After five decades of dormancy, the Cumbre Vieja volcano on La Palma in the Canary Islands began erupting on Sept. 19, 2021. This image is from October 2021. Credit: Credit: Esteban Gazel/Provided
Cornell University researchers have unearthed precise, microscopic clues to where magma is stored, offering a way to better assess the risk of volcanic eruptions.
In recent years, scientists have used satellite imagery, earthquake data and GPS to search for ground deformation near active volcanoes, but those techniques can be inaccurate in locating the depth of magma storage.
By finding microscopic, carbon dioxide-rich fluids encased in cooled volcanic crystals, scientists can accurately determine — within one hundred meters — where magma is located.
“A fundamental question is where magma is stored in Earth’s crust and mantle,” said Esteban Gazel, professor of engineering and lead author of the study, published in Science Advances. “That location matters because you can gauge the risk of an eruption by pinpointing the specific location of magma, instead of other signals like hydrothermal system of a volcano.”
Gazel notes that speed and precision are essential. “We’re demonstrating the enormous potential of this improved technique in terms of its rapidity and unprecedented accuracy,” he said. “We can produce data within days of the samples arriving from a site, which provides better, near real-time results.”
In volcanic events, magma reaches the Earth’s surface, and it erupts as lava and — depending on how much gas it contains — could be explosive in nature. When deposited as part of the fallout of the eruption, fragmented fine-grained material — called tephra — can be collected and evaluated.
Gazel and doctoral student Kyle Dayton deduced how to use inclusions of carbon dioxide-rich fluids trapped within olivine crystals to precisely indicate depth, as the carbon dioxide density of these inclusions is controlled by pressure.
These fluids can be measured quickly using an instrument to determine — in terms of kilometers — how far down the magma was stored and the depth of the scorching reservoir.
Gazel and Dayton joined a small, elite team of international researchers to study the Cumbre Vieja volcano on La Palma in the Canary Islands. Gazel and Dayton picked through tephra to find crystals, which in turn provide data to improve eruption models and forecasts.
Reference:
Kyle Dayton, Esteban Gazel, Penny Wieser, Valentin R. Troll, Juan Carlos Carracedo, Hector La Madrid, Diana C. Roman, Jamison Ward, Meritxell Aulinas, Harri Geiger, Frances M. Deegan, Guillem Gisbert, Francisco J. Perez-Torrado. Deep magma storage during the 2021 La Palma eruption. Science Advances, 2023; 9 (6) DOI: 10.1126/sciadv.ade7641
Note: The above post is reprinted from materials provided by Cornell University. Original written by Blaine Friedlander, courtesy of the Cornell Chronicle.
Eggs of deep-sea skates have been discovered near the hottest type of hydrothermal vents, where super-heated water emerges out of the sea floor. These vents, called black smokers, emit dark, sulphurous plumes. Credit: Ocean Exploration Trust
Hydrothermal vents have been identified as a previously undiscovered source of dissolved black carbon in the oceans, furthering the understanding of the role of oceans as a carbon sink.
The ocean is one of the largest dynamic carbon sinks in the world, and is susceptible to increased carbon emissions from human activities. There are even proposals to use the ocean to sequester carbon in an effort to reduce the carbon emissions. However, much of the processes by which the ocean functions as a carbon sink are not fully understood.
Associate Professor Youhei Yamashita and grad student Yutaro Mori at Hokkaido University, along with Professor Hiroshi Ogawa at AORI, The University of Tokyo, have revealed conclusive evidence that hydrothermal vents are a previously unknown source of dissolved black carbon in the deep ocean. Their discoveries were published in the journal Science Advances.
“One of the largest carbon pools on the Earth’s surface is the dissolved organic carbon in the ocean,” explains Ogawa. “We were interested in a portion of this pool, known as dissolved black carbon (DBC), which cannot be utilized by organisms. The source of DBC in the deep sea was unknown, although hydrothermal vents were suspected to be involved.”
The researchers analyzed the distribution of DBC in the ocean basins of the North Pacific Ocean and Eastern South Pacific Ocean, and compared the data with previously reported concentrations of a helium isotope that is associated with hydrothermal vent emissions, as well as oxygen utilization in these areas.
Their findings showed that hydrothermal vents were an important source of DBC in the Pacific Ocean. This hydrothermal DBC is most likely formed due to the mixing of the hot fluids from hydrothermal vents with cold seawater, and is transported over long distances — up to thousands of kilometers away.
“Most importantly, our research indicates that the DBC from hydrothermal vents is an important source of dissolved organic carbon in the deep ocean. In terms of DBC inputs to the ocean, hydrothermal vents may contribute up to half as much DBC as that which is formed by biomass burning or fossil fuel combustion and subsequently transported via rivers or atmospheric deposition,” concluded Yamashita. Further research is required to understand exactly how DBC is formed from hydrothermal vents.
Reference:
Youhei Yamashita, Yutaro Mori, and Hiroshi Ogawa. Hydrothermal-derived black carbon as a source of recalcitrant dissolved organic carbon in the ocean. Science Advances, 2023 DOI: 10.1126/sciadv.ade3807
Meteorites have told Imperial researchers the likely far-flung origin of Earth’s volatile chemicals, some of which form the building blocks of life.
They found that around half the Earth’s inventory of the volatile element zinc came from asteroids originating in the outer Solar System — the part beyond the asteroid belt that includes the planets Jupiter, Saturn, and Uranus. This material is also expected to have supplied other important volatiles such as water.
Volatiles are elements or compounds that change from solid or liquid state into vapour at relatively low temperatures. They include the six most common elements found in living organisms, as well as water. As such, the addition of this material will have been important for the emergence of life on Earth.
Prior to this, researchers thought that most of Earth’s volatiles came from asteroids that formed closer to the Earth. The findings reveal important clues about how Earth came to harbour the special conditions needed to sustain life.
Senior author Professor Mark Rehka?mper, of Imperial College London’s Department of Earth Science and Engineering, said: “Our data show that about half of Earth’s zinc inventory was delivered by material from the outer Solar System, beyond the orbit of Jupiter. Based on current models of early Solar System development, this was completely unexpected.”
Previous research suggested that the Earth formed almost exclusively from inner Solar System material, which researchers inferred was the predominant source of Earth’s volatile chemicals. In contrast, the new findings suggest the outer Solar System played a bigger role than previously thought.
Professor Rehka?mper added: “This contribution of outer Solar System material played a vital role in establishing the Earth’s inventory of volatile chemicals. It looks as though without the contribution of outer Solar System material, the Earth would have a much lower amount of volatiles than we know it today — making it drier and potentially unable to nourish and sustain life.”
The findings are published today in Science.
To carry out the study, the researchers examined 18 meteorites of varying origins — eleven from the inner Solar System, known as non-carbonaceous meteorites, and seven from the outer Solar System, known as carbonaceous meteorites.
For each meteorite they measured the relative abundances of the five different forms — or isotopes — of zinc. They then compared each isotopic fingerprint with Earth samples to estimate how much each of these materials contributed to the Earth’s zinc inventory. The results suggest that while the Earth only incorporated about ten per cent of its mass from carbonaceous bodies, this material supplied about half of Earth’s zinc.
The researchers say that material with a high concentration of zinc and other volatile constituents is also likely to be relatively abundant in water, giving clues about the origin of Earth’s water.
First author on the paper Rayssa Martins, PhD candidate at the Department of Earth Science and Engineering, said: “We’ve long known that some carbonaceous material was added to the Earth, but our findings suggest that this material played a key role in establishing our budget of volatile elements, some of which are essential for life to flourish.”
Next the researchers will analyse rocks from Mars, which harboured water 4.1 to 3 billion years ago before drying up, and the Moon. Professor Rehka?mper said: “The widely held theory is that the Moon formed when a huge asteroid smashed into an embryonic Earth about 4.5 billion years ago. Analysing zinc isotopes in moon rocks will help us to test this hypothesis and determine whether the colliding asteroid played an important part in delivering volatiles, including water, to the Earth.”
This work was funded by the Science and Technology Facilities Council (STFC — part of UKRI) and Rayssa Martins is funded by an Imperial College London Presidents’ PhD Scholarship.
Reference:
Rayssa Martins, Sven Kuthning, Barry J. Coles, Katharina Kreissig, Mark Rehkämper. Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth’s volatiles. Science, 2023; 379 (6630): 369 DOI: 10.1126/science.abn1021
Microscopic photograph of a lower jaw from Funcusvermis gilmorei soon after it was recovered during microscopic sorting of sediment from the Thunderstorm Ridge fossil site in the Petrified Forest National Park Paleontology Lab. Photo by Ben Kligman for Virginia Tech.
The smallest of newly found fossils can upend what paleontologists know about our history.
A team of paleontologists from Virginia Tech and the U.S. Petrified Forest National Park, among others, have discovered the first “unmistakable” Triassic-era caecilian fossil — the oldest-known caecilian fossils — thus extending the record of this small, burrowing animal by roughly 35 million years. The find also fills a gap of at least 87 million years in the known historical fossil record of the amphibian-like creature.
The fossil was first co-discovered by Ben Kligman, a doctoral student in the Department of Geosciences, part of the Virginia Tech College of Science, at Arizona’s Petrified Forest National Park during a dig in 2019. Named by Kligman as Funcusvermis gilmorei, the fossil extends the history of caecilians 35 million years back to Triassic Period, roughly 250 million to 200 million years ago.
Prior to this new study, published today in the journal Nature, only 10 fossil caecilian occurrences were known, dating back to the Early Jurassic Period, about 183 million years ago. However, previous DNA studies estimated evolutionary origins of caecilians back to the Carboniferous or Permian eras, some 370 million to 270 million years ago, according to Kligman, marking that 87-million-year gap. However, no such fossils had been found.
“The discovery of the oldest caecilian fossils highlights the crucial nature of new fossil evidence. Many of the biggest outstanding questions in paleontology and evolution cannot be resolved without fossils like this,” said Kligman, who previously discovered a 220-million-year-old species of cynodont or stem-mammal, a precursor of modern-day mammals. “Fossil caecilians are extraordinarily rare, and they are found accidentally when paleontologists are searching for the fossils of other more common animals. Our discovery of one was totally unexpected, and it transformed the trajectory of my scientific interests.”
