored in the ocean crust.

Prof Müller explains: “To find out how this process contributes to the slow carbon cycle, we reconstructed the average bottom water temperature of the oceans through time, and plugged it into a global computer model for the evolution of the ocean crust over the past 230 million years. This allowed us to compute how much carbon dioxide is stored in any new chunk of crust created by seafloor spreading.”

Dr Dutkiewicz adds: “Our plate tectonic model also allows us to track each package of ocean floor until it eventually reaches its final destination—a subduction zone. At the subduction zone, the crust and its calcite are recycled back into the Earth’s mantle, releasing a portion of the carbon dioxide into the atmosphere through volcanoes.”

The computer model reveals that the capacity of the ocean crust to store carbon dioxide changes through time with a regular periodicity of about 26 million years.

Several geological phenomena including extinctions, volcanism, salt deposits and atmospheric carbon dioxide fluctuations reconstructed independently from the geological record all display 26 million-year cycles.

A previous hypothesis had attributed these fluctuations to cycles of cosmic showers, thought to reflect the Solar System’s oscillation about the plane of the Milky Way Galaxy.

Prof Müller says: “Our model suggests that characteristic 26 million-year periodicity in the slow carbon cycle is instead driven by fluctuations in seafloor spreading rates that in turn alter the capacity of the ocean crust to store carbon dioxide. This raises the next question: what ultimately drives these fluctuations in crustal production?”

Subduction, the sinking of tectonic plates deep into the convecting mantle, is regarded as the dominant plate driving force of plate tectonics. It follows that cyclicities in seafloor spreading rates should be driven by equivalent cycles in subduction.

An analysis of subduction zone behaviour suggests that the driving force in the 26 million-year periodicity originates from an episodicity in subduction zone migration. This component of the slow carbon cycle needs to be built into global carbon cycle models.

Better understanding of the slow carbon cycle will help us predict how the Earth will react to the human-induced rise in atmospheric carbon dioxide. It will help us answer the question: To what extent will the continents, oceans and the ocean crust take up the extra carbon dioxide in the long run?

Reference:
R.D. Müller el al., “Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities,” Science Advances (2018). DOI: 10.1126/sciadv.aaq0500

Note: The above post is reprinted from materials provided by University of Sydney.

Scientists eavesdrop on volcanic rumblings to forecast eruptions

February 16, 2018

Aerial view of Villarica volcano. Credit: Iain and Sarah/Creative Commons

A new study has shown that monitoring inaudible low frequencies called infrasound produced by a type of active volcano could improve the forecasting of significant, potentially deadly eruptions.

Scientists from Stanford and Boise State University analyzed the infrasound detected by monitoring stations on the slopes of the Villarrica volcano in southern Chile, one of the most active volcanoes in the world. The distinctive sound emanates from the roiling of a lava lake inside a crater at the volcano’s peak and changes depending on the volcano’s activity.

The study demonstrated how changes in this sound signaled a sudden rise in the lake level, along with rapid up-and-down motions of the surging lake near the crater’s rim just ahead of a major eruption in 2015. Tracking infrasound in real time and integrating it with other data, such as seismic readings and gas emission, might help alert nearby residents and tourists that a volcano is about to blow its stack, the researchers said.

“Our results point to how infrasound could aid in forecasting volcanic eruptions,” said study co-author Leighton Watson, a graduate student in the lab of Eric Dunham, an associate professor in the Department of Geophysics of the Stanford School of Earth, Energy & Environmental Sciences and also a co-author. “Infrasound is potentially a key piece of information available to volcanologists to gauge the likelihood of an eruption hours or days ahead.”

The study, published Feb. 14 in the journal Geophysical Research Letters, is led by Jeffrey Johnson, an Associate Professor of Geophysics at Boise State University in Idaho.

Table of Contents

Sleeping giant roars awake

Villarrica is a picturesque mountain with an altitude of 9,300 feet. The snowcapped volcano looms over a lake and across from the city of Pucón, which swells to a quarter million people in the summer tourist season. At night, residents of Pucón can often see a scarlet glow from Villarrica’s lava lake, normally hidden well below the volcano’s rim.

The ominous serenity that had held at Villarrica since its last eruption in the mid-1980s ended in the early morning hours on March 3, 2015. An incandescent fountain of lava rocketed from the mountaintop nearly a mile into the sky, spewing ash and debris and triggering bolts of lightning from the thick heat-generated clouds enveloping the summit. Around 4,000 people evacuated the immediate area. The eruption proved short-lived, however, and with risks of mudslides and flooding from melted snow minimal, evacuees soon returned to their homes.

