Geologists have disproved a theory about what stopped the formation of the Midcontinent Rift, which is responsible for creating the dramatic cliffs on the shores of Lake Superior. Credit: Northwestern University
Geologists have corrected a mix-up that made an ancient geological structure in the central U.S. seem hundreds of miles shorter than it really is. The biggest failed rift known to geologists is even bigger than originally thought, according to research that will be presented at the American Geophysical Union fall meeting Dec. 11 in New Orleans.
The Midcontinent Rift, which started but failed to split North America in two pieces 1.1 billion years ago, is the biggest failed rift ever discovered. It was formed when 350,000 cubic miles of volcanic rock poured out of the rift and formed the beautiful cliffs around Lake Superior. South of Lake Superior, the volcanic rocks are covered by younger rocks, so it wasn’t clear how far the rift extended.
For decades, geologists believed the rift stopped in southern Michigan, but a joint study by geologists at the University of Illinois at Chicago (UIC), Northwestern University, the University of Oklahoma and the University of Göttingen, Germany, reveals the rift extends much farther – as far south as Oklahoma.
Successful geologic rifts cut through the Earth’s surface, splitting continents in two and forming new ocean basins, but something prevented the Midcontinent Rift from completing this process. Until now, geologists believed the Grenville Front halted the Midcontinent Rift’s growth.
“Geologists got confused by the Grenville Front, which appears in southeast Canada,” said Carol Stein, lead author of the study and professor of Earth and environmental sciences at UIC. “It marks where another continent collided with North America after the Midcontinent Rift formed.”
“Somehow the idea developed that the Grenville Front extended south into the U.S., cutting off the Midcontinent Rift in Southern Michigan,” explained coauthor Seth Stein, professor of Earth and planetary sciences in Northwestern’s Weinberg College of Arts and Sciences. “That didn’t make sense because there wasn’t any good reason for the rift to stop there.
To sort this out, the researchers used gravity data to “see” underground.
“The Midcontinent Rift shows up nicely,” explained coauthor Reece Elling, a graduate student in Earth and planetary sciences at Northwestern. “The rift’s volcanic rocks are very dense, so they pull downward strongly. In contrast, the Grenville Front doesn’t have these dense rocks, and so it doesn’t cause the gravity high we see.”
The gravity high shows that the underground rift has an east arm that extends south from Lake Superior through Michigan, Ohio, Kentucky, Tennessee and Alabama. The gravity high also maps a western arm that extends as far south as Oklahoma.
“This make sense in terms of how continents grow,” said coauthor Jonas Kley of the University of Göttingen, Germany.
The new analysis “makes the Midcontinent Rift great again,” explains coauthor Randy Keller, professor emeritus of geology and geophysics at the University of Oklahoma. “It’s a major structure and should be recognized accordingly.”
The results of the study will be published in GSA Today.
Reconstruction of Wakaleo schouteni challenging the thylacinid Nimbacinus dicksoni over a kangaroo carcass in the late Oligocene forest at Riversleigh. Credit: Illustration by Peter Schouten in the Journal of Systematic Palaeontology
A team of Australian scientists has discovered a new species of marsupial lion which has been extinct for at least 19 million years. The findings, published in the Journal of Systematic Palaeontology, are based on fossilised remains of the animal’s skull, teeth, and humerus (upper arm bone) found by University of New South Wales (UNSW) scientists in the Riversleigh World Heritage Area of remote north-western Queensland.
Named in honour of palaeoartist Peter Schouten, Wakaleo schouteni was a predator that stalked Australia’s abundant rainforests some 18 to 26 million years ago in the late Oligocene to early Miocene era. This meat-eating marsupial is estimated to have been about the size of a dog and weighed around 23 kilograms.
The new species is about a fifth of the weight of the largest and last surviving marsupial lion, Thylacoleo carnifex, that weighed in at around 130 kilograms and which has been extinct for 30,000 years. Members of this family, the Thylacoleonidae, had highly distinct large, blade-like, flesh-cutting premolars that they used to tear up prey.
The discovery comes just a year after the fossilised remains of a kitten-sized marsupial lion were found in the same famous fossil site in Queensland. The UNSW scientists named that miniature predator Microleo attenboroughi after broadcasting legend Sir David Attenborough.
With this new find, the researchers believe that two different species of marsupial lion were present in the late Oligocene at least 25 million years ago. The other, originally named Priscileo pitikantensis, but renamed Wakaleo pitikantensis, was slightly smaller and was identified from teeth and limb bones discovered near Lake Pitikanta in South Australia in 1961.
This latest discovery reveals that the new species (W. schouteni) exhibits many skull and dental features of the genus Wakaleo but it also shared a number of similarities with P. pitikantensis — particularly the presence of three upper premolars and four molars, previously the diagnostic feature of Priscileo. Further similarities of the teeth and humerus which are shared with W. schouteni indicate that P. pitikantensis is a species of Wakaleo.
According to the authors, these dental similarities distinguish W. schouteni and W. pitikantensis from later species of this genus, all of which show premolar and molar reduction, and suggest that they are the most primitive members of the genus.
Lead author Dr Anna Gillespie, a palaeontologist from the University of New South Wales (UNSW) in Sydney, Australia says that the latest finding raises new questions about the evolutionary relationships of marsupial lions: “The identification of these new species have brought to light a level of marsupial lion diversity that was quite unexpected and suggest even deeper origins for the family.”
Reference:
Anna K. Gillespie, Michael Archer, Suzanne J. Hand. A new Oligo–Miocene marsupial lion from Australia and revision of the family Thylacoleonidae. Journal of Systematic Palaeontology, 2017; 1 DOI: 10.1080/14772019.2017.1391885
Caption Transparent skulls of an extinct plesiosaur (top) and a living crocodile (bottom). The inner ear is the pink structure towards the back of the head. Credit: James Neenan
A new study led by Oxford University Museum of Natural History has revealed that an extinct group of marine reptiles called sauropterygians evolved similar inner ear proportions to those of some modern day aquatic reptiles and mammals. The research is published in Current Biology today.
Sauropterygians were swimming reptiles from the ‘Age of Dinosaurs’ that included some semi-aquatic forms, nearshore swimmers and fully-aquatic ‘underwater-flyers’. Their most well-known members are the plesiosaurs, ferocious sea monsters with four flippers, which hunted anything from small fish and squid to large marine reptiles.
The inner ear is a structure shared by all vertebrates, containing an important sense organ that helps maintain balance and orientation. Aquatic animals move more naturally in a three-dimensional environment, so have different sensory inputs compared to animals which live on land. The inner ear is therefore very useful for detecting differences in locomotion in extinct animals, especially by comparing with living organisms.
Researchers were surprised when sauropterygians with very different lifestyles had evolved inner ears that were very similar to those of some modern animals.
“Sauropterygians are completely extinct and have no living descendants,” said Dr James Neenan, lead author of the study. “So I was amazed to see that nearshore species with limbs that resemble those of terrestrial animals had ears similar to crocodylians, and that the fully-aquatic, flippered plesiosaurs had ears similar to sea turtles.”
The similarities don’t end there. Some groups of plesiosaurs, the ‘pliosauromorphs’, evolved enormous heads and very short necks, a body shape that is shared by modern whales. Whales have the unusual feature of highly miniaturized inner ears (blue whales have a similar-sized inner ear to humans), possibly the result of having such a short neck. Neenan and colleagues have now shown that ‘pliosauromorph’ plesiosaurs also have a reduced inner ear size, supporting this idea.
These interesting results are the product of convergent evolution, the process in which completely unrelated organisms evolve similar solutions to the same evolutionary hurdles.
“Nearshore sauropterygians swam in a similar way and had comparable lifestyles to modern-day crocodiles, so had similar inputs on the inner ear organ,” said Dr Neenan. “Plesiosaurs also ‘flew’ under water with similar flippers to those of sea turtles. So it’s not surprising that the organ of balance and orientation evolved to be a similar shape between these unrelated groups.”
Reference:
James M. Neenan, Tobias Reich, Serjoscha W. Evers, Patrick S. Druckenmiller, Dennis F.A.E. Voeten, Jonah N. Choiniere, Paul M. Barrett, Stephanie E. Pierce, Roger B.J. Benson. Evolution of the Sauropterygian Labyrinth with Increasingly Pelagic Lifestyles. Current Biology, 2017; DOI: 10.1016/j.cub.2017.10.069
Map of sites and postulated migratory pathways associated with modern humans dispersing across Asia during the Late Pleistocene. Credit: Bae et al. 2017. On the origin of modern humans: Asian perspectives. Science. Image by: Katerina Douka and Michelle O’Reilly
Most people are now familiar with the traditional “Out of Africa” model: modern humans evolved in Africa and then dispersed across Asia and reached Australia in a single wave about 60,000 years ago. However, technological advances in DNA analysis and other fossil identification techniques, as well as an emphasis on multidisciplinary research, are revising this story. Recent discoveries show that humans left Africa multiple times prior to 60,000 years ago, and that they interbred with other hominins in many locations across Eurasia.
A review of recent research on dispersals by early modern humans from Africa to Asia by researchers from the Max Planck Institute for the Science of Human History and the University of Hawai’i at Manoa confirms that the traditional view of a single dispersal of anatomically modern humans out of Africa around 60,000 years ago can no longer be seen as the full story. The analysis, published in the journal Science, reviews the plethora of new discoveries being reported from Asia over the past decade, which were made possible by technological advances and interdisciplinary collaborations, and shows that Homo sapiens reached distant parts of the Asian continent, as well as Near Oceania, much earlier than previously thought. Additionally, evidence that modern humans interbred with other hominins already present in Asia, such as Neanderthals and Denisovans, complicates the evolutionary history of our species.
