The seismological station Patache is located at an altitude of 830 meters less then two kilometers away from the coast. Credit: C. Sens-Schönfelder, GFZ
Using a single seismometer, researchers have shown that seismic waves excited by the surf, together with the effect of the Earth’s tides on the subsoil, can be used to better understand the properties of the Earth without having to drill into the ground. Knowledge of subsurface stress or strain fluctuations is important for safety in construction and mining, and monitoring geological processes in volcanoes and fault zones, for example.
Anyone who wants to take a look inside the Earth needs a signal that can penetrate rocks, minerals and other opaque material. Seismic waves represent such a signal. If you record them with a seismometer, you can draw conclusions from the recorded data about the state of the subsurface through which the waves have passed. Knowledge of subsurface stress or strain fluctuations is just as important for safety in construction and mining, for example, as it is for monitoring geological processes in volcanoes and fault zones. Now Christoph Sens-Schönfelder from the GFZ German Research Centre for Geosciences in Potsdam and Tom Eulenfeld from the University of Jena have been able to show that the seismic waves excited by the surf, together with the effect of the Earth’s tides on the subsoil, can be used to better understand the properties of the Earth.
Seismic waves not only provide information about the structure of the Earth’s material, but also about the forces acting on it. For example, deformations of the subsurface change the velocity at which a wave travels. In order to draw conclusions about the subsurface forces from the velocity, however, data is required on how the material reacts to deformations under known conditions. Until now, such data have only been available from laboratory experiments, not from the field.
Christoph Sens-Schönfelder and Tom Eulenfeld have now succeeded for the first time in using a single seismometer to measure how sensitively seismic waves react to the deformation of the Earth’s material they propagate in. In order to achieve that, they evaluated the velocity of the seismic noise generated by the surf. They report on this in the journal Physical Review Letters.
Measuring deformations in the Earth’s interior from the surface
“We use two different signals that the environment provides us with naturally,” explains Christoph Sens-Schönfelder. “Due to the tidal effect of the moon and the sun, the universe conducts a permanent deformation experiment with the Earth. The luminaries pull with great regularity on our planet. To observe this pulling, we use the seismic noise in the underground that is generated by the surf.”
The relation investigated by Christoph Sens-Schönfelder and Tom Eulenfeld allows in principle a measurement of the deformations inside the Earth by means of recordings of seismographs on the Earth’s surface. And that without having to drill into the ground.
The data that the two researchers investigated was recorded by the Integrated Plate Boundary Observatory in the Atacama Desert in northern Chile. Improved software was needed to detect even the slightest changes in wave velocity and to combine these changes with the deformation of the subsurface by the tides. Since this tidal deformation is known with high accuracy, it is possible to characterize the subsurface more comprehensively than before.
Reference:
Christoph Sens-Schönfelder and Tom Eulenfeld. Probing the in situ elastic nonlinearity of rocks with earth tides and seismic noise. Phys. Rev. Lett., 2019 [link]
CO2 greenhouse gas amounts in the atmosphere are likely higher today than ever before in the past 3 million years. For the first time, a team of scientists succeeded to do a computer simulation that fits ocean floor sediment data of climate evolution over this period of time. Ice age onset, hence the start of the glacial cycles from cold to warm and back, the study reveals, was mainly triggered by a decrease of CO2-levels. Yet today, it is the increase of greenhouse gases due to the burning of fossil fuels that is fundamentally changing our planet, the analysis further confirms. Global mean temperatures never exceeded the preindustrial levels by more than 2 degrees Celsius in the past 3 million years, the study shows — while current climate policy inaction, if continued, would exceed the 2 degrees limit already in the next 50 years.
Changes in CO2 levels were a main driver of the ice ages
“We know from the analysis of sediments on the bottom of our seas about past ocean temperatures and ice volumes, but so far the role of CO2 changes in shaping the glacial cycles has not been fully understood,” says Matteo Willeit of the Potsdam Institute for Climate Impact Research, lead author of the study now published in Science Advances. “It is a breakthrough that we can now show in computer simulations that changes in CO2 levels were a main driver of the ice ages, together with variations of how the Earth’s orbits around the sun, the so-called Milankovitch cycles. These are actually not just simulations: we compared our results with the hard data from the deep sea, and they prove to be in good agreement. Our results imply a strong sensitivity of the Earth system to relatively small variations in atmospheric CO2. As fascinating as this is, it is also worrying.”
Studying Earth’s past and its natural climate variability is key to understanding possible future pathways of humanity. “It seems we’re now pushing our home planet beyond any climatic conditions experienced during the entire current geological period, the Quaternary,” says Willeit. “A period that started almost 3 million years ago and saw human civilization beginning only 11,000 years ago. So, the modern climate change we see is big, really big; even by standards of Earth history.”
Learning from Earth’s past to understand the future
Building on previous research at PIK, the researchers reproduced the main features of natural climate variability over the last few million years with an efficient numerical model — a computer simulation based on astronomical and geological data and algorithms representing the physics and chemistry of our planet. The simulation was driven only by well-known changes in the ways the Earth circles the sun, the so-called orbital cycles, and different scenarios for slowly varying boundary conditions, namely CO2 outgassing from volcanoes. The study also lookedt into changes in sediment distribution of the Earth surface, since ice sheets slide more easily on gravel than on bedrock. It has also accounted for the role of atmospheric dust, which makes the ice surface darker and thereby contributes to melting.
“The fact that the model can reproduce the main features of the observed climate history gives us confidence in our general understanding of how the climate system works,” says co-author Andrey Ganopolski, author of several previous groundbreaking studies the new analysis now builds upon. “The simulations we develop have to be simple enough to allow for thousands of calculation runs of many thousands of years, and yet have to capture the critical factors that drive our climate. This is what we have achieved. And it is confirming how outstandingly important changes in CO2 levels are for Earth’s climate.”
Reference:
M. Willeit, A. Ganopolski, R. Calov, V. Brovkin. Mid-Pleistocene transition in glacial cycles explained by declining CO2 and regolith removal. Science Advances, 2019; 5 (4): eaav7337 DOI: 10.1126/sciadv.aav7337
Data produced by internet users can help to speed up the detection of earthquakes. Fast and accurate information is essential in the case of earthquakes: Epicentre location, depth and magnitude are minimum requirements to reliably estimate their possibly catastrophic consequences.
An international team of scientists has presented a method to combine in real time data from seismic networks with information derived from users looking for earthquake information on specific websites, the smartphone LastQuake app and via Twitter. This method significantly reduces the time needed to detect and locate those earthquakes that are felt by the public. The team reported about their results in the journal Science Advances.
Robert J. Steed, Amaya Fuenzalida and Remy Bossu of the European-Mediterranean Seismological Centre (EMSC) in France carried out the research with colleagues from France, Hungary and Germany. The EMSC is one of the top global earthquake information centers which distributes global seismic data for free to the public via its websites (http://www.emsc-csem.org, m.emsc.eu) and its LastQuake smartphone app and Twitter.
It also promotes the use of crowdsourcing to collect eyewitness reports, photos and videos following earthquakes in order to improve situational awareness. This research was done in collaboration with István Bondár (MTA CSFK), an expert in seismic location and the global earthquake monitoring service of the German Centre for Geosciences, GEOFON, which is among the fastest sources for earthquake information world-wide. GEOFON operates a network of around one hundred stations and combines this real-time data with that of other open networks to automatically analyze earthquake activity world-wide.
Usually within three to eight minutes after an earthquake, software developed at GFZ is able to compute location and magnitude of the earthquake. This information is made available online and shared immediately with partner organizations. The new method to compute location can accelerate the detection time to only one to three minutes for felt earthquakes. After feeling an earthquake, people tend to rapidly seek information from the internet or tweet about their observations.
The sudden increase in demand for earthquake information from websites like the EMSC can be detected and an approximate determination made of their geographical origin. This crowdsourcing data collected by the EMSC, in combination with seismic data provided by GFZ, accelerates the detection of felt earthquakes. The algorithm incorporates usage of the EMSC websites and the EMSC’s smartphone app LastQuake as well as searching for the word “earthquake” in 59 languages on Twitter.
The team used the crowdsourcing approach to analyze more than 1500 earthquakes during the years 2016 and 2017. The time required to arrive at a reliable detection could be reduced by on average more than a minute compared to the analysis of only seismic data.
Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Credit: Wikipedia.
There have been no major ground rupturing earthquakes along California’s three highest slip rate faults in the past 100 years. A new study published in Seismological Research Letters concludes that this current “hiatus” has no precedent in the past 1000 years.