Infrasound monitoring stations established at Villarrica just two months before the 2015 event and maintained by co-author Jose Palma from the University of Concepcion in Chile captured its before-and-after sonic activity. Studying these data, the research team saw that in the build-up to the eruption, the pitch of the infrasound increased, while the duration of the signal decreased. Flyovers in aircraft documented the changes in Villarrica’s lava lake, allowing researchers to explore connections between its height and the sound generation.

Watson offered a music analogy to explain this relationship. Similar to a person blowing into a trombone, explosions from gas bubbles rising and then bursting at the surface of the lava lake create sound waves. Just as the shape of a trombone can change the pitch of the notes it produces, the geometry of the crater that holds the lava lake modulates its sounds. When the lava lake is deep down in the volcano’s crater, the sound registers at a lower pitch or frequency — “just like when a trombone is extended,” said Watson. When the lava lake rises up in the crater, potentially heralding an eruption, the pitch or frequency of the sound increases, “just like when the trombone is retracted,” said Watson.

Warning signs

Future research will seek to tie infrasound generation to other critical variables in volcano monitoring and eruption forecasting, such as seismicity. Ahead of an eruption, seismic activity in the form of small earthquakes and tremors almost always increases. This seismicity emanates from several miles underground as magma moves through the volcano’s “plumbing system” of fractures and conduits that connect the volcano’s opening to magma chambers in our planet’s crust. Volcanologists think that changes in lava lake levels — and their attendant infrasound — result from the injection of new magma through volcanic plumbing, increasing the odds of a violent outburst.

In this way, the collection of infrasound should prove beneficial for forecasting purposes at “open vent” volcanoes like Villarrica, where an exposed lake or channels of lava connect the volcano’s innards to the atmosphere. Closed vent volcanoes, however, where the pooling magma remains trapped under rock until an explosive eruption occurs, do not generate the same kind of infrasound and thus pose additional forecasting challenges. An example of a closed vent volcano is Mount St. Helens in southwestern Washington state, whose eruption in 1980 remains the most lethal and destructive eruption in the history of the United States.

“Volcanoes are complicated and there is currently no universally applicable means of predicting eruptions. In all likelihood, there never will be,” Dunham said. “Instead, we can look to the many indicators of increased volcanic activity, like seismicity, gas emissions, ground deformation, and — as we further demonstrated in this study — infrasound, in order to make robust forecasts of eruptions.”

Reference:
Jeffrey B. Johnson, Leighton M. Watson, Jose L. Palma, Eric M. Dunham, Jacob F. Anderson. Forecasting the eruption of an open-vent volcano using resonant infrasound tones. Geophysical Research Letters, 2018; DOI: 10.1002/2017GL076506

Note: The above post is reprinted from materials provided by Stanford’s School of Earth, Energy & Environmental Sciences.

Soft tissue fossil clues could help search for ancient life on Earth and other planets

February 16, 2018

The fossil Waptia from the Burgess Shale, Canada. New Oxford University research suggests that the mineralogy of the surrounding earth is key to conserving soft parts of organisms, and finding more exceptional fossils like the Waptia. Credit: Yale University

Fossils that preserve entire organisms (including both hard and soft body parts) are critical to our understanding of evolution and ancient life on Earth. However, these exceptional deposits are extremely rare. The fossil record is heavily biased towards the preservation of harder parts of organisms, such as shells, teeth and bones, as soft parts such as internal organs, eyes, or even completely soft organisms, like worms, tend to decay before they can be fossilised. Little is known about the environmental conditions which stop this process soon enough for the organism to be fossilised.

New Oxford University research suggests that the mineralogy of the surrounding earth is key to conserving soft parts of organisms, and finding more exceptional fossils. Part-funded by NASA, the work could potentially support the Mars Rover Curiosity in its sample analysis, and speed up the search for traces of life on other planets.

Perhaps the most iconic of all exceptional fossil deposits is the Burgess Shale of Canada, popularised by Stephen J. Gould’s Wonderful Life. Dating to around 500 million years ago, the deposit preserves exceptional fossils from the Cambrian Explosion, an event which saw the rapid diversification of early animal life from simpler single-celled ancestors. Burgess Shale-type fossil localities are now known across the globe and without them roughly 80% of Cambrian organisms (those that have no hard skeleton or shell) would be unknown, distorting our picture of early animal evolution.

Published in Geology, the study, conducted by researchers from Oxford’s Department of Earth Sciences, Yale University, and Pomona College, builds on their previous research which revealed that certain clay minerals are toxic to bacteria that decay marine animals. This time around, the team set out to find geological evidence that rocks composed of the same clay minerals are the hosts of Burgess Shale-type fossils.