New model: Multiple dispersals of modern humans out of Africa, beginning as early as 120,000 years ago
The authors brought together findings from multiple recent studies to refine the picture of human dispersals out of Africa and into Asia. While scientists once thought that humans first left Africa in a single wave of migration about 60,000 years ago, recent studies have identified modern human fossils in far reaches of Asia that are potentially much older. For example, H. sapiens remains have been found at multiple sites in southern and central China that have been dated to between 70,000 and 120,000 years ago. Additional finds indicate that modern humans reached Southeast Asia and Australia prior to 60,000 years ago.
However, other recent studies do confirm that all present-day non-African populations branched off from a single ancestral population in Africa approximately 60,000 years ago. This could indicate that there were multiple, smaller dispersals of humans out of Africa beginning as early as 120,000 years ago, followed by a major dispersal 60,000 years ago. While the recent dispersal contributed the bulk of the genetic make-up of present-day non-Africans, the earlier dispersals are still evident.
“The initial dispersals out of Africa prior to 60,000 years ago were likely by small groups of foragers, and at least some of these early dispersals left low-level genetic traces in modern human populations. A later, major ‘Out of Africa’ event most likely occurred around 60,000 years ago or thereafter,” explains Michael Petraglia of the Max Planck Institute for the Science of Human History.
Multiple interbreeding events
Recent genetic research has resolved the question of whether or not modern humans interbred with other ancient hominins — they definitely did. Modern humans interbred not only with Neanderthals, but also with our recently-discovered relatives the Denisovans, as well as a currently unidentified population of pre-modern hominins. One estimate is that all present-day non-Africans have 1-4% Neanderthal heritage, while another group has estimated that modern Melanesians have an average of 5% Denisovan heritage. In all, it is now clear that modern humans, Neanderthals, Denisovans and perhaps other hominin groups likely overlapped in time and space in Asia, and they certainly had many instances of interaction.
The increasing evidence of interactions suggests that the spread of material culture is also more complicated than previously thought. “Indeed, what we are seeing in the behavioral record is that the spread of so-called modern human behaviors did not occur in a simple time-transgressive process from west to east. Rather, ecological variation needs to be considered in concert with behavioral variation between the different hominin populations present in Asia during the Late Pleistocene,” explains Christopher Bae of the University of Hawai’i at Manoa.
In light of these new discoveries, our understanding of human movements across the Old World has become much more complex, and there are still many questions left open. The authors argue for the development of more complicated models of human dispersals and for conducting new research in the many areas of Asia where none has been done to date. Additionally, it will be important to review materials collected prior to the development of modern analytic methods, to see what more can now be learned from them. “Fortunately,” states Katerina Douka, also of the Max Planck Institute for the Science of Human History, “there have been an increasing number of multidisciplinary research programs launched in Asia over the past few decades. The information that is being reported is helping to fill in the gaps in the evolutionary records.”
“It is an exciting time to be involved with interdisciplinary research projects across Asia,” adds Bae.
Reference:
Christopher J. Bae, Katerina Douka, Michael D. Petraglia. On the origin of modern humans: Asian perspectives. Science, 2017; 358 (6368): eaai9067 DOI: 10.1126/science.aai9067
Researchers from Cologne, Tallinn, and Edinburgh have found out that the compound eyes of today’s arthropods are still constructed in much the same way as they were in their ancestors 500 million years ago. The research team looked at fossil trilobites. However, these arthropods lacked the lenses of contemporary compound eyes. The zoologist Dr Brigitte Schoenemann and her colleagues have now published the results of their research in the Proceedings of the National Academy of Sciences.
Dr Brigitte Schoenemann (University of Cologne) and her colleagues Helje Pärnaste (Tallinn, Estonia), and Euan Clarkson (Edinburgh, Scotland) have succeeded in unraveling the structure and functioning of the oldest known compound eye. The researchers used an exceptionally well-preserved fossil trilobite (Schmidtiellus reetae), which is over half a billion years old, showing the cellular structure of a compound eye. It not only shows how this eye was constructed, but also its functioning, its performance, and how it differs from contemporary compound eyes. The results show that modern compound eyes work in ways strikingly similar to those of half a billion years ago. They are very conservative in their structure — and quite successfully so. “The principle of the modern compound eye most likely goes back to before the times of our first fossil records. Half a billion years ago, it was in the early stage of its development, and with our work we have succeeded in uncovering the first visible steps of this extremely successful visual principle,” says Schoenemann.
The eye belongs to a trilobite found in Estonia, an extinct arthropod that lived in the oceans of the Palaeozoic. The findings from this geological layer have brought to light the very first fossils of complex animals. The right eye of the trilobite is slightly abraded, allowing for a view into its interior. It is a typical compound eye consisting of approximately 100 subunits placed relatively far apart compared to modern forms. The authors were able to show that each of these subunits (ommatidia) consists of about eight sensory cells — just like modern compound eyes — grouped around a central rhabdom, a light-guiding receptive structure. The latter contains the visual pigments and conveys the brightness of the surrounding environment to the animal’s central nervous system.
“However, in contrast to the modern compound eyes of bees, dragonflies, and many crabs, this very old compound eye does not have a lens,” Schoenemann explains. “This is likely due to the fact that these rather soft-shelled arthropods lacked the necessary layer in their shell responsible for lens formation.” The physical features of the central rhabdom ensures that each element of the compound eye has a limited field of vision and that the animal’s overall visual impression already has the mosaic-like character of a modern compound eye. The precision of such an eye can be determined by the number of its elements — just like the number of pixels determines the precision of a computer graphic. “With approximately 100 ‘pixels,’ the performance of this eye dating back more than half a billion years is certainly not outstanding. But it was sufficient to provide the trilobite with information on movement in its field of vision, for example approaching predators. It could roughly discern the distribution of light in its surroundings or avoid obstacles in its path,” says Schoenemann.
The biologist and her team were also able to show that only a few million years after Schmidtiellus, new and improved compound eyes with higher resolution developed in another trilobite from the Baltic region: Holmia kjerulfi. The performance of this species’ eyes even approximated that of modern dragonflies. A physical analysis of the compound eyes of both trilobites showed that the organism inhabited bright waters, most likely coastal shelf regions of a Palaeozoic ocean.
Reference:
Brigitte Schoenemann, Helje Pärnaste, Euan N. K. Clarkson. Structure and function of a compound eye, more than half a billion years old. Proceedings of the National Academy of Sciences, 2017; 201716824 DOI: 10.1073/pnas.1716824114
Reconstruction of Halszkaraptor escuilliei. This small dinosaur was a close relative of Velociraptor, but in both body shape and inferred lifestyle it much closely recalls some waterbirds like modern swans. Credit: Lukas Panzarin; and Andrea Cau for scientific supervision
An exceptionally well-preserved dinosaur skeleton from Mongolia unites an unexpected combination of features that defines a new group of semi-aquatic predators related to Velociraptor. Detailed 3D synchrotron analysis allowed an international team of researchers to present the bizarre 75 million-year-old predator, named Halszkaraptor escuilliei, in Nature. The study not only describes a new genus and species of bird-like dinosaur that lived during the Campanian stage of the Cretaceous in Mongolia but also sheds light on an unexpected amphibious lifestyle for raptorial dinosaurs.
Theropods encompass all carnivorous dinosaurs, including the largest land-living predators in the history of life on Earth, such as Tyrannosaurus, and iconic agile hunters like Velociraptor. During 160 million years of the Mesozoic Era, theropods became the dominant predators on all continents, yet never conquered aquatic environments. Although some theropods reportedly incorporated fish in their diet, proposed indications for aquatic locomotion associated with exclusively aquatic lifestyles remain controversial.
A swan-necked and flipper-forelimbed new dinosaur species that combines an unexpected mix of features now demonstrates that some bird-like dinosaurs did adopt a semi-aquatic lifestyle. The fossil, nicknamed “Halszka” for Halszkaraptor escuilliei, was found at Ukhaa Tolgod. This locality in southern Mongolia has been known by palaeontologists for decades and is often targeted by poachers. “Illicit fossil trade presents a great challenge to modern palaeontology and accounts for a dramatic loss of Mongolian scientific heritage,” says Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels. “Illegally exported from Mongolia, Halszka resided in private collections around the world before it was acquired in 2015 and offered to palaeontologists for study and to prepare its return to Mongolia.”
Although several important groups of predatory dinosaurs have been discovered in Mongolia, Halszka does not belong to any of them, having a number of strange features that are mostly absent among dinosaurs, but are shared by reptilian and avian groups with aquatic or semiaquatic ecologies. “The first time I examined the specimen, I even questioned whether it was a genuine fossil” says Andrea Cau of the Geological Museum Capellini in Bologna. Although Halszka is unique in many ways, certain parts of the skeleton, including the sickle-shaped “killer claws” on its feet, are shared with well-known dinosaurs such as Velociraptor. “This unexpected mix of traits makes it difficult to place Halszka within traditional classifications,” Cau remarks.
In order to ascertain the integrity of the fossil, the specimen was visualised and reconstructed in three dimensions using synchrotron multi-resolution X-ray microtomography. “This technique is currently the most powerful and sensitive method to image internal details without damaging invaluable fossils. The ESRF has become the worldwide leader for high quality X-ray imaging of such precious specimens,” notes Paul Tafforeau of the ESRF. “We had to mobilise an ESRF team of palaeontologists to study the complete anatomy of Halzka. So far, it’s the specimen for which the greatest number of experiments were made on a single fossil,” adds Tafforeau.