The discovery of the fossils was made in 2019 by Kligman and Petrified Forest National Park student intern Xavier Jenkins, now a Ph.D. student at Idaho State University, while the duo was processing fossiliferous sediment from the park’s nicknamed Thunderstorm Ridge via a microscope. Funcusvermis was found in a layer of the Chinle Formation dated to approximately 220 million years ago, when Arizona was positioned near the equator at the central part of the supercontinent Pangaea, Kligman said. This region at the time was subject to a hot, humid climate. Today, Arizona is still hot, but has low humidity.
“Seeing the first jaw under the microscope, with its distinctive double row of teeth, sent chills down my back,” Kligman said. “We immediately knew it was a caecilian, the oldest caecilian fossil ever found, and a once-in-a-lifetime discovery.”
Previous to this find, the 87-million-year gap in the fossil record hid the early evolutionary history of caecilians, leading to a decades-long debate amongst scientists over the relationships of caecilians to their amphibian relatives, frogs and salamanders.
“Funcusvermis extends the humid equatorial pattern of occurrence seen in all known fossil and living caecilians, suggesting that the biogeographic history of caecilians has been guided by restriction to these ecological settings, likely due to physiological constraints linked to humidity, and constrained by the drift of continental plates into and out of the humid-equatorial zone after the fragmentation of Pangaea,” Kligman said.
Modern caecilians are limbless amphibians with cylindrical bodies with a compact, bullet-shaped skull that helps them burrow underground. Now exclusively home to South and Central America, Africa, and southern Asia, caecilians spend their lives burrowing in leaf-litter or soil searching for prey such as worms and insects. This underground existence has made studying caecilians difficult for scientists. Kligman, tongue in cheek, describes modern caecilians as an “eyeless sock puppet with the body of a worm.”
Funcusvermis actually shares skeletal features related more with early frog and salamander fossils, strengthening evidence for a shared origin and close evolutionary relationship between caecilians and these two groups. Funcusvermis also shares skeletal features with an ancient group of amphibians known to paleontologists as dissorophoid temnospondyls. Kligman adds, “Unlike living caecilians, Funcusvermis lacks many adaptations associated with burrowing underground, indicating a slower acquisition of features associated with an underground lifestyle in the early stages of caecilian evolution.”
Now, here’s the fun part: The genus name ‘Funcusvermis’ was inspired by the Ohio Players’ 1972 song “Funky Worm” from their album Pleasure, a favorite song of the authors that was often played while excavating fossils at Thunderstorm Ridge. ‘Funcus’ is derived from the Latinized form of the English word Funky for the upbeat, rhythmic form of dance music, while ‘vermis’ is derived from the Latin word for worm. (It’s an excellent song, by the way. Instant earworm, so to speak.)
The species name, gilmorei, honors Ned Gilmore, the collections manager at the Academy of Natural Sciences of Philadelphia’s Drexel University. (Kligman is from Philadelphia and volunteered with Gilmore’s herpetology wet collection as an undergraduate student. “He was an important mentor who helped inspire my interest in fossils and amphibians,” Kligman said.)
Co-authors on the study include Michelle Stocker, an assistant professor, and Sterling Nesbitt, an associate professor, in the Virginia Tech Department of Geosciences and members of the Global Change Center that is part of the Fralin Life Sciences Institute. Other authors include Adam Marsh, lead paleontologist; Matthew Smith, museum curator; and William Parker, chief of science and resource management, all at the Petrified Forest National Park; and Bryan Gee, postdoctoral fellow at the University of Washington’s Burke Museum and Department of Biology.
“As the eponymous song says, it’s the funkiest worm in the world,” Marsh quipped.
Stocker added, “What we collect really determines what we can say about which animals that were present, how many of them there were, and what they looked like. Without using these methods for fossil collection and analysis we would be missing out on knowing so many important aspects of this Triassic ecosystem. Now that we have a search image of what bones to look for and how to look for them, it will be exciting to see what other fossil localities preserve these early lissamphibians.”
Nesbitt said finds such as this can reset the game board on paleontology, in the best sense of the phrase. “This find clearly demonstrates that some fossils that you can barely see can greatly change our understanding of entire groups that you can see today,” he said.
What’s happened since 2019
At the Petrified Forest National Park, where the initial discovery was found in 2019, the lower jaws of at least 70 individuals of Funcusvermis have been recovered as of summer 2022, making the area “the most abundant fossil caecilian-producing bonebed ever discovered,” Kligman said.
Only a handful of bones of Funcusvermis have been found, including upper and lower jaws, a vertebra, and part of a hind-limb, Kligman said. All of the found bones were disarticulated, not as complete skeletons. Without complete skeletons, Kligman and his fellow researchers cannot exactly determine the body length of Funcusvermis, but inferences from isolated elements, such as the lower jaw being less than a quarter of an inch long, indicate that Funcusvermis was a tiny animal.
“Since its discovery in 2017, the Thunderstorm Ridge site has produced a diverse assemblage of over 60 animals ranging from freshwater sharks to dinosaurs,” Kligman said. “Several other new species discovered at this site have been recently described. Many other new species from this site are currently under study and will be published in upcoming years.”
In other words, fully expect more upending of what paleontologists know about the history of fossils.
Reference:
Ben T. Kligman, Bryan M. Gee, Adam D. Marsh, Sterling J. Nesbitt, Matthew E. Smith, William G. Parker, Michelle R. Stocker. Triassic stem caecilian supports dissorophoid origin of living amphibians. Nature, 2023; DOI: 10.1038/s41586-022-05646-5
Earth’s inner core, a hot iron ball the size of Pluto, has stopped spinning faster than the planet’s surface and might now be rotating slower than it, research suggested on Monday.
Roughly 5,000 kilometers (3,100 miles) below the surface we live on, this “planet within the planet” can spin independently because it floats in the liquid metal outer core.
Exactly how the inner core rotates has been a matter of debate between scientists—and the latest research is expected to prove controversial.
What little is known about the inner core comes from measuring the tiny differences in seismic waves—created by earthquakes or sometimes nuclear explosions—as they pass through the middle of the Earth.
Seeking to track the inner core’s movements, new research published in the journal Nature Geoscience analyzed seismic waves from repeating earthquakes over the last six decades.
“We believe the inner core rotates, relative to the Earth’s surface, back and forth, like a swing,” the study’s authors, Xiaodong Song and Yi Yang of China’s Peking University, told AFP.
“One cycle of the swing is about seven decades,” the authors said.
The inner core started rotating slightly faster than the rest of the planet in the early 1970s, the study said.
But it had been slowing down before coming in sync with Earth’s rotation around 2009, it added.
There has been a “negative trend” since, the study said, meaning the inner core is now rotating slower than the surface.
The researchers predicted the next change would occur in the mid-2040s.
They said this rotation timeline roughly lines up with changes in what is called the “length of day”—small variations in the exact time it takes Earth to rotate on its axis.
So far there is little to indicate that what the inner core does has much effect on surface dwellers.
But the researchers said they believed there were physical links between all Earth’s layers, from the inner core to the surface.
“We hope our study can motivate some researchers to build and test models which treat the whole Earth as an integrated dynamic system,” they said.
Experts not involved in the study expressed caution about its findings, pointing to several other theories and warning that many mysteries remain about the center of the Earth.
“This is a very careful study by excellent scientists putting in a lot of data,” said John Vidale, a seismologist at the University of Southern California.
“(But) none of the models explain all the data very well in my opinion,” he added.
Vidale published research last year suggesting that the inner core oscillates far more quickly, swinging around every six years or so.
His work was based on seismic waves from two nuclear explosions in the late 1960s and early 1970s.
That timeframe is around the point when Monday’s research says the inner core was last in sync with Earth’s rotation—which Vidale called “kind of a coincidence”.
Geophysicists ‘divided’
Another theory—which Vidale said has some good evidence supporting it—is that the inner core only moved significantly between 2001 to 2013 and has stayed put since.
Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the inner core’s cycle is every 20 to 30 years, rather than the 70 proposed in the latest study.
“These mathematical models are most likely all incorrect because they explain the observed data but are not required by the data,” Tkalcic said.
“Therefore, the geophysical community will be divided about this finding and the topic will remain controversial.”
He compared seismologists to doctors “who study the internal organs of patients’ bodies using imperfect or limited equipment”.
Lacking something like a CT scan, “our image of the inner Earth is still blurry”, he said, predicting more surprises ahead.
That could include more about a theory that the inner core might have yet another iron ball inside it—like a Russian doll.
“Something’s happening and I think we’re gonna figure it out,” Vidale said. “But it may take a decade.”
Reference:
Yi Yang et al, Multidecadal variation of the Earth’s inner-core rotation, Nature Geoscience (2023). DOI: 10.1038/s41561-022-01112-z
Rotation of the Earth’s inner core changes over decades and has come to near-halt, Nature Geoscience (2023). DOI: 10.1038/s41561-022-01113-y
Correction note (January 25, 2023): Corrects throughout story dated January 23 to say that core’s rotation has slowed compared to Earth’s surface, not changed direction.
Note: The above post is reprinted from materials provided by AFP.
The new study in Geophysical Research Letters shows a previously undiscovered change in tectonic plate thickness across the Denali Fault in Alaska impacts where it is located, shedding light on how major faults and earthquakes occur. Credit: Isabella Gama and Karen Fischer.
When the rigid plates that make up the Earth’s lithosphere brush against one another, they often form visible boundaries, known as faults, on the planet’s surface. Strike-slip faults, such as the San Andreas Fault in California or the Denali Fault in Alaska, are among the most well-known and capable of seriously powerful seismic activity.
Studying these faults can help geoscientists not only better understand the process of plate tectonics, which helped form the planet’s continents and mountains, but also better model their earthquake hazards. The problem is that most studies on these types of faults are (quite literally) shallow, looking only at the upper layer of the Earth’s crust where the faults form.
New research led by Brown University seismologists digs deeper into the Earth, analyzing how the part of the fault that’s near the surface connects to the base of the tectonic plate in the mantle. The scientists found that changes in how thick the plate is and how strong it is deep into the Earth play a key role in the location of Alaska’s Denali Fault, one of the world’s major strike-slip faults.