U.S. Geological Survey researchers Glenn Biasi and Kate Scharer analyzed long paleoseismic records from the San Andreas, San Jacinto and Hayward Faults for the past 1000 years, to determine how likely it might be to have a 100-year gap in earthquakes across the three faults. They found that the gap was very unlikely—along the lines of a 0.3% chance of occurring, given the seismic record of the past 1000 years.
The results emphasize that the hiatus is exceptional, and that the gap isn’t some sort of statistical fluke created by incomplete paleoseismic records, said Biasi.
The analysis also indicates that the next 100 years of California earthquakes along these faults could be a busy one, he noted. “If our work is correct, the next century isn’t going to be like the last one, but could be more like the century that ended in 1918.”
Between 1800 and 1918, there were eight large ground-rupturing earthquakes along the faults, including the well-known 1906 earthquake in San Francisco and the similar-sized 1857 rupture of the San Andreas in southern California, but nothing so large since.
“We know these big faults have to carry most of the [tectonic] motion in California, and sooner or later they have to slip,” said Biasi. “The only questions are how they’re going to let go and when.”
The three faults and their major branches analyzed by the researchers accommodate the majority of the slip between the Pacific and North American plate boundary. Paleoseismic records from the faults predict that there would be three to four large ground-rupturing earthquakes (magnitude 6.5 or larger) each century.
Biasi and Scharer examined the best available paleoseismic records from sites along the three faults to determine whether the current gap could be explained by missing data, or incorrect radiocarbon dating of past earthquakes. From these data, they calculated the probability that there would be a 100-year gap in ground-rupturing earthquakes across all three faults.
“Our paper confirms that this hiatus is very improbable and it’s our view that our efforts will be better spent considering explanations for this, rather than trying to bend the data to make the hiatus a ‘statistically improbable but could happen’ kind of thing,” said Biasi.
“We’re saying, no, it’s not a data problem, it’s not a data choice problem, it doesn’t matter how you slice this,” he added. “We just have not had earthquakes that past records predict that we should have had.”
He likened the hiatus to what a person might see if they pulled up a chair alongside a freeway to count passing cars. “You might say that a certain number of cars per hour is kind of representative, and then something happens and you go ten minutes of seeing no cars. If it’s just ten minutes, you could say it was a statistical fluke.”
But if the freeway stays clear of traffic for a long time, “the other reason there might be no cars is that up around the bend, there’s a wreck,” said Biasi.
The researchers would like more seismologists to focus on the reasons—”the wreck around the bend”— behind the current hiatus.
“We had the flurry of very large earthquakes from 1800 to 1918,” Biasi said. “It’s possible that among them they just wrung out—in the sense of wringing out a dishrag—a tremendous amount of energy out the system.”
There may be stronger long-range interactions between the faults than suspected, or there may be unknown features of the mantle and lower crust below the faults that affect the probability of ground-rupturing earthquakes, he noted.
Reference:
“The Current Unlikely Earthquake Hiatus at California’s Transform Boundary Paleoseismic Sites,” Seismological Research Letters (2019). DOI: 10.1785/0220180244
Paleontologists from Hokkaido University in Japan, in cooperation with paleontologists from the Perot Museum of Nature and Science in Dallas, Texas, have discovered the first-confirmed occurrence of a lambeosaurine (crested ‘duck-billed’ dinosaur) from the Arctic – part of the skull of a lambeosaurine dinosaur from the Liscomb Bonebed (71-68 Ma) found on Alaska’s North Slope. The discovery proves for the first time that lambeosaurines inhabited the Arctic during the Late Cretaceous. See paper in Scientific Reports. Credit – Illustration by Masato Hattori. Credit: Masato Hattori
Paleontologists from Hokkaido University in Japan, in cooperation with paleontologists from the Perot Museum of Nature and Science in Dallas, Texas, have discovered the first-confirmed occurrence of a lambeosaurine (crested ‘duck-billed’ dinosaur) from the Arctic—part of the skull of a lambeosaurine dinosaur from the Liscomb Bonebed (71-68 Ma) found on Alaska’s North Slope. The bonebed was previously known to be rich in hadrosaurine hadrosaurids (non-crested ‘duck-billed’ dinosaurs).
The discovery proves for the first time that lambeosaurines inhabited the Arctic during the Late Cretaceous. In addition, the numeric abundance of hadrosaurine fossils compared to the lambeosaurine fossils in the marine-influenced environment of the Liscomb Bonebed suggests the possibility that hadrosaurines and lambeosaurines had different habitat preferences.
The paleontologists’ findings were published today in Scientific Reports. The paper, titled “The first definite lambeosaurine bone from the Liscomb Bonebed of the Upper Cretaceous Prince Creek Formation, Alaska, United States,” is co-authored by Yoshitsugu Kobayashi, Ph.D., and Ryuji Takasaki, of Hokkaido University, in cooperation with Anthony R. Fiorillo, Ph.D., of the Perot Museum of Nature and Science. Other authors are Ronald Tykoski, Ph.D. of the Perot Museum and Paul McCarthy, Ph.D., of the University of Alaska.
“This new discovery illustrates the geographic link between lambeosaurines of North America and the Far East,” said Takasaki. “Hopefully, further work in Alaska will reveal how closely the dinosaurs of Asia and North America are connected.”
The newly discovered fossil, which is housed in the collections of the Perot Museum of Nature and Science, is a supraoccipital, one of the bones that forms the braincase. The new supraoccipital differs from those of hadrosaurines by the presence of large supraoccipital bosses and it’s short, front-to-back length. Since these features are commonly seen in other members of Lambeosaurinae, the newly discovered supraoccipital was assigned to that group.
“This first definitive evidence of a crested hadrosaur in the Cretaceous Arctic tells us that we still have much to learn about the biodiversity and the biologically productive environments of the ancient north, and that the story these fossils tell us is continually evolving,” adds Dr. Fiorillo.
The Arctic is an extreme environment that is low in temperature, lacks sunlight during winters, and has seasonally limited food resources. Though it was warmer during the Late Cretaceous, the Arctic was surely one of the most challenging places to live for large vertebrates at the time. The Prince Creek Formation on the North Slope of Alaska is a world-famous rock unit for studying dinosaurs of the ancient Arctic. Because the dinosaurs found there lived in the ancient Arctic rather than in tropical or sub-tropical conditions, these dinosaurs challenge much of what we think we know about dinosaurs. The Liscomb Bonebed (71-68 Ma), which was deposited near the ancient Arctic shoreline, is especially rich in dinosaur bones, with more than 6,000 bones collected from it thus far.
More than 99 percent of dinosaur fossils known from the Liscomb Bonebed are hadrosaurs, a group of large, duck-billed herbivorous dinosaurs who lived during the Late Cretaceous and were found throughout much of the northern hemisphere. All of the hadrosaur fossils from the Liscomb Bonebed were long considered to belong to a hadrosaurine duck-billed dinosaur called Edmontosaurus. Up until now, all of the hadrosaurids known from across the Arctic, including those from the Liscomb Bonebed, were considered to belong to crest-less hadrosaurines.
The discovery of a fossil from a lambeosaurine hadrosaurid in the Liscomb Bonebed is historically important for Japanese paleontologists. The first “Japanese” dinosaur, Nipponosaurus, is a lambeosaurine hadrosaur. Based on the new discovery, Hokkaido University and the Perot Museum together used this discovery to further investigate the ecology of the Arctic hadrosaurids.
Although the new discovery reveals Arctic inhabitance by lambeosaurines, more specific taxonomic status and potential functional adaptations to the severe Arctic environment remain unknown due to incompleteness of the specimen. Additional excavation and further research will help answer these questions.
Reference:
Ryuji Takasaki et al, The First Definite Lambeosaurine Bone From the Liscomb Bonebed of the Upper Cretaceous Prince Creek Formation, Alaska, United States, Scientific Reports (2019). DOI: 10.1038/s41598-019-41325-8
The presence of methane has long been a point of contention among Mars experts. Credit: EUROPEAN SPACE AGENCY/AFP/File / HO
The mystery of methane on Mars may finally be solved as scientists Monday confirmed the presence of the life-indicating gas on the Red Planet as well as where it might have come from.
In the 15 years since a European probe reported traces of the gas in the Martian atmosphere, debate has raged over the accuracy of the readings showing methane, which on Earth is produced by simple lifeforms.
Because methane gas dissipates relatively quickly—within around 12 years on Earth—and due to the difficulty of observing Mars’ atmosphere, many scientists questioned previous studies that relied on a single data set.
Now an international team of experts have compared observations from two separate spacecraft, taken just one day apart in 2013, to find independent proof of methane on our neighbouring planet.
Furthermore, they conducted two parallel experiments to determine the most likely source of methane on Mars to be an ice sheet east of Gale Crater—itself long assumed to be a dried up lake.