“Our first goal was to demonstrate that this bizarre and unexpected fossil is indeed a genuine animal: multi-resolution scanning confirmed that the skeleton is not a composite assembled from parts of different dinosaurs,” explains Dennis Voeten of the ESRF. “We implemented new methods for the acquisition and optimisation of tomographic scan data, which not only confirmed the integrity of the specimen, but also revealed additional palaeontological information,” Vincent Fernandez of the ESRF clarifies.
The synchrotron was even able to reveal, in astonishing detail, those parts of the skeleton that have remained deep within the rock ever since the dinosaur got buried. “Our analysis demonstrated that numerous teeth, which are not visible externally, are still preserved inside the mouth,” says Vincent Beyrand of the ESRF. “We also identified a neurovascular mesh inside its snout that resembles those of modern crocodiles to a remarkable degree. These aspects suggest that Halszka was an aquatic predator.”
The ESRF data revealed that the fossil represents a new genus and species of amphibious dinosaur that walked on two legs on land, with postural adaptations similar to short-tailed birds (like ducks), but used its flipper-like forelimbs to manoeuvre in water (like penguins and other aquatic birds), relying on its long neck for foraging and ambush hunting.
This new species was named Halszkaraptor escuilliei. Its generic name honours the late palaeontologist Halszka Osmólska. “This important genus is named in recognition of Halszka’s contribution to the study of Mongolian dinosaurs from the Gobi,” comments Rinchen Barsbold of the Mongolian Academy of Sciences. “The specific name refers to François Escuillié and thereby acknowledges his role in the first recognition and in the return of this specimen to Mongolia,” adds Khishigjav Tsogtbaatar of the Institute of Paleontology and Geology in Ulaanbaatar.
Halszkaraptor is not the only strange dinosaur recovered from the Gobi. Several previously described enigmatic Mongolian theropods were closely related to the new species, the study found. United in a new group, named Halszkaraptorinae, “is an unexpected subfamily of dromaeosaurs — the group colloquially known as raptors. This bizarre subfamily appears to have evolved a lifestyle different from all other predatory dinosaurs,” says Philip Currie of the University of Alberta.
“When we look beyond fossil dinosaurs, we find most of Halszkaraptor’s unusual features among aquatic reptiles and swimming birds,” concludes lead author Andrea Cau. “The peculiar morphology of Halszkaraptor fits best with that of an amphibious predator that was adapted to a combined terrestrial and aquatic ecology: a peculiar lifestyle that was previously unreported in these dinosaurs. Thanks to synchrotron tomography, we now demonstrate that raptorial dinosaurs not only ran and flew, but also swam!”
Reference:
Andrea Cau, Vincent Beyrand, Dennis F. A. E. Voeten, Vincent Fernandez, Paul Tafforeau, Koen Stein, Rinchen Barsbold, Khishigjav Tsogtbaatar, Philip J. Currie, Pascal Godefroit. Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs. Nature, 2017; DOI: 10.1038/nature24679
This is a Vadasaurus herzogi fossil. Credit: Mick Ellison Used with permission from the American Museum of Natural History
Using modern research tools on a 155-million-year-old reptile fossil, scientists at Johns Hopkins and the American Museum of Natural History report they have filled in some important clues to the evolution of animals that once roamed land and transitioned to life in the water.
A report on the new discoveries about the reptile, Vadasaurus herzogi, appears online in the Nov. 8 issue of Royal Society Open Science, and suggests that some of the foot-long animal’s features, including its elongated, whip-like tail, and triangular-shaped head, are well suited to aquatic life, while its relatively large limbs link it to land-loving species.
Vadasaurus, which is the Latin term for “wading lizard,” was discovered in limestone quarries near Solnhofen, Germany, part of a once-shallow sea long explored for its rich trove of fossil finds.
The well-preserved fossil is housed in the American Museum of Natural History in New York, where the job of unlocking its evolutionary secrets fell to museum research associate Gabriel Bever, Ph.D., who is also assistant professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine, and Mark Norell, Ph.D., the museum’s paleontology division chair.
“Anatomic and behavioral characteristics of modern groups of living things accumulated over long spans of time,” says Bever. “Fossils can teach us a lot about that evolutionary history, including the order in which those features evolved and their adaptive role in a changing environment.”
“Anytime we can get a fossil like this that is so well preserved, and so significant in understanding a major environmental transition, it is very important,” says Norell. “It’s so important,” he adds, “that we can consider Vadasaurus to be the Archaeopteryx of rynchocephalians.”
According to Bever, their work adds to the list of sea creatures whose ancestors were land-dwelling vertebrates. They include modern-day whales, seals, and sea snakes, and ancient (and now-extinct) species of ichthyosaurs, mosasaur, and plesiosaurs.
Bever says their study offers evidence that Vadasaurus, likely an adult when it died, can be linked by its anatomy to a small group of marine species called pleurosaurs, which have long been thought to have terrestrial roots. Pleurosaurs lived during the Jurassic period, 185 to 150 million years ago. The eel-like creatures had reduced limbs that were probably used for steering rather than propulsion in the water. Until now, fossils of only three ancient species of pleurosaurs have been discovered.
Using two types of statistical algorithms and reconstructions of evolutionary “trees,” Bever and Norell say that Vadasaurus and the pleurosaurs are part of a larger lineage of reptiles called Rhynchocephalia. Like the sea-loving pleurosaurs, Vadasaurus’ skull was a triangular shape, an adaptation found among many streamlined, water-dwelling animals, such as most fish, eels and whales. An elongated snout, common among sea animals, featured teeth farther away from the body for ensnaring fish.
By examining the shape and structure of the Vadasaurus’ skull, Bever and Norell also concluded that Vadasaurus’ bite was likely a quick, side-to-side motion, compared with the slower, stronger bite typical of many land-dwelling animals.
Some 155 million years ago, Vadasaurus’ tail had begun to lengthen like most modern sea animals, says Bever, but not to the size of the 5-foot pleurosaur. Vadasaurus, they found, had 24 pre-sacral vertebrae, which span from the head to the beginning of the tail, whereas pleurosaurus had more than 50 such back bones.
Despite its aquatic features, Vadasaurus retained some features more often found among land vertebrates. For example, Vadasaurus still had the large limbs, relative to the size of its body, expected of a land-dwelling reptile. Bever speculates that Vadasaurus did not use its limbs for propulsion in the water, but to steer. He says Vadasaurus may have swum like a modern sea snake, moving its spinal column with an undulating kind of motion.
“Our data indicate that Vadasaurus is an early cousin of the pleurosaur,” says Bever. “And these two reptiles are closely related to modern tuatara.” The modern tuatara is a lizard-like, land-dwelling reptile that lives on New Zealand’s coastal islands and is the single remaining species of rhynchocephalian still left on Earth.
Bever notes that a complete evolutionary history of Vadasaurus will require more data and fossil finds.
“We don’t know exactly how much time Vadasaurus was spending on land versus in the water. It may be that the animal developed its aquatic adaptations for some other reason, and that these changes just happened to be advantageous for life in the water,” says Bever.
Reference:
Gabriel S. Bever, Mark A. Norell. A new rhynchocephalian (Reptilia: Lepidosauria) from the Late Jurassic of Solnhofen (Germany) and the origin of the marine Pleurosauridae. Royal Society Open Science, 2017; 4 (11): 170570 DOI: 10.1098/rsos.170570
Professor Ron Clarke busy excavating the Little Foot Skull from the Sterkfontein Caves. Credit: Wits University
South Africa’s status as a major cradle in the African nursery of humankind has been reinforced with today’s unveiling of “Little Foot,” the country’s oldest, virtually complete fossil human ancestor.
Little Foot is the only known virtually complete Australopithecus fossil discovered to date. It is by far the most complete skeleton of a human ancestor older than 1.5 million years ever found. It is also the oldest fossil hominid in southern Africa, dating back 3.67 million years. The unveiling will be the first time that the completely cleaned and reconstructed skeleton can be viewed by the national and international media.
Discovered by Professor Ron Clarke from the Evolutionary Studies Institute at the University of the Witwatersrand in Johannesburg, South Africa, the fossil was given the nickname of “Little Foot” by Prof. Phillip Tobias, based on Clarke’s initial discovery of four small footbones. Its discovery is expected to add a wealth of knowledge about the appearance, full skeletal anatomy, limb lengths and locomotor abilities of one of the species of our early ancestral relatives.
“This is one of the most remarkable fossil discoveries made in the history of human origins research and it is a privilege to unveil a finding of this importance today,” says Clarke.
After lying undiscovered for more than 3.6 million years deep within the Sterkfontein caves about 40km north-west of Johannesburg, Clarke found several foot bones and lower leg bone fragments in 1994 and 1997 among other fossils that had been removed from rock blasted from the cave years earlier by lime miners. Clarke sent his assistants Stephen Motsumi and Nkwane Molefe into the deep underground cave to search for any possible broken bone surface that might fit with the bones he had discovered in boxes. Within two days of searching, they found such a contact, in July 1997.
Clarke realised soon after the discovery that they were on to something highly significant and started the specialised process of excavating the skeleton in the cave up through 2012, when the last visible elements were removed to the surface in blocks of breccia. “My assistants and I have worked on painstakingly cleaning the bones from breccia blocks and reconstructing the full skeleton until the present day,” says Clarke.
In the 20 years since the discovery, they have been hard at work to excavate and prepare the fossil. Now Clarke and a team of international experts are conducting a full set of scientific studies on it. The results of these studies are expected to be published in a series of scientific papers in high impact, peer reviewed international journals in the near future.
This is the first time that a virtually complete skeleton of a pre-human ancestor from a South African cave has been excavated in the place where it was fossilised.