The findings begin to fill major gaps in understanding about how geological faults behave and appear as they deepen, and they could eventually help lead future researchers to develop better earthquake models on strike-slip faults, regions with frequent and major earthquakes.
“That means when geoscientists model earthquake cycles, they’ll have new information on the strength of the deeper rocks that would be useful for understanding the dynamics of these faults, how stress will build up on them, and how they might rupture in the future,” said Karen M. Fischer, a study author and geophysics professor at Brown.
The study, published in Geophysical Research Letters, was led by Brown alumna Isabella Gama, who completed the work last year while she was a Ph.D. student in the University’s Department of Earth, Environmental and Planetary Sciences. The paper focuses primarily on the Denali Fault, a 1,200-mile-long fault that arcs across most of Alaska and some of Western Canada. In 2002, it was the site of a magnitude 7.9 earthquake that sloshed lakes as far away as Seattle, Texas and New Orleans.
The researchers used new data from a cutting-edge network of seismic stations to create a new 3D model of seismic wave velocities throughout Alaska. With this innovative tool, the researchers discovered changes in the thickness and internal strength of the tectonic plate that Alaska sits on. The model shows how these changes in plate strength, that extend as deeply as about 80 kilometers, feed back into the mechanics of where the Denali fault line is produced.
Geoscientists have known that the Earth’s crust that is south of the Denali Fault is thicker, while north of the fault, the crust is thinner. What’s been less clear is data on changes in the deeper, mantle portion of the plate.
In the new study, the researchers documented for what is believed to be the first time that the Denali Fault forms because of an increase in strength on the northern side of the fault that goes all the way through the upper plate.
They found that when they looked at the base of the plate or lithosphere, the lithosphere is stronger and thicker on the northern side of the fault vs. being much thinner and weaker on the southern side. The deeper part of the plate to the north can act almost as a backstop, they describe in the paper. They conclude that the fault at the surface formed and stayed at the edge of this thicker, stronger lithosphere.
“There has been this controversy that faults in the shallower brittle crust wouldn’t connect to structures in the deepest part of the plate, but here we show that they do,” Gama said. “And this could mean a variety of things. For example, it means that we could expect earthquakes occurring deeper than previously thought for strike-slip faults such as the Denali fault, and that plate motions could occur on clear boundaries that extend from shallow faults all the way to the base of the plate.”
The scientists’ avenue of research opened up when IRIS, a research consortium funded by the National Science Foundation and dedicated to exploring the Earth’s interior, deployed the EarthScope Transportable Array in Alaska from 2014 to 2021. The advanced technology — a large collection of seismographs installed temporarily at sites across the U.S. — gave researchers like Gama and Fischer the capability to measure properties of the deeper crust and mantle that hadn’t been possible before.
The researchers next plan to look closer at other strike-slip fault lines around the world to see if they can find similar variations in the structure of tectonic plates the deeper they go. Other well-known strike-slip fault lines include the San Andreas Fault in California and the Anatolian Fault in Turkey, both of which have caused major earthquakes in the past. The San Andreas Fault, for instance, caused the earthquake of 1906 in San Francisco that killed thousands.
“We hope that projects such as the EarthScope Transportable Array will continue to receive support so that we can obtain higher-resolution images of the Earth’s interior from anywhere on the planet,” Gama said. “We hope to gain a better understanding of plate tectonics by using these images and will begin by investigating how other strike-slip faults appear and behave, looking for parallels with Alaska. This information could then be fed back into improving models for how earthquakes occur.”
This research was supported by the NSF EarthScope Program.
Reference:
Isabella Gama, Karen M. Fischer, Colleen A. Dalton, Zachary Eilon. Variations in Lithospheric Thickness Across the Denali Fault and in Northern Alaska. Geophysical Research Letters, 2022; 49 (24) DOI: 10.1029/2022GL101256
A view of Kīlauea’s summit lava lake. The lava lake is contained within a crater, which is set within the larger Halema‘uma‘u Crater. New research aims to understand the activity that led to the eruption in 2018 in Kīlauea’s lower East Rift Zone. Credit: USGS
In 2015, a submarine volcano in the South Pacific erupted, forming the Hunga Tonga Hunga Ha’apai island, destined to a short, seven-year life. A research team led by the University of Colorado Boulder and Cooperative Institute for Research in Environmental Sciences (CIRES) jumped on the rare opportunity to study the early microbial colonizers of a newly formed landmass and to their surprise, the researchers discovered a unique microbial community that metabolizes sulfur and atmospheric gases, similar to organisms found in deep sea vents or hot springs.
“These types of volcanic eruptions happen all over the world, but they don’t usually produce islands. We had an incredibly unique opportunity,” said Nick Dragone, CIRES PhD student and lead author of the study published this month in mBio. “No one had ever comprehensively studied the microorganisms on this type of island system at such an early stage before.”
“Studying the microbes that first colonize islands provides a glimpse into the earliest stage of ecosystem development — before even plants and animals arrive,” said Noah Fierer, CIRES fellow, professor of ecology and evolutionary biology at CU Boulder and corresponding author on the study.
A multi-institutional team of researchers on the ground collected soil samples from the island, then shipped them to CU Boulder’s campus. Dragone and Fierer could then extract and sequence DNA samples from the samples.
“We didn’t see what we were expecting,” said Dragone. “We thought we’d see organisms you find when a glacier retreats, or cyanobacteria, more typical early colonizer species — but instead we found a unique group of bacteria that metabolize sulfur and atmospheric gases.”
And that wasn’t the only unexpected twist in this work: On January 15, 2022, seven years after it formed, the volcano erupted again, obliterating the entire landmass in the largest volcanic explosion of the 21st century. The eruption completely wiped out the island and eliminated the option for the team to continue monitoring their site.
“We were all expecting the island to stay,” said Dragone. “In fact, the week before the island exploded we were starting to plan a return trip.”
However, the same fickle nature of the Hunga Tonga Hunga Ha’apai (HTHH) that made it explode also explains why the team found such a unique set of microbes on the island. Hunga Tonga was volcanically formed, like Hawaii.
“One of the reasons why we think we see these unique microbes is because of the properties associated with volcanic eruptions: lots of sulfur and hydrogen sulfide gas, which are likely fueling the unique taxa we found,” Dragone said. “The microbes were most similar to those found in hydrothermal vents, hot springs like Yellowstone, and other volcanic systems. Our best guess is the microbes came from those types of sources.”
The expedition to HTHH required close collaboration with members of the government of the Kingdom of Tonga, who were willing to work with researchers to collect samples from land normally not visited by international guests. Coordination took years of work by collaborators at the Sea Education Association and NASA: a Tongan observer must approve and oversee any sample collection that takes place within the Kingdom.
“This work brought in so many people from around the world, and we learned so much. We are of course disappointed that the island is gone, but now we have a lot of predictions about what happens when islands form,” said Dragone. “So if something formed again, we would love to go there and collect more data. We would have a game plan of how to study it.”
Reference:
Nicholas B. Dragone, Kerry Whittaker, Olivia M. Lord, Emily A. Burke, Helen Dufel, Emily Hite, Farley Miller, Gabrielle Page, Dan Slayback, Noah Fierer. The Early Microbial Colonizers of a Short-Lived Volcanic Island in the Kingdom of Tonga. mBio, 2023; DOI: 10.1128/mbio.03313-22
(A) Completely unhatched egg from the clutch P43. (B) Almost fully intact circular outline of egg possibly indicating it to be unhatched and no loose eggshells are found in the clutch P6. (C) Compressed egg from clutch DR10 showing hatching window (arrow showing gap) and few eggshells collected just around the hatching window (circled) which possibly represent the remnants of hatching window. (D) Egg from clutch P26 showing curved outline. (E) Deformed egg from clutch P30 showing egg surfaces slipping past each other. Credit: Dhiman et al., 2023, PLOS ONE, CC-BY 4.0 (creativecommons.org/licenses/by/4.0/)
The discovery of more than 250 fossilized eggs reveals intimate details about the lives of titanosaurs in the Indian subcontinent, according to a study published January 18, 2022 in the open-access journal PLOS ONE by Harsha Dhiman of the University of Delhi, New Delhi and colleagues.
The Lameta Formation, located in the Narmada Valley of central India, is well-known for fossils of dinosaur skeletons and eggs of the Late Cretaceous Period. Recent work in the area uncovered 92 nesting sites containing a total of 256 fossil eggs belonging to titanosaurs, which were among the largest dinosaurs to have ever lived. Detailed examination of these nests has allowed Dhiman and colleagues to make inferences about the life habits of these dinosaurs.
The authors identified six different egg-species (oospecies), suggesting a higher diversity of titanosaurs than is represented by skeletal remains from this region. Based on the layout of the nests, the team inferred that these dinosaurs buried their eggs in shallow pits like modern-day crocodiles. Certain pathologies found in the eggs, such as a rare case of an “egg-in-egg,” indicate that titanosaur sauropods had a reproductive physiology that parallels that of birds and possibly laid their eggs in a sequential manner as seen in modern birds. The presence of many nests in the same area suggests these dinosaurs exhibited colonial nesting behavior like many modern birds. But the close spacing of the nests left little room for adult dinosaurs, supporting the idea that adults left the hatchlings (newborns) to fend for themselves.
Details of dinosaur reproductive habits can be difficult to determine. These fossil nests provide a wealth of data about some of the largest dinosaurs in history, and they come from a time shortly before the age of dinosaurs came to an end. The insights gleaned from this study contribute significantly to paleontologists’ understanding of how dinosaurs lived and evolved.
Harsha Dhiman, lead author of the research, adds: “Our research has revealed the presence of an extensive hatchery of titanosaur sauropod dinosaurs in the study area and offers new insights into the conditions of nest preservation and reproductive strategies of titanosaur sauropod dinosaurs just before they went extinct.”
Guntupalli V.R. Prasad, co-author and leader of the research team, adds: “Together with dinosaur nests from Jabalpur in the upper Narmada valley in the east and those from Balasinor in the west, the new nesting sites from Dhar District in Madhya Pradesh (Central India), covering an east-west stretch of about 1000 km, constitute one of the largest dinosaur hatcheries in the world.”