“This is very exciting and largely unexpected,” Marco Giuranna, from Rome’s National Astrophysics Institute, told AFP.
“Two completely independent lines of investigation pointed to the same general area of the most likely source for the methane.”
Europe’s Mars Express probe measured 15.5 parts per billion in the atmosphere above the Gale Crater on June 16, 2013. The presence of methane in the vicinity was confirmed by readings taken 24 hours earlier by NASA’s Curiosity rover.
Using the data, Giuranna and the team divided the region around the crater into grids of 250 by 250 square kilometres.
One study then ran a million computer-modelled emissions scenarios for each section while another team studied images of the planet surface for features associated on Earth with the release of methane.
‘Indicator of life’
The most likely source was a sheet of frozen methane beneath a rock formation, which the team believes periodically ejects the gas into the atmosphere.
Giuranna said that while methane is a sign of life on Earth, its presence on Mars doesn’t necessarily constitute evidence of something similar on the Red Planet.
“Methane is important because it could be an indicator of microbial life,” he said. “But life is not required to explain these detections because methane can be produced by abiotic processes.”
“Though not a direct biosignature of life, methane can add to the habitability of martian settings, as certain types of microbes can use methane as a source of carbon and energy,” he added.
Though there is no liquid water on Mars, the European Space Agency said in February its imaging equipment had shown further evidence of dried up river beds, suggesting the Red Planet may once have been home to simple organisms.
Giuranna said that further research was needed to determine the extent of the methane ice sheet near Gale Crater.
If founded to be extensive, the methane it contains “could support a sustained human presence” on Mars as a possible source of fuel for industrial processes and a propellant for returning manned missions to Earth, he said.
The study is reported in Nature Geoscience this week.
Reference:
Independent confirmation of a methane spike on Mars and a source region east of Gale Crater, Nature Geoscience (2019). DOI: 10.1038/s41561-019-0331-9
Note: The above post is reprinted from materials provided by AFP .
Iron-oxidizing bacteria live in environments as extreme as the deep ocean and as common as roadside ditches. A recent paper in Frontiers proposes distributing the iron that these bacteria naturally produce to ‘fertilize’ phytoplankton and help remove excess carbon dioxide from the atmosphere. Credit: Bigelow Laboratory for Ocean Sciences
Distributing iron particles produced by bacteria could “fertilize” microscopic ocean plants and ultimately lower atmospheric carbon levels, according to a new paper in Frontiers.
“It is important that we explore ideas for climate change mitigation that can supplement the effects of decreasing carbon emissions,” said David Emerson, a senior research scientist at Bigelow Laboratory for Ocean Sciences and author of the paper. “The more ideas we test, the better decisions we can make for our planet’s future.”
Emerson’s paper proposes a novel way to provide iron to large areas of the ocean, 30 percent of which is poor in the essential element. This method takes advantage of minerals synthesized by iron-oxidizing bacteria, which feed on the tiny spark of energy they generate by transferring electrons between iron and oxygen. This process produces rust minerals as byproducts, which are of the right chemical composition to be used by the tiny ocean plants called phytoplankton that help remove carbon dioxide from the atmosphere.
Iron-oxidizing bacteria live in environments as extreme as the deep ocean and as common as roadside ditches. Emerson believes that cultivating iron-oxidizing bacteria in shallow ponds could be a simple, inexpensive way to produce nanoparticles of iron that have specific properties needed to “fertilize” the ocean. Using iron fertilization as a climate change mitigation tool was first proposed in the 1990s, and Emerson believes implementing a controlled research program is the next step in exploring its efficacy.
“This research has tremendous potential to integrate disciplines from phytoplankton ecology, to atmospheric science, to engineering,” Emerson said. “At minimum, we would gain a better sense of how the ocean works. At best, iron additions would act on a short time scale to help mitigate climate change.”
Most iron enters the ocean as dust that blows seaward from the Sahara and other major deserts. Emerson believes that using aircraft to distribute a fine iron powder over deficient ocean regions would approximate natural iron inputs. Timing flights with seasonal phytoplankton “blooms” would stimulate growth and boost populations.
Phytoplankton live in the sunlit upper layer of the ocean, which is kept in chemical equilibrium with the atmosphere through constant exchanges between the air and sea. They grow using carbon dissolved in the upper ocean. When they die, some of the phytoplankton sink, sending that carbon to the deep ocean, where it remains for thousands of years. As this cycle pumps carbon into the remote ocean depths, more atmospheric carbon diffuses into the upper ocean. Stimulating phytoplankton growth with iron fertilization could ramp up this process, ultimately shuttling more of the excess atmospheric carbon into the deep ocean.
“In addition to cutting carbon emissions, we need to remove more carbon from the atmosphere to limit global climate change,” Emerson said. “These geoengineering approaches are not solutions to the whole problem, but they are potential ways we can mitigate the worst effects.”
Evidence in the geologic record indicates that the amount of iron captured by the ocean may have helped moderate global climate in the past and played an important role in controlling earlier ice ages. When events like volcanic eruptions add large amounts of iron to the atmosphere, they may have the effect of fertilizing the ocean—increasing phytoplankton activity and ultimately carbon drawdown.
“It’s important to start investing in thoughtful and extensive research programs now,” Emerson said. “The worst thing would be if, in several decades, people faced with horrible consequences of climate change started taking dramatic action without understanding the long-term effects. We need to explore and develop a continuum of solutions, from actions we can take as individuals to large-scale efforts.”
Reference:
David Emerson, Biogenic Iron Dust: A Novel Approach to Ocean Iron Fertilization as a Means of Large Scale Removal of Carbon Dioxide From the Atmosphere, Frontiers in Marine Science (2019). DOI: 10.3389/fmars.2019.00022
Hurricane Irma forming over the Atlantic Ocean in September 2017. A new study finds that volcanic eruptions can influence the strength and frequency of hurricanes around the world. Credit: NASA
A new study led by Lamont-Doherty Earth Observatory researcher Suzana Camargo and Université du Québec à Montréal’s Francesco Pausata provides deeper insight into how large volcanic eruptions affect hurricane activity.
Previous studies could not clearly determine the effects of volcanic eruptions on hurricanes, because the few large volcanic eruptions in the last century coincided with El Niño-Southern Oscillation events, which also influence hurricane activity.
In the study published today in the Proceedings of the National Academy of Sciences of the United States of America, Camargo and Pausata approached this relationship by simulating very large volcanic eruptions in the tropics multiple times. Their modeling told a more complex story than previous papers had indicated.
“This is the first study to explain the mechanism of how large volcanic eruptions influences hurricanes globally,” said Camargo.
According to their findings, large tropical volcanic eruptions can affect hurricanes by shifting the Intertropical Convergence Zone, a region that circles the Earth near the Equator and greatly influences rainfall and hurricane activity.
As the Intertropical Convergence Zone moves after a large volcanic eruption, it affects both the intensity and frequency of hurricanes, causing some regions to experience an increase in activity and other regions to experience a decrease. For example, a large eruption in the tropical regions of the Northern Hemisphere leads to a southward shift of the Intertropical Convergence Zone.
This results in an increase in hurricane activity between the Equator and the 10°N line, and a decrease further north. The zone’s southward shift has further effects in the Southern Hemisphere, causing a decrease in activity on the coasts of Australia, Indonesia, and Tanzania, while Madagascar and Mozambique experience an increase. These changes can last for up to four years following the eruption.
Camargo and Pausata were able to separate the effects of volcanic eruptions and El Niño-Southern Oscillation on hurricane activity and show the different impacts that the two factors have on hurricanes globally. Their findings are important in helping scientists better understand the relationship between volcanoes and hurricanes.
Reference:
Francesco S. R. Pausata et al. Tropical cyclone activity affected by volcanically induced ITCZ shifts, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1900777116
Crocodylomorphs were a highly morphologically and ecologically diverse clade. These extinct crocodile relatives had a much richer variety of skull shapes than living crocodilians, suggesting a wide range of feeding strategies. Credit: Darren Naish, Tetrapod Zoology
Ancient aquatic crocodiles fed on softer and smaller prey than their modern counterparts and the evolution of skull shape and function allowed them to spread into new habitats, reveal paleobiology researchers from the University of Bristol and UCL.
For the study, published today in Paleontology, the team digitally reconstructed the skull of an extinct species of marine crocodile and compared it to similar living species to gain new insights into the diet of ancient crocodiles and their role in ecosystems around 230 million years ago.
Modern crocodiles are known for their characteristic anatomy and apex predator role in semiaquatic ecosystems but their ancient ancestors, which lived side-by-side with the first dinosaurs in the Late Triassic period, were tiny land-dwellers that soon gave rise to a great diversity of forms.