“Many of the bones of the skeleton are fragile, yet they were all deeply embedded in a concrete-like rock called breccia,” Clarke explains.
“The process required extremely careful excavation in the dark environment of the cave. Once the upward-facing surfaces of the skeleton’s bones were exposed, the breccia in which their undersides were still embedded had to be carefully undercut and removed in blocks for further cleaning in the lab at Sterkfontein,” says Clarke.
The 20-year long period of excavation, cleaning, reconstruction, casting, and analysis of the skeleton has required a steady source of funding, which was provide by the Palaeontological Scientific Trust (PAST) — a Johannesburg-based NGO that promotes research, education and outreach in the sciences related to our origins. Among its many initiatives aimed at uplifting the origin sciences across Africa, PAST has been a major funder of research at Sterkfontein for over two decades.
Professor Adam Habib, Vice-Chancellor and Principal of the University of the Witwatersrand says: “This is a landmark achievement for the global scientific community and South Africa’s heritage. It is through important discoveries like Little Foot that we obtain a glimpse into our past which helps us to better understand our common humanity.”
PAST’s chief scientist Professor Robert Blumenschine labels the discovery a source of pride for all Africans. “Not only is Africa the storehouse of the ancient fossil heritage for people the world over, it was also the wellspring of everything that makes us human, including our technological prowess, our artistic ability, and our supreme intellect,” he says.
The scientific value of the find and much more will be unveiled in a series of papers that Prof Clarke and a team of international experts have been preparing, with many expected in the next year.
The time variation of seismic velocity relative to the averaged pre-earthquake value are displayed. Each panel shows the central date within the 30-day window: (a) 8 March, (b) 1 May, (c) 1 June, and (d) 1 October 2016. Warm colors indicate regions where seismic velocity was decreased. During the 2016 earthquake, seismic velocity around the seismogenic Hinagu-Futagawa fault system and Mount Aso decreased greatly. Cold colors indicate regions where seismic velocity was increased. Seismic velocity at Mount Aso recovered rapidly and was faster than the pre-earthquake velocity after the eruption. The date described above shows the central date within the 30-day window. Yellow or white dots are Hi-net stations. Credit: Science Advances
Most of what we know about earthquakes and volcanoes is based on what we can observe at the Earth’s surface. However, most of the action — especially early activity that could help with disaster prediction and preparedness — occurs deep underground.
Developing a clearer picture of changes in subsurface conditions, together with continuous monitoring, could provide life-saving information in advance of future disasters. In earthquake-prone Japan, especially, there is ongoing need for effective means of foreseeing seismic activity.
Japan’s National Research Institute for Earth Science and Disaster Prevention (NIED) has developed the Hi-net network of hundreds of high-sensitivity seismographs evenly distributed across the country. High-resolution seismic data from Hi-net shed light on the workings far below the country’s surface. A key source of information from Hi-net is the velocity of seismic waves as they travel between stations. Faults, fractures, and fluids in the subsurface, among other factors, can influence seismic velocity. Thus, changes in seismic velocity can signal changes occurring underground but not yet apparent at the surface.
Until recently, little variation in seismic velocity had been detected in central Kyushu, Japan’s southernmost major island. However, in April 2016, the MW 7.0 Kumamoto earthquake struck the region, shortly after a MW 6.2 foreshock. These destructive earthquakes were followed by eruptions of Japan’s largest active volcano, Mount Aso, in April, May, and October of the same year.
A trio of researchers at Kyushu University and its International Institute for Carbon-Neutral Energy Research (I2CNER) investigated Hi-net seismic velocity data, collected continuously from December 2015 to November 2016, to better understand the subsurface conditions associated with these disasters. They reported their findings in Science Advances.
“We applied seismic interferometry to the ambient noise recorded at 36 Hi-net seismic stations,” Tatsunori Ikeda explains. “We found that during the earthquake, velocity slowed significantly, which may have been related to damage and pressure changes around the deep rupture fault. This was followed by gradual ‘healing’ of the fault over the following months, although different areas recovered to different extents.”
The earthquakes also may have mobilized fluids around Aso’s magma body. Velocity below the caldera decreased when the earthquake struck, but recovered relatively rapidly after the eruptions; this may have released pressure.
“Although past studies have used similar approaches for velocity estimation, the higher spatial resolution we achieved over a broad area allowed us to identify the spatial distribution of the damage zone or stress state,” corresponding author Takeshi Tsuji says. “Denser deployment allows local anomalies to be more accurately resolved. Velocity changes thus identified could be useful in the estimation of future earthquakes and volcanic activity.”
Reference:
Hiro Nimiya, Tatsunori Ikeda, Takeshi Tsuji. Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake. Science Advances, 2017; 3 (11): e1700813 DOI: 10.1126/sciadv.1700813
Scientists have discovered a planetary-scale tug-of-war between life, deep Earth and the upper atmosphere that is expressed in atmospheric nitrogen. Credit: ISS Expedition 7 Crew, EOL, NASA
A team of scientists using a state-of-the-art UCLA instrument reports the discovery of a planetary-scale “tug-of-war” of life, deep Earth and the upper atmosphere that is expressed in atmospheric nitrogen.
Earth’s atmosphere differs from the atmospheres of most other rocky planets and moons in our solar system in that it is rich in nitrogen gas, or N2; Earth’s atmosphere is 78 percent nitrogen gas. Titan, the largest of Saturn’s more than 60 moons, is the other body in our solar system with a nitrogen-rich atmosphere that resembles ours.
Compared with other key elements of life — such as oxygen, hydrogen and carbon — molecular nitrogen is very stable. Two nitrogen atoms combine to form N2 molecules that stay in the atmosphere for millions of years.
The majority of nitrogen has an atomic mass of 14. Less than one percent of nitrogen has an extra neutron. While this heavy isotope, nitrogen-15, is rare, N2 molecules that contain two nitrogen-15s — which chemists call 15N15N — are the rarest of all N2 molecules.
The team of scientists measured the amount of 15N15N in air and discovered that this rare form of nitrogen gas is far more abundant than scientists had expected. Earth’s atmosphere contains about two percent more 15N15N than can be accounted for by geochemical processes occurring near Earth’s surface.
“This excess was not known before because nobody could measure it,” said senior author Edward Young, a UCLA professor of geochemistry and cosmochemistry. “Our one-of-a-kind Panorama mass spectrometer allows us to see this for the first time. We conducted experiments showing that the only way for this excess of 15N15N to occur is by rare reactions in the upper atmosphere. Two percent is a huge excess.”
Young said the enrichment of 15N15N in Earth’s atmosphere is a signature that’s unique to our planet. “But it also gives us a clue about what signatures of other planets might look like, especially if they are capable of supporting life as we know it.”
The research is published in the journal Science Advances.
“We didn’t believe the measurements at first, and spent about a year just convincing ourselves that they were accurate,” said lead author Laurence Yeung, an assistant professor of Earth, environmental and planetary sciences at Rice University.
The study began four years ago when Yeung, then a UCLA postdoctoral scholar in Young’s laboratory, learned about the first-of-its-kind mass spectrometer that was being installed in Young’s laboratory.
“At that time, no one had a way to reliably quantify 15N15N,” said Yeung, who joined Rice’s faculty in 2015. “It has an atomic mass of 30, the same as nitric oxide. The signal from nitric oxide usually overwhelms the signal from 15N15N in mass spectrometers.”
The difference in mass between nitric oxide and 15N15N is about two one-thousandths the mass of a neutron. When Yeung learned that the new machine in Young’s laboratory could discern this slight difference, he applied for grant funding from the National Science Foundation to learn exactly how much 15N15N is in Earth’s atmosphere.
Co-authors Joshua Haslun and Nathaniel Ostrom at Michigan State University conducted experiments on N2-consuming and N2-producing bacteria that allowed the team to determine their 15N15N signatures.
These experiments suggested that one should see a bit more 15N15N in air than random pairings of nitrogen-14 and nitrogen-15 would produce — an enrichment of about 1 part per 1,000, Yeung said.
“There was a bit of enrichment in the biological experiments, but not nearly enough to account for what we’d found in the atmosphere,” Yeung said. “In fact, it meant that the process causing the atmospheric 15N15N enrichment has to fight against this biological signature. They are locked in a tug-of-war.”
The team found that zapping mixtures of air with electricity, which simulates the chemistry of the upper atmosphere, could produce enriched levels of 15N15N like they measured in air samples.
The researchers tested air samples from ground level and from altitudes of about 20 miles, as well as dissolved air from shallow ocean water samples.
“We think the 15N15N enrichment fundamentally comes from chemistry in the upper atmosphere, at altitudes close to the orbit of the International Space Station,” Yeung said. “The tug-of-war comes from life pulling in the other direction, and we can see chemical evidence of that. We can see the tug-of-war everywhere.”
Reference:
Laurence Y. Yeung, Shuning Li, Issaku E. Kohl, Joshua A. Haslun, Nathaniel E. Ostrom, Huanting Hu, Tobias P. Fischer, Edwin A. Schauble, Edward D. Young. Extreme enrichment in atmospheric 15 N 15 N. Science Advances, 2017; 3 (11): eaao6741 DOI: 10.1126/sciadv.aao6741
This is a reflected light image of a metal-sulphide clast in the enstatite chondrite ALH 77295. The central portion of the clast is a mineral called djerfisherite, an important host for chlorine in these meteorites. Credit: Dr Patricia Clay, The University of Manchester
Scientists have found the halogen levels in the meteorites that formed the Earth billions of years ago are much lower than previously thought.
The research was carried out by international team of researchers, led by the Universities of Manchester and Oxford, and has recently been published in Nature.