Reference:
Harsha Dhiman et al, New Late Cretaceous titanosaur sauropod dinosaur egg clutches from lower Narmada valley, India: Palaeobiology and taphonomy, PLoS ONE (2023). DOI: 10.1371/journal.pone.0278242
Scanning electron microscope images of tiny, ancient planktonic foraminifera, recovered from Gubbio, Italy. Credit: Gabriella Kitch
Nearly 100 million years ago, the Earth experienced an extreme environmental disruption that choked oxygen from the oceans and led to elevated marine extinction levels that affected the entire globe.
Now, in a pair of complementary new studies, two Northwestern University-led teams of geoscientists report new findings on the chronology and character of events that led to this occurrence, known as Ocean Anoxic Event 2 (OAE2), which was co-discovered more than 40 years ago by late Northwestern professor Seymour Schlanger.
By studying preserved planktonic microfossils and bulk sediment extracted from three sites around the world, the team collected direct evidence indicating that ocean acidification occurred during the earliest stages of the event, due to carbon dioxide (CO2) emissions from the eruption of massive volcanic complexes on the sea floor.
In one of the new studies, the researchers also propose a new hypothesis to explain why ocean acidification led to a strange blip of cooler temperatures (dubbed the “Plenus Cold Event”), which briefly interrupted the otherwise intensely hot greenhouse period.
By analyzing how an influx of CO2 from volcanoes affected ocean chemistry, biomineralization and climate, the researchers hope to better understand how today’s Earth is responding to an increase of CO2 due to human activities, which potentially could lead to solutions for adapting to and mitigating anticipated consequences.
A paper, with findings from deep-sea cores, including a newly drilled site near southwest Australia, will be published on Thursday (Jan. 19) in the journal Nature Geoscience. A complementary paper detailing findings from ancient malformed microfossils was published on Dec. 13, in the Nature journal Communications Earth & Environment.
“Ocean acidification and anoxia resulted from massive CO2 release from volcanoes,” said Northwestern’s Brad Sageman, a senior co-author of both studies. “These major CO2 emission events in Earth’s history provide the best examples we have of how the Earth system responds to very large inputs of CO2. This work has fundamental applicability to our understanding of the climate system, and our ability to predict what will happen in the future.”
“Based on isotopic analyses of the element calcium, we propose a possible explanation for the Plenus Cold Event, which is that a slowdown in biocalcification rates due to ocean acidification allowed alkalinity to accumulate in seawater,” said Northwestern’s Andrew Jacobson, a senior co-author of both studies. “Increased alkalinity led to a drawdown of CO2 from the atmosphere. It could very well be the case that such cooling is a predictable—but transitory—consequence of warming. Our results for OAE2 provide a geological analog for ocean alkalinity enhancement, which is a leading strategy for mitigating the anthropogenic climate crisis.”
Experts on climate during the Cretaceous Period and isotope geochemistry, Sageman and Jacobson are both professors of Earth and planetary sciences in Northwestern’s Weinberg College of Arts and Sciences. The two studies were led by their former Ph.D. students, Gabriella Kitch and Matthew M. Jones, who initiated this research while at Northwestern.
Based on over 40 years of study, OAE2 is one of the most significant perturbations of the global carbon cycle to have occurred on planet Earth. Researchers have hypothesized that oxygen levels in the oceans dropped so low during OAE2 that marine extinction rates increased significantly. To better understand this event and the conditions leading up to it, the researchers studied ancient organic carbon-rich and fossil-bearing layers of sedimentary rock in widely distributed outcrop sites, as well as deep-sea cores obtained by the International Ocean Discovery Program (IODP).
The sites included Gubbio, Italy (a famous area in mainland Italy that used to be a deep ocean basin), the Western Interior Seaway (an ancient seabed stretching from the Gulf of Mexico to the Arctic Ocean in North America) and a several deep-sea sites, including a new one from the eastern Indian Ocean, offshore of southwest Australia.
Deep-sea cores provide an invaluable record of conditions in parts of the paleo-oceans that were completely unknown prior to the development of ocean drilling programs. In all three cores, the researchers focused on sections from the mid-Cretaceous Period, just before the boundary of the Turonian and Cenomanian Ages, in order to reconstruct conditions leading up to OAE2.
“The challenging part of studying ocean acidification in the geologic past is that we don’t have ancient seawater,” said Jones, who is now a Peter Buck Postdoctoral Fellow at the Smithsonian Institution. “It’s extremely rare that you would find anything that resembles ancient seawater trapped in a rock or mineral. So, we have to look for indirect evidence, particularly changes in the chemistry of fossil shells and lithified sediments.”
Malformed fossils
For the study published in Communications Earth & Environment, Kitch and her co-authors focused on fossilized foraminifera, ocean-dwelling unicellular organisms with an external shell made of calcium carbonate, which were collected at the Gubbio site by an Italian collaborator, Professor Rodolfo Coccioni at the University of Urbino.
Kitch and her collaborators were drawn to the Gubbio specimens because Coccioni’s optical observations and measurements of their shells showed abnormalities, including a consistent pattern of “dwarfing,” or a decrease in overall size, coincident with the onset of OAE2.
“These are optical signs of stress,” said Kitch, who is now a Knauss Fellow at the National Oceanic and Atmospheric Administration. “We hypothesized that the stress could have been caused by ocean acidification, which then affected the way the organisms built their shells.”
To test this hypothesis, Kitch analyzed the calcium isotope composition of the fossils. After dissolving the fossilized shells and analyzing their composition with a thermal ionization mass spectrometer, the Northwestern team observed that calcium isotope ratios shifted in the malformed specimens in a way consistent with stress from acidification.
“This is the first paper to marry calcium isotopic evidence for acidification with observations of biological indicators of stress,” Sageman said. “It’s these independent biological and geochemical observations that confirm there was an impact on biomineralization during the onset of OAE2.”
‘Cause-and-effect relationship’
For the second study, published in Nature Geoscience, Jones and his co-authors focused on deep sea cores of lithified sediments from offshore southwest Australia, which he and colleagues collected during an IODP expedition in 2017. For this piece of the puzzle, the researchers were less interested in what was in the sediment and more interested in what the sediment was noticeably lacking.
The core contains stacks of limestone, rich with calcium carbonate minerals, but is punctuated by a sudden absence of carbonate right before OAE2.
“For this time interval, we found that calcite is absent,” Jones said. “There are no carbonate minerals. This section of the core is visibly darker; it jumped right out at us. The carbonate either dissolved at the seafloor or fewer organisms were making calcium carbonate shells in the surface water. It’s a direct observation of an ocean acidification event.”
In his geochemical analyses conducted in collaboration with Professor Dave Selby at Durham University, Jones noticed that carbonate was not the only component showing significant change. Coincident with the onset of OAE2, there is also a marked shift in osmium isotope ratios that signal a massive input of mantle-derived osmium, the fingerprint of a major submarine volcanism event. This observation is consistent with the work of many other researchers, who have found evidence for the eruption of a large igneous province (LIP) preceding OAE2.
These events of massive volcanic activity occur throughout Earth history and are increasingly recognized as major agents of global change. Many LIPs were submarine, injecting tons of CO2 directly into the oceans. When CO2 dissolves into seawater, it forms a weak acid that can inhibit calcium carbonate formation and may even dissolve preexisting carbonate shells and sediments.
“Right at the onset of OAE2, osmium isotope ratios shift to really, really low values,” Jones said. “The only way that can happen is through a large igneous province eruption. That helps us establish a cause-and-effect relationship. We can see the evidence that volcanoes were really active because the osmium values crash. Then, suddenly, there’s no carbonate.”
Biological feedback
While ocean acidification following a LIP is not necessarily surprising, the Northwestern team did uncover something unusual. Acidic conditions during OAE2 lasted much longer than other widely recognized acidification events in the ancient world. Jones posits that the lack of oxygen in ocean waters may have extended the acidification state.
“Organisms that consumed sinking plankton and organic matter in the water column during OAE2 were also respiring CO2, which contributed to the ocean acidification that was initially triggered by CO2 emission from LIP volcanic activity,” Jones said. “So, marine anoxia can be a ‘positive feedback’ on ocean acidification. That’s important because the global ocean today, in addition to having its pH levels decrease, is losing oxygen content as well. That suggests that decreases in oxygen may prolong acidification and highlights that the two phenomena are closely related.”
In Kitch’s study, she found that biology played yet another role during the event. Global warming and ocean acidification did not just passively affect foraminifera. The organisms also actively responded by reducing calcification rates when building their shells. As calcification slowed, the foraminifera consumed less alkalinity from seawater, which helped buffer the ocean’s increasing acidity. This also heightened the ocean’s ability to absorb CO2, potentially triggering the Plenus Cold Event.
“We call this phase a ‘hothouse period’ because temperatures were really, really warm,” Kitch said. “However, there is evidence for relative cooling during the OAE2 interval. No one has been able to explain why this cooling happened. Our study shows that by decreasing carbonate production in the ocean, you actually bump up alkalinity, which gives the ocean a buffering capacity to absorb CO2. The ocean suddenly has the capacity to draw down CO2 and balance carbon fluxes.”
Stabilization ‘comes with a cost’
But just because brief cooling interrupted this otherwise hothouse period, the researchers caution that the oceans’ natural ability to buffer CO2 is not the answer to current human-caused climate change. Sageman explains the scenario by comparing climate change to cancer.
“It’s like if a patient had cancer, and the cancer went away for a month,” Sageman said. “But then it came back and killed the patient. Don’t get fooled into thinking the ocean will cool us off and everything will be OK. It was cool for a tiny sliver of time.”
“Although the Earth rebounded and healed itself, extinctions in the marine realm helped achieve that,” Jacobson added. “The Earth has some stabilizing feedbacks, but they come with a cost.”
Reference:
Matthew Jones, Abrupt episode of mid-Cretaceous ocean acidification triggered by massive volcanism, Nature Geoscience (2023). DOI: 10.1038/s41561-022-01115-w. www.nature.com/articles/s41561-022-01115-w
Gabriella D. Kitch et al, Calcium isotope ratios of malformed foraminifera reveal biocalcification stress preceded Oceanic Anoxic Event 2, Communications Earth & Environment (2022). DOI: 10.1038/s43247-022-00641-0
Note: The above post is reprinted from materials provided by Northwestern University.