One group, the thalattosuchians, went into the sea and became marine specialists. They had long, thin snouts, resembling that of the living gharial, which feeds on fish in rivers in India. An early member of this group, Pelagosaurus typus, inhabited shallow marine environments in what is now Europe during the Early Jurassic.
By looking at the different shapes of their skulls, scientists were able to work out what crocodiles were eating. As reported in the journal Palaeontology today, the biomechanical and macro-evolutionary approaches applied during this latest study show how ancient crocodiles came to occupy diverse and specialized ecological niches.
Ph.D. student Antonio Ballell, from the University of Bristol’s School of Earth Sciences and lead author of the study, said: “We used up-to-date techniques to explore how the skull of these extinct crocodilians functioned and evolved. Our first aim was to compare how the skull stressed and strained under simulated feeding loads in Pelagosaurus compared to the living gharial and gain new understanding of how the extinct species fed.”
Using modern computational methods, coupled with 3-D digital skull models obtained from CT scans of Pelagosaurus and the gharial, the research team was able to look for muscle scars in the fossils that mark where the muscles once attached to reconstruct the jaw-closing musculature.
This approach was coupled with finite element analysis, an engineering technique that predicts how biological structures behave under specific loading scenarios such as feeding loads.
Co-author, Dr. Laura Porro from UCL Cell and Development Biology, said “Modern computational techniques allow palaeobiologists to ‘bring extinct species back to life’ and infer how they fed and lived from the anatomical information provided by fossils. Using CT scans, we are able to visualise internal areas of the skull and scars on the bones, indicating where muscles attached, that scientists had never observed before. Engineering methods allowed us to test how the skull responds to biting, 230 million years after this animal’s last meal.”
Their results show that the weaker jaw of Pelagosaurus might indicate that it specialized on softer and smaller prey than the modern gharial.
The team also analysed how fast feeding-related characters of the jaws evolved in a wide range of extinct crocodilian species. This showed that traits related to the long snouts of thalattosuchians evolved rapidly, suggesting that they occupied a very specific marine ecological niche soon after the origin of the lineage.
Co-author Dr. Benjamin Moon from the University of Bristol added: “Pelagosaurus and closely related species differ from other crocs in their slender lower jaws, and this helped their evolutionary success in the Early Jurassic, when marine ecosystems were still recovering from the devastating End-Triassic mass extinction.”
The study contributes to the increasing understanding of functional evolution of crocodylomorphs and the ecological dynamics of Mesozoic marine reptiles.
Antonio Ballell concluded: “Our findings highlight the spectacular diversity of feeding strategies present in extinct crocodile relatives and how this was important in the evolution and diversification of the group. We found that different lineages explored and conquered ecological niches in different ways.
“The evolutionary history of crocodiles was very complex and looking at it from a functional perspective is fundamental to understand it”.
Reference:
Antonio Ballell et al. Convergence and functional evolution of longirostry in crocodylomorphs, Palaeontology (2019). DOI: 10.1111/pala.12432
Horseshoe Bend is a horseshoe-shaped incised meander of the Colorado River located near the town of Page, Arizona, in the United States.
Horseshoe Bend is located 5 miles (8.0 km) downstream from the Glen Canyon Dam and Lake Powell within Glen Canyon National Recreation Area, about 4 miles (6.4 km) southwest of Page.
It is accessible via hiking a 1.5-mile (2.4 km) round trip from U.S. Route 89. Horseshoe Bend can be viewed from the steep cliff above.
The overlook is 4,200 feet (1,300 m) above sea level, and the Colorado River is at 3,200 feet (980 m) above sea level, making it a 1,000-foot (300 m) drop.
The rock walls of Horseshoe Bend contain hematite, platinum, garnet, and other minerals.
How to get there
Horseshoe Bend is just south of Page, Arizona. From the Glen Canyon Dam on US-89 head south for 5.1 miles. You’ll pass along the edge of Page, Arizona. At around 5 miles from the Glen Canyon Dam, you’ll see a sign for Horseshoe Bend Overlook. Turn right into parking area. If coming from the south, take US-89 north to Page, Arizona and before coming into town you’ll see a Horseshoe Bend Overlook sign. Turn left into the parking lot.
Plate boundaries are the edges where two plates meet. Most geologic activities, including volcanoes, earthquakes, and mountain building, take place at plate boundaries. “Read More about: What is Plate Tectonics? “
What are the 4 types of plate boundary?
There are four types of plate boundaries: Divergent boundaries — where new crust is generated as the plates pull away from each other. Convergent boundaries — where crust is destroyed as one plate dives under another.
Divergent boundaries: where new crust is generated as the plates pull away from each other.
Convergent boundaries: where crust is destroyed as one plate dives under another.
Transform boundaries: where crust is neither produced nor destroyed as the plates slide horizontally past each other.
Plate boundary zones: broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.
Plate Boundary Types
Divergent boundary (Constructive)
Occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magma—molten rock—rises from the mantle.
Divergent plate boundaries
It oozes up into the gap and hardens into solid rock, forming new crust on the torn edges of the plates. Magma from the mantle solidifies into basalt, a dark, dense rock that underlies the ocean floor. Thus at divergent boundaries, oceanic crust, made of basalt, is created.
Convergent boundary (Destructive)
Convergent plate boundaries
When two plates come together, The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. A chain of volcanoes often forms parallel to the boundary, to the mountain range, and to the trench. Powerful earthquakes shake a wide area on both sides of the boundary.
If one of the colliding plates is topped with oceanic crust, it is forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into new crust. Magma formed from melting plates solidifies into granite, a light colored, low-density rock that makes up the continents. Thus at convergent boundaries, continental crust, made of granite, is created, and oceanic crust is destroyed.
Transform boundaries (Conservative)
Transform plate boundaries
Two plates sliding past each other, Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. As the plates alternately jam and jump against each other, earthquakes rattle through a wide boundary zone. In contrast to convergent and divergent boundaries, no magma is formed. Thus, crust is cracked and broken at transform margins, but is not created or destroyed.
Plate boundary zones
Plate boundary zones occur where the effects of the interactions are unclear, and the boundaries, usually occurring along a broad belt, are not well defined and may show various types of movements in different episodes.
The Cretaceous–Tertiary extinction event, now called the Cretaceous–Palaeogene extinction event. It may be called the K/T extinction event or K/Pg event for short. This is the famous event which killed the dinosaurs at the end of the Cretaceous period.
Sixty-five million years ago about 70% of all species then living on Earth disappeared within a very short period. The disappearances included the last of the great dinosaurs. Paleontologists speculated and theorized for many years about what could have caused this “mass extinction,” known, as the K-T event (Cretaceous-Tertiary Mass Extinction event). Then in 1980 Alvarez, Alvarez, Asaro, and Michel reported their discovery that the peculiar sedimentary clay layer that was laid down at the time of the extinction showed an enormous amount of the rare element iridium.
First seen in the layer near Gubbio, Italy, the same enhancement was soon discovered to be world wide in that one particular 1-cm (0.4-in.) layer, both on land and at sea. The Alvarez team suggested that the enhancement was the product of a huge asteroid impact. On Earth most of the iridium and a number of other rare elements such as platinum, osmium, ruthenium, rhodium, and palladium are believed to have been carried down into Earth’s core, along with much of the iron, when Earth was largely molten.
Primitive “chondritic” meteorites (and presumably their asteroidial parents) still have the primordial solar system abundances of these elements. A chondritic asteroid 10 km (6 mi.) in diameter would contain enough iridium to account for the worldwide clay layer enhancement. This enhancement appears to hold for the other elements mentioned as well.
Since the original discovery, many other pieces of evidence have come to light that strongly support the impact theory. The high temperatures generated by the impact would have caused enormous fires, and indeed soot is found in the boundary clays. A physically altered form of the mineral quartz that can only be formed by the very high pressures associated with impacts has been found in the K-T layer.
Geologists who preferred other explanations for the K-T event said, “show us the crater.” In 1990 a cosmochemist named Alan Hildebrand became aware of geophysical data taken 10 years earlier by geophysicists looking for oil in the Yucatan region of Mexico. There a 180-km (112-mi.) diameter ring structure called “Chicxulub” seemed to fit what would be expected from a 65-million-year-old impact, and further studies have largely served to confirm its impact origin. The Chicxulub crater has been age dated (by the 40Ar/39Ar method) at 65 million years! Such an impact would cause enormous tidal waves, and evidence of just such waves at about that time has been found all around the Gulf.
