Artist’s conception of an oviraptor using its tail feathers in a mating display. Credit: Sydney Mohr
Paleontologists at the University of Alberta have discovered evidence of a prehistoric romance and the secret to sexing some dinosaurs.
“Determining a dinosaur’s gender is really hard,” says graduate student Scott Persons, lead author of the research. “Because soft anatomy seldom fossilizes, a dinosaur fossil usually provides no direct evidence of whether it was a male or a female.”
Instead, the new research focuses on indirect evidence. Modern birds, the living descendants of dinosaurs, frequently show sexually dimorphic display structures. Such structures—like the fans of peacocks, the tall crests of roosters or the long tail feathers of some birds of paradise—are used to attract and court mates, and are almost always much larger in males (who do the courting) than in females (who do the choosing).
Back in 2011, Persons and his colleagues published research on the tails of a group of birdlike dinosaurs called oviraptors. Oviraptors were strictly land-bound animals, but according to the study, they possessed fans of long feathers on the ends of their tails. If these dinosaurs weren’t able to fly, what good were their tail feathers?
“Our theory,” explains Persons, “was that these large feather fans were used for the same purpose as the feather fans of many modern ground birds, like turkeys, peacocks and prairie chickens: they were used to enhance courtship displays. My analysis of the tail skeletons supported this theory, because the skeletons showed adaptations for both high tail flexibility and enlarged tail musculature—both traits that would have helped an oviraptor to flaunt its tail fan in a mating dance.”
The U of A researchers took the idea a step further. “The greatest test of any scientific theory is its predictive power,” says Persons. “If we were right, and oviraptors really were using their tail fans to court mates, then, just as in modern birds, the display structures ought to be sexually dimorphic. We published the prediction that careful analysis of more oviraptor tails would reveal male and female differences within the same species.”
That prediction has come home to roost. In the new study, published this week in the journal Scientific Reports, Persons and his team have confirmed sexual dimorphism, after meticulous observation of two oviraptor specimens. The two raptors were discovered in the Gobi Desert of Mongolia. Both died and were buried next to each other when a large sand dune collapsed on top of them.
When they were first unearthed, the two oviraptors were given the nicknames “Romeo and Juliet,” because they seemed reminiscent of Shakespeare’s famously doomed lovers. It turns out that the nickname may have been entirely appropriate.
“We discovered that, although both oviraptors were roughly the same size, the same age and otherwise identical in all anatomical regards, ‘Romeo’ had larger and specially shaped tail bones,” says Persons. “This indicates that it had a greater capacity for courtship displays and was likely a male.” By comparison, the second specimen, “Juliet,” had shorter and simpler tail bones, suggesting a lesser capacity for peacocking, and has been interpreted as a female.
According to Persons, the two may very well have been a mated pair, making for an altogether romantic story, as the dinosaur couple was preserved side by side for more than 75 million years.
Reference:
“A possible instance of sexual dimorphism in the tails of two oviraptorosaur dinosaurs.” Scientific Reports 5, Article number: 9472 DOI: 10.1038/srep09472
Rhawn Denniston (right), professor of geology at Cornell College, with Dan Cleary ’13, a member of his student research team, examining stalagmites in an Australian cave. Credit: Image courtesy of Cornell College
Stalagmites, which crystallize from water dropping onto the floors of caves, millimeter by millimeter, over thousands of years, leave behind a record of climate change encased in stone. Newly published research by Rhawn Denniston, professor of geology at Cornell College, and his research team, applied a novel technique to stalagmites from the Australian tropics to create a 2,200-year-long record of flood events that might also help predict future climate change.
A paper by Denniston and 10 others, including a 2014 Cornell College graduate, is published this week in the journal Proceedings of the National Academy of Sciences. The article, “Extreme rainfall activity in the Australian tropics reflects changes in the El Niño/Southern Oscillation over the last two millennia,” presents a precisely dated stalagmite record of cave flooding events that are tied to tropical cyclones, which include storms such as hurricanes and typhoons.
Denniston is one of few researchers worldwide using stalagmites to reconstruct past tropical cyclone activity, a field of research called paleotempestology. His work in Australia began in 2009 and was originally intended to focus on the chemical composition of the stalagmites as a means of reconstructing past changes in the intensity of Australian summer monsoon rains. But Denniston and his research team found more than just variations in the chemical composition of the stalagmites they examined; they discovered that the interiors of the stalagmites also contained prominent layers of mud.
“Seeing mud accumulations like these was really unusual,” Denniston said. “There was no doubt that the mud layers came from the cave having flooded. The water stirred up the sediment and when the water receded, the mud coated everything in the cave — the floor, the walls, and the stalagmites. Then the stalagmites started forming again and the mud got trapped inside.”
The stalagmites were precisely dated by Denniston, Cornell College geology majors, and Denniston’s colleagues at the University of New Mexico. Once the ages of the stalagmites were known, the mud layers were measured. Angelique Gonzales ’14, who worked with Denniston on the research and is third author on the paper, examined nearly 11 meters of stalagmites, measuring them in half millimeter increments and recording the location and thickness of mud layers. This work gave the team more than 2,000 years of data about the frequency of cave flooding.
But the origins of the floods were still unclear. Given the area’s climatology, Denniston found that these rains could have come from the Australian monsoon or from tropical cyclones.
“We were sort of stuck,” Denniston said, “but then I started working with Gabriele.” Gabriele Villarini, an assistant professor of engineering at the University of Iowa and the second author of the paper, studies extreme meteorological events, what drives the frequency and magnitude of those events, and their impact on policy and economics. With Denniston and Gonzales, Villarini examined historical rainfall records from a weather station near the cave.
“The largest rainfall events, almost regardless of duration, are tied to tropical cyclones,” Villarini said.
Next, they compared flood events recorded in a stalagmite that grew over the past several decades to historical records of tropical cyclones. This analysis revealed that timing of flood events in the cave was consistent with the passing of tropical cyclones through the area. Thus, the researchers interpreted the flood layers in their stalagmites largely as recording tropical cyclone activity.
The resulting data tell scientists about more than just the frequencies of tropical cyclones in one part of Australia over the past 2,200 years. A major driver of year-to-year changes in tropical cyclones around the world is the El Niño/Southern Oscillation, which influences weather patterns across the globe. During El Niño events, for example, Australia and the Atlantic generally experience fewer tropical cyclones, while during La Niña events, the climatological opposite of El Niño, the regions see more tropical cyclones.
“Our work, and that of several other researchers, reveals that the frequency of storms has changed over the past hundreds and thousands of years,” Denniston said. “But why? Could it have been due to El Niño? Direct observations only go back about a hundred years, and there hasn’t been much variation in the nature of El Niño/Southern Oscillation over that time. Further back there was more, and so our goal was to test the link between storms and El Niño in prehistory.”
Denniston noted that the variations over time in the numbers of flood events recorded by his stalagmites matched reconstructed numbers of hurricanes in the Atlantic, Gulf of Mexico, and Caribbean.
“Tropical cyclone activity in these regions responds similarly to El Niño, and previous studies had also suggested that some periods, such as those when we had lots of flood layers in our stalagmites, were likely characterized by more frequent La Niñas. Similarly, times with fewer storms were characterized by more frequent El Niños.” The results of this study mark an important step towards understanding how future climate change may be expressed.
“It is difficult to use climate models to study hurricane activity, and so studies such as ours, which produced a record of storms under different climate conditions, are important for our understanding of future storm activity,” Denniston said.
Gonzales, who is planning to pursue a Ph.D. in geology, said that her experience with Denniston and his research, including two senior seminars and an honors thesis, was valuable because she got both field and lab experience as she helped determine not just what had happened in the past, but what that meant.
“There were a lot of different aspects to put this together — dating, measuring, literature review, and modeling,” she said. “It was really exciting.”
Denniston is now gearing up to establish a detailed cave monitoring program in this and other regional caves. “We want to extend this study,” he said, “to examine what conditions trigger cave flooding.”
In addition to Denniston, Villarini, and Gonzales, the other authors on the paper were Karl-Heinz Wyrwoll from the University of Western Australia, Victor J. Polyak from the University of New Mexico, Caroline C. Ummenhofer from the Woods Hole Oceanographic Institution, Matthew S. Lachniet from the University of Nevada Las Vegas, Alan D. Wanamaker Jr. from Iowa State University, William F. Humphreys from the Western Australian Museum, David Woods from the Australian Department of Parks and Wildlife, and John Cugley from the Australian Speleological Federation.
Reference:
Rhawn F. Denniston, Gabriele Villarini, Angelique N. Gonzales, Karl-Heinz Wyrwoll, Victor J. Polyak, Caroline C. Ummenhofer, Matthew S. Lachniet, Alan D. Wanamaker, Jr., William F. Humphreys, David Woods, and John Cugley. Extreme rainfall activity in the Australian tropics reflects changes in the El Niño/Southern Oscillation over the last two millennia. PNAS, 2015 DOI: 10.1073/pnas.1422270112
A plume of the active Hawaiian shield volcano Kilauea exposes residents to a highly acidic atmospheric pollutant mix. Photo: Jesse Kroll
Since 1983, the 180,000 residents of the Big Island of Hawaii have lived in the wake of the pollution caused by the active shield volcano Kilauea. The destructive nature of the volcanic smog (“vog”) has imprinted a significant ecological footprint on the surrounding infrastructure, vegetation, and human health.