The team examined more than 200 Cambrian rock samples using powder X-ray diffraction analysis to determine their mineralogical composition, comparing rocks with Burgess Shale-type fossils with those with only fossilised shells and bones. Nicholas Tosca, Associate Professor of Sedimentary Geology at Oxford, said: ‘The number of samples required for this study was made possible because the diffractometer at Oxford collects mineralogical data 250 times faster than a conventional instrument.’

The findings reveals that soft tissue fossils are generally found in rocks rich in the mineral berthierine, one of the main clay minerals identified by the previous study as being toxic to decay bacteria. Ross Anderson, lead author and fellow at All Souls College, Oxford, explains: ‘Berthierine is an interesting mineral because it forms in tropical settings when the sediments contain elevated concentrations of iron. This means that Burgess Shale-type fossils are likely confined to rocks which were formed at tropical latitudes and which come from locations or time periods that have enhanced iron. This observation is exciting because it means for the first time we can more accurately interpret the geographic and temporal distribution of these iconic fossils, crucial if we want to understand their biology and ecology.’

The study provides a mineralogical signature which can be used to find the more elusive sites that are home to these extraordinary fossils. ‘The mineralogical associations we identified mean that for a given Cambrian sedimentary mudrock we can predict with around 80% accuracy whether it is likely to contain Burgess Shale-type fossils,’ explains Anderson.

Of the project’s wider applications, potentially supporting the search for life beyond our own planet, Anderson adds: ‘For the vast majority of Earth’s history, life has not possessed hard shells or skeletons. This means that if we want to look for fossil evidence of life on other planets like Mars, the chances are we probably need to find fossils of entirely soft organisms, and Burgess Shale-type fossilisation provides a way. NASA’s Curiosity rover has the ability to record mineralogy on the Martian surface, so it could potentially look for the types of rocks which might be most conducive to preserving these fossils.’

To expand their understanding of the exceptional preservation of soft organisms, the team are currently delving further back into Earth history, to investigate the preservation of microbes before macroscopic organisms with skeletons or shells evolved.

Reference:
Ross P. Anderson, Nicholas J. Tosca, Robert R. Gaines, Nicolás Mongiardino Koch, Derek E.G. Briggs. A mineralogical signature for Burgess Shale–type fossilization. Geology, 2018; DOI: 10.1130/G39941.1

Note: The above post is reprinted from materials provided by University of Oxford.

Ancient trail of Columbian mammoths uncovered in south-central Oregon

February 16, 2018

Footprints of mammoths, dated to 43,000 years ago, are seen in a portion of a trackway that was uncovered by researchers in 2017 in an ancient dry lake bed in Lake County, Oregon. Credit: Photos by Greg Shine, Bureau of Land Management

A fossilized trackway on public lands in Lake County, Oregon, may reveal clues about the ancient family dynamics of Columbian mammoths.

Recently excavated by a team from the University of Oregon Museum of Natural and Cultural History, the Bureau of Land Management and the University of Louisiana, the trackway includes 117 footprints thought to represent a number of adults as well as juvenile and infant mammoths.

Discovered by Museum of Natural and Cultural History paleontologist Greg Retallack during a 2014 class field trip on fossils at the UO, the Ice Age trackway is the focus of a new study appearing online ahead of print in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

Retallack returned to the site with the study’s coauthors, including UO science librarian Dean Walton, in 2017. The team zeroed in on a 20-footprint track, dating to roughly 43,000 years ago, that exhibited some intriguing features.

“These prints were especially close together, and those on the right were more deeply impressed than those on the left-as if an adult mammoth had been limping,” said Retallack, also a professor in the UO Department of Earth Sciences and the study’s lead author.

But, as the study reveals, the limping animal wasn’t alone: Two sets of smaller footprints appeared to be approaching and retreating from the limper’s trackway.

“These juveniles may have been interacting with an injured adult female, returning to her repeatedly throughout the journey, possibly out of concern for her slow progress,” Retallack said. “Such behavior has been observed with wounded adults in modern, matriarchal herds of African elephants.”

The tracks were made in a layer of volcanic soil at Fossil Lake, a site first excavated by UO science professor Thomas Condon in 1876 and today administered by the Bureau of Land Management.

“America’s public lands are some of the world’s greatest outdoor laboratories. Localities such as this mammoth tracksite are unique parts of America’s heritage and indicate that there are many special sites still to be discovered,” said study co-author Brent Breithaupt, a paleontologist in the Wyoming State Office of the Bureau of Land Management.

Specimens from the 1876 Fossil Lake excavation-along with the rest of Condon’s extensive assemblage of fossils and geologic specimens-were donated to UO in the early 1900s and form the core of the museum’s Condon Fossil Collection, now under Retallack’s direction and boasting upwards of 50,000 fossil specimens.