One can never prove that an asteroid impact “killed the dinosaurs.” Many species of dinosaurs (and smaller flora and fauna) had in fact died out over the millions of years preceding the K-T events. The impact of a 10-km asteroid would most certainly have been an enormous insult to life on Earth. Locally, there would have been enormous shock wave heating and fires, tremendous earthquake, hurricane winds, and trillions of tons of debris thrown everywhere. It would have created months of darkness and cooler temperatures globally. There would have been concentrated nitric acid rains worldwide. Sulfuric acid aerosols may have cooled Earth for years. Life certainly could not have been easy for those species which did survive. Fortunately such impacts occur only about once every hundred million years.
What killed the dinosaurs?
Dinosaur fossils are only found below the K/T boundary. This shows they became extinct before, or during the event. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct.
Mammalian and bird groups got through the event with some extinctions. Those that survived became widespread and varied during their later evolutionary radiation.
Scientists think the K/T extinctions were caused by something sudden and powerful, such as one or more massive asteroid or meteor impacts, and increased volcanic activity.
Scientists study what happened to the dinosaurs and other groups to learn what caused the K/T extinction event. How quickly they died out around the world is an important clue.
Scientists also study patterns in rocks to learn the causes. Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, are dated to about the same time as the extinctions. Those impacts and volcanoes would have reduced sunlight and hindered photosynthesis, disrupting Earth’s ecology.
The Cretaceous–Paleogene (K–Pg) extinction event, was a sudden mass extinction of some three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.
In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth’s crust, but abundant in asteroids.
As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago, which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton.
The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometer-wide (112 mi) Chicxulub crater in the Gulf of Mexico’s Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid.
A 2016 drilling project into the Chicxulub peak ring, confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain.
Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change, and sea level change.
A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs. It also destroyed a plethora of other terrestrial organisms, including certain mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards (Mosasauridae) and devastated fish, sharks, mollusks (especially ammonites, which became extinct), and many species of plankton.
It is estimated that 75% or more of all species on Earth vanished. Yet the extinction also provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales, bats, and primates. Birds, fish, and perhaps lizards also radiated.
K-Pg Boundary Extinction
The K–Pg extinction event was severe, global, rapid, and selective, eliminating a vast number of species. Based on marine fossils, it is estimated that 75% or more of all species were made extinct.
The event appears to have affected all continents at the same time. Non-avian dinosaurs, for example, are known from the Maastrichtian of North America, Europe, Asia, Africa, South America, and Antarctica, but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico, Alaska, China, and New Zealand.
Despite the event’s severity, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the ground. This plant extinction caused a major reshuffling of the dominant plant groups. Omnivores, insectivores, and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects, worms, and snails, which in turn fed on detritus (dead plant and animal matter).
In stream communities, few animal groups became extinct because such communities rely less directly on food from living plants and more on detritus washed in from the land, protecting them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals on the ocean floor always or sometimes feed on detritus. Coccolithophorids and mollusks (including ammonites, rudists, freshwater snails, and mussels), and those organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary. The largest air-breathing survivors of the event, crocodyliforms and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.
After the K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches.
Radiolaria have left a geological record since at least the Ordovician times, and their mineral fossil skeletons can be tracked across the K–Pg boundary. There is no evidence of mass extinction of these organisms, and there is support for high productivity of these species in southern high latitudes as a result of cooling temperatures in the early Paleocene. Approximately 46% of diatom species survived the transition from the Cretaceous to the Upper Paleocene, a significant turnover in species but not a catastrophic extinction.
The occurrence of planktonic foraminifera across the K–Pg boundary has been studied since the 1930s. Research spurred by the possibility of an impact event at the K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary; however, there is ongoing debate between groups that think the evidence indicates substantial extinction of these species at the K–Pg boundary, and those who think the evidence supports multiple extinctions and expansions through the boundary.
Numerous species of benthic foraminifera became extinct during the event, presumably because they depend on organic debris for nutrients, while biomass in the ocean is thought to have decreased. As the marine microbiota recovered, however, it is thought that increased speciation of benthic foraminifera resulted from the increase in food sources. Phytoplankton recovery in the early Paleocene provided the food source to support large benthic foraminiferal assemblages, which are mainly detritus-feeding. Ultimate recovery of the benthic populations occurred over several stages lasting several hundred thousand years into the early Paleocene.
Duration of K–Pg extinction
The rapidity of the extinction is a controversial issue, because some theories about the extinction’s causes imply a rapid extinction over a relatively short period (from a few years to a few thousand years) while others imply longer periods.
The issue is difficult to resolve because of the Signor–Lipps effect; that is, the fossil record is so incomplete that most extinct species probably died out long after the most recent fossil that has been found. Scientists have also found very few continuous beds of fossil-bearing rock that cover a time range from several million years before the K–Pg extinction to a few million years after it.
The sedimentation rate and thickness of K–Pg clay from three sites suggest rapid extinction, perhaps less than ten thousand years. At one site in the Denver Basin of Colorado, the ‘fern spike’ lasted about one thousand years (no more than 71 thousand years); the earliest Cenozoic mammals appeared about 185,000 years (no more than 570,000 years) after the K–Pg boundary layer was deposited.
Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the wave from the seiche withdrew. Credit: Photo courtesy of Robert DePalma
The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota.
Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.
The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud. The torrent of rocks, like fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them from the world for 66 million years.
This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.
“This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary,” said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. “At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”
In a paper to appear next week in the journal Proceedings of the National Academy of Sciences, he and his American and European colleagues, including two University of California, Berkeley, geologists, describe the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico’s Yucatan Peninsula 66 million years ago. That impact created a huge crater, called Chicxulub, in the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere. The cloud eventually enveloped Earth, setting the stage for Earth’s last mass extinction.
“It’s like a museum of the end of the Cretaceous in a layer a meter-and-a-half thick,” said Mark Richards, a UC Berkeley professor emeritus of earth and planetary science who is now provost and professor of earth and space sciences at the University of Washington.
Richards and Walter Alvarez, a UC Berkeley Professor of the Graduate School who 40 years ago first hypothesized that a comet or asteroid impact caused the mass extinction, were called in by DePalma and Dutch scientist Jan Smit to consult on the rain of glass beads and the tsunami-like waves that buried and preserved the fish. The beads, called tektites, formed in the atmosphere from rock melted by the impact.
Tsunami vs. seiche
Richards and Alvarez determined that the fish could not have been stranded and then buried by a typical tsunami, a single wave that would have reached this previously unknown arm of the Western Interior Seaway no less than 10 to 12 hours after the impact 3,000 kilometers away, if it didn’t peter out before then. Their reasoning: The tektites would have rained down within 45 minutes to an hour of the impact, unable to create mudholes if the seabed had not already been exposed.
Instead, they argue, seismic waves likely arrived within 10 minutes of the impact from what would have been the equivalent of a magnitude 10 or 11 earthquake, creating a seiche (pronounced saysh), a standing wave, in the inland sea that is similar to water sloshing in a bathtub during an earthquake. Though large earthquakes often generate seiches in enclosed bodies of water, they’re seldom noticed, Richards said. The 2011 Tohoku quake in Japan, a magnitude 9.0, created six-foot-high seiches 30 minutes later in a Norwegian fjord 8,000 kilometers away.
“The seismic waves start arising within nine to 10 minutes of the impact, so they had a chance to get the water sloshing before all the spherules (small spheres) had fallen out of the sky,” Richards said. “These spherules coming in cratered the surface, making funnels — you can see the deformed layers in what used to be soft mud — and then rubble covered the spherules. No one has seen these funnels before.”
The tektites would have come in on a ballistic trajectory from space, reaching terminal velocities of between 100 and 200 miles per hour, according to Alvarez, who estimated their travel time decades ago.
“You can imagine standing there being pelted by these glass spherules. They could have killed you,” Richards said. Many believe that the rain of debris was so intense that the energy ignited wildfires over the entire American continent, if not around the world.
“Tsunamis from the Chicxulub impact are certainly well-documented, but no one knew how far something like that would go into an inland sea,” DePalma said. “When Mark came aboard, he discovered a remarkable artifact — that the incoming seismic waves from the impact site would have arrived at just about the same time as the atmospheric travel time of the ejecta. That was our big breakthrough.”
At least two huge seiches inundated the land, perhaps 20 minutes apart, leaving six feet of deposits covering the fossils. Overlaying this is a layer of clay rich in iridium, a metal rare on Earth, but common in asteroids and comets. This layer is known as the K-T, or K-Pg boundary, marking the end of the Cretaceous Period and the beginning of the Tertiary Period, or Paleogene.
Iridium
In 1979, Alvarez and his father, Nobelist Luis Alvarez of UC Berkeley, were the first to recognize the significance of iridium that is found in 66 million-year-old rock layers around the world. They proposed that a comet or asteroid impact was responsible for both the iridium at the K-T boundary and the mass extinction.