Dimitri Laurent explores a typical gallery in the Nébélé Cave, which was formed by sulfuric acid speleogenesis. You can see a deep notch that indicates the former presence of a river, and sodium sulfate on the left that is produced from weathering by sulfuric acid. Credit: Christophe Durlet
A study published in the journal Geology uses isotopes of sulfur to fingerprint the sources of sulfuric acid that have carved unique and beautiful cave systems in the Pyrenees mountains of southern France.
Networks of caves form when carbonate rocks like limestone dissolve. These are also known as karsts. In most caves, water has trickled down through Earth’s surface, picking up carbon dioxide and becoming slightly acidic along the way; this is the same type of mild carbonic acid that you’ll find in a can of soda that has carbon dioxide dissolved in it.
A rarer type of cave forms from transport of fluids up through the crust and through fault zones, forming vertical caves that can connect with horizontal caverns, forming large networks. In some cases, when sulfur is present, sulfuric acid forms and acts to dissolve limestone much faster—forming caves 10–100 times faster than its carbonic acid counterparts.
When sulfur compounds are present in water or in the minerals in the cave walls, chemical-loving bacteria use the sulfate as an energy source, producing hydrogen sulfide as a by-product. Oxidation of this hydrogen sulfide then forms sulfuric acid. Sulfuric acid can also come from hydrothermal springs or from minerals within the rock, and both are true in the northern Pyrenees.
Sulfur comes in four different isotopes—each weighing a slightly different amount. Researchers were able to estimate the relative contributions of sulfuric acid from different sources by using these isotopes as a marker of where the sulfur originated.
The large network of limestone caves in the foothills of the French Pyrenees mountains was formed by a combination of acid-forming processes that left their imprint on the minerals left behind. Sulfur-containing minerals like gypsum and mirabilite in the caves hinted that sulfuric acid was involved in their formation. Mirabilite is a rare mineral that forms long, thin crystals up to 50 cm in length that radiate out like flowers.
For the first time, researchers studying limestone caves carved out by sulfuric acid have estimated how much of the cave-forming acid was produced by bacteria within the cave versus how much was produced by thermochemical processes. This innovation in separating the various sources of limestone dissolution has also allowed them to make the first estimate of how much carbon dioxide was emitted by the formation of the caves.
Dimitri Laurent, lead author of this study, explains, “We tried to identify hydrothermal springs close to measured faults, and then we contacted the local speleological clubs to visit the caves near the springs. We see that at depth in the Northern Pyrenees, in the northern foothills, there are Triassic evaporites that produced hydrogen sulfide through thermochemical processes 65 million years ago.”
That hydrogen sulfide then traveled through fractures in the rock and has been trapped within the cave host rock since then. As water began to dissolve this sulfur-rich rock, the fossil hydrogen sulfide was liberated and oxidized to form sulfuric acid. The Triassic evaporites have also delivered sulfates to the caves more recently, via deep hydrothermal fluids, which are then used by bacteria within the cave.
Combining chemistry with physical observations of the landscape, the researchers reconstructed the history of how these spectacular caves came to be.
Reference:
D. Laurent et al, Unravelling biotic versus abiotic processes in the development of large sulfuric-acid karsts, Geology (2023). DOI: 10.1130/G50658.1
A view from the summit of Hunga Tonga-Hunga Ha’apai in 2017 (CC BY-SA 4.0 Damien Grouille/Wikimedia Commons)
A new analysis of seismic data recorded after the massively violent eruption of the underwater volcano Hunga Tonga-Hunga Ha’apai, on January 15, 2022, has revealed new and useful information on the sequence of events. Kotaro Tarumi and Kazunori Yoshizawa at Hokkaido University discuss their methods and findings in an article in Earth and Planetary Science Letters.
“We showed that the eruption consisted of two distinct sequences of events, some of which occurred quasi-periodically in the first sequence. It will be worthwhile to investigate the mechanisms involved in such eruption cycles further,” says seismologist and geophysicist Yoshizawa.
The volcano generated seismic, tsunami and atmospheric waves that were recorded worldwide. Recent studies have estimated that it was one of the most energetic eruptions recorded by modern instruments.
“Eruption episodes are difficult to analyze fully from seismic surface waves, but we have teased out more details using what are called teleseismic-P waves,” says Ph.D. student Tarumi. These are seismic waves that have traveled through the planet to locations distant from the eruption site. In this case, the team used seismic data collected from sites as far as at a 93-degree angle around the circumference of the planet.
The team’s “back-projection” analysis successfully detected the locations and timing of multiple explosions, even though P-waves from each eruption overlapped and were masked by other seismic signals and noises.
The back-projection technique reverses the transmission of seismic signals to reveal details of a potential source that radiated seismic waves. It was originally developed and applied for imaging the source processes of large earthquakes, but is now proving equally applicable to large scale volcanic events.
The results revealed that the sequence of eruptions occurred in two main parts. The first sequence began at 04:02 UTC on January 15, then escalated into major explosions at 04:15 UTC and 200 to 300 seconds after. The entire sequence lasted at least until 04:35 UTC.
A second sequence of eruptions began about four hours later and continued from six to seven minutes, including a massive eruption at 08:31. Satellite imagery recorded the resulting dramatic ash cloud from the first eruption sequence, but until now the precise details of the underwater events have remained elusive.
One interesting finding was that significant explosive eruptions intermittently occurred at 270 to 280 second intervals, a frequency suggesting a resonance effect with the atmosphere and the Earth. “This apparent agreement of the eruption cycle and the atmospheric resonant oscillation with the Earth could be coincidental, but it certainly deserves further exploration,” Yoshizawa concludes.
Reference:
Kotaro Tarumi et al, Eruption sequence of the 2022 Hunga Tonga-Hunga Ha’apai explosion from back-projection of teleseismic P waves, Earth and Planetary Science Letters (2023). DOI: 10.1016/j.epsl.2022.117966
The extensive accumulations of obsidian artefacts in level C. a,b, General view of the level and detail of artefact density along the MS cliff (a) and inset (b). c,d, General view (c) and detail (d) of the artefact concentration (mainly handaxes) in the test pit of 2004. Credit: Nature Ecology & Evolution (2023). DOI: 10.1038/s41559-022-01970-1
A team of researchers affiliated with several institutions in Spain, working with two colleagues from France and another from Germany has discovered an Obsidian handaxe-making workshop from 1.2 million years ago in the Awash valley in Ethiopia. In their paper published in the journal Nature Ecology & Evolution, the group describes where the handaxes were found, their condition and their age.
The Stone Age lasted from approximately 2.6 million years ago, to approximately 3,300 BCE, when the Bronze Age began. Historians generally break the era down into the Paleolithic, Mesolithic and Neolithic periods. Prior research has shown that “knapping workshops” appeared sometime during the Middle Pleistocene, in Europe—approximately 774,000 to 129,000 years ago.
Such workshops developed as tool-making evolved into a skill. Individuals who developed such skills worked together in workshops to crank out enough of whatever tools were needed by those in the general area. One such tool was the handaxe, which could be used for chopping or as a weapon.
Handaxes were made by chipping bits off of a stone to make a sharp edge. They were not attached to anything; they were simply held in the hand when in use. The stones used were typically flint or, in latter times, obsidian—a type of volcanic glass. Obsidian, even in modern times, is considered a difficult material to work with because it is so rough on the hands. In this new effort the researchers have found evidence of an obsidian handaxe knapping workshop established far earlier than one has ever been seen before.
The researchers were working at the Melka Kunture dig site when they found a handaxe buried in a layer of sediment. They soon found more. They found 578 in all, and all but three were made of obsidian. Dating of the material around the axes showed them to be from approximately 1.2 million years ago.
Study of the axes showed them all to have been crafted in like manner, indicating that the researchers had found an ancient knapping workshop. The find marks the oldest known example of such a workshop, and the first of its kind not in Europe. The researchers note that the work was done so long ago that they are not even able to identify the hominids that made them.
Reference:
Margherita Mussi et al, A surge in obsidian exploitation more than 1.2 million years ago at Simbiro III (Melka Kunture, Upper Awash, Ethiopia), Nature Ecology & Evolution (2023). DOI: 10.1038/s41559-022-01970-1
Note: The above post is reprinted from materials provided by Science X Network.
A figure from the study showing teeth from a megaraptor dinosaur from various view points. The black tooth preserves most of the tooth crow. The tan tooth is missing the crown apex and base. Credit: Davis et al.
A study led by The University of Texas at Austin is providing a glimpse into dinosaur and bird diversity in Patagonia during the Late Cretaceous, just before the non-avian dinosaurs went extinct.
The fossils represent the first record of theropods — a dinosaur group that includes both modern birds and their closest non-avian dinosaur relatives — from the Chilean portion of Patagonia. The researchers’ finds include giant megaraptors with large sickle-like claws and birds from the group that also includes today’s moA study is providing a glimpse into dinosaur and bird diversity in Patagonia during the Late Cretaceous, just before the non-avian dinosaurs went extinct.dern species.
“The fauna of Patagonia leading up to the mass extinction was really diverse,” said lead author Sarah Davis, who completed this work as part of her doctoral studies with Professor Julia Clarke at the UT Jackson School of Geosciences Department of Geological Sciences. “You’ve got your large theropod carnivores and smaller carnivores as well as these bird groups coexisting alongside other reptiles and small mammals.”
The study was published in the Journal of South American Earth Sciences.
Since 2017, members of the Clarke lab, including graduate and undergraduate students, have joined scientific collaborators from Chile in Patagonia to collect fossils and build a record of ancient life from the region. Over the years, researchers have found abundant plant and animal fossils from before the asteroid strike that killed off the dinosaurs.
The study focuses specifically on theropods, with the fossils dating from 66 to 75 million years ago.
Non-avian theropod dinosaurs were mostly carnivorous, and include the top predators in the food chain. This study shows that in prehistoric Patagonia, these predators included dinosaurs from two groups — megaraptors and unenlagiines.