Halogens such as Chlorine, Bromine and Iodine, form naturally occurring salts which are essential for most life forms — but too much can prohibit life. When previously comparing halogen levels in meteorites that formed the planet, the Earth should have unhealthy levels of salt.
Many theories have been put forward to explain the mystery of why, instead, Earth salt concentrations are ‘just right’. The answer turns out to be quite simple — previous estimates meteorites were just too high.
Using a new analytical technique, the team looked at different kinds of chondrite meteorites, a type of primitive meteorite approximately 4.6 billion years old.
Dr Patricia Clay, lead author of the study from the University of Manchester’s School of Earth and Environmental Sciences (SEES), said: ‘These kinds of meteorites are remnants of the solar nebula, a molecular cloud made up of interstellar dust and hydrogen gas that predates our Solar System. Studying them provides important clues for our understanding of the origin and age of the Solar System.’
How the Earth acquired its volatile elements has long interested scientists. To answer the question the team re-examined one of the largest collection of meteorites assembled for this type of study.
They found that previous estimates of halogen levels in meteorites were too high, but the technique used by the team helped them avoid contaminated sources.
Dr Clay explains: “No single model of Earth formation using the old meteorite measurements could easily account for the halogens we see today. Some of these models needed catastrophic planetary wide removal of halogens without affecting related elements — which just didn’t make sense.”
Professor Ray Burgess, co-author and also from The University of Manchester, added: “The new simplified model we have developed is a big step forward in understanding how key ingredients essential for life were brought to our planet, including water that probably helped distribute the halogens between the planetary interior and surface.”
The results were a huge surprise, and time after time each meteorite measured was found to have halogen levels far lower than previously thought, and remarkably consistent between different types of meteorites.
Professor Chris Ballentine, co-author from the University of Oxford and who designed the study, added: “Another big surprise of the study was just how uniform the halogen content of very different meteorites actually is — this is an incredibly important picture into the processes that formed the meteorites themselves — but also means that whatever meteorites formed the earth the halogen ingredients for Earth’s recipe remains the same.”
Reference:
Patricia L. Clay, Ray Burgess, Henner Busemann, Lorraine Ruzié-Hamilton, Bastian Joachim, James M. D. Day, Christopher J. Ballentine. Halogens in chondritic meteorites and terrestrial accretion. Nature, 2017; 551 (7682): 614 DOI: 10.1038/nature24625
Shan Dou (from left), Jonathan Ajo-Franklin, and Nate Lindsey were on a Berkeley Lab team that used fiber optic cables for detecting earthquakes and other subsurface activity. Credit: Berkeley Lab
Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have shown for the first time that dark fiber – the vast network of unused fiber-optic cables installed throughout the country and the world – can be used as sensors for detecting earthquakes, the presence of groundwater, changes in permafrost conditions, and a variety of other subsurface activity.
In a pair of recently published papers, a team led by Berkeley Lab researcher Jonathan Ajo-Franklin announced they had successfully combined a technology called “distributed acoustic sensing,” which measures seismic waves using fiber-optic cables, with novel processing techniques to allow reliable seismic monitoring, achieving results comparable to what conventional seismometers can measure.
“This has huge potential because you can just imagine long stretches of fibers being turned into a massive seismic network,” said Shan Dou, a Berkeley Lab postdoctoral fellow. “The idea is that by using fiber that can be buried underground for a long time, we can transform traffic noise or other ambient vibrations into usable seismic signals that can help us to monitor near-surface changes such as permafrost thaw and groundwater-level fluctuations.”
Dou is the lead author of “Distributed Acoustic Sensing for Seismic Monitoring of the Near Surface: A Traffic-Noise Interferometry Case Study,” which was published in September in Nature’s Scientific Reports and verified the technique for monitoring the Earth’s near surface. More recently, Ajo-Franklin’s group published a follow-up study led by UC Berkeley graduate student Nate Lindsey, “Fiber-Optic Network Observations of Earthquake Wavefields,” in Geophysical Research Letters (GRL), which demonstrates the viability of using fiber-optic cables for earthquake detection.
Dark fiber refers to unused fiber-optic cable, of which there is a glut thanks to a huge rush to install the cable in the early 1990s by telecommunications companies. Just as the cables were buried underground, the technology for transmitting data improved significantly so that fewer cables were needed. There are now dense corridors of dark fiber crisscrossing the entire country.
Distributed acoustic sensing (DAS) is a novel technology that measures seismic wavefields by shooting short laser pulses across the length of the fiber. “The basic idea is, the laser light gets scattered by tiny impurities in the fiber,” said Ajo-Franklin. “When fiber is deformed, we will see distortions in the backscattered light, and from these distortions, we can measure how the fiber itself is being squeezed or pulled.”
Using a test array they installed in Richmond, California – with fiber-optic cable placed in a shallow L-shaped trench, one leg of about 100 meters parallel to the road and another perpendicular – the researchers verified that they could use seismic waves generated by urban traffic, such as cars and trains, to image and monitor the mechanical properties of shallow soil layers.
The measurements give information on how “squishy” the soil is at any given point, making it possible to infer a great deal of information about the soil properties, such as its water content or texture. “Imagine a slinky – it can compress or wiggle,” Ajo-Franklin said. “Those correspond to different ways you can squeeze the soil, and how much energy it takes to reduce its volume or shear it.”
He added: “The neat thing about it is that you’re making measurements across each little unit of fiber. All the reflections come back to you. By knowing all of them and knowing how long it takes for a laser light to travel back and forth on the fiber you can back out what’s happening at each location. So it’s a truly distributed measurement.”
Having proven the concept under controlled conditions, the team said they expect the technique to work on a variety of existing telecommunications networks, and they are currently conducting follow-up experiments across California to demonstrate this. Ongoing research in Alaska is also exploring the same technique for monitoring the stability of Arctic permafrost.
Added Dou: “We can monitor the near surface really well by using nothing but traffic noise. It could be fluctuations in groundwater levels, or changes that could provide early warnings for a variety of geohazards such as permafrost thaw, sinkhole formation, and landslides.”
Using fiber for quake detection
Building on five years of Berkeley Lab-led research exploring the use of DAS for subsurface monitoring using non-earthquake seismic sources, Ajo-Franklin’s group has now pushed the envelope and has shown that DAS is a powerful tool for earthquake monitoring as well.
In the GRL study led by Lindsey in collaboration with Stanford graduate student Eileen Martin, the research team took measurements using the DAS technique on fiber-optic arrays in three locations – two in California and one in Alaska. In all cases, DAS proved to be comparably sensitive to earthquakes as conventional seismometers, despite its higher noise levels. Using the DAS arrays, they assembled a catalog of local, regional, and distant earthquakes and showed that processing techniques could take advantage of DAS’ many channels to help understand where earthquakes originate from.
Ajo-Franklin said that dark fiber has the advantage of being nearly ubiquitous, whereas traditional seismometers, because they are expensive, are sparsely installed, and subsea installations are particularly scarce. Additionally, fiber allows for dense spatial sampling, meaning data points are only meters apart, whereas seismometers typically are separated by many kilometers.
Lindsey added: “Fiber has a lot of implications for earthquake detection, location, and early warning. Fiber goes out in the ocean, and it’s all over the land, so this technology increases the likelihood that a sensor is near the rupture when an earthquake happens, which translates into finding small events, improved earthquake locations, and extra time for early warning.”
The GRL paper notes other potential applications of using the dark fiber, including urban seismic hazard analysis, global seismic imaging, offshore submarine volcano detection, nuclear explosion monitoring, and microearthquake characterization.
Reference:
Nathaniel J. Lindsey et al, Fiber-optic network observations of earthquake wavefields, Geophysical Research Letters (2017). DOI: 10.1002/2017GL075722
Shan Dou et al. Distributed Acoustic Sensing for Seismic Monitoring of The Near Surface: A Traffic-Noise Interferometry Case Study, Scientific Reports (2017). DOI: 10.1038/s41598-017-11986-4
New research from The University of Texas at Austin adds evidence to a theory that claims the metallic cores of rocky planets like Earth were formed when molten metal trapped between grains of silicate rock percolated to the center of the planet during its early formation. Credit: UT Austin
Scientists have long pondered how rocky bodies in the solar system — including our own Earth — got their metal cores. According to research conducted by The University of Texas at Austin, evidence points to the downwards percolation of molten metal toward the center of the planet through tiny channels between grains of rock.
The finding calls into question the interpretation of prior experiments and simulations that sought to understand how metals behave under intense heat and pressure when planets are forming. Past results suggested that large portions of molten metals stayed trapped in isolated pores between the grains. In contrast, the new research suggests that once those isolated pores grow large enough to connect, the molten metal starts to flow, and most of it is able to percolate along grain boundaries. This process would let metal trickle down through the mantle, accumulate in the center, and form a metal core, like the iron core at the heart of our home planet.
“What we’re saying is that once the melt network becomes connected, it stays connected until almost all of the metal is in the core,” said co-author Marc Hesse, an associate professor in the UT Jackson School of Geosciences Department of Geological Sciences, and a member of UT’s Institute for Computational Engineering and Sciences.
The research was published on Dec. 4 in the Proceedings of the National Academy of Sciences. The work was the doctoral thesis of Soheil Ghanbarzadeh, who earned his Ph.D. while a student in the UT Department of Petroleum and Geosystems Engineering (now the Hildebrand Department of Petroleum and Geosystems Engineering). He currently works as a reservoir engineer with BP America. Soheil was jointly advised by Hesse and Maša Prodanovic, an associate professor in the Hildebrand Department and a co-author.