The impact would have melted the bedrock under the seafloor and pulverized the asteroid, sending dust and melted rock into the stratosphere, where winds would have carried them around the planet and blotted out the sun for months, if not years. Debris would have rained down from the sky: not only tektites, but also rock debris from the continental crust, including shocked quartz, whose crystal structure was deformed by the impact.
The iridium-rich dust from the pulverized meteor would have been the last to fall out of the atmosphere after the impact, capping off the Cretaceous.
“When we proposed the impact hypothesis to explain the great extinction, it was based just on finding an anomalous concentration of iridium — the fingerprint of an asteroid or comet,” said Alvarez. “Since then, the evidence has gradually built up. But it never crossed my mind that we would find a deathbed like this.”
Key confirmation of the meteor hypothesis was the discovery of a buried impact crater, Chicxulub, in the Caribbean and off the coast of the Yucatan in Mexico, that was dated to exactly the age of the extinction. Shocked quartz and glass spherules were also found in K-Pg layers worldwide. The new discovery at Tanis is the first time the debris produced in the impact was found along with animals killed in the immediate aftermath of the impact.
“And now we have this magnificent and completely unexpected site that Robert DePalma is excavating in North Dakota, which is so rich in detailed information about what happened as a result of the impact,” Alvarez said. “For me, it is very exciting and gratifying!”
Tektites
Jan Smit, a retired professor of sedimentary geology from Vrije Universiteit in Amsterdam in The Netherlands who is considered the world expert on tektites from the impact, joined DePalma to analyze and date the tektites from the Tanis site. Many were found in near perfect condition embedded in amber, which at the time was pliable pine pitch.
“I went to the site in 2015 and, in front of my eyes, he (DePalma) uncovered a charred log or tree trunk about four meters long which was covered in amber, which acted as sort of an aerogel and caught the tektites when they were coming down,” Smit said. “It was a major discovery, because the resin, the amber, covered the tektites completely, and they are the most unaltered tektites I have seen so far, not 1 percent of alteration. We dated them, and they came out to be exactly from the K-T boundary.”
The tektites in the fishes’ gills are also a first.
“Paddlefish swim through the water with their mouths open, gaping, and in this net, they catch tiny particles, food particles, in their gill rakers, and then they swallow, like a whale shark or a baleen whale,” Smit said. “They also caught tektites. That by itself is an amazing fact. That means that the first direct victims of the impact are these accumulations of fishes.”
Smit also noted that the buried body of a Triceratops and a duck-billed hadrosaur proves beyond a doubt that dinosaurs were still alive at the time of the impact.
“We have an amazing array of discoveries which will prove in the future to be even more valuable,” Smit said. “We have fantastic deposits that need to be studied from all different viewpoints. And I think we can unravel the sequence of incoming ejecta from the Chicxulub impact in great detail, which we would never have been able to do with all the other deposits around the Gulf of Mexico.”
“So far, we have gone 40 years before something like this turned up that may very well be unique,” Smit said. “So, we have to be very careful with that place, how we dig it up and learn from it. This is a great gift at the end of my career. Walter sees it as the same.”
Reference:
DePalma, Robert A.; Smit, Jan; Burnham, David; Kuiper, Klaudia; Manning, Phillip; Oleinik, Anton; Larson, Peter; Maurrasse, Florentin; Vellekoop, Johan; Richards, Mark A.; Gurche, Loren; Alvarez, Walter. Prelude to Extinction: a seismically induced onshore surge deposit at the KPg boundary, North Dakota. PNAS, 2019
Young’s team collecting samples from a site once submerged under ancient oceans west of Nashville, Tennessee. Former FSU master’s student Andrew Kleinberg is pictured in the plaid shirt. Credit: Stephen Bilenky
Roughly 430 million years ago, during the Earth’s Silurian Period, global oceans were experiencing changes that would seem eerily familiar today. Melting polar ice sheets meant sea levels were steadily rising, and ocean oxygen was falling fast around the world.
At around the same time, a global die-off known among scientists as the Ireviken extinction event devastated scores of ancient species. Eighty percent of conodonts, which resembled small eels, were wiped out, along with half of all trilobites, which scuttled along the seafloor like their distant, modern-day relative the horseshoe crab.
Now, for the first time, a Florida State University team of researchers has uncovered conclusive evidence linking the period’s sea level rise and ocean oxygen depletion to the widespread decimation of marine species. Their work highlights a dramatic story about the urgent threat posed by reduced oxygen conditions to the rich tapestry of ocean life.
The findings from their study were published in the journal Earth and Planetary Science Letters.
Although other researchers had produced reams of data on the Ireviken event, none had been able to definitively establish a link between the mass extinction and the chemical and climatic changes in the oceans.
“The connection between these changes in the carbon cycle and the marine extinction event had always been a mystery,” said lead author Seth Young, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science.
To address this old and obstinate question, Young and his co-authors deployed new and innovative strategies. They developed an advanced multiproxy experimental approach using stable carbon isotopes, stable sulfur isotopes and iodine geochemical signatures to produce detailed, first-of-their-kind measurements for local and global marine oxygen fluctuation during the Ireviken event.
“Those are three separate, independent geochemical proxies, but when you combine them together you have a very powerful data set to unravel phenomena from local to global scales,” Young said. “That’s the utility and uniqueness of combining these proxies.”
Young and his team applied their multiproxy approach to samples from two geologically important field sites in Nevada and Tennessee, both of which were submerged under ancient oceans during the time of the extinction event. After analyzing their samples at the FSU-based National High Magnetic Field Laboratory, the connections between changes in ocean oxygen levels and mass extinction of marine organisms became clear.
The experiments revealed significant global oxygen depletion contemporaneous with the Ireviken event. Compounded with the rising sea level, which brought deoxygenated waters into shallower and more habitable areas, the reduced oxygen conditions were more than enough to play a central role in the mass extinction. This was the first direct evidence of a credible link between expansive oxygen loss and the Ireviken extinction event.
But, Young found, that oxygen loss wasn’t universal. Only about 8 percent or less of the global oceans experienced significantly reducing conditions with very little to no oxygen and high levels of toxic sulfide, suggesting that these conditions didn’t need to advance to whole-ocean scale to have an outsized, destructive effect.
“Our study finds that you don’t necessarily need the entire ocean to be reducing to generate these kind of geochemical signatures and to provide a kill mechanism for this significant extinction event,” Young said.
Today, like 430 million years ago, sea level is on the rise and ocean oxygen is hemorrhaging at an alarming rate. As parallels continue to emerge between today’s changes and past calamities, peering into the Earth’s distant past could be a critical tool in preparing for the future.
“There are common threads with other climatic and extinction events throughout Earth’s history, and future work will continue to help us understand the similarities and differences of these events to constrain future climate predictions,” said co-author Jeremy Owens, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science who has worked on other extinction events in the Jurassic and Cretaceous periods.
“I think it’s important to see how these events played out all the way from extinction interval through recovery period, how severe they were and their connections to the ancient environment along the way,” added Young. “That could help us figure out what’s in store for our future and how we can potentially mitigate some of the negative outcomes.”
This study was funded by the National Science Foundation and the Geological Society of America.
Reference:
Seth A. Young, Andrew Kleinberg, Jeremy D. Owens. Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction. Earth and Planetary Science Letters, 2019; 513: 187 DOI: 10.1016/j.epsl.2019.02.023
Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Credit: Wikipedia.
A new high-resolution map of a poorly known section of the northern San Andreas Fault reveals signs of the 1906 San Francisco earthquake, and may hold some clues as to how the fault could rupture in the future, according to a new study published in the Bulletin of the Seismological Society of America.
Samuel Johnson of the U.S. Geological Survey and Jeffrey Beeson of Fugro USA Marine Inc. compiled the map for the 35-kilometer-long section of the fault between Tomales Point and Fort Ross, California. They discovered two large zones, each covering about two square miles, of slope failure on the seafloor offshore of the Russian River, marked by lobes that appear to have formed when the intense shaking of the 1906 earthquake caused sand liquefaction.
The mapping also demonstrates that there are two active strands of the fault within the northern part of Bodega Bay, each of which has moved tens of meters within the past 10,000 years.
The findings “are not going to affect what we know about the recurrence interval or slip rate” on the Northern San Andreas Fault, “but it will affect what we know about how the northern San Andreas fault ruptures,” Johnson said.
“Normally if you were studying a fault zone on land and found a prominent fault strand, you would probably assume that was the strand that has most recently ruptured,” he explained. “Because we found two here, it’s a cautionary tale for earthquake geologists to comprehensively map fault zones. You may only capture part of the earthquake history or slip rate along a fault if you only know about one strand in a multi-strand zone”
The northern offshore areas of the fault have been intensively studied only within the past eight years, said Johnson. While much of the rest of the San Andreas fault has become a natural laboratory for studying earthquakes, “it’s a major geoscience oversight that these northern areas have not been studied before,” said Johnson. “We have been waiting for technology to produce the tools to look at these areas in high resolution.”