With the volcano’s eruption now in its 33rd year, research from the Department of Civil and Environmental Engineering (CEE) provides an improved understanding of the atmospheric pollutant mix that island residents are exposed to on a daily basis.
In particular, a new study uncovers two fundamental features of Kilauea’s volcanic plume: a strong dependence of sulfur partitioning on meteorology and time of day, and the presence of particles that are exceedingly high in acidity. The findings were published March 18 in the journal Environmental Science and Technology, and were carried out by 28 CEE undergraduate students; lead authors Jesse Kroll, associate professor in CEE, and CEE research scientist Eben Cross; and nine other MIT researchers and collaborators.
On-site research through TREX
The study was conducted in coordination with CEE’s Traveling Research Environmental eXperience (TREX) in 2012 and 2013, a program that is offered to Course 1 undergraduates during the Independent Activities Period and which involves an annual trip to carry out environmental fieldwork.
“As a sophomore, TREX was an excellent chance for me to develop my research skills so I could apply them to other projects in the future,” says Theresa Oehmke, now a fourth-year Course 1 undergraduate. “It is a program that not many other universities offer.” The support system she gained in CEE and the opportunity to participate in published research were two invaluable benefits earned from the program, she adds.
According to Sidhant Pai ’14, a Course 1 undergraduate participant in the 2013 trip, TREX was one of the “most enjoyable and memorable MIT experiences” and “really got [him] excited about environmental science.” After TREX, Pai continued to study Kilauea with Kroll and Cross as part of the Course 1 Undergraduate Research Opportunities Program (UROP).
“Given that millions of people live close to volcanoes globally, it is important to understand plume chemistry before we can characterize the impact that the emissions have on human health and the environment,” Pai says. “The work done by TREX is an important step in that direction.” The team’s unique approach to studying the sulfur emissions allowed them to better understand the intensity of the vog and the acidity of the particles.
Connecting with locals
During their time on the island, the CEE team spoke with a wide range of residents regarding the volcano’s influence on the locals’ daily lives. One Pahala rancher, Lani Petrie, recently had to replace her fences for the second time, attributing her property’s rotted infrastructure to the volcanic emissions. Originally constructed from steel, Petrie’s fences corroded when Kilauea’s vent opened in 2008 and spewed higher amounts of sulfuric acid into the air. She then attempted to replace the material with stainless steel, only to result in similar deterioration. Petrie is now testing fences constructed from fiberglass—a resilient, but more expensive material.
“The whole island is impacted from the volcano, and we’re just exposed to it constantly—Pahala especially,” says Lisa Wallace, a chemist from the Hawaii State Department of Health. “Residents, mostly downwind, complain of respiratory complications, eye, and throat irritation. A couple of my coworkers even experience chronic bronchitis that just will not go away, and this isn’t unheard of.” Wallace herself experienced the firsthand effects of the vog, when the roof on her home completely corroded after only five years.
To have similar, in-depth studies such as this conducted on the chemical nature of Kilauea, she said, would “certainly help to improve the way construction processes, construction materials and even plumbing are handled” on the island.
“The majority of the data was collected by the students in 2013,” says Kroll. “The 2012 group, however, set the precedent for how to collect the data. They gave us all of the information we needed on how to make the 2013 TREX mission work.”
In 2013, the students carried out real-time measurements of the key chemical components from Kilauea’s volcanic plume, and produced a detailed characterization of sulfur partitioning with unprecedented time resolution.
“Sulfur dioxide (SO2) oxidizes in the air to form sulfuric acid particles, and these can then neutralize to create ammonium sulfate,” says Kroll. “Our intention with this project was to understand the extent and the rate at which these chemical processes happen and what the people are exposed to on the island: SO2 versus sulfuric acid versus more neutralized particles.”
Breaking through the vog
Vog, a type of pollution formed from acidic gases and particles, is released by active volcanoes. These gases are primarily composed of sulfur dioxide gas and its oxidation products, such as sulfate aerosol.
Over the course of the study, the students analyzed the emissions from the vent of Kilauea’s crater at two different locations—seven days at Kilauea Military Camp located on the north rim of the crater and 12 days directly downwind of the vent in the town of Pahala. The team used a sulfur dioxide monitor and an aerosol chemical speciation monitor to measure the relative amounts of gas-phase SO2 and particulate sulfate every five minutes.
According to Cross, the particles within the plume were measured to have a pH value of as low as -0.8.
“It’s rare that you would see such a highly acidic aerosol plume persisting over space and time,” he says. “In most environments, there’s going to be a sufficient amount of ammonia present in the gas phase, both from natural and anthropogenic sources. This would normally turn that sulfate from sulfuric acid to more neutralized forms.” However, the team found that the amount of sulfuric acid was much too high to be neutralized by the available ammonia, giving it an acidity level lower than that of battery acid.
SO2 is highly toxic to both humans and plants; since it is emitted directly from the volcano, it is known as a “primary pollutant.” In the atmosphere, SO2 will oxidize to form sulfuric acid (H2SO4), a “secondary pollutant,” that can contribute to harmful particulate matter and acid deposition. As secondary pollutants are formed by chemistry and not simple emissions, they can be exceedingly problematic to isolate. In this case, the TREX team knew that the vast majority of the measured SO2 and H2SO4 came from the volcano, allowing them to monitor out the conversion of one pollutant to the other.
Further studies
Today, the team’s goal is to employ measurements from this study in upcoming TREX expeditions to the Big Island.
“The next important step in this exploration is to make robust measurements with lower-cost equipment,” says Cross. This objective drove the most recent TREX expedition, during which the students increased the instruments used at the Pahala site and built and deployed homemade SO2 sensors in various locations.
“In 2013, we got a clear snapshot of one place,” Kroll says. “We need to perform this experiment all around the island and attempt to truly understand where the SO2 is going and how fast its chemistry is occurring.” Future findings will lend themselves to the development and implementation of solutions for the island’s infrastructural challenges.
Course 1’s TREX subject for undergraduates will continue its exploration of the influence of Kilauea’s plume on the environment, enabling communities to understand the vog’s ongoing impact on local air quality and ecological health.
“Since TREX, I have gotten more exposure to the field and intend to eventually apply to grad school to pursue it further,” says Pai. “To be credited in the publication alongside my instructors is an honor, and I’m really glad I could be a part of the process.”
Video
Reference:
“Atmospheric Evolution of Sulfur Emissions from Kı̅lauea: Real-Time Measurements of Oxidation, Dilution, and Neutralization within a Volcanic Plume” Environ. Sci. Technol., Article ASAP DOI: 10.1021/es506119x
Hong Kong’s first dinosaur-era fish – a specimen of the Chinese osteoglossoid osteoglossomorph fish Paralycoptera. Credit: Copyright IVPP
A ~147 million-year-old Jurassic-aged osteoglossoid osteoglossomorph fish Paralycoptera from outcrops at Lai Chi Chong has been described. This fossil represents the first dinosaur-era fish — as well as vertebrate — from Hong Kong to be identified.
The fossil was rediscovered in the collections of the Stephen Hui Geological Museum by Mr. Edison Tse Tze-kei, graduate of the Class of 2014, Department of Earth Sciences, Faculty of Science, the University of Hong Kong (HKU). Mr. Tse studied the specimen during his HKU Faculty of Science Summer Research Fellowship and Earth Sciences Major final-year project, under the supervision of Dr. Michael Pittman who leads the University’s Vertebrate Palaeontology Laboratory and is an expert on dinosaur evolution, as well as Professor Chang Mee-mann, an Academician of the Chinese Academy of Sciences from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing. A paper on this study has recently been published in the open-access journal PeerJ, demonstrating international recognition of the outstanding ability of HKU undergraduate students in conducting scientific research.
The fossil consists of the posterior portion of a small, about 4cm long osteoglossoid osteoglossomorph fish from the genus Paralycoptera, and was collected at Lai Chi Chong, Tolo Channel, from rocks that have been previously radiometrically dated to 146.6 ± 0.2 million years old (Tithonian stage of the Late Jurassic). Paralycoptera is a typical member of the Mesoclupea fish fauna of Southeast China. Its discovery in Hong Kong extends the geographic range of the genus — and potentially of the Mesoclupea fish fauna — by about 700 km further south. The Jurassic-age of the Hong Kong specimen extends the temporal range of the genus about 40 million years back in time because all mainland specimens are currently known from the Early Cretaceous.
Hong Kong’s last major vertebrate fossil identification was the discovery of a ~370 million-year-old early fish (Devonian-aged placoderm fish) by Mr. Lee Cho-min 35 years ago on the north shore of Tolo Channel, Hong Kong, almost directly opposite to Lai Chi Chong.
When asked about the impact of the new specimen towards our broader knowledge of osteoglossomorph fish, Research Assistant Professor Dr. Pittman replied, ‘The fossil’s Late Jurassic age also adds support to the hypothesis that osteoglossomorph fish originated on the portion of the ancient supercontinent of Pangaea (which broke apart about 200 million years ago) that is now East Asia.’
This study improves our understanding of the habitat of Paralycoptera, based on the geological information preserved at Lai Chi Chong, a beautiful tidal rock outcrop within the Hong Kong Global Geopark of China. Elaborating on this, Mr. Tse said, ‘Our Paralycoptera specimen appears to have lived in a tropical-subtropical freshwater lake that was periodically subjected to catastrophic volcanic eruptions and earthquakes.’