Reaching over 25 feet long, megaraptors were among the larger theropod dinosaurs in South America during the Late Cretaceous. The unenlagiines — a group with members that ranged from chicken-sized to over 10 feet tall — were probably covered with feathers, just like their close relative the velociraptor. The unenlagiinae fossils described in the study are the southernmost known instance of this dinosaur group.
The bird fossils were also from two groups — enantiornithines and ornithurines. Although now extinct, enantiornithines were the most diverse and abundant birds millions of years ago. These resembled sparrows — but with beaks lined with teeth. The group ornithurae includes all modern birds living today. The ones living in ancient Patagonia may have resembled a goose or duck, though the fossils are too fragmentary to tell for sure.
The researchers identified the theropods from small fossil fragments; the dinosaurs mostly from teeth and toes, the birds from small bone pieces. Davis said that the enamel glinting on the dinosaur teeth helped with spotting them among the rocky terrain.
Some researchers have suggested that the Southern Hemisphere faced less extreme or more gradual climatic changes than the Northern Hemisphere after the asteroid strike. This may have made Patagonia, and other places in the Southern Hemisphere, a refuge for birds and mammals and other life that survived the extinction. Davis said that this study can aid in investigating this theory by building up a record of ancient life before and after the extinction event.
Study co-author Marcelo Leppe, the director of the Antarctic Institute of Chile, said that these past records are key to understanding life as it exists today.
“We still need to know how life made its way in that apocalyptic scenario and gave rise to our southern environments in South America, New Zealand and Australia,” he said. “Here theropods are still present — no longer as dinosaurs as imposing as megaraptorids — but as the diverse array of birds found in the forests, swamps and marshes of Patagonia, and in Antarctica and Australia.”
The research was funded by the National Science Foundation, the National Agency for Research and Development of Chile, and the Jackson School of Geosciences.
The study’s co-authors include Clarke and researchers at the University of Chile, Major University, the University of Concepción and the Chilean National Museum of Natural History.
Reference:
Sarah N. Davis, Sergio Soto-Acuña, Roy A. Fernández, Jared Amudeo-Plaza, Marcelo A. Leppe, David Rubilar-Rogers, Alexander O. Vargas, Julia A. Clarke. New records of Theropoda from a Late Cretaceous (Campanian-Maastrichtian) locality in the Magallanes-Austral Basin, Patagonia, and insights into end Cretaceous theropod diversity. Journal of South American Earth Sciences, 2023; 122: 104163 DOI: 10.1016/j.jsames.2022.104163
Boudinage in brecciated dolostone rocks of the Panamint Range (Wildrose Area, Death Valley National Park). New research shows that periclase is stronger than bridgmanite in earth’s lower mantle, analogous to boudins developing in rigid (“stronger”) rocks among less competent (“weaker”) rocks. Credit: Jennifer M. Jackson, Caltech
As you are reading this, more than 400 miles below you is a massive world of extreme temperatures and pressures that has been churning and evolving for longer than humans have been on the planet. Now, a detailed new model from Caltech researchers illustrates the surprising behavior of minerals deep in the planet’s interior over millions of years and shows that the processes are actually happening in a manner completely opposite to what had been previously theorized.
The research was conducted by an international team of scientists, including Jennifer M. Jackson, William E. Leonhard Professor of Mineral Physics. A paper describing the study appears in the journal Nature on January 11.
“Despite the enormous size of the planet, the deeper parts are often overlooked because they’re literally out of reach—we can’t sample them,” Jackson says. “Additionally, these processes are so slow they seem imperceptible to us. But the flow in the lower mantle communicates with everything it touches; it’s a deep engine that affects plate tectonics and may control volcanic activity.”
The lower mantle of the planet is solid rock, but over hundreds of millions of years it slowly oozes, like a thick caramel, carrying heat throughout the planet’s interior in a process called convection.
Many questions remain unanswered about the mechanisms that allow this convection to happen. The extreme temperatures and pressures at the lower mantle—up to 135 gigapascals and thousands of degrees Fahrenheit—make it difficult to simulate in the laboratory.
For reference, the pressure at the lower mantle is almost a thousand times the pressure at the deepest point of the ocean. Thus, while many lab experiments on mineral physics have provided hypotheses about the behavior of lower mantle rocks, the processes occurring at geologic timescales to drive the sluggish flow of lower-mantle convection have been uncertain.
The lower mantle is mostly made up of a magnesium silicate called bridgmanite yet also includes a small but significant amount of a magnesium oxide called periclase mixed in among the bridgmanite in addition to small amounts of other minerals. Laboratory experiments had previously shown that periclase is weaker than bridgmanite and deforms more easily, but these experiments did not take into account how minerals behave on a timescale of millions of years. When incorporating these timescales into a complex computational model, Jackson and colleagues found that grains of periclase are actually stronger than the bridgmanite surrounding them.
“We can use the analogy of boudinage in the rock record [image at right], where boudins, which is French for sausage, develop in a rigid, ‘stronger,’ rock layer among less competent, ‘weaker,’ rock,” Jackson says.
“As another analogy, think about chunky peanut butter,” Jackson explains. “We had thought for decades that periclase was the ‘oil’ in peanut butter, and acted as the lubricant between the harder grains of bridgmanite. Based on this new study, it turns out that periclase grains act as the ‘nuts’ in chunky peanut butter. Periclase grains just go with the flow but don’t affect the viscous behavior, except in circumstances when the grains are strongly concentrated. We show that under pressure, mobility is much slower in periclase compared to bridgmanite. There is an inversion of behavior: periclase hardly deforms, while the major phase, bridgmanite, controls deformation in Earth’s deep mantle.”
Understanding these extreme processes happening far below our feet is important for creating accurate four-dimensional simulations of our planet, and it helps us comprehend more about other planets as well. Thousands of exoplanets (planets outside of our solar system) have now been confirmed, and discovering more about mineral physics under extreme conditions gives new insights into the evolution of planets radically different from our own.
Reference:
Patrick Cordier et al, Periclase deforms more slowly than bridgmanite under mantle conditions, Nature (2023). DOI: 10.1038/s41586-022-05410-9
A. The lithospheric breakup-collision coupling system, in which collisional thickening of the continental crust is coupled with lithospheric breakup due to asthenospheric upwelling for active rifting. B. The seafloor spreading-lithospheric subduction coupling system, in which the oceanic slab is subducted to depths of >80–100 km for the gravitational pull, providing far-field stresses for passive rifting. Credit: Science China Press
The emergence of plate tectonics in the late 1960s led to a paradigm shift from fixism to mobilism of global tectonics, providing a unifying context for the previously disparate disciplines of Earth sciences. Although plate tectonics was originally defined by the kinematics of the Earth’s outer shell (lithosphere) on the underlying asthenosphere, a number of dynamic interpretations for its operation have developed in the past five decades.
This has advanced plate tectonics as a holistic theory of kinematics-dynamics for the motion of large and small plates in both horizontal and vertical directions. Because modern plate boundaries occur as a global network of mobile belts on the spherical Earth, the difficulty was encountered in deciphering the operation of ancient plate tectonics in geological history.
A synthetic study presented by Prof. Yong-Fei Zheng at University of Science and Technology of China and published in Science China Earth Sciences, focuses on an advanced version of plate tectonics in its basic principles and geological corollaries along active and fossil plate margins. This is achieved by inspection of natural observations and their tectonic interpretations in the fields of geology, geochemistry, geophysics and geodynamics.
The advances are significant and fundamental to our understanding of various phenomena at present and past plate margins, setting general standards to determine the spatiotemporal relationships between material movement, energy transfer, dynamic regime and geothermal gradient along plate margins. Therefore, they provide new insights not only into many first-order problems regarding tectonic occurrences in continental regions but also into the origin of hotspot magmatism in relation to the mantle plume hypothesis.
According to the geometric structure, dynamic regime and thermal state of plate margins, Zheng highlights the importance of plate divergent-convergent coupling systems in the operation of plate tectonics on Earth. These coupling systems are categorized into two types.
One is the lithospheric breakup-collision due to active rifting, with the push effect of lithospheric breakup on collisional thickening and shallow subduction to smaller depths of <60–80 km. The other is the seafloor spreading-lithospheric subduction due to passive rifting, with the pull effect of subducting oceanic slab on deep subduction to greater depths of >80–100 km. Because plates may be of different sizes since their generation, they may move in different directions to exchange matter and energy not only between lithosphere and asthenosphere but also between the crust and the mantle.
As generalized by Zheng, matter and energy transfers at plate margins proceed in bottom-up and top-down ways, respectively. They correspond to changes of not only their dynamic regime from extension to compression and from compression to extension but also their thermal state from hot to warm and from cold to warm. In the rifting zone, heat is preferentially transferred from the asthenosphere into the crust, resulting in heat loss from the Earth’s interior to exterior. In subduction zones, the cold lithosphere sinks into the hotter asthenosphere, leading to cooling of the Earth’s interior.
Therefore, both rifting and subduction zones are two basic sites for the matter and energy exchanges between the Earth’s spheres. As such, recognition of their geodynamic mechanisms and tectonic effects on the formation and evolution of plate margins is the key to advance plate tectonics.
Although modern plate tectonics is characterized by a global network of mobile belts on the present Earth, its operation on the ancient Earth history can be tested by inspection of plate divergent-convergent coupling systems. This is outlined by Zheng through characterizing two of the fundamental components in plate tectonics. One is the initiation of rifting zones, eventually forming new ocean basins, and the other is the initiation of subduction zones, recycling the crust into the mantle.
Subduction initiation and lithospheric rifting are the two key processes for the onset of plate tectonics. Their operation has great bearing on the structure, processes and geodynamics of plate margins. These elements also fundamentally explain the onset and operation of plate tectonics in Precambrian time.
Reference:
Yong-Fei Zheng, Plate tectonics in the twenty-first century, Science China Earth Sciences (2022). DOI: 10.1007/s11430-022-1011-9
Note: The above post is reprinted from materials provided by Science China Press.
Superdeep diamonds that originate hundreds of kilometers beneath Earth’s surface are like time capsules revealing how they were formed, thanks to unique combinations of minerals trapped inside the diamonds. Credit: University of Alberta
A unique combination of minerals trapped inside a “superdeep” diamond that originated hundreds of kilometers beneath Earth’s surface sheds new light on plate tectonics, the geological processes that give rise to mountains, oceans and continents.