Planets and planetesimals (small planets and large asteroids) are formed primarily from silicate rocks and metal. Part of the planet formation process involves the initial mass of material separating into a metallic core and a silicate shell made up of the mantle and the crust. For the percolation theory of core formation to work, the vast majority of metal in the planetary body must make its way to the center.
In this study, Ghanbarzadeh developed a computer model to simulate the distribution of molten iron between rock grains as porosity, or melt fraction, increased or decreased. The simulations were perfomed at the Texas Advanced Computing Center. Researchers found that once the metal starts to flow, it can continue flowing even as the melt fraction decreases significantly. This is in contrast to previous simulations that found that once the metal starts flowing, it only takes a small dip in the volume of melt for percolation to stop.
“People have assumed that you disconnect at the same melt fraction at which you initially connected…and it would leave significant amounts of the metal behind,” Hesse said. “What we found is that when the metallic melt connects and when it disconnects is not necessarily the same.”
According to the computer model, only 1 to 2 percent of the initial metal would be trapped in the silicate mantle when percolation stops, which is consistent with the amount of metal in the Earth’s mantle.
The researchers point to the arrangement of the rock grains to explain the differences in how well-connected the spaces between the grains are. Previous work used a geometric pattern of regular, identical grains, while this work relied on simulations using an irregular grain geometry, which is thought to more closely mirror real-life conditions. The geometry was generated using data from a polycrystalline titanium sample that was scanned using X-ray microtomography.
“The numerical model Soheil developed in his Ph.D. thesis allowed for finding three-dimensional melt networks of any geometrical complexity for the first time,” said Prodanovic. “Having a three-dimensional model is key in understanding and quantifying how melt trapping works.”
The effort paid off because researchers found that the geometry has a strong effect on melt connectivity. In the irregular grains, the melt channels vary in width, and the larges ones remain connected even as most of the metal drains away.
“What we did differently in here was to add the element of curiosity to see what happens when you drain the melt from the porous, ductile rock,” said Ghanbarzadeh.
The researchers also compared their results to a metallic melt network preserved in an anchondrite meteorite, a type of meteorite that came from a planetary body that differentiated into discernable layers. X-ray images of the meteorite taken in the Jackson School’s High-Resolution X-Ray CT Facility revealed a metal distribution that is comparable to the computed melt networks. Prodanovic said that this comparison shows that their simulation capture the features observed in the meteorite.
The study was funded by the Statoil Fellows Program at UT Austin and the National Science Foundation.
Reference:
Soheil Ghanbarzadeh, Marc A. Hesse, Maša Prodanović. Percolative core formation in planetesimals enabled by hysteresis in metal connectivity. Proceedings of the National Academy of Sciences, 2017; 201707580 DOI: 10.1073/pnas.1707580114
Artistic rendering of a large collision on the early Earth. Credit: SwRI/Marchi.
Southwest Research Institute scientists recently modeled the protracted period of bombardment following the Moon’s formation, when leftover planetesimals pounded the Earth. Based on these simulations, scientists theorize that moon-sized objects delivered more mass to the Earth than previously thought.
Early in its evolution, Earth sustained an impact with another large object, and the Moon formed from the resulting debris ejected into an Earth-orbiting disk. A long period of bombardment followed, the so-called “late accretion,” when large bodies impacted the Earth delivering materials that were accreted or integrated into the young planet.
“We modeled the massive collisions and how metals and silicates were integrated into Earth during this ‘late accretion stage,’ which lasted for hundreds of millions of years after the Moon formed,” said SwRI’s Dr. Simone Marchi, lead author of a Nature Geoscience paper outlining these results. “Based on our simulations, the late accretion mass delivered to Earth may be significantly greater than previously thought, with important consequences for the earliest evolution of our planet.”
Previously, scientists estimated that materials from planetesimals integrated during the final stage of terrestrial planet formation made up about half a percent of the Earth’s present mass. This is based on the concentration of highly “siderophile” elements—metals such as gold, platinum and iridium, which have an affinity for iron—in the Earth’s mantle. The relative abundance of these elements in the mantle points to late accretion, after Earth’s core had formed. But the estimate assumes that all highly siderophile elements delivered by the later impacts were retained in the mantle.
Late accretion may have involved large differentiated projectiles. These impactors may have concentrated the highly siderophile elements primarily in their metallic cores. New high-resolution impact simulations by researchers at SwRI and the University of Maryland show that substantial portions of a large planetesimal’s core could descend to, and be assimilated into, the Earth’s core—or ricochet back into space and escape the planet entirely. Both outcomes reduce the amount of highly siderophile elements added to Earth’s mantle, which implies that two to five times as much material may have been delivered than previously thought.
“These simulations also may help explain the presence of isotopic anomalies in ancient terrestrial rock samples such as komatiite, a volcanic rock,” said SwRI co-author Dr. Robin Canup. “These anomalies were problematic for lunar origin models that imply a well-mixed mantle following the giant impact. We propose that at least some of these rocks may have been produced long after the Moon-forming impact, during late accretion.”
The paper, “Heterogeneous delivery of silicate and metal to the Earth by large planetesimals,” was published Dec. 4 online in Nature Geoscience.
Reference:
Heterogeneous delivery of silicate and metal to the Earth by large planetesimals, Nature Geoscience (2017). DOI:10.1038/s41561-017-0022-3
Mount Everest North Face as seen from the path to the base camp, Tibet. Credit: Luca Galuzzi/Wikipedia
Earthquakes that happen in densely populated mountainous regions, such as the Himalaya, spell bigger earthquakes because of a fast tectonic-plate collision, according to a new study in Earth and Planetary Science Letters. Researchers from Geophysical Fluid Dynamics — ETH Zürich in Switzerland, say their findings give people a more complete view of the risk of earthquakes in mountainous regions.
The new study shows that the frequency and magnitude of large earthquakes in the densely populated regions close to mountain chains — such as the Alps, Apennines, Himalaya and Zagros — depend on the collision rate of the smaller tectonic plates.
In 2015, a magnitude 7.8 earthquake struck Gorkha-Nepal, and a year later, Norcia, Italy suffered a magnitude 6.2 earthquake. Previous research has attempted to explain the physical causes of earthquakes like these, but with ambiguous results. For the first time, the new study shows that the rate at which tectonic plates collide controls the magnitude of earthquakes in mountainous regions.
“The impact of large earthquakes in mountain belts is devastating,” commented Luca Dal Zilio, lead author of the study from Geophysical Fluid Dynamics — ETH Zürich. “Understanding the physical parameters behind the frequency and magnitude of earthquakes is important to improve the seismic hazard assessment. By combining classical earthquake statistics and newly developed numerical models, our contribution addresses a crucial aspect of the seismic hazard, providing an intuitive physical explanation for a global-scale problem. Our scientific contribution can help the society to develop a more complete view of earthquake hazard in one of the most densely populated seismic zones of the world and ultimately take action accordingly.”
There are seven large tectonic plates and several smaller ones in the earth’s lithosphere — its outermost layers. These plates move, sliding and colliding, and that movement causes mountains and volcanoes to form, and earthquakes to happen.
The researchers developed 2D models that simulate the way the tectonic plates move and collide. The seismo-thermo-mechanical (STM) modelling approach utilises long-time scale processes to explain short time scale problems namely replicate the results observed from the historical earthquake catalogues. Also, it shows graphically the distribution of earthquakes by their magnitude and frequency that are caused by movement in the orogeny — a belt of the earth’s crust involved in the formation of mountains.
The simulations suggest that the magnitude and frequency of the earthquakes in mountainous regions are directly related to the rate at which the tectonic plates collide. The researchers say this is because the faster they collide, the cooler the temperatures and the larger the areas that generate earthquakes. This increases the relative number of large earthquakes.
The team confirmed the link by comparing earthquakes recorded in four mountain ranges: the Alps, Apennines and Himalaya and Zagros. Their results imply that the plate collisions in the Alps are more ductile than those in the Himalaya, reducing the hazard of earthquakes.
Reference:
Luca Dal Zilio, Ylona van Dinther, Taras V. Gerya, Casper C. Pranger. Seismic behaviour of mountain belts controlled by plate convergence rate. Earth and Planetary Science Letters, 2018; 482: 81 DOI: 10.1016/j.epsl.2017.10.053
Note: The above post is reprinted from materials provided by Elsevier.
A steam plume rises from Bogoslof volcano as hot lava heats the seawater during an eruption in August 2017. Credit: Dave Withrow (NOAA/Fisheries)
Most volcanoes erupt beneath the ocean, but scientists know little about them compared to what they know about volcanoes that eject their lava on dry land. Gabrielle Tepp of the Alaska Volcano Observatory and the U.S. Geological Survey thinks that with improved monitoring, scientists can learn more about these submarine eruptions, which threaten travel and alter the ocean soundscape.
During the 174th Meeting of the Acoustical Society of America, held Dec. 4-8, 2017, in New Orleans, Louisiana, Tepp will discuss the challenges and benefits of remote monitoring and what it can teach us about submarine volcanoes.
“It’s very difficult to study underwater volcanoes because it’s hard to put instruments in the water, especially long-term,” Tepp said.
Depending on the size and depth of an underwater eruption, gas and ash may never break the ocean surface, or the gas and ash could create a volcanic plume with the potential to interfere with air travel. “The ocean is a big place so it’s pretty unlikely that you’re going to have a situation where a ship haphazardly wanders over an eruption, but there are a few that have come close,” Tepp said. These unpredictable eruptions may also create a floating blanket of rocks, called a pumice raft, which can clog harbors and damage boats.