Dr Pittman said that undergraduate students worldwide typically do not publish peer-reviewed research, so Edison’s valuable contribution towards Hong Kong palaeontology is a credit to him and the research ability of HKU students. The detailed identification and description of the specimen was also aided by Professor Mee-mann Chang, a global expert on Chinese fossil fish.
Reference:
Tze-Kei Tse, Michael Pittman, Mee-mann Chang. A specimen ofParalycopteraChang & Chou 1977 (Teleostei: Osteoglossoidei) from Hong Kong (China) with a potential Late Jurassic age that extends the temporal and geographical range of the genus. PeerJ, 2015; 3: e865 DOI: 10.7717/peerj.865
This image shows the Little Foot skull (STW 573). Credit: Photo courtesy of the University of the Witwatersrand
A skeleton named Little Foot is among the oldest hominid skeletons ever dated at 3.67 million years old, according to an advanced dating method.
Little Foot is a rare, nearly complete skeleton of Australopithecus first discovered 21 years ago in a cave at Sterkfontein, in central South Africa. The new date places Little Foot as an older relative of Lucy, a famous Australopithecus skeleton dated at 3.2 million years old that was found in Ethiopia. It is thought that Australopithecus is an evolutionary ancestor to humans that lived between 2 million and 4 million years ago.
Stone tools found at a different level of the Sterkfontein cave also were dated at 2.18 million years old, making them among the oldest known stone tools in South Africa.
A team of scientists from Purdue University; the University of the Witwatersrand, in South Africa; the University of New Brunswick, in Canada; and the University of Toulouse, in France, performed the research, which will be featured in the journal Nature.
Ronald Clarke, a professor in the Evolutionary Studies Institute at the University of the Witwatersrand who discovered the Little Foot skeleton, said the fossil represents Australopithecus prometheus, a species very different from its contemporary, Australopithecus afarensis, and with more similarities to the Paranthropus lineage.
“It demonstrates that the later hominids, for example, Australopithecus africanus and Paranthropus did not all have to have derived from Australopithecus afarensis,” he said. “We have only a small number of sites and we tend to base our evolutionary scenarios on the few fossils we have from those sites. This new date is a reminder that there could well have been many species of Australopithecus extending over a much wider area of Africa.”
There had not been a consensus on the age of the Little Foot skeleton, named for four small foot bones found in a box of animal fossils that led to the skeleton’s discovery. Previous dates ranged from 2 million to 4 million years old, with an estimate of 3 million years old preferred by paleontologists familiar with the site, said Darryl Granger, a professor of earth, atmospheric and planetary sciences at Purdue, who in collaboration with Ryan Gibbon, a former postdoctoral researcher, led the team and performed the dating.
The dating relied on a radioisotopic dating technique pioneered by Granger coupled with a powerful detector originally intended to analyze solar wind samples from NASA’s Genesis mission. The result was a a relatively small margin of error of 160,000 years for Little Foot and 210,000 years for the stone tools.
The technique, called isochron burial dating, uses radioisotopes within several rock samples surrounding a fossil to date when the rocks and the fossil were first buried underground.
The burial dating relies on measuring radioactive isotopes aluminum-26 and beryllium-10 in quartz within the rock. These isotopes are only created when the rock is exposed to cosmic rays. When a rock is on the surface, it builds up these isotopes. When it is buried or deposited in a cave, the isotopes decay at known rates. The ratio of the remaining aluminum-26 and beryllium-10 can be used to determine how long the rock has been underground, Granger said.
A graph of the isotope ratios, called an isochron, is created for the rock samples. If a strong isochron line forms, it increases the confidence that the samples on the line meet the criteria to be good candidates for accurate dating. Samples that have been compromised, due to reburial or natural movement of sediment within a site, fall above or below the line can be tossed out of the analysis, Granger said.
“If we had only one sample and that rock happened to have been buried, then re-exposed and buried again, the date would be off because the amount of radioisotopes would have increased during its second exposure,” he said. “With this method we can tell if that has happened or if the sample has remained undisturbed since burial with the fossil. It is expensive and a lot of work to take and run multiple samples, but I think this is the future of burial dating because of the confidence one can have in the results.”
Out of 11 samples collected from the site over the past decade, nine fell into a single isochron line, which is a very robust result, he said.
This was Granger’s second attempt at dating the fossil through the burial dating technique and a chance to prove its abilities. In 2003 he estimated the fossil to be around 4 million years old, give or take a few hundred thousand years. The dates were questioned because this earlier work could not show whether the burial dates were compromised by earlier burial elsewhere in the cave, he said.
“The original date we published was considered to be too old, and it wasn’t well received,” Granger said. “However, dating the Little Foot fossil as 3.67 million years old actually falls within the margin of error we had for our original work. It turns out it was a good idea after all.”
Granger’s original attempt was the first time aluminum-26 and beryllium-10 radioisotopic dating had been used to determine the age of a fossil. He developed the method in 1997 and first used it to study changes in mountains, rivers and other geological formations. Because of their very slow rate of decay, these particular radioisotopes allow dating to reach back millions of years, much further in history than the more commonly known carbon-14 dating that can only stretch back about 50,000 years, he said.
Only a small amount of the radioisotopes remain in the quartz after millions of years, and it can only be measured by the ultrasensitive analysis of accelerator mass spectrometry. Purdue’s Rare Isotope Measurement Laboratory, or PRIME Lab, is one of only two laboratories in the nation with equipment capable of performing this kind of dating, said Marc Caffee, a Purdue professor of physics and director of the PRIME Lab who was involved in the research.
Gibbon joined Granger in his work on the Sterkfontein samples in 2010 and was a key player in the research. Granger and Gibbon decided to use the new isochron technique to test whether the quartz was reworked and if the dates could be trusted.
To measure the radioisotopes the quartz is separated from the rocks and then pulverized and dissolved into a solution that can be analyzed by the accelerator and detector. A common difficulty in measuring the presence of trace amounts of specific radioisotopes is the presence of other radioisotopes. In past measurement attempts of the Sterkfontein samples using a different detector, aluminum-26 was especially difficult to measure because of magnesium-26.
“We had given up and nearly walked away from the project thinking we had failed,” he said. “Then the new detector was completed, and we thought we would give it one last try.”
This time the team used the PRIME Lab’s powerful accelerator mass spectrometer and a new detector, called a gas-filled magnet detector, to measure the radioisotopes.
“We succeeded in our measurement, but we were surprised the dates were so old,” Granger said. “We double-and triple-checked our results, running the measurement again and again.”
The gas-filled magnet creates a different charge on the two radioisotopes and throws the magnesium-26 on a different path with a curvature that misses the detector. This lowers the magnesium ratio and increases the aluminum-26 count in the sample that makes it to the detector, which results in a much smaller margin of error in the measurement, Caffee said.
The gas-filled magnet detector was originally to be used to analyze samples of solar wind collected by the Genesis spacecraft. Unfortunately, the space capsule carrying the samples crashed in 2004 on its return to Earth. The crash delayed analysis of the Genesis samples, but Caffee continued to build the detector and it was completed the summer of 2014. Caffee has since used it to perform analysis for other projects, including those from the Sterkfontein site.
“Only a few detectors of this kind exist in the world,” Caffee said. “One of the reasons I came to Purdue was to be a part of the revolutionary science that can be done when such resources are applied to challenging problems. These results highlight what can be accomplished through a collaboration that spans multiple disciplines. It couldn’t have happened without the unique skills and resources each person brought to the table.”
In addition to Granger, Clarke, Gibbon and Caffee, co-authors of the paper include Kathleen Kuman, a professor in earlier and middle stone age archaeology in the School of Geography, Archaeology and Environmentla Studies at the University of the Witwatersrand in Johannesburg, South Africa; and Laurent Bruxelles, a researcher in geomorphology and karstology at the French National Institute for Preventive Archaeological Research in Nimes, France.
The tools from the site had earlier been determined to be Oldowan, a simple flaked stone tool technology considered the earliest stone tool industry in prehistory.
The new Sterkfontein date for the Oldowan artifacts shows that this industry is consistently present in South Africa by 2 million years ago, a much earlier age for tool-bearing hominids than previously anticipated in this part of Africa, Kuman said.
“It is now clear that the small number of Oldowan sites in southern Africa is due only to limited research and not to the absence of these hominids,” she said.
Granger looks forward to applying the technique to more fossils at Sterkfontein and elsewhere.
Video
Reference:
Darryl E. Granger, Ryan J. Gibbon, Kathleen Kuman, Ronald J. Clarke, Laurent Bruxelles, Marc W. Caffee. New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan. Nature, 2015; DOI: 10.1038/nature14268
Note: The above story is based on materials provided by Purdue University. The original article was written by Elizabeth K. Gardner.
Mofettes close to the Czech river Plesná. These small openings in the ground are leaking carbon dioxide, which originates in the magma chambers of the earth’s mantel or the earth’s crust. Credit: Felix Beulig/FSU
Researchers of the University Jena analyze the microbial community in volcanically active soils. In a mofette close to the Czech river Plesná in north-western Bohemia, the team working with Prof. Dr. Kirsten Küsel found numerous organisms that were thriving in this environment which seems to be so hostile to life.
The “Villa trans lacum” at the eastern shore of the Laacher See (lake) in the volcanic part of the Eifel — a rural landscape in Germany — was a highly dangerous place. In the 19th century the Jesuit order bought the abbey Maria Laach and built a villa at the shore of the lake. This is where the friars congregated to pray far away from everyday life. But numerous Jesuits paid with their lives for the religious beliefs in the villa. Between 1864 and 1888 17 of them died in the building — literally in their sleep.