Last month a new state law went into effect, making the UO museum Oregon’s default repository for fossils found on state lands. The museum is also a designated repository for artifacts and paleontological specimens collected from BLM-administered lands in Oregon, ensuring they are available to future generations for education and research.

As part of the 2017 study, Neffra Matthews of the BLM’s National Operations Center in Denver, helped survey, map and document the trackway using photogrammetry, which helps scientists perform accurate measurements based on land-based or aerial photographs.

“There is a vast storehouse of natural history found on BLM-managed land, and it’s exciting to work with researchers like Professor Retallack in capturing 3D data on fragile paleontological resources,” she said.

Retallack said that trace fossils such as trackways can provide unique insights into natural history.

“Tracks sometimes tell more about ancient creatures than their bones, particularly when it comes to their behavior,” he said. “It’s amazing to see this kind of interaction preserved in the fossil record.”

Elephants once roamed across much of North America. Woolly mammoths (Mammuthus primigenius) were common in Canada and Alaska. Columbian mammoths (Mammuthus columbi) occupied the region that became Washington state to South Dakota and south into Mexico. Most mammoths went extinct about 11,500 years ago, but some isolated Arctic island populations of woolly mammoth persisted until 4,000 years ago.

Reference:
Gregory J. Retallack, James E. Martin, Adrian P. Broz, Brent H. Breithaupt, Neffra A. Matthews, Dean P. Walton. Late Pleistocene mammoth trackway from Fossil Lake, Oregon. Palaeogeography, Palaeoclimatology, Palaeoecology, 2018; DOI: 10.1016/j.palaeo.2018.01.037

Note: The above post is reprinted from materials provided by University of Oregon. Original written by Kristin Strommer.

When it comes to extinction, body size matters

February 16, 2018

On a certain level, extinction is all about energy. Animals move over their surroundings like pacmen, chomping up resources to fuel their survival. If they gain a certain energy threshold, they reproduce, essentially earning an extra life. If they encounter too many empty patches, they starve, and by the end of the level it’s game over.

Models for extinction risk are necessarily simple. Most reduce complex ecological systems to a linear relationship between resource density and population growth — something that can be broadly applied to infer how much resource loss a species can survive.

This week in Nature Communications, an interdisciplinary team of scientists proposes a more nuanced model for extinction that also shows why animal species tend to evolve toward larger body sizes. The Nutritional State-structured Model (NSM) by ecologist Justin Yeakel (UC Merced), biologist Chris Kempes (Santa Fe Institute), and physicist Sidney Redner (Santa Fe Institute) incorporates body size and metabolic scaling into an extinction model where ‘hungry’ or ‘full’ animals, great and small, interact and procreate on a landscape with limited resources.

“Unlike many previous forager models, this one accounts for body size and metabolic scaling,” Kempes explains. “It allows for predictions about extinction risk, and also gives us a systematic way of assessing how far populations are from their most stable states.”

In the NSM, hungry animals are susceptible to mortality, and only full animals have the capacity to reproduce. Because animals’ energetic needs change with body size, the researchers based their calculations for replenishment and reproduction on biological scaling laws that relate body size to metabolism.

They found that species of different sizes gravitate toward population states most stable against extinction. The states they derived in the model reproduce two oft-observed patterns in biology. The first, Damuth’s law, is an inverse relationship between body size and population density: the bigger the species, the fewer of individuals cohabitate in a given area. Within the NSM, this fewer/larger more/smaller pattern emerges because large species are most stable against starvation in small numbers, while small species can afford to reach larger population densities.

The second relationship, Cope’s rule, holds that terrestrial mammals tend to evolve toward larger body sizes. This NSM shows that, overall, larger animals with slower metabolisms are the most stable against extinction by starvation. It even predicts an energetically “ideal” mammal, robust in the face of starvation, which would be 2.5 times the size of an African elephant.

“As we incorporated more realism into how quickly organisms gain or lose body fat as they find or don’t find resources, the results of our model began aligning with large-scale ecological and evolutionary relationships. Most surprising was the observation that the NSM accurately predicts the maximum mammalian body size observed in the fossil record,” explains Yeakel. Though the model doesn’t account for predation, it does offer a dynamic and systematic framework for understanding how foragers survive on limited resources.

“The dynamics of foraging and the interaction of body size in foraging and resource availability, these are all rich problems for which there is beautiful phenomenology,” says Redner. “I hope some of this will have relevance in managing resources and ensuring species don’t go extinct.”

Reference:
Justin D. Yeakel, Christopher P. Kempes, Sidney Redner. Dynamics of starvation and recovery predict extinction risk and both Damuth’s law and Cope’s rule. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-02822-y

Note: The above post is reprinted from materials provided by Santa Fe Institute.

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