The researchers used data drawn from several techniques, including high-resolution seismic reflection profiles and multibeam bathymetry, both of which use multiple directed sound waves to image layers on or below the seafloor. Collection of some of the bathymetry data was funded by the California Ocean Protection Council as part of its work to designate and develop monitoring strategies for Marine Protected Areas, and by the National Oceanic and Atmospheric Administration (NOAA) to improve nautical charts.
The liquefaction lobes, which are similar to the ground failure seen offshore of the Klamath River delta during the magnitude 7.2 Eureka earthquake in northern California in 1980, were one of the surprises uncovered during the mapping, said Johnson.
The researchers were lucky to have caught a glimpse of the lobes before they disappeared, as some of the features are already being smoothed over by sediments deposited after 1906, Johnson said. “If you came back in another 50 to 100 years, you might not see these features because they would be all covered up. You can see their lifespan in the data and images we have now.”
Other insights from the map include a look at how movement along this portion of the fault has affected the onshore landscape, including the uplift of marine terraces and rapid formation of beaches and coastal sand dunes. For instance, the researchers noted that uplift west of the Northern San Andreas Fault has blocked the southward drift of sediment from the Russian River and Salmon Creek, leading to the swiftly growing South Salmon Creek Beach and its background of high coastal sand dunes.
Reference:
Samuel Y. Johnson, Jeffrey W. Beeson. Shallow Structure and Geomorphology along the Offshore Northern San Andreas Fault, Tomales Point to Fort Ross, California. Bulletin of the Seismological Society of America, 2019 DOI:10.1785/0120180158
Deep below the Earth in the Tonga-Fiji region of the South Pacific, one enormous earthquake triggered another. Credit: David Broad.
In the waning months of 2018, two of the mightiest deep earthquakes ever recorded in human history rattled the Tonga-Fiji region of the South Pacific.
In the first-ever study of these deep earthquakes — generally defined as any earthquake occurring 350 kilometers or more below the Earth’s surface — a Florida State University-led research team characterized these significant seismological events, revealing new and surprising information about our planet’s mysterious, ever-changing interior.
The team’s findings, published in the journal Geophysical Research Letters, delineate the complex geological processes responsible for the earthquakes and suggest that the first powerful perturbation may have actually triggered the second.
“We don’t have these kind of large earthquakes too often,” said study author Wenyuan Fan, an earthquake seismologist in FSU’s Department of Earth, Ocean and Atmospheric Science. “These deep earthquakes, especially larger earthquakes, aren’t really promoted by the ambient environment. So why is this happening? It’s a compelling question to ask.”
While deep earthquakes are rarely felt on the Earth’s surface, studying these titanic events can help researchers better understand the systems and structures of the inner Earth.
But the precise mechanisms of deep earthquakes have long been a mystery to earthquake scientists. The extreme temperature and pressure conditions of the deep Earth aren’t suitable for the kinds of mechanical processes typically responsible for earthquakes — namely the movement and sudden slippage of large plates.
Instead, the extraordinary pressure holds things firmly in place, and the soaring temperatures make rocky material behave like chocolate — moving around viscously instead of like ice cubes as is seen in the shallow surface.
“We did not expect to have deep earthquakes,” Fan said. “It should not happen. But we do have observations of deep earthquakes. So why? How? What kind of physical processes operate under such conditions?”
Using advanced waveform analyses, Fan and his team found that the first quake — a behemoth clocking in at magnitude 8.2, making it the second-largest deep earthquake ever recorded — was the product of two distinct physical processes.
The earthquake, they found, began in one of the region’s seismically important slabs, a portion of one tectonic plate subducted beneath another. Slab cores are cooler than their seething hot surroundings, and therefore more amenable to earthquake nucleation.
Once the earthquake began forming in the slab core, it propagated out into its warmer and more ductile surroundings. This outward propagation moved the earthquake from one mechanical process to another.
“This is interesting because before Tonga was thought to predominantly only have one type of mechanism, which is within the cold slab core,” Fan said. “But we’re actually seeing that multiple physical mechanisms are involved.”
The dual mechanism propagation pattern present in the magnitude 8.2 earthquake wasn’t wholly surprising to Fan and his team. The process was reminiscent of a similarly deep, 7.6 magnitude quake that shook the region in 1994. These recognizable patterns were a promising sign.
“To see that something is predictable, like the repeated patterns observed in the magnitude 8.2 earthquake, is very satisfying,” Fan said. “It brings up the hope that we do know something about this system.”
But the second earthquake, which occurred 18 days after the first, was more of a puzzle. The magnitude 7.9 convulsion struck in an area that previously experienced very little seismic activity. The distinct physical mechanisms present in the second quake shared more similarities with South American deep earthquakes than with the massive quakes that rock the South Pacific. And, puzzlingly for researchers, the magnitude 7.9 earthquake produced surprisingly few aftershocks relative to its considerable size.
Somehow, Fan said, a large earthquake was triggered in a previously aseismic region that then immediately returned to normal.
It’s this triggering process that most interests Fan going forward. He said this earthquake “doublet” illustrates the dynamic and interrelated nature of deep-Earth processes and the urgent need to better understand how these complicated processes operate.
“It’s important that we address the question of how large earthquakes trigger other large earthquakes that are not far away,” he said. “This is a good demonstration that there seem to be physical processes involved that are still unknown. We’ve gradually learned to identify the pattern, but not to a degree where we know exactly how it works. I think this is important to any kind of hazard forecast. It’s more than an intellectual interest. It’s important for human society.”
This study was funded by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution.
Reference:
Wenyuan Fan, S. Shawn Wei, Dongdong Tian, Jeffrey J. McGuire, Douglas A. Wiens. Complex and Diverse Rupture Processes of the 2018 Mw 8.2 and Mw 7.9 Tonga‐Fiji Deep Earthquakes. Geophysical Research Letters, 2019 DOI: 10.1029/2018GL080997
Massachusetts State Geologist Stephen Mabee and colleagues recently annoucned that newly digitized surficial geology maps of the entire state are available online now. They provide details of what Mabee calls the ‘kitty litter’ mix of glacial tills, various sands and gravels on the earth’s surface. Credit: USGS/MassGIS
Anyone who digs in the earth needs a geologic map, says State Geologist Stephen Mabee at the University of Massachusetts Amherst, and now he and colleagues have finished a federal-state collaboration that began 81 years ago to create the first complete set of 189 surficial geologic maps of Massachusetts in 7.5-minute quadrangles, the same useful scale as the topographical maps used by hikers.
Civil engineers, geotechnology firms, state, county and town planners, transportation engineers, geologists, developers, “anyone who disturbs the ground for any project needs this resource,” Mabee says, “because running into an unexpected obstacle can cost tens of thousands, even millions of dollars. That’s the benefit of this information now publicly available. It’s been estimated that the benefit-to-cost ratio of such maps is 34/1, so every dollar spent on mapping saves the taxpayer $34.”
The newly digitized maps available online this month provide details of what Mabee calls the “kitty litter” mix of glacial tills, various sands and gravels on the earth’s surface. The uniform, portable maps use a unique standard color for each geologic material, with legends and supporting notes, and are “not just more accurate, but more convenient,” he adds. “You can use GIS to overlay them with any number of layers of other information for all kinds of spatial analyses.”
“These are very detailed for a statewide map,” he says. Another plus is that the maps are in a layered vector format, which means that the superimposed geologic units will be shown in the correct place on the Earth’s surface.
The senior lecturer in geosciences collaborated with research geologists Janet and Byron Stone and Mary DiGiacomo-Cohen at the U.S. Geological Survey (USGS) office in East Hartford, Conn. and others at the Massachusetts Bureau of Geographic Information (MassGIS) to resurrect this project that was begun in 1938. It was abandoned for many years, with roughly half the maps published on paper, when the USGS reorganized in 1978.
Mabee recalls, “I became the state geologist in 2002 and the first thing I did was tell the USGS ‘let’s get started again.’ All it took was someone to say we need to finish the job. There was once a great partnership between USGS and the state and I’m really glad to have helped to revive it. This is a huge accomplishment and one of my main goals when I started.”
At its peak, the project had been pumping out up to 18 quadrangles per decade, Mabee says, and by 1980 the Massachusetts Department of Public Works and USGS partners had mapped the entire state but only 105 maps were published on paper, a little more than half of what would be needed to cover the state. “We saw the last few maps published in the 1980s, then nothing,” he notes.