“The monks possibly died of carbon dioxide emssions, coming up from the ground at the eastern shore of the lake in large quantities, which could, over time accumulate in the building,” as Prof. Dr. Kirsten Küsel of the Friedrich-Schiller Universiy Jena, explains the mysterious series of deaths. The lake is the crater of a volcano which last erupted about 12,000 years ago, reports the chair of Aquatic Geomicrobiology, “and up to now there are traces of volcanicity, which we regularly analyze on a yearly basis in an outdoor seminar in the degree course Biogeosciences.” Hints of volcanism are given by so-called mofettes. These are small openings in the ground, leaking carbon dioxide, which originates in the magma chambers of the earth’s mantel or the earth’s crust.
Small wonder then, that mofettes were places that are supposed to be very hostile to life. However, as the team of researchers working with Prof. Küsel was able to demonstrate in a new study: there is life even there, although hidden underground. In a mofette close to the Czech river Plesná in north-western Bohemia the researchers followed the path of the carbon dioxide along its last few meters through the ground up to the surface and found numerous organisms that were thriving in this environment which seems to be so hostile to life.
“Our investigation was aiming at examining microbial communities of a mofette and to find out if organisms profit from carbon dioxide emissions, and if so, which.” Felix Beulig from Küsels team says. “We could show, that the carbon dioxide degassing from the interior of the earth is being absorbed by a number of groups of microorganisms and is being transformed into biomass and in chemical bonds like methane and acetic acid. These in turn offer the basic food resource for other organisms in the mofette, and that is why the emitting carbon dioxide plays an important role in the carbon cycle of the soil,” the postgraduate student and first author of the study points out.
However, the new study shows that the biodiversity in a mofette is far less than that found in comparable soils. “But we are not dealing with a environment that is so hostile to life as seems to be the case above ground,” Kirsten Küsel sums up and reports, that there are habitually dead birds, mice and other small animals around mofettes, and only a few plants defy the “poisonous breath of the sleeping volcanos.”
Apart from these elementary findings about the carbon cycle in the soil, the research results of the Uni Jena can be useful in the long run to forecast the potential impact of unwanted degassing from underground carbon dioxide storage (“Carbon Capture and Storage”-technology) and to estimate possible future risks.
Reference:
Felix Beulig, Verena B Heuer, Denise M Akob, Bernhard Viehweger, Marcus Elvert, Martina Herrmann, Kai-Uwe Hinrichs, Kirsten Küsel. Carbon flow from volcanic CO2 into soil microbial communities of a wetland mofette. The ISME Journal, 2014; 9 (3): 746 DOI: 10.1038/ismej.2014.148
Three of the newly described species, Conus carlottae (left column), Conus garrisoni (middle column), and Conus bellacoensis (right column) photographed under regular light (top row) and ultraviolet light (middle row). The brightly fluorescing regions revealed under ultraviolet light would have been darkly pigmented in life (bottom row). Credit: Jonathan Hendricks; CC-BY
Nearly 30 ancient seashell species coloration patterns were revealed using ultraviolet (UV) light, according to a study published April 1, 2015 in the open-access journal PLOS ONE by Jonathan Hendricks from San Jose State University, CA.
Unlike their modern relatives, the 4.8-6.6 million-year-old fossil cone shells often appear white and without a pattern when viewed in regular visible light. By placing these fossils under ultraviolet (UV) light, the organic matter remaining in the shells fluoresces, revealing the original coloration patterns of the once living animals. However, it remains unclear which compounds in the shell matrix are emitting light when exposed to UV rays.
Using this technique, the author of this study was able to view and document the coloration patterns of 28 different cone shell species from the northern Dominican Republic, 13 of which appear to be new species. Determining the coloration patterns of the ancient shells may be important for understanding their relationships to modern species.
Hendricks compared the preserved patterns with those of modern Caribbean cone snail shells and found that many of the fossils showed similar patterns, indicating that some modern species belong to lineages that survived in the Caribbean for millions of years. According to the author, a striking exception in this study was the newly described species Conus carlottae, which has a shell covered by large polka dots, a pattern that is apparently extinct among modern cone snails.
Reference:
Hendricks JR. Glowing Seashells: Diversity of Fossilized Coloration Patterns on Coral Reef-Associated Cone Snail (Gastropoda: Conidae) Shells from the Neogene of the Dominican Republic. PLoS ONE, 2015 DOI: 10.1371/journal.pone.0120924
Note: The above story is based on materials provided by PLOS.
The female ensign scale (Ortheziidae) carries an egg sac formed out of wax plated on the the ventral side. Credit Photo: Dr. Bo Wang
Scientists at the University of Bonn, together with colleagues from China, UK and Poland, have described the oldest evidence of brood care in insects: it is in a female scale insect with her young that is encased in amber as a fossil. The approximately100-million-year-old “snapshot” from the Earth’s history shows the six millimetre long tiny insect with a wax cocoon, which protected the eggs from predators and drying out plus associated young nymphs. The researchers are now presenting their results in the respected journal eLIFE.
The small female insect with the waxy cocoon or reticulum is clearly visible in the brownish translucent amber. The wax cover protected both the scale insect and her approximately 60 eggs from predators and from drying out. In contrast to male scale insects, the female has no wings and is specialized to suck on leaves and provide for her offspring.
“Fossils of fragile female scale insects are extremely rare”, says Chinese paleontologist Dr. Bo Wang, who as a fellow at the Alexander von Humboldt Foundation researching at the Steinmann Institute of the University of Bonn. “What is unique here is the age of the discovery: 100-million-year-old evidence of brood care among insects has not been found until now.” The age of the site of the discovery was determined using the radiometric uranium-lead dating method. In addition to the insect, its eggs and the waxy cover, six young insects are also preserved in this “snapshot” of the Earth’s history captured in amber.
The fossil is named after a Buddhist goddess
Dr. Wang used his good contact with collectors in northern Myanmar to find this extraordinarily rare amber inclusion. The international team of scientists gave the 100-million-year-old scale insect the name “Wathondara kotejai” – after the Buddhist earth goddess Wathondara and the Polish entomologist Jan Koteja.
That the female scale insect was preserved in amber was a very rare occurrence, explains Associate Professor and co-author Dr. Torsten Wappler of the Steinmann Institute at the University of Bonn. Usually, it is the male scale insects that are encased by the resin when they stop on the trunks or branches of trees. In this case, resin probably dripped from a branch onto a leaf which enclosed the female scale insect with her cocoon, eggs and nymphs.
Then the resin fossilized. The scientists cut and polish the amber until only a thin layer remained over the enclosed insect. Like looking through a window, the researchers were then able to take three-dimensional, high-resolution photographs of this witness of the past under the microscope.
Brood care increases the survival chances of the offspring
“With brood care, the scale insect increases the survival chances of its offspring”, says Dr. Wappler. Once the young scale insect is far enough along in its development, it slips out of the protective wax coating and looks for a new plant where to suck its high-sugar and high-energy sap. Even today, common scale insects have a wax cocoon. Their wax gland is found on the hind end. While turning in circles, they discharge the secretion. The result is a round structure with grooves. “The wax case then looks sort of like a record album from the top”, says the paleontologist with a grin. If the animal grows, it moults and discharges wax again. Skin and wax layers therefore alternate in the cocoon.
Amber as a window to the past
From comparing modern scale insects with the amber discovery, the paleontologists concludes that the lifestyle and reproductive behaviour of these insects around 100 million years ago was already quite similar to the current forms. “Inclusions in amber are a unique opportunity to look at life in the past”, explains Dr. Wappler. Insects in fossilized resin are usually very well preserved, whereas articulated animals embedded in sediment either do not remain intact at all or are often crushed or crimped by the pressure of the weight of the overlying layers. “That is why the amber discovery of Wathondara kotejai is unique”, the scientists at the University of Bonn are convinced.
Reference:
Publication: Brood Care in a 100-million-year-old scale insect, Journal eLIFE; DOI: 10.7554/eLife.05447.001
Note : The above story is based on materials provided by University of Bonn.
Life of the Triassic met a choking end in a runaway greenhouse climate, heating the seas into warm stagnation. Credit: Victor Leshyk
Changes in the biochemical balance of the ocean were a crucial factor in the end-Triassic mass extinction, during which half of all plant, animal and marine life on Earth perished, according to new research involving the University of Southampton.
The study, published in the upcoming edition of Geology, reveals that a condition called ‘marine photic zone euxinia’ took place in the Panathalassic Ocean- the larger of the two oceans surrounding the supercontinent of Pangaea.
Photic zone euxinia occurs when the sun-lit surface waters of the ocean become devoid of oxygen and are poisoned by hydrogen sulphide — a by-product of microorganisms that live without oxygen that is extremely toxic to most other lifeforms.
The international team of researchers studied fossilised organic molecules extracted from sedimentary rocks that originally accumulated on the bottom of the north-eastern Panthalassic Ocean, but are now exposed on the Queen Charlotte Islands, off the coast of British Columbia, Canada.
The team found molecules derived from photosynthesising brown-pigmented green sulphur bacteria — microorganisms that only exist under severely anoxic conditions — proving severe oxygen depletion and hydrogen sulphide poisoning of the upper ocean at the end of Triassic, 201 million years ago.
The researchers also documented marked changes in the nitrogen composition of organic matter, indicating that disruptions in marine nutrient cycles coincided with the development of low oxygen conditions.