One of the inclusions found in the diamond was a very pure example of the mineral olivine, a variety of which is more commonly known as the gemstone peridot. Most olivine found on Earth has some iron in it, so the purity of this olivine speaks to the unique conditions under which it was formed, according to an international study published last week in Nature.
The olivine’s purity, as well as some of the other minerals that were inclusions in this diamond, indicate a far deeper origin than usual for a diamond, between what’s called the transition zone and the lower mantle zone—420 kilometers to 660 kilometers beneath Earth’s surface. It also shows that the environment between these zones has an extremely variable oxygen content.
“To make this extreme composition [of olivine] and the overall mineral assemblage that we’ve got, the only way of doing that is to have a very deeply subducted oceanic plate or slab that goes down into the mantle, so you’re essentially pushing material from the surface of the Earth into the depths of the Earth,” says study co-author Graham Pearson, professor in the Department of Earth and Atmospheric Sciences and director of the Diamond Exploration and Research Training School.
“You get huge gradients in oxygen activity when you do that, and these big gradients are very conducive to driving extreme variations in composition of minerals,” he adds.
An understanding of these oxygen gradients helps explain how plate tectonics brings volatile elements back up into the mantle, and can also offer clues to how superdeep diamonds are formed—knowledge that can’t be gained any other way, according to Pearson.
“You can see oceanic slabs descending into the Earth in seismic images, but you don’t have any idea of the detailed structures they develop, or the mechanisms and chemistry going on in those slabs,” he says. “These diamonds provide a unique trace of that detailed chemical evolution as the slab’s going down.
“It’s amazing to document the buckling of these huge oceanic plates as they descend into the bowels of the Earth, by probing minerals that are tens of microns in size, trapped in diamonds.”
As we gain more insight into the movement of those slabs into the mantle, called subduction, we’re able to better understand plate tectonics, Pearson explains.
“Subduction drives the whole of plate tectonics. If you don’t understand the details of subduction, that limits your understanding of how plate tectonics work.”
Plate tectonics is responsible for the formation of everything from mountains to oceans to continents, and even has an influence on Earth’s climate. Advancing our understanding of plate tectonics could also help us better comprehend natural events like earthquakes and volcanic eruptions, Pearson notes.
Diamonds are a scientist’s best friend
Superdeep diamonds, which originate from depths of more than 300 kilometers below Earth’s surface, are a treasure trove of scientific information because diamonds are uniquely able to preserve information about where they’re formed, including many of the physical and chemical processes that occurred during their formation.
Most other minerals lose much of that information by the time they make their way to Earth’s surface, but as Pearson explains, diamonds act almost as time capsules.
“There are many things at the surface of the Earth that can only be explained by processes happening at deep depths,” says Pearson.
“If you want to explain things you see at the surface—whether it’s economic mineralization, surface uplift or subsidence phenomena related to oil-bearing basins—you need an understanding of the structure, mechanics and properties of the deep Earth. Diamond is uniquely able to bolster that understanding.”
Reference:
Fabrizio Nestola et al, Extreme redox variations in a superdeep diamond from a subducted slab, Nature (2023). DOI: 10.1038/s41586-022-05392-8
The Northwestern research team of seismologists and statisticians has developed an earthquake probability model that is more comprehensive and realistic than what is currently available.
Results of a new study by Northwestern University researchers will help earthquake scientists better deal with seismology’s most important problem: when to expect the next big earthquake on a fault.
Seismologists commonly assume that big earthquakes on faults are fairly regular and that the next quake will occur after approximately the same amount of time as between the previous two. Unfortunately, Earth often doesn’t work that way. Although earthquakes sometimes come sooner or later than expected, seismologists didn’t always have a way to describe this.
Now they do. The Northwestern research team of seismologists and statisticians has developed an earthquake probability model that is more comprehensive and realistic than what is currently available. Instead of just using the average time between past earthquakes to forecast the next one, the new model considers the specific order and timing of previous earthquakes. It helps explain the puzzling fact that earthquakes sometimes come in clusters—groups with relatively short times between them, separated by longer times without earthquakes.
“Considering the full earthquake history, rather than just the average over time and the time since the last one, will help us a lot in forecasting when future earthquakes will happen,” said Seth Stein, William Deering Professor of Earth and Planetary Sciences in the Weinberg College of Arts and Sciences.
“When you’re trying to figure out a team’s chances of winning a ball game, you don’t want to look only at the last game and the long-term average. Looking back over additional recent games can also be helpful. We now can do a similar thing for earthquakes.”
The study, titled “A More Realistic Earthquake Probability Model Using Long-Term Fault Memory,” was published recently in the Bulletin of the Seismological Society of America. Authors of the study are Stein, Northwestern professor Bruce D. Spencer and recent Ph.D. graduates James S. Neely and Leah Salditch. Stein is a faculty associate of Northwestern’s Institute for Policy Research (IPR), and Spencer is an IPR faculty fellow.
“Earthquakes behave like an unreliable bus,” said Neely, now at the University of Chicago. “The bus might be scheduled to arrive every 30 minutes, but sometimes it’s very late, other times it’s too early. Seismologists have assumed that even when a quake is late, the next one is no more likely to arrive early. Instead, in our model if it’s late, it’s now more likely to come soon. And the later the bus is, the sooner the next one will come after it.”
Traditional model and new model
The traditional model, used since a large earthquake in 1906 destroyed San Francisco, assumes that slow motions across the fault build up strain, all of which is released in a big earthquake. In other words, a fault has only short-term memory—it “remembers” only the last earthquake and has “forgotten” all the previous ones. This assumption goes into forecasting when future earthquakes will happen and then into hazard maps that predict the level of shaking for which earthquake-resistant buildings should be designed.
However, “Large earthquakes don’t occur like clockwork,” Neely said. “Sometimes we see several large earthquakes occur over relatively short time frames and then long periods when nothing happens. The traditional models can’t handle this behavior.”
In contrast, the new model assumes that earthquake faults are smarter—have longer-term memory—than seismologists assumed. The long-term fault memory comes from the fact that sometimes an earthquake didn’t release all the strain that built up on the fault over time, so some remains after a big earthquake and can cause another. This explains earthquakes that sometimes come in clusters.
“Earthquake clusters imply that faults have long-term memory,” said Salditch, now at the U.S. Geological Survey. “If it’s been a long time since a large earthquake, then even after another happens, the fault’s ‘memory’ sometimes isn’t erased by the earthquake, leaving left-over strain and an increased chance of having another. Our new model calculates earthquake probabilities this way.”
For example, although large earthquakes on the Mojave section of the San Andreas fault occur on average every 135 years, the most recent one occurred in 1857, only 45 years after one in 1812. Although this wouldn’t have been expected using the traditional model, the new model shows that because the 1812 earthquake occurred after a 304-year gap since the previous earthquake in 1508, the leftover strain caused a sooner-than-average quake in 1857.
“It makes sense that the specific order and timing of past earthquakes matters,” said Spencer, a professor of statistics. “Many systems’ behavior depends on their history over a long time. For example, your risk of spraining an ankle depends not just on the last sprain you had, but also on previous ones.”
Reference:
James S. Neely et al, A More Realistic Earthquake Probability Model Using Long-Term Fault Memory, Bulletin of the Seismological Society of America (2022). DOI: 10.1785/0120220083
UV light from the sun slowly breaks down plastics on the ocean’s surfaces. Floating microplastic is broken down into ever smaller, invisible nanoplastic particles that spread across the entire water column, but also to compounds that can then be completely broken down by bacteria. This is shown by experiments in the laboratory of the Royal Netherlands Institute for Sea Research, NIOZ, on Texel. In the latest issue of Marine Pollution Bulletin, PhD student Annalisa Delre and colleagues calculate that about two percent of visibly floating plastic may disappears from the ocean surface in this way each year. “This may seem small, but year after year, this adds up. Our data show that sunlight could thus have degraded a substantial amount of all the floating plastic that has been littered into the oceans since the 1950s,” says Delre.
Since the mass production of plastics began in the 1950s, a significant portion of plastic waste has made its way to the ocean via rivers, blown of from land by winds or directly dumped from ships. But the amount of plastic that is actually found in the ocean is only a fraction of what has entered the ocean. The majority is literally lost. In science, this problem is known as the Missing Plastic Paradox. To investigate if degradation by UV light can explain some of the vanished plastic, Delre and colleagues conducted experiments in the laboratory.
Artificial sun and sea
In a container filled with simulated seawater, the researchers mixed small plastic pieces. They then stirred this plastic soup automatically under a lamp that mimiced UV light from the sun. Gases and dissolved compounds including nanoplastics that leached from the degrading plastic pieces were then captured and analysed.
Slow degradation
From these measurements, the researchers measured that at least 1.7 percent of (visible) microplastics break down annually. For the most part it breaks down into ever smaller pieces including the (invisible) nanoplastics as well as into molecules that one also finds in crude oil. Potentially, some of these can be broken down further by bacteria. Only a small fraction is fully oxidized to the relatively harmless CO2.
Fed into a more complex calculation, accounting for the release of floating plastic to the ocean, beaching and ongoing photodegradation at the ocean surface, the breakdown by sunlight could have transformed a fifth (22%) of all floating plastic that has ever been released to the ocean, mostly to smaller, dissolved particles and compounds.
“With these calculations, we put an important piece in the jigsaw of the Missing Plastic Paradox in place,” says Helge Niemann, researcher at NIOZ and professor at Utrecht University and one of the supervisors of PhD student Delre.
Effects on marine life
Potentially, there may be good news in this research, says Niemann. “In part, the plastic breaks down into substances that can be completely broken down by bacteria. But for another part, the plastic remains in the water as invisible nanoparticles.”
In an earlier study with ‘real’ Wadden Sea water and North Sea water, Niemann and colleagues already showed that a substantial part of the missing plastics floats in the oceans as invisible nanoparticles. “The precise effects of these particles on algae, fish and other life in the oceans are still largely unclear,” says Niemann. “With these experiments under UV light, we can explain another part of the plastic paradox. We need to continue investigating the fate of the remaining plastic. Also, we need to investigate what all this micro and nano plastic does to marine life. Even more important,” Niemann stresses, “is to stop plastic littering all together, as this thickens the ocean’s plastic soup.”