When Congress passed the National Environmental Policy Act of 1970, the Clean Water Act of 1972 and Superfund legislation in 1980, plus other environmental regulations, many environmental and consulting groups urgently needed surficial geologic maps but couldn’t find them, Mabee says. “For 20 years we had almost nothing, and what we had was only on paper. I had worked in consulting, so I knew the frustration.”
With the project revived in 2002 and supported by the USGS National Cooperative Geologic Mapping Program, MassGIS scanned all the paper maps on hand, while “squads” of Mabee’s UMass Amherst geosciences students hand-traced every map and created digital versions. The USGS professionals used old field notes to fill in gaps, digitized all the unpublished maps, matching all areas where different materials met, and added legends and definitions.
“They had to match the work done by people in the 1940s to what was produced by the next generation in the 1970s for all 189 quads,” he adds. “It was a huge undertaking, and finally, 17 years later, we got it done. People have been screaming for this data that once was all on paper, and now it’s all digital and online.”
A QUT geologist has published a new theory on the thermal evolution of Earth billions of years ago that explains why diamonds have formed as precious gemstones rather than just lumps of common graphite.
In the study, published in the journal Chemical Geology, the researchers looked at the magnesium oxide levels in thousands of volcanic rocks, dating at least 2.5 billion years old, that had been collected from around the world.
Professor Balz Kamber, from QUT’s Earth, Environmental and Biological Sciences School, co-authored the study with Professor Emma Tomlinson, from the Department of Geology at Trinity College Dublin. The research challenges a common theory about the evolution of the Earth and offers an explanation as to why the Earth’s mantle was cool enough to produce diamonds in the Archaean era between 4 billion and 2.5 billion years ago.
Professor Kamber said the analysis of the magnesium oxide levels in rock samples from the Archaean era contradicts the conventional belief that the Earth’s mantle was a lot hotter than it is in the current day.
“We know for a fact that the Earth produced a lot more heat back then — three to two-and-a-half times,” Professor Kamber said.
The prevailing theory among petrologists who study the origin, structure and composition of rocks, is that the Earth’s whole mantle was significantly hotter until 2.5 billion years ago.
But Professor Kamber’s analysis is that the prevailing theory is only half right. He said that while the lower mantle was significantly hotter, the upper mantle which is the area down to 670km was no hotter than it is in the present day.
“It’s the upper mantle that matters because the volcanic rocks that we observe, they come from the upper mantle,” Professor Kamber said.
To explain the theory, Professor Kamber uses the analogy of someone trying to warm their bedroom in winter by turning up the heater but failing to close the windows.
“You can produce as much heat as you like but it doesn’t get any warmer,” he said.
“So what we’re actually interested in is not how much heat we’re producing, but how warm it was in the interior of the earth.
“The assumption has been: more heat, therefore it was hotter. But what we show is: more heat but not hotter.
“The Earth was producing more heat but was also getting rid of it, opening more windows so to speak.”
The theory comes from the evidence stored in the ancient rocks on their level of magnesium oxide. Professor Kamber said the magnesium oxide levels in the vast majority of rock samples from that date similar to modern lavas, which indicated the temperatures were similar.
“Experimentalists can recreate the conditions that lead to the melting of the mantle,” Professor Kamber said. “And these experiments inform us without any doubt that the hotter the mantle at which it melts, the more magnesium in the melt.
“Our assumption had been we would find more magnesium in the older rocks compared to today.
“There are rocks that have more magnesium but they don’t come from the upper mantle.”
The cool upper mantle theory helps to explain the formation of diamonds, most of which were formed during this time period and would have turned into lumps of graphite if the upper mantle was too hot.
Professor Kamber’s paper outlining how evidence that the upper mantle was relatively cool has since been supported by a study coincidently published a few days later in the journal AGU100 by a team of German, American and British geologists who put forward a similar theory.
The understanding that the upper mantle 2.5 billion years ago was a lot cooler than previously thought also answers another long-standing area of dispute that has split geologists concerning the movement of tectonic plates.
If the upper mantle had been much hotter 2.5 million years ago, then the oceanic plates would have been thicker and difficult to move under each other.
The new evidence of a cooler upper mantle, which would have been churning hot rocks from the lower mantle upwards towards the surface to release the heat, explains how the plates riding on top of this would have moved fast and collided with each other.
Professor Kamber said understanding the thermal evolution of the Earth was critical to understanding the many aspects of our planet, such as the evolution of the atmosphere, the emergence of land, and the evolution of life.
“A geologist views the present state as the accumulated history of more than 4 billion years,” Professor Kamber said.
“We can’t understand the present fully if we don’t understand this journey.”
Reference:
Balz S. Kamber, Emma L. Tomlinson. Petrological, mineralogical and geochemical peculiarities of Archaean cratons. Chemical Geology, 2019; 511: 123 DOI: 10.1016/j.chemgeo.2019.02.011
Cross-sections of Earth’s mantle down to 1,400 km depth showing changes in its flow as ancient ocean beds fall into Earth’s deep interior. Credit: Ana M. G. Ferreira et al.
As ancient ocean floors plunge over 1,000 km into the Earth’s deep interior, they cause hot rock in the lower mantle to flow much more dynamically than previously thought, finds a new UCL-led study.
The discovery answers long-standing questions on the nature and mechanisms of mantle flow in the inaccessible part of deep Earth. This is key to understanding how quickly Earth is cooling, and the dynamic evolution of our planet and others in the solar system.
“We often picture the Earth’s mantle as a liquid that flows but it isn’t — it’s a solid that moves very slowly over time. Traditionally, it’s been thought that the flow of rock in Earth’s lower mantle is sluggish until you hit the planet’s core, with most dynamic action happening in the upper mantle which only goes to a depth of 660 km. We’ve shown this isn’t the case after all in large regions deep beneath the South Pacific Rim and South America,” explained lead author, Dr Ana Ferreira (UCL Earth Sciences and Universidade de Lisboa).
“Here, the same mechanism we see causing movement and deformation in the hot, pressurised rock in the upper mantle is also occurring in the lower mantle. If this increased activity is happening uniformly over the globe, Earth could be cooling more rapidly than we previously thought,” added Dr Manuele Faccenda, Universita di Padova.
The study, published today in Nature Geoscience by researchers from UCL, Universidade de Lisboa, Universita di Padova, Kangwon National University and Tel Aviv University, provides evidence of dynamic movement in the Earth’s lower mantle where ancient ocean floors are plunging towards the planet’s core, crossing from the upper mantle (up to ~660 km below the crust) to the lower mantle (~660 — 1,200 km deep).
The team found that the deformation and increased flow in the lower mantle is likely due to the movement of defects in the crystal lattice of rocks in the deep Earth, a deformation mechanism called “dislocation creep,” whose presence in the deep mantle has been the subject of debate.
The researchers used big data sets collected from seismic waves formed during earthquakes to probe what’s happening deep in Earth’s interior. The technique is well established and comparable to how radiation is used in CAT scans to see what’s happening in the body.
“In a CAT scan, narrow beams of X-rays pass through the body to detectors opposite the source, building an image. Seismic waves pass through the Earth in much the same way and are detected by seismic stations on the opposite side of the planet to the earthquake epicentre, allowing us to build a picture of the structure of Earth’s interior,” explained Dr Sung-Joon Chang, Kangwon National University.
By combining 43 million seismic data measurements with dynamic computer simulations using the UK’s supercomputing facilities HECToR, Archer and the Italian Galileo Computing Cluster, CINECA the researchers generated images to map how the Earth’s mantle flows at depths of ~1,200 km beneath our feet.
They revealed increased mantle flow beneath the Western Pacific and South America where ancient ocean floors are plunging towards Earth’s core over millions of years.
This approach of combining seismic data with geodynamic computer modelling can now be used to build detailed maps of how the whole mantle flows globally to see if dislocation creep is uniform at extreme depths.
The researchers also want to model how material moves up from the Earth’s core to the surface, which together with this latest study, will help scientists better understand how our planet evolved into its present state.
“How mantle flows on Earth might control why there is life on our planet but not on other planets, such as Venus, which has a similar size and location in the solar system to Earth, but likely has a very different style of mantle flow. We can understand a lot about other planets from revealing the secrets of our own,” concluded Dr Ferreira.
The study was funded by the Leverhulme Trust, NERC, the Korea Meteorlogical Administration Research and Development Program, the Progetto di Ateneo FACCPTRAT12 granted by the Università di Padova and by the ERC StG #758199 NEWTON.
Reference:
Ana M. G. Ferreira, Manuele Faccenda, William Sturgeon, Sung-Joon Chang, Lewis Schardong. Ubiquitous lower-mantle anisotropy beneath subduction zones. Nature Geoscience, 2019; DOI: 10.1038/s41561-019-0325-7