Previous studies have reported evidence of photic zone euxinia from terrestrial and shallow, near-shore environments during the latest Triassic, but the new research is the first to provide such evidence from an open ocean setting, indicating these changes may have occurred on a global scale.
The University of Southampton’s Professor Jessica Whiteside, who co-authored the study, explains: “As tectonic plates shifted to break up Pangaea, huge volcanic rifts would have spewed carbon dioxide into the atmosphere, leading to rising temperatures from the greenhouse effect. The rapid rises in CO2 would have triggered changes in ocean circulation, acidification and deoxygenation.”
“These changes have the potential to disrupt nutrient cycles and alter food chains essential for the survival of marine ecosystems. Our data now provides direct evidence that anoxic, and ultimately euxinic, conditions severely affected food chains.”
“The same CO2 rise that led to the oxygen depleted oceans also led to a mass extinction on land, and ultimately to the ecological take-over by dinosaurs, although the mechanisms are still under study.”
Although the Earth was very different during the Triassic Period compared to today, the rate of carbon dioxide release from volcanic rifts are similar to those that we are experiencing now through the burning of fossil fuels.
Professor Whiteside comments: “The release of CO2 was probably at least as rapid as that caused by the burning of fossil fuels today, although the initial concentrations were much higher in the Triassic. The consequences of rapidly rising CO2 in ancient times inform us of the possible consequences of our own carbon dioxide crisis.”
Reference:
A. H. Kasprak, J. Sepulveda, R. Price-Waldman, K. H. Williford, S. D. Schoepfer, J. W. Haggart, P. D. Ward, R. E. Summons, J. H. Whiteside. Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction. Geology, 2015; 43 (4): 307 DOI: 10.1130/G36371.1
An outcrop of Peach Spring Tuff is a remnant of a supereruption that occurred in the American Southwest about 19 million years ago. Credit: Ayla Pamukcu
To understand when and why volcanoes erupt, scientists study the rocks left behind by eruptions past. A method called geobarometry uses the composition of volcanic rocks to estimate the pressure and depth at which molten magma was stored just before it erupted.
A research team led by a Brown University geologist has tested a new type of geobarometer that is well-suited to study the kind of magma often produced in explosive and destructive volcanic eruptions, particularly supereruptions—volcanic events hundreds of times larger than any eruption that has occurred during human history. The research, published in Contributions to Mineralogy and Petrology, shows that the new method is able to calculate depths and pressures of these magma bodies more precisely than other methods.
That makes this new geobarometer—the rhyolite-MELTS geobarometer—a useful tool in understanding how supereruptive systems work, according to Ayla Pamukcu, a postdoctoral researcher at Brown and the new paper’s lead author. There haven’t been any supereruptions during human history, but there are several sites around the world where such eruptions could happen in the future. “Understanding supereruptive systems is something that we care about,” Pamukcu said. “The Yellowstone hotspot, for example, has been the source of multiple supereruptions in the past and is an active system that could create one again.”
The underlying principle of geobarometry is the fact that different minerals crystalize in magma at different pressures. Many geobarometers are mathematical models that calculate pressure based on assemblages of certain minerals present in magmatic rock. That pressure estimate is used to calculate the depth in the crust where the magma was stored.
The rhyolite-MELTS geobarometer looks specifically for the pressure where quartz and feldspar minerals are crystallizing simultaneously. The geobarometer was developed by researchers at Vanderbilt University, where Pamukcu received her Ph.D. and conducted this work, and OFM Research. Some other commonly used barometers use crystals of amphibole along with a suite of five or six other minerals to determine pressure. Because the rhyolite-MELTS geobarometer uses a smaller assemblage of minerals, it could be more broadly applicable than other barometers.
To test the rhyolite-MELTS geobarometer, the researchers looked at a supereruption that happened around 19 million years ago in the southwestern United States. The eruption spewed magma across a large swath of Arizona, Nevada, and California. It’s a rare system that happens to have the right minerals for both the rhyolite-MELTS barometer and amphibole barometers, enabling researchers to compare the performance of each.
They found that the rhyolite-MELTS geobarometer returned much more consistent pressure measurements compared to other barometers. As such, the new technique was able to put tighter constraints on magma depths.
“Some of the amphibole geobarometers are useful for establishing broad crustal locations of magmas—whether they were in the upper, middle, lower crust,” Pamukcu said. “But they are not so good for getting at variations within a crustal horizon. Understanding these small variations is of critical importance, though, and we find that the new geobarometer is effective at garnering such information.”
The research also showed that the new system is good at weeding out rocks that have had their composition altered after they erupted. Interactions with water and a number of other weathering processes can all change the composition of a rock. That can cause geobarometers to return inaccurate pressures. But when the rhyolite-MELTS geobarometer encounters an altered composition, it doesn’t return a pressure.
“So instead of putting bad data in and getting a result out that is wrong, if you put bad data into the rhyolite-MELTS geobarometer, you don’t get anything out at all.”
Now that they have this new validation of the rhyolite-MELTS geobarometer, the researchers are looking forward to using it on other volcanic systems. And because the minerals it uses are widespread, it can be used on many other systems.
“We’re always striving to get new and better barometers,” Pamukcu said. “The fact that this one is more widely applicable is exciting.”
Reference:
“Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS—Part 3: Application to the Peach Spring Tuff (Arizona–California–Nevada, USA).” Contributions to Mineralogy and Petrology. DOI: 10.1007/s00410-015-1122-y
Note : The above story is based on materials provided by Brown University.
Dickinsonia fossil from Nilpena, South Australia. Black arrow points to lifted portion of the specimen and is pointed in the direction the waves would have moved during the Ediacaran. Photo credit: Droser Lab, UC Riverside.
Certain specimens of the fossil Dickinsonia are incomplete because ancient currents lifted them from the sea floor, a team of researchers led by paleontologists at the University of California, Riverside has found. Sand then got deposited beneath the lifted portion, the researchers report, strongly suggesting that Dickinsonia was mobile, easily separated from the sea floor and not attached to the substrate on which it lived.
Resembling a symmetrical ribbed oval, Dickinsonia is a fossil of the Ediacaran biota that could reach several feet in size (the Ediacaran Period extended from about 635 million years ago to about 542 million years ago).
“Basically the fossils we studied are exceptionally well preserved, but some samples appear to be missing a part of their body,” said Scott D. Evans, a graduate student in the UC Riverside Department of Earth Sciences. “We believed this to be the result of wave action. So we measured the direction of this missing part and showed that this feature was actually aligned, that is, all of the missing parts ‘pointed’ in the same direction. The alignment of this feature matched the alignment of other features that formed under wave action found with these fossils, indicating that it did, in fact, form from moving water currents in the ancient ocean. This idea shows us that these Dickinsonia weren’t ‘missing’ parts of their body but instead that those parts were not preserved.
“These aren’t just organisms frozen in time but show evidence of what the environment they lived in looked like and how that environment affected them,” he added. “By looking at these fossils we can see that they were altered by a current that flowed over them more than 550 million years ago.”
Study results appeared online last month in Palaeogeography, Palaeoclimatology, Palaeoecology.
“When we look at a fossil, we aren’t just looking at an animal frozen in time but an animal that has gone through many process in the more than 550 million years since it was living on the seafloor,” Evans explained. “There are also questions about whether Dickinsonia was capable of movement and this research shows that it was able to be lifted off the seafloor, indicating that it wasn’t attached to the bottom of the ocean. This doesn’t prove that it could move but it does support the hypothesis that it was a free-living organism.”
Dickinsonia are of interest to paleontologists because these animals are the first to become big and complex and the first also to form communities. Much remains unknown about what exactly they are. Scientists such as UCR’s Mary L. Droser, in whose lab Evans works, have been trying to better understand these animals — how they got nutrients, how they reproduced, what interactions, if any, they had with each other and what the environment in which they lived looked like.
“These questions may seem simple to a modern biologist but these fossils are so different from the animals we see today,” said Droser, a professor of paleontology. “Since we can’t observe them in real life these questions become very difficult to answer. This project adds a small piece to our knowledge of these animals.”
To do the research Droser and Evans spent several months over the last two summers in South Australia, where Dickinsonia fossils are abundantly found. They also spent more than two months in Australia’s desert outback (in an old sheep shearing shed with beds, electricity and running water, and not much else) to study the fossils.
“We spent pretty much every available hour of sunlight looking at the fossils that occur in the Outback,” Evans said. “The fossils we report on in the research paper are actually on rock beds that have been previously excavated and laid out as individual layers. These beds that are about the size of a small classroom allow us to see what the seafloor would have actually looked like. We were able to measure the angles of the missing pieces and orient them with respect to each other.”
Evans is surprised that despite decades of paleontological research scientists know very little about Dickinsonia.
“I want to add to our knowledge of what they were, how they existed, and what they tell us about how the complex animals we are familiar with today evolved from very primitive organisms,” he said. “I am currently working on a research paper that looks at the size distributions of different populations of Dickinsonia which will tell us a little bit about how they lived and reproduced. I then want to investigate how they grew and possibly how they moved and what material they might have been made of.”
Reference:
Scott D. Evans, Mary L. Droser, James G. Gehling. Dickinsonia liftoff: Evidence of current derived morphologies. Palaeogeography, Palaeoclimatology, Palaeoecology, 16 February 2015 “Dickinsonia liftoff: Evidence of current derived morphologies”
This image shows the skull and skeleton of Iberian Worm Lizard, (Blanus). Credit: Nick Longrich
Tiny, burrowing reptiles known as worm lizards became widespread long after the breakup of the continents, leading scientists to conclude that they must have dispersed by rafting across oceans soon after the extinction of the dinosaurs, rather than by continental drift as previously thought.