Reference:
Annalisa Delre, Maaike Goudriaan, Victor Hernando Morales b, Annika Vaksmaa, Rachel Tintswalo Ndhlovu, Marianne Baas, Edwin Keijzer, Tim de Groot, Emna Zeghal, Matthias Egger Thomas Röckmann, Helge Niemann Plastic photodegradaton under simulated marine concitions. Plastic photodegradaton under simulated marine concitions. Marine Pollution Bulletin, Jan 2023 DOI: 10.1016/j.marpolbul.2022.114544
Lava fountains at Kilauea in Hawaii created a spatter cone, which was estimated to be 180 feet tall in this June 2018 photo. Credit: U.S. Geological Survey
Magma pumping through a massive complex of flat, interconnected chambers deep beneath volcanoes in Hawai’i appears to be responsible for an unexplained swarm of tiny earthquakes felt on the Big Island over the past seven years, in particular since the 2018 eruption and summit collapse of Kīlauea.
The pancake-like chambers, called “sills,” channel magma laterally and upward to recharge the magma chambers of at least two of the island’s active volcanoes: Mauna Loa and Kīlauea. Using a machine-learning algorithm, geoscientists at Caltech were able to use data gathered from seismic stations on the island to chart out the structure of the sills, mapping them with never-before-seen precision and demonstrating that they link the volcanoes.
More than 192,000 small seismic events, each represented here as a single black dot, reveal in 3D the shape and location of the sills beneath Hawai’i
Further, the researchers were able to monitor the progress of the magma as it pushed upward through the sills, and to link that to Kīlauea’s activity. They analyzed a period that ended in May 2022, so it is not yet possible to say whether they can spot the magma flow that led to the November 27 eruption of Mauna Loa, but the team intends to look at that next.
“Before this study, we knew very little about how magma is stored and transported deep beneath Hawai’i. Now, we have a high-definition map of an important part of the plumbing system,” says John D. Wilding (MS ’22), Caltech graduate student and co-lead author of a paper describing the research that was published in the journal Science on December 22. The study represents the first time scientists have been able to directly observe a magma structure located this deep underground. “We know pretty well what the magma is doing in the shallow part of the system above 15 kilometer depth, but until now, everything below that has just been the subject of speculation,” Wilding says.
With data on more than 192,000 small temblors (less than magnitude 3.0) that occurred over the 3.5-year period from 2018 to mid-2022, the team was able to map out more than a dozen sills stacked on top of one another. The largest is about 6 kilometers by 7 kilometers. The sills tend to be around 300 meters thick, and are separated by a distance of about 500 meters.
“Volcanic earthquakes are typically characterized by their small magnitude and frequent occurrence during magmatic unrest,” says Weiqiang Zhu, postdoctoral scholar research associate in geophysics and co-lead author of the Science paper. “We are excited about recent advances in machine learning, particularly deep learning, which are helping to accurately detect and locate these small seismic signals recorded by dense seismic networks. Machine learning can be an effective tool for seismologists to analyze large archived datasets, identify patterns in small earthquakes, and gain insights into underlying structures and physical mechanisms.”
Wilding and Zhu worked with Jennifer Jackson, the William E. Leonhard Professor of Mineral Physics; and Zachary Ross, assistant professor of geophysics and William H. Hurt Scholar; who are both senior authors on the paper. In October, Ross was named one of the 2022 Packard Fellows for Science and Engineering, which will provide funding to support this research moving forward.
The team did not have to place a single piece of hardware to do the study; rather, they relied on data gathered by United States Geological Survey seismometers on the island. However, the machine-learning algorithm developed in Ross’s lab gave them an unprecedented ability to separate signal from noise — that is, to clearly identify earthquakes and their locations, which create a sort of 3-D “point cloud” that illustrates the sills.
“It’s analogous to taking a CT [computerized tomography] scan, the way a doctor can visualize the inside of a patient’s body,” Ross says. “But instead of using controlled sources with X-rays, we use passive sources, which are earthquakes.”
The team was able to catalog about 10 times as many earthquakes as was previously possible, and they were able to pinpoint their locations with a margin of error of less than a kilometer; previous locations were determined with error margins of a few kilometers. The work was accomplished using a deep-learning algorithm that had been taught to spot earthquake signals using a training dataset of millions of previously identified earthquakes. Even with small earthquakes, which might not stand out to the human eye on a seismogram, the algorithm finds patterns that distinguish quakes from background noise. Ross previously used the technique to reveal how a naturally occurring injection of underground fluids drove a four-year-long earthquake swarm near Cahuilla, California.
The sills appear to be at depths ranging from around 36-43 kilometers. (For reference, the deepest humans have ever drilled into the Earth is a little over 12 kilometers.) Scientists have long known that a phase boundary is present at a depth of around 35 kilometers beneath Hawai’i; at such a phase boundary, rock of the same chemical composition transitions from one group of minerals above to a different group below. Studying the new data, Jackson recognized that the transitions occurring in this rock coupled to magma injections could host chemical reactions and processes that stress or weaken the rock, possibly explaining the existence of the sills — and by extension, the active seismicity.
“The transition of spinel to plagioclase within the lherzolite rock may be occurring through diffuse migration, entrapment, and crystallization of magma melts within the shallow lithospheric mantle underneath Hawai’i,” Jackson says. “Such assemblages can exhibit transient weakening arising from coupled deformation and chemical reactions, which could facilitate crack growth or fault activation. Recurrent magma injections would continuously modulate grain sizes in the sill complex, prolonging conditions for seismic deformation in the rock. This process could exploit lateral variations in strength to produce and sustain the laterally compact seismogenic features that we observe.”
It is unclear whether the sills beneath the Big Island are unique to Hawai’i or whether this sort of subvolcanic structure is common, the researchers say. “Hawai’i is the best-monitored island in the world, with dozens of seismic stations giving us a window into what’s going on beneath the surface. We have to wonder, at how many other locations is this happening?” Wilding says.
Also unclear is exactly how the magma’s movement triggers the tiny quakes. The earthquakes map out the structures, but the actual mechanism of earthquakes is not well understood. It could be that the injection of a lot of magma into a space creates a lot of stress, the researchers say.
Reference:
John D. Wilding, Weiqiang Zhu, Zachary E. Ross, Jennifer M. Jackson. The magmatic web beneath Hawai‘i. Science, 2022; DOI: 10.1126/science.ade5755
New study reveals, how foreshock waves interact with Earth’s magnetosphere. Foreshock waves are able to tune the shock, making it alternatively stronger or weaker. These waves could only be detected in a narrow region behind the shock. (Image: Lucile Turc)
An international team of scientists led by Lucile Turc, an Academy Research Fellow at the University of Helsinki and supported by the International Space Science Institute in Bern has studied the propagation of electromagnetic waves in near-Earth space for three years. The team has studied the waves in the area where the solar wind collides with Earth’s magnetic field called foreshock region, and how the waves are transmitted to the other side of the shock. The results of the study are now published in Nature Physics.
“How the waves would survive passing through the shock has remained a mystery since the waves were first discovered in the 1970s. No evidence of those waves has ever been found on the other side of the shock,” says Turc.
The team has used a cutting-edge computer model, Vlasiator, developed at the University of Helsinki by a group led by professor Minna Palmroth, to recreate and understand the physical processes at play in the wave transmission. A careful analysis of the simulation revealed the presence of waves on the other side of the shock, with almost identical properties as in the foreshock.
“Once it was known what and where to look for, clear signatures of the waves were found in satellite data, confirming the numerical results,” says Lucile Turc.
The waves in the foreshock can enter the Earth’s magnetic field
Around our planet is a magnetic bubble, the magnetosphere, which shields us from the solar wind, a stream of charged particles coming from the Sun. Electromagnetic waves, appearing as small oscillations of the Earth’s magnetic field, are frequently recorded by scientific observatories in space and on the ground. These waves can be caused by the impact of the changing solar wind or come from the outside of the magnetosphere.
The electromagnetic waves play an important role in creating adverse space weather around our planet: they can for example accelerate particles to high energies, which can then damage spacecraft electronics, and cause these particles to fall into the atmosphere.
On the side of Earth facing the Sun, scientific observatories frequently record oscillations at the same period as those waves that form ahead of the Earth’s magnetosphere, singing a clear magnetic song in a region of space called the foreshock.
This has led space scientists to think that there is a connection between the two, and that the waves in the foreshock can enter the Earth’s magnetosphere and travel all the way to the Earth’s surface. However, one major obstacle lies in their way: the waves must cross the shock before reaching the magnetosphere.
“At first, we thought that the initial theory proposed in the 1970s was correct: the waves could cross the shock unchanged. But there was an inconsistency in the wave properties that this theory could not reconcile, so we investigated further,” says Turc.
“Eventually, it became clear that things were much more complicated than it seemed. The waves we saw behind the shock were not the same as those in the foreshock, but new waves created at the shock by the periodic impact of foreshock waves.”
When the solar wind flows through the shock, it is compressed and heated. The shock strength determines how much compression and heating take place. Turc and her colleagues showed that foreshock waves are able to tune the shock, making it alternatively stronger or weaker when wave troughs or crests arrive at the shock. As a result, the solar wind behind the shock changes periodically and creates new waves, in concert with the foreshock waves.
The numerical model also pinpointed that these waves could only be detected in a narrow region behind the shock, and that they could easily be hidden by the turbulence in this region. This likely explains why they had not been observed before.
While the waves originating from the foreshock only play a limited role in space weather at Earth, they are of great importance to understand the fundamental physics of our universe.
Reference:
L. Turc, O. W. Roberts, D. Verscharen, A. P. Dimmock, P. Kajdič, M. Palmroth, Y. Pfau-Kempf, A. Johlander, M. Dubart, E. K. J. Kilpua, J. Soucek, K. Takahashi, N. Takahashi, M. Battarbee, U. Ganse. Transmission of foreshock waves through Earth’s bow shock. Nature Physics, 2022; DOI: 10.1038/s41567-022-01837-z