Tepp is presenting observations from two submarine volcanoes: Ahyi, a seamount in the Northern Mariana Islands in the Pacific Ocean, and Bogoslof, a shallow submarine volcano in the Aleutian Islands. The volcanoes made very different sounds, suggesting that different processes occurred during eruption. In 2014, Ahyi erupted for two weeks, with short, repetitive gunshotlike explosions every few minutes. In 2016 and 2017, Bogoslof had more sustained eruptions, lasting minutes to hours, which occurred every few days.
Evidence of these eruptions showed up on distant seismometers, which measure waves passing through the ground to record earthquakes, and hydrophone arrays that pick up underwater sound to detect covert nuclear detonations. When volcanoes erupt directly into the water, the sounds can travel for thousands of miles before dissipating.
Questions remain, however, such as if seismometers are sufficient for remote monitoring or if the more accurate information provided by cabled hydrophone arrays is worth the greater expense. Researchers are also interested in how the movement of waves from water into rock, and vice versa, affects signal detection.
Tepp and colleagues at National Oceanic and Atmospheric Administration and USGS recently deployed a hydrophone array in the Northern Mariana Islands. They will collect the data next summer and hope to determine where and how often local volcanoes erupt to see if the area needs better hazard monitoring.
Due to the long distances that eruption signals travel, they likely show up as anomalies on far-off monitoring devices used to study earthquakes, land-based volcanoes or even whale songs.
“Eruptions that create a loud enough sound, in the right location, can travel pretty far, even from one ocean to another,” Tepp said. “It makes you wonder, how many of these signals have we seen on distant instruments where nobody knew what they were, and it’s a submarine volcano from halfway around the world?”
Overview of the “Haarlem specimen”, holotype of Ostromia crassipes (Meyer, 1857). Credit: Oliver Rauhut
Paleontologists at Ludwig-Maximilians-Universitaet (LMU) in Munich correct a case of misinterpretation: The first fossil “Archaeopteryx” to be discovered is actually a predatory dinosaur belonging to the anchiornithid family, which was previously known only from finds made in China.
Even 150 million years after its first appearance on our planet, Archaeopteryx is still good for surprises. The so-called Urvogel has attained an iconic status well beyond the world of paleontology, and it is one of the most famous fossils ever recovered. In all, a dozen fossil specimens have been assigned to the genus. Archaeopteryx remains the oldest known bird fossil, not only documenting the evolutionary transition from reptiles to birds, but also confirming that modern birds are the direct descendants of carnivorous dinosaurs. LMU paleontologist Oliver Rauhut and Christian Foth from the Staatliches Museum für Naturkunde in Stuttgart have re-examined the so-called Haarlem specimen of Archaeopteryx, which is kept in Teylers Museum in that Dutch city and has gone down in history as the first member of this genus to be discovered.
In the journal BMC Evolutionary Biology, Foth and Rauhut now report that this fossil differs in several important respects from the other known representatives of the genus Archaeopteryx. In fact, their taxonomic analysis displaces it from its alleged perch on the phylogenetic tree: “The Haarlem specimen is not a member of the Archaeopteryx clade,” says Rauhut, a paleontologist in the Department of Earth and Environmental Sciences at LMU who is also affiliated with the Bavarian State Collections for Paleontology and Geology in Munich.
Instead, the two scientists assign the fossil to a group of bird-like maniraptoran dinosaurs known as anchiornithids, which were first identified only a few years ago based on material found in China. These rather small dinosaurs possessed feathers on all four limbs, and they predate the appearance of Archaeopteryx. “The Haarlem fossil is the first member of this group found outside China. And together with Archaeopteryx, it is only the second species of bird-like dinosaur from the Jurassic discovered outside eastern Asia. This makes it even more of a rarity than the true specimens of Archaeopteryx,” Rauhut says.
Made in China
The Haarlem specimen was found about 10 km to the northeast of the closest Archaeopteryx locality known (Schamhaupten) a full four years before the discovery of the skeleton that would introduce the Urvogel to the scientific world in 1861. Schamhaupten was once part of the so-called Solnhofen archipelago in the Altmühl Valley in southern Bavaria, the area from which all known specimens of the genus Archaeopteryx originated. Its taxonomic reassignment therefore provides new insights into the evolution of the bird-like dinosaurs in the Middle to Late Jurassic. “Our biogeographical analysis demonstrates that the group of dinosaurs that gave rise to birds originated in East Asia — all of the oldest finds have been made in China. As they expanded westward, they also reached the Solnhofen archipelago,” says Christian Foth. Thus, the fossil hitherto incorrectly assigned to the genus Archaeopteryx must have been one of the first members of the group to arrive in Europe.
Around 150 million years ago, the area known today as the Altmühl Valley was dotted with the coral and sponge reefs and lagoons of the Solnhofen archipelago, and the open sea lay to the West and South. The Haarlem fossil was originally recovered from what was then the eastern end of the archipelago, quite close to the mainland. Unlike Archaeopteryx, anchiornithids were unable to fly, and might not have been able to reach areas further offshore. On the other hand, all true fossils of Archaeopteryx found so far were recovered from the lithographic limestone strata further to the west, closer to the open sea. Based on the new findings, Rauhut argues that other known Archaeopteryx fossils may need reassessment: “Not every bird-like fossil that turns up in the fine-grained limestones around Solnhofen need necessarily be a specimen of Archaeopteryx,” he points out.
The authors of the new study have proposed that the Haarlem specimen be assigned to a new genus, for which they suggest the name Ostromia — in honor of the American paleontologist John Ostrom, who first identified the fossil as a theropod dinosaur.
Reference:
Christian Foth, Oliver W. M. Rauhut. Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs. BMC Evolutionary Biology, 2017; 17 (1) DOI: 10.1186/s12862-017-1076-y
The massive emerald, which weighs 794 pounds (360kg) and stands around 4.3 feet high (1.3metres), was unearthed a month ago,
An enormous £238million emerald rock discovered in a gem mining field in Brazil is being kept under heavy security in a secret location as the owner exclusively revealed he is living in fear of kidnapping, extortion and armed robbery.
The private holder, who can only be identified by his initials FG, said the giant stone is extremely rare because of its ‘considerable size and the quality of its gigantic crystals’.
He revealed that while it would need a forklift truck to lift the huge cluster of jewels, the risks of a heist are high in Brazil where criminal gangs use explosives to raid banks and carry powerful firearms.
The massive emerald, which weighs 794 pounds (360kg) and stands around 4.3 feet high (1.3metres), was unearthed a month ago, 200 metres deep inside the Carnaiba Mine, a gem-rich mineral exploration area in Bahia, north east Brazil.
The cautious owner said this week: ‘I can’t reveal anything about the whereabouts of the stone, how it’s being kept and how much I paid for it.
‘All I can say is the stone is being moved frequently from secure location to secure location under armed guard.
‘I cannot take any chances with my family’s lives by keeping the stone in one place where it could be found.’
There are only two giant stones with this density of crystals in the world, and according to FG, the other one, the Bahia emerald, which was the subject of a legal dispute over ownership between Brazil and America, ‘does not possess the same pure quality as the new Carnaiba emerald’.
The secretive keeper, who is currently finalising the legal paperwork for ownership, described the find as ‘a majestic and beautiful monument’.
He said: ‘This stone has emerald beryls spread all over it. Their quality is superb and by far the best I’ve ever seen and I’ve been in the industry for nearly 30 years.’
Experts predict the impressive jewelled stone, which contains around 180,000 carats of emerald crystals, could fetch around £238million.
The owner, a 50-year-old married father of one, revealed: ‘I’ve already had calls from interested parties including potential buyers fromEurope, Arab Emirates, America, India and China, who are keen to open negotiations.
‘Personally, I don’t know what the value of this piece is because it will be led by market demands.’
The Carnaiba emerald was found by members of the Bahia Mineral Cooperative, a group of workers legally authorised to explore the area.
FG explained: ‘Extracting the stone was extremely difficult. It took ten of us more than a week to get it out because it was 200 metres down in the ground.
‘It was cut out of the area, where it was embedded, in one piece and all hands were needed to lift it to the mine shaft where it was raised to the surface by a winch.’
FG paid each member of the Coop for their share of the gemstone, leaving him as the sole owner of the Carnaiba Emerald.
This jumbo jewel was found in the same mine just one hundred metres from where the Bahia emerald was discovered sixteen years ago.
FG said: ‘I saw the Bahia emerald when it was found in 2001. It was shaped flat like a basin and they had to chip away at it to reveal the emeralds underneath. Doing that made it lose a little of its value.
‘To my recollection the Bahia emerald doesn’t compare to my find which is magnificent in height and sumptuous to look at.
‘My one has simply been washed down with water to get rid of the dirt and it retains its appeal and value.’
According to reports, the Bahia emerald, which weighed 44 pounds (20 kg) more than the Carnaiba emerald, was illegally taken out of Brazil to the United States.
Although the Brazilian government claimed the emerald cluster, which was valued at 310 million US dollars, should be returned as part of the nation’s heritage, judges ruled otherwise in 2015 and the stone remains in America.
A confident FG said there is no risk of this happening to the new Carnaiba discovery.
His lawyer, Marcio Jandir, explained: ‘We have done all the issuance of the certificate of origin, a requirement of the Department of Mineral Production.
‘The owner of the stone will have the authorisation to do with it legally what he wants. And any transaction will be handled legitimately.’
FG said: ‘For now, I’m keeping the rock heavily guarded and out of sight until I reach a decision on whether to sell it or display it in museums here in Brazil.’
Hatton Garden emerald expert Marcus McCallum commented: ‘This is not the type of emerald used for making jewellery, it’s more a collector’s item which would look spectacular as an ornament in the foray of a wealthy home or make exceptional viewing in a museum.’