Scientists at the Universities of Bath, Bristol, Yale University and George Washington University used information from fossils and DNA from living species to create a molecular clock to give a more accurate timescale of when the different species split apart from each other.
The team studied fossils of worm lizards (Amphisbaenia), a type of burrowing lizards that live almost exclusively underground. The six families of worm lizards are found in five different continents, puzzling biologists as to how these creatures became so widespread.
They found that the worm lizards evolved rapidly and expanded to occupy new habitats around 65 million years ago, just after the impact of an asteroid that caused the mass extinction of around 75 per cent of living things on Earth, including the dinosaurs.
Since this event occurred after the break-up of the super-continent Pangaea, the researchers conclude that these animals could not have dispersed across the globe using land bridges.
Instead they argue that this evidence supports a theory proposed by Charles Darwin and Alfred Russell Wallace in the 19th Century that creatures crossed from continent to continent crossing land bridges or floating across oceans — in this case being carried across the oceans on floating vegetation.
Dr Nick Longrich, from the University of Bath, explained: “Continental drift clearly can’t explain the patterns we’re seeing. Continental breakup was about 95 million years ago, and these animals only become widespread 30 million years later.
“It seems highly improbable not only that enough of these creatures could have survived a flood clinging to the roots of a fallen tree and then travelled hundreds of miles across an ocean, but that they were able to thrive and flourish in their new continent.
“But having looked at the data, it is the only explanation for the remarkable diversity and spread of not just worm lizards, but nearly every other living thing as well.
“Once you eliminate the impossible, whatever you’re left with, no matter how improbable, must be the truth.”
The researchers suggest that mass extinction actually helped the survivors of the asteroid hit colonise new places and diversify because there was less competition for food from other species.
Dr Jakob Vinther, from the University of Bristol, said: “The asteroid hit would have killed most of the plants, meaning there was no new food.
“However, scavengers like worm lizards that live off dead and decaying matter were able to survive and thrive. Their tunnels would have acted like bomb shelters, allowing them to withstand the asteroid impact and without any competition for food and space, they flourished.”
Their study, published in the Proceedings of the Royal Society B, describes the earliest definitive fossil evidence of worm lizards, around 100-1000 years after the asteroid hit and long after the break-up of Pangaea. The data suggest that the lizards must have travelled across the oceans at least three times: from North America to Europe, from North America to Africa and from Africa to South America.
The summit caldera of Tambora, which is about 6 kilometers wide and 7 kilometers long and more than 1 kilometer deep, was created by the 1815 eruption. Gray eruptive products form the top of the caldera wall (foreground) and appear to be 200-year-old pyroclastic flow or late surge deposits. On the floor of the caldera is an ephemeral lake (center) and a small cone from a post-1815 eruption (lower right of lake). Credit: Katie Preece
The 2010 eruption of the Icelandic volcano Eyjafjallajökull grounded thousands of air flights and spread ash over much of western Europe, yet it was puny compared to the eruption 200 years ago of Tambora, a volcano that probably killed more than 60,000 people in what is now Indonesia and turned summer into winter over much of the Northern Hemisphere.
“Because Tambora ejected sulfurous gas that generated sulfate aerosols in the atmosphere, which block sunlight, the eruption created a ‘year without a summer,’ leading to food shortages — people were eating cats and rats — and very general hardship throughout Europe and eastern North America,” said Stephen Self, an adjunct professor of earth and planetary science at the University of California, Berkeley, and an expert on volcanoes, in particular supervolcano eruptions 10 times larger than Tambora.
Tambora, which blew its top on April 10 and 11, 1815, is an example of the destruction volcanoes can wreak, he said, possibly made worse today by denser populations and our reliance on air transport. Self will deliver an invited talk April 7 at the opening of a four-day conference on Tambora in Bern, Switzerland, and will publish a commentary on the risk posed by volcanic eruptions in the April issue of the journal Nature Geoscience.
“An eruption of that size today would certainly have major effects on air traffic as well as atmospheric circulation around the globe, so we would like to know when the next big one is coming,” Self said. “But we can’t predict that if we don’t know the size of past eruptions and when they took place.”
That information is simply unavailable even for big, Tambora-like eruptions over the past thousand years, he said.
“Even in a country with well-studied volcanoes, like Japan, at least 40 percent of the big eruptions are missing from the record,” he said. “And if you look back beyond the past 1,000 years, to 3,000 or 4,000 years ago, the record gets worse and worse. We know there are big eruptions hiding from the record that we don’t know about.”
Many explosive eruptions send sulfate molecules, primarily sulfuric acid, around the globe that fall as acidic snow on glaciers and ice caps, leaving traces that can be seen in ice cores from Greenland and elsewhere. Self recently suggested that one mysterious ice-core sulfate peak, dating from 1452, resulted from an eruption off the island of Vanuatu in the Pacific Ocean that left behind a submerged hole, or caldera, remembered only through local legend.
“It is high time for a systematic exploration of all the available eruption archives — ice cores, ocean sediments, remotely sensed caldera volumes and geochronological analysis of eruption deposits — so that we have a better chance to understand potential future hazards,” he wrote in Nature Geosciences with coauthor Ralf Gertisser of Keele University in the United Kingdom.
Volcano risk study urged
In January, the Global Volcano Model and the International Association of Volcanology and Chemistry of Earth’s Interior issued a report on the hazards and risks of eruptions around the world. The groups noted a lack of information on the frequency and size of eruptions like Tambora, which makes it hard to estimate the danger to life and property from historically active but not currently erupting volcanoes.
Not surprisingly, the report identified Indonesia as the most dangerous place for volcanoes. Tambora, located on the island of Sumbawa in Indonesia, was the largest and deadliest known eruption of the last 750 years; a possibly larger explosion occurred on the nearby island of Lombok in 1257. Krakatau, on the western end of the Indonesian archipelago, is perhaps the best-known of the Indonesian volcanoes. Its 1883 eruption killed more than 34,000 people and was the second deadliest after Tambora. Tambora erupted three times the amount of ash and lava as Krakatau, Self said.
Recently, scientists have proposed that the eruption of Toba on the island of Sumatra 74,000 years ago was the most destructive super-eruption ever recorded: the explosion created a 100 by 60 kilometer caldera now occupied by Lake Toba, and spread ash as far away as the Himalayas 3,000 kilometers to the northwest.
According to the January report, 90 percent of the volcano risk worldwide is in the five nations of Indonesia, Philippines, Japan, Mexico and Ethiopia.
Self has spent much of his career visiting the calderas of major volcanic eruptions and collecting samples of ash and lava in order to determine when and how much they erupted in the past. In 1979, he was the first modern-day scientist to visit Tambora, a shield volcano somewhat like those in Hawaii, to collect rock for analysis. He later estimated that when it exploded in 1815, it blew out 30 to 50 cubic kilometers of material, a major change from the volcano’s earlier behavior.
Sulfur gas ascended into the stratosphere, spawning sulfate aerosol particles that were carried around the world, blocking sunlight for more than a year. This is the best-known example of volcano-induced global cooling, Self said. Some estimate that the global average temperature dropped more than 1 degree Celsius (1.4 degrees Fahrenheit) as a result, causing crop failures in Asia as well as Europe and North America.
For comparison, Mount St. Helens in Washington erupted about 1 cubic kilometer of material in 1980, while Pinatubo’s output in 1991 was about 5 cubic kilometers.
California’s smoking Long Valley caldera
Mainland North America has its own worrisome volcanoes. Crater Lake was created by an eruption of Tambora’s size 7,700 years ago, while the area around Yellowstone National Park was ground zero for a long series of super-eruptions, the most recent about 640,000 years ago, that blanketed much of the North American continent with ash. Long Valley caldera east of California’s Sierra Nevada, within which sits the town of Mammoth, is considered an active supervolcano, though it’s one and only huge eruption was 760,000 years ago.
Smaller volcanoes, such as Mount Rainier and Mount Hood in Washington and Oregon, respectively, are still considered active, while California’s Mount Lassen erupted just 100 years ago.
“We can’t stop an eruption, but we can prepare to adapt to the immediate impact of ash on air traffic and the delayed effect of sulfate aerosols on crops and vegetation,” Self said. Aside from the immediate, ground-level danger from ash flows, lava and hot gas to people living around an erupting volcano, ash thrown into the air, and sulfate aerosols, can pit airplane windows and damage jet engines, while both can cause respiratory problems downwind.
Self said that the 1816 “year without a summer” was not immediately associated with the Mount Tambora eruption because the western world didn’t learn of its explosion until months later, when reports finally made their way by ship from the Dutch East Indies. Krakatau’s fame comes as much from the existence of a new device, the telegraph, which immediately carried news of the eruption around the world in 1883, as from its size and global impact.
The Tambora eruption may have had one famous outcome. Had it not been for the cold, wet weather it brought to Europe, Mary and Percy Shelley and Lord Byron might not have spent the summer of 1816 telling ghost stories around a log fire in a rented house on Lake Geneva, and Mary Shelley might never have turned the best of those tales into a famous book, Frankenstein.
“Frankenstein was wrought from the year without a summer, all due to this volcano that nobody’s ever heard of,” Self said.