Emerald weighing more than 600 pounds found in Brazil Read more: http://www.dailymail.co.uk/wi...
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The massive emerald, which weighs 794 pounds (360kg) and stands around 4.3 feet high (1.3metres), was unearthed a month ago.
This photo released by the Bahia Mineral Cooperative shows a 4.3-foot tall emerald weighing more than 600 pounds in Bahia, Brazil, Monday, May 22, 2017. Paulo Santana of Brazil's National Mineral Production Department said the emerald was found about 20 days ago by miners of the Bahia Mineral Cooperative, but would not estimate the value of the emerald. It was sold to a mine owner in the region. (Bahia Mineral Cooperative via AP)
Fisher holding an intact mammoth rib collected at James Bristle’s farm near Chelsea on Nov. 29, 2017.
University of Michigan paleontologists conducted a second excavation this week at the Chelsea-area farm where the skull, tusks and dozens of intact bones of an ice age mammoth were pulled from the ground in late 2015.
A U-M news video of the skull and two attached tusks being hoisted from the muddy excavation pit with a backhoe on Oct. 1, 2015, has been viewed more than 875,000 times on YouTube.
Nothing that dramatic happened during the two-day follow-up. But 40 additional bones and bone fragments from the Bristle Mammoth were recovered, and the researchers were able to thoroughly document the site. That just wasn’t possible two years ago, in the one-day rush to get the skull and tusks out of the ground.
“This return to the Bristle site was absolutely a success. We got the kind of information that we need to do the science right, and we were also able to recover an impressive amount of additional material from this animal,” said U-M paleontologist Daniel Fisher, who led both Bristle digs and who is overseeing the analysis of the bones and the environmental samples.
“So I’m confident that as a result of this second excavation, we’ll have more insight into what happened here,” said Fisher, director of the U-M Museum of Paleontology.
Bristle’s farm deserved a second visit in part because a single radiocarbon date from one of the mammoth bones showed the animal to be more than 15,000 years old. Also, several lines of evidence point to human processing of the mammoth carcass for food.
If additional studies substantiate those preliminary findings, the Bristle Mammoth “would represent the earliest instance of human interaction with a mammoth in the eastern Great Lakes basin,” Fisher said.
The U-M team had been trying to make a return trip to Bristle’s farm for a while but needed to find a time that worked for Fisher, excavator James Bollinger and farmer James Bristle, who harvested corn from the dig site in October.
“The crops are off, so it’s really a perfect time to do it,” Bristle said Tuesday morning as Bollinger began removing soil from a site directly south of the October 2015 excavation.
“It was such a hurried thing the first time around,” said Bristle, who renamed his farm Mammoth Acres after that find. “So this is an opportunity to complete the discovery process.”
The first mammoth bones were discovered while Bristle was installing a drainage system at a low spot in one of his fields. The farmer gave U-M researchers one day to recover whatever remains they could find; after that, the drainage project and his harvest for the year needed to resume.
Bristle later donated the mammoth remains to the university, and some of them are now on display at the U-M Museum of Natural History. This week, additional bones were found in clays that were disturbed in 2015 when a sump pump was installed as part of the drainage project. The newly discovered bones will also be donated to the university, Bristle said.
During the first Bristle dig, 55 to 60 nearly complete mammoth bones were found, accounting for 30 to 40 percent of the animal’s skeletal mass. The animal was a male in its mid-40s and would have weighed about 9 tons.
In addition to the skull with teeth and tusks, most of the vertebrae and ribs were found, along with parts of the shoulder blades and the pelvis. Notably missing are the limb and foot bones and the tail vertebrae.
This week, the researchers added 40 more bones and bone fragments, including several vertebrae, skull fragments, an intact rib, part of a shoulder blade, a piece of the pelvis, and what appears to be part of the mandible.
Most of the workers in the muddy pit with Fisher were current or former U-M students. Scott Johnston, a 2017 graduate in the Department of Earth and Environmental Sciences who has worked at the U-M Museum of Natural History since he was 14, found a jagged, softball-sized fragment of the mammoth’s skull on Wednesday.
“I knew immediately that it was skull bone because nothing else looks exactly like it,” Johnston said. “The feeling was pure euphoria.”
Nichole Lohrke was a double major in German and evolutionary anthropology two years ago when she heard about the Bristle mammoth discovery. A few months later, she went to work in Fisher’s lab, repairing the Bristle tusks and skull. She added a minor in paleontology, graduated last spring, and on Wednesday found a plum-sized piece of the animal’s skull.
“The first Bristle excavation is what inspired me to get into paleontology,” she said. “I heard about it on the news and thought, ‘That is so cool. I would love to be part of that.’ And now I’m here.”
One goal of the second Bristle excavation was to find more bones and, possibly, additional evidence of human involvement. But an even higher priority was to reconstruct the geological context of the mammoth remains, something that simply wasn’t possible during 2015’s get-what-you-can-in-a-day dig.
The Bristle bones were found about 10 feet below the current land surface, in fine-grained clays and marls from the bottom of a pond that no longer exists.
On Tuesday of this week, the researchers dug a pit just south of the October 2015 location and collected sediment samples from the layers exposed in one of the walls. They collected samples at 2-inch intervals, from a couple feet below the top of the pit wall to the gravel at its bottom, a distance of about 13 feet. The gravel at the bottom of the pit is from a time 17,000 to 18,000 years ago, when glacial ice still covered the region, Fisher said.
Organic material from some of the samples will be radiocarbon-dated. If the dates grow steadily older with increasing depth, as expected, the researchers can have increased confidence in the dates of the Bristle Mammoth bones.
Pollen grains and fungal spores will be extracted from the sediments and analyzed to help reconstruct ancient environments and to provide proper context for the mammoth find.
Spores from the Sporormiella fungus are found today in the dung of domestic livestock animals as well as wild herbivores. The spores are preserved in recognizable form for thousands of years and are used in paleoecological studies as a proxy for the abundance of ancient grazing mammals such as mammoths.
If the fungal spores are found in the various ancient sediment layers at the Bristle site, their distribution could reveal when grazing mammals were present at the site as well as the timing of their local extinction.
Pollen grains would show what types of plants were growing at the time of the Bristle Mammoth and how the vegetation mix changed over time as the climate shifted.
The oldest well-documented, published evidence for humans in Michigan is about 13,000 years ago, the age of the spear-wielding Clovis hunters. But several lines of evidence from the Bristle Mammoth, including the single radiocarbon date, imply that humans processed the carcass more than 2,000 years before the Clovis hunters arrived.
The Bristle Mammoth remains were found in pond sediments. Fisher suspects early humans butchered the carcass and placed selected portions at the bottom of the pond for storage, using boulders to anchor their meat stash.
Examination of the sediments revealed during this week’s dig suggest the pond was small, perhaps only 20 to 30 yards across, said Fisher, a professor in the Department of Earth and Environmental Sciences and in the Department of Ecology and Evolutionary Biology.
The weather was ideal for this week’s two-day dig, with sunny skies and unseasonably warm temperatures both days. Excavation costs of the second dig are being covered by Friends of the University of Michigan Museum of Paleontology, a group of avocational paleontologists associated with the university.
New early signals to quantify the magnitude of strong earthquakes
After an earthquake, there is a disturbance in the field of gravity almost instantaneously. This could be recorded before the seismic waves that seismologists usually analyze. In a study published in Science on December 1, 2017, a team formed of researchers from CNRS, IPGP, the Université Paris Diderot and Caltech has managed to observe these weak signals related to gravity and to understand where they come from. Because they are sensitive to the magnitude of earthquakes, these signals may play an important role in the early identification of the occurrence of a major earthquake.
This work came out of the interaction between seismologists who wanted to better understand earthquakes and physicists who were developing fine gravity measurements with a view to detecting gravitational waves. Earthquakes change the equilibrium of forces on Earth brutally and emit seismic waves whose consequences may be devastating. But these same waves also disturb Earth’s field of gravity, which emits a different signal. This is particularly interesting with a view to fast quantification of tremors because it moves at the speed of light, unlike tremor waves, which propagate at speeds between 3 and 10 km/s. So seismometers at a station located 1000 km from the epicenter may potentially detect this signal more than two minutes before the seismic waves arrive.
The work presented here, which follows on a 2016 study which demonstrated this signal for the first time, greatly increases its understanding. First, the scientists did indeed observe these signals on the data from about ten seismometers located between 500 and 3000 km from the epicenter of the 2011 Japanese earthquake (magnitude 9.1). From their observations, the researchers then demonstrated that these signals were due to two effects. The first is the gravity change that occurs at the location of the seismometer, which changes the equilibrium position of the instrument’s mass. The second effect, which is indirect, is due to the gravity change everywhere on Earth, which disturbs the equilibrium of the forces and produces new seismic waves that will reach the seismometer.
Taking account of these two effects, the researchers have shown that this gravity-related signal is very sensitive to the earthquake’s magnitude, which makes it a good candidate for rapidly quantifying the magnitude of strong earthquakes. The future challenge is to manage to exploit this signal for magnitudes below about 8 to 8.5, because below this threshold, the signal is too weak relative to the seismic noise emitted naturally by Earth, and dissociating it from this noise is complicated. So several technologies, including some inspired from instruments developed to detect gravitational waves, are being envisaged to take a new step forward in detection of these precious signals.
Reference:
Martin Vallée, Jean Paul Ampuero, Kévin Juhel, Pascal Bernard, Jean-Paul Montagner, Matteo Barsuglia. Observations and modeling of the elastogravity signals preceding direct seismic waves. Science, 2017; DOI: 10.1126/science.aao0746
Note: The above post is reprinted from materials provided by CNRS.