Reference:
Stephen Self, Ralf Gertisser. Tying down eruption risk. Nature Geoscience, 2015; 8 (4): 248 DOI: 10.1038/ngeo2403
Esteban Gazel, a geoscientist at Virginia Tech, collects samples of lava in a variety of locations, in this case Etna, Italy, to probe the chemical evolution of the planet. Credit: Virginia Tech
An international research team, led by a Virginia Tech geoscientist, has revealed information about how continents were generated on Earth more than 2.5 billion years ago — and how those processes have continued within the last 70 million years to profoundly affect the planet’s life and climate.
Published online today in Nature Geoscience, the study details how relatively recent geologic events — volcanic activity 10 million years ago in what is now Panama and Costa Rica — hold the secrets of the extreme continent-building that took place billions of years earlier.
The discovery provides new understanding about the formation of the Earth’s continental crust — masses of buoyant rock rich with silica, a compound that combines silicon and oxygen.
“Without continental crust, the whole planet would be covered with water,” said Esteban Gazel, an assistant professor of geology with Virginia Tech’s College of Science. “Most terrestrial planets in the solar system have basaltic crusts similar to Earth’s oceanic crust, but the continental masses — areas of buoyant, thick silicic crust — are a unique characteristic of Earth.”
The continental mass of the planet formed in the Archaean Eon, about 2.5 billion years ago. The Earth was three times hotter, volcanic activity was considerably higher, and life was probably very limited.
Many scientists think that all of the planet’s continental crust was generated during this time in Earth’s history, and the material continually recycles through collisions of tectonic plates on the outermost shell of the planet.
But the new research shows “juvenile” continental crust has been produced throughout Earth’s history.
“Whether the Earth has been recycling all of its continental crust has always been the big mystery,” Gazel said. “We were able to use the formation of the Central America land bridge as a natural laboratory to understand how continents formed, and we discovered while the massive production of continental crust that took place during the Archaean is no longer the norm, there are exceptions that produce ‘juvenile’ continental crust.”
The researchers used geochemical and geophysical data to reconstruct the evolution what is now Costa Rica and Panama, which was generated when two oceanic plates collided and melted iron- and magnesium-rich oceanic crust over the past 70 million years, Gazel said.
Melting of the oceanic crust originally produced what today are the Galapagos islands, reproducing Achaean-like conditions to provide the “missing ingredient” in the generation of continental crust.
The researchers discovered the geochemical signature of erupted lavas reached continental crust-like composition about 10 million years ago. They tested the material and observed seismic waves traveling through the crust at velocities closer to the ones observed in continental crust worldwide.
Additionally, the researchers provided a global survey of volcanoes from oceanic arcs, where two oceanic plates interact. The western Aleutian Islands and the Iwo-Jima segment of the Izu-Bonin islands of are some other examples of juvenile continental crust that has formed recently, the researchers said.
“This is an interesting paper that makes the case that andesitic melts inferred to derive ultimately by melting of subducted slabs in some modern arcs are a good match for the composition of the average continental crust,” said Roberta L. Rudnick, a Distinguished University Professor and chair of the Department of Geology at the University of Maryland, who was not involved in conducting the research. “The authors focus primarily on Central America, but incorporate global data to strengthen their case that slab melting is important in unusual conditions of modern continent generation — and probably in the past.”
The study raises questions about the global impact newly generated continental crust has had over the ages, and the role it has played in the evolution of not just continents, but life itself.
For example, the formation of the Central American land bridge resulted in the closure of the seaway, which changed how the ocean circulated, separated marine species, and had a powerful impact on the climate on the planet.
“We’ve revealed a major unknown in the evolution of our planet,” said Gazel, who was the senior and corresponding author of the study.
Reference:
Esteban Gazel, Jorden L. Hayes, Kaj Hoernle, Peter Kelemen, Erik Everson, W. Steven Holbrook, Folkmar Hauff, Paul van den Bogaard, Eric A. Vance, Shuyu Chu, Andrew J. Calvert, Michael J. Carr, Gene M. Yogodzinski. Continental crust generated in oceanic arcs. Nature Geoscience, 2015; 8 (4): 321 DOI: 10.1038/ngeo2392
Note: The above story is based on materials provided by Virginia Tech.
This image shows Saurichthys rieppeli, a new species of bony fish from the Middle Triassic of Monte San Giorgio, UNESCO world heritage in Southern Switzerland (length 60 cm). Credit: University of Zurich
Working with an international team, paleontologists at the University of Zurich have discovered two new species of Saurichthys. The ~242 million year old predatory fishes were found in the fossil Lagerstätte Monte San Giorgio, in Ticino. They are distinct from previously known Saurichthys species in the shape of the head and body, suggesting different habitats and diet.
Saurichthys is a predatory fish characterized by a long thin body and a sharply pointed snout with numerous teeth. This distinctive ray-finned fish lived in marine and freshwater environments all over the world 252-201 million years ago during the Triassic period. Two new species of this extinct fish have been discovered by paleontologists at the University of Zurich, working in collaboration with researchers in Germany and China. The first species, “Saurichthys breviabdominalis,” is named for its relatively short body and the second, “Saurichthys rieppeli,” is named after Olivier Rieppel, a Swiss paleontologist formerly based at the University of Zurich. Including the new finds, there are now six species of Saurichthys known from Monte San Giorgio, making it both the most abundant and diverse fish at this classic Middle Triassic locality.
Evidence of different diet and habitat
Both 40 to 60 cm long fishes differ from other species of Saurichthys in skull and body shape. “These differences indicate different hunting styles and habitats in the shallow sea. This enabled multiple species to co-exist,” clarified Heinz Furrer, paleontologist at the University of Zurich and author of this research project. According to Furrer, the ability to occupy multiple specialized feeding and habitat niches may be responsible for the evolutionary success of these fishes, both in the Monte San Giorgio basin and globally.
Monte San Giorgio is world-renowned for its beautifully preserved fossils from the Middle Triassic time (~239-243 million years ago). Large-scale excavations conducted by the University of Zürich between 1924 and 2004 yielded a substantial number of fossil reptiles and fishes. As part of a research project funded by the Swiss National Science Foundation, scientists at the Paleontological Institute and Museum, University of Zurich have prepared and studied over a hundred well-preserved specimens over the last three years.
Reference:
Erin E. Maxwell, Carlo Romano, Feixiang Wu, Heinz Furrer. Two new species ofSaurichthys(Actinopterygii: Saurichthyidae) from the Middle Triassic of Monte San Giorgio, Switzerland, with implications for character evolution in the genus. Zoological Journal of the Linnean Society, 2015; 173 (4): 887 DOI: 10.1111/zoj.12224
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This image shows a house damaged by Sept. 2013 debris flow in Big Thompson Canyon, Colorado Front Range; deposit covers part of US Hwy 34. Credit: Photo by Jonathan Godt, 20 Sept. 2013; published on the cover of the Oct. 2014 issue of GSA Today.
Scott W. Anderson and colleagues use repeat aerial LiDAR to quantify the erosional impact of the heavy rains that inundated the Colorado Front Range in September 2013. The five-day storm triggered more than 1,100 landslides and debris flows in a 3,430-square-kilometer area due to 200-450 mm of heavy, steady rainfall. This number of hillslope failures in a single event represents unprecedented activity for the region in its ~150 years of written history.
This study for Geology addresses the role of such large, rare events in shaping landscapes by documenting the location and size of landslides and debris flows. Anderson and colleagues use before-and-after high-resolution topographic data from airborne laser mapping (LiDAR) to quantify landslide erosion.
The “before” LiDAR mapping of Boulder Creek was completed in 2010. With a few weeks of the storm, the authors repeated the aerial survey. They then subtracted the 2013 topographic data from the 2010 topographic data where the datasets overlapped — west of Boulder, Colorado — to produce a digital elevation model (DEM) of difference.
They located 120 landslides and debris flows ranging in size from 10 to 21,000 cubic meters, all on slopes greater than 20 degrees. On average, about 15 mm of lowering occurred in basins in which landslides occurred.
Other methods have shown that it takes hundreds to thousands of years to loosen this much sediment from rock. These results therefore show that it is these rare debris flows that transport the sediment off the steep hillslopes along the eastern edge of the Front Range.
This study both highlights the importance of rare events in long-term erosion of this landscape and helps to explain why modern sediment yields may greatly underestimate long-term denudation rates in such settings. Debris flows dominate sediment export from storage on the steep hillslopes that bound the canyons draining the Colorado Front Range. Landscapes evolve over time scales that greatly exceed the period of historical records. It is therefore important to understand the degree to which modern observations capture the full range of geologically formative processes and process rates.
Refernce:
Scott W. Anderson et al., Dept. of Geography and Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado, USA; currently at U.S. Geological Survey, Tacoma, Washington 98402, USA. Published online ahead of print on 27 Mar. 2015; DOI: 10.1130/G36507.1
DRI and NASA JPL engineers prepare coring device to sample thermokarst lake sediments in early November on the North Slope of Alaska. Credit: Alison Murray, DRI
New research into the changing ecology of thousands of shallow lakes on the North Slope of Alaska suggests that in scenarios of increasing global temperatures, methane-generating microbes, found in thawing lake sediments, may ramp up production of the potent greenhouse gas – which has a global warming potential 25 times greater than carbon dioxide.
A study published this month in Geobiology – resulting from five-years of collaborative research led by Nevada’s Desert Research Institute (DRI) and including scientists from NASA’s Jet Propulsion Laboratory (JPL), Montana State University, and University of California, Riverside – illustrates how the decomposition of organic matter in thermokast lake sediments can produce up to three times more biological methane gas emissions when subjected to increased temperatures in a simulated environment.
Further, researchers found that the methane detected in in lake sediments in this region can arise from both ancient theremogenic sources deep in the earth, or from shallow contemporary biological sources. Interestingly, the coastal plain in the North Slope of Alaska is estimated to contain 53-billion cubic feet of natural gas trapped under the permafrost ice cap.
Thermokarst lakes occur as permafrost thaws and creates surface depressions where meltwater accumulates , converting what was previously frozen land into small freshwater lakes with active decomposing sediment layers.
While scientists have long understood that methane and carbon dioxide releases from thawing permafrost are important sources of global greenhouse gas emissions, little is known about the sources and rates of methane production (known as methanogensis) from microbial communities found in these changing environments.
“The large amount of organic matter stored in the thaw layer between the water column and the permafrost table serves as a significant source of carbon for methanogensis,” explained Paula Matheus Carnevali, a doctoral student at DRI and the study’s lead author. “Identifying and understanding the production sources of methane will improve our ability to generate accurate predictions about the changing climate in the Arctic.”
The study focused on methane dynamics within 16 sediment cores collected over a period of four years from two Alaskan thermokarst lakes, near Barrow, Alaska. Samples were obtained from three sites, one proximal to an active, submerged natural gas seep and another from a site approximately one-kilometer away from the seep site. The second lake was located about 13-km to the northwest, and did not have visibly active seeps.
Simulated climate scenarios were performed in a controlled DRI laboratory in Reno, Nevada and scientists analyzed the potential for increased biological production of methane from methanogens found in the lake sediments; the role of the sediment geochemistry in this process; and the temperature dependency of this process.
“This study marks an important step in recognizing that there are different methane sources in close proximity that may respond differently in the changing Alaskan arctic ecosystems,” said Alison Murray, Ph.D., a principal investigator on the study and expert in microbial ecology and archaea found in some of Earth’s most extreme environments.
“In scenarios of warming climate,” Murray said, “our measurements indicate that biological methane production may play a larger role in total methane emissions in the future, which could have a significant impact on our climate.”
Reference:
Methane sources in arctic thermokarst lake sediments on the North Slope of Alaska. DOI: 10.1111/gbi.12124
Fumaroles escape from Fourpeaked volcano through a fissure in Fourpeaked Glacier on 24 September 2006 Credit: Read, Cyrus, USGS
Particles emitted during major volcanic eruptions cool the atmosphere due to a ‘parasol’ effect that reflects sunlight. The direct impact of these particles in the atmosphere is fairly short, lasting two to three years. However, they alter for more than 20 years the North Atlantic Ocean circulation, which connects surface and deep currents and influences the climate in Europe. This is the conclusion of a study by researchers from the CNRS, IRD, CEA and Météo‐France* who combined, for the first time, climate simulations, recent oceanographic data, and information from natural climate records. Their findings** are published in Nature Communications on March 30th.
The Atlantic Ocean is home to variations in surface temperatures that last for several decades, affecting Europe’s climate. This slow variability is caused by changes in the ocean circulation, which connects surface to deep currents and transports heat from the tropics to the Norway and Greenland seas. However, the reason for this variability is still poorly understood.
In order to elucidate its mechanisms, the researchers first used information from the natural climate record covering the last millennium. By studying the chemical composition of water from ice cores in Greenland, they were able to estimate past temperature changes. The data highlights the close connection between the surface temperature of the Atlantic Ocean and air temperatures over Greenland, showing that climate variability in the region is a periodic phenomenon some of whose cycles, or oscillations, last around twenty years.
By using numerical simulations from more than twenty different climate models, the researchers also showed that major volcanic eruptions, like that of Mount Agung, Indonesia, in 1963, or Pinatubo in the Philippines in 1991, could significantly alter ocean circulation in the North Atlantic. This is because the large quantities of particles emitted by these eruptions into the upper atmosphere reflect part of the solar radiation, rather like a parasol, causing the climate at Earth’s surface to cool. The cooling, which only lasts two or three years, then triggers a rearrangement of ocean circulation in the North Atlantic Ocean. Around fifteen years after the beginning of the eruption, the circulation speeds up. It then slows down after twenty-five years, before accelerating again thirty-five years after the phenomenon. Volcanic eruptions thus appear to act on the ocean circulation in the North Atlantic rather like a pacemaker, causing variability over a twenty-year period.
The scientists confirmed these results by comparing them with observations of ocean salinity, a key factor for the sinking of water and therefore for ocean circulation. In numerical simulations and modern oceanographic data they detected similar variations in the early 1970s and 1990s connected to the eruption of the Agung volcano. Using data from Greenland ice cores and observations carried out on bivalve molluscs collected to the north of Iceland and dating back more than 500 years, as well as a simulation of the climate over the last thousand years, the researchers systematically identified acceleration of ocean circulation fifteen years after five volcanic eruptions that took place several hundred years ago.
Lastly, the researchers revealed the interference produced by the latest three main eruptions, Agung in 1963, El Chichón in Mexico in 1982, and Pinatubo in 1991, explaining for the first time the recent variability of currents in the North Atlantic ocean. They conclude that a major eruption in the near future could have an impact on the currents in the North Atlantic Ocean — and hence on our ability to predict the variability of the climate in Europe — over several decades. They now hope to consolidate these findings by collecting data from additional sources, especially in paleoclimatology.
* From the Laboratoire Environnements et Paléo-environnements Océaniques et Continentaux (CNRS/Université de Bordeaux), Centre National de Recherches Météorologiques — Groupe d’Etude de l’Atmosphère Météorologique (CNRS/Météo France), and Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (CNRS/UPMC/MNHN/IRD) and Laboratoire des Sciences du Climat et de l’Environnement (CNRS/CEA/UVSQ), both part of the Institut Pierre Simon Laplace.
**The project was funded by the Agence Nationale de la Recherche via the ‘Groenland Vert’ project in the ‘Changements Environnementaux Planétaires et Société’ program (2011-2015).
Reference:
Didier Swingedouw, Pablo Ortega, Juliette Mignot, Eric Guilyardi, Valérie Masson-Delmotte, Paul G. Butler, Myriam Khodri, Roland Séférian. Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions. Nature Communications, 2015; 6: 6545 DOI: 10.1038/ncomms7545
Note: The above story is based on materials provided by CNRS.
Microscopic gold-rich and lead-rich particles in a municipal biosolids sample. Credit: Heather Lowers, USGS Denver Microbeam Laboratory
Poop could be a goldmine — literally. Surprisingly, treated solid waste contains gold, silver and other metals, as well as rare elements such as palladium and vanadium that are used in electronics and alloys. Now researchers are looking at identifying the metals that are getting flushed and how they can be recovered. This could decrease the need for mining and reduce the unwanted release of metals into the environment.
“If you can get rid of some of the nuisance metals that currently limit how much of these biosolids we can use on fields and forests, and at the same time recover valuable metals and other elements, that’s a win-win,” says Kathleen Smith, Ph.D.
“There are metals everywhere,” Smith says, noting they are “in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odors.” Whatever their origin, the wastes containing these metals all end up being funneled through wastewater treatment plants, where she says many metals end up in the leftover solid waste.
At treatment plants, wastewater goes through a series of physical, biological and chemical processes. The end products are treated water and biosolids. Smith, who is at the U.S. Geological Survey (USGS), says more than 7 million tons of biosolids come out of U.S. wastewater facilities each year. About half of that is used as fertilizer on fields and in forests, while the other half is incinerated or sent to landfills.
Smith and her team are on a mission to find out exactly what is in our waste. “We have a two-pronged approach,” she says. “In one part of the study, we are looking at removing some regulated metals from the biosolids that limit their use for land application.
“In the other part of the project, we’re interested in collecting valuable metals that could be sold, including some of the more technologically important metals, such as vanadium and copper that are in cell phones, computers and alloys,” Smith said. To do this, they are taking a page from the industrial mining operations’ method book and are experimenting with some of the same chemicals, called leachates, which this industry uses to pull metals out of rock. While some of these leachates have a bad reputation for damaging ecosystems when they leak or spill into the environment, Smith says that in a controlled setting, they could safely be used to recover metals in treated solid waste.
So far, her group has collected samples from small towns in the Rocky Mountains, rural communities and big cities. For a more comprehensive picture, they plan to combine their information with many years’ worth of existing data collected by the Environmental Protection Agency and other groups at the USGS.
In the treated waste, Smith’s group has already started to discover metals like platinum, silver and gold. She states that they have observed microscopic-sized metal particles in biosolids using a scanning electron microscope. “The gold we found was at the level of a minimal mineral deposit,” she says, meaning that if that amount were in rock, it might be commercially viable to mine it. Smith adds that “the economic and technical feasibility of metal recovery from biosolids needs to be evaluated on a case-by-case basis.”
In a recent Environmental Science & Technology paper another research group also studying this issue calculated that the waste from 1 million Americans could contain as much as $13 million worth of metals. That’s money that could help fuel local economies.
The researchers acknowledge funding from the U.S. Geological Survey Mineral Resources Program.
Reference:
Paul Westerhoff, Sungyun Lee, Yu Yang, Gwyneth W. Gordon, Kiril Hristovski, Rolf U. Halden, Pierre Herckes. Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide. Environmental Science & Technology, 2015; 150127115347007 DOI: 10.1021/es505329q
