Earth-like biospheres on other planets may be rare

June 26, 2021

An artistic representation of the potentially habitable planet Kepler 422-b (left), compared with Earth (right). Credit: Ph03nix1986 / Wikimedia Commons — An artistic representation of the potentially habitable planet Kepler 422-b (left), compared with Earth (right).
Credit: Ph03nix1986 / Wikimedia Commons

A new analysis of known exoplanets has revealed that Earth-like conditions on potentially habitable planets may be much rarer than previously thought. The work focuses on the conditions required for oxygen-based photosynthesis to develop on a planet, which would enable complex biospheres of the type found on Earth. The study is published today in Monthly Notices of the Royal Astronomical Society.

The number of confirmed planets in our own Milky Way galaxy now numbers into the thousands. However planets that are both Earth-like and in the habitable zone — the region around a star where the temperature is just right for liquid water to exist on the surface — are much less common.

At the moment, only a handful of such rocky and potentially habitable exoplanets are known. However the new research indicates that none of these has the theoretical conditions to sustain an Earth-like biosphere by means of ‘oxygenic’ photosynthesis — the mechanism plants on Earth use to convert light and carbon dioxide into oxygen and nutrients.

Only one of those planets comes close to receiving the stellar radiation necessary to sustain a large biosphere: Kepler-442b, a rocky planet about twice the mass of the Earth, orbiting a moderately hot star around 1,200 light years away.

The study looked in detail at how much energy is received by a planet from its host star, and whether living organisms would be able to efficiently produce nutrients and molecular oxygen, both essential elements for complex life as we know it, via normal oxygenic photosynthesis.

By calculating the amount of photosynthetically active radiation (PAR) that a planet receives from its star, the team discovered that stars around half the temperature of our Sun cannot sustain Earth-like biospheres because they do not provide enough energy in the correct wavelength range. Oxygenic photosynthesis would still be possible, but such planets could not sustain a rich biosphere.

Planets around even cooler stars known as red dwarfs, which smoulder at roughly a third of our Sun’s temperature, could not receive enough energy to even activate photosynthesis. Stars that are hotter than our Sun are much brighter, and emit up to ten times more radiation in the necessary range for effective photosynthesis than red dwarfs, however generally do not live long enough for complex life to evolve.

“Since red dwarfs are by far the most common type of star in our galaxy, this result indicates that Earth-like conditions on other planets may be much less common than we might hope,” comments Prof. Giovanni Covone of the University of Naples, lead author of the study.

He adds: “This study puts strong constraints on the parameter space for complex life, so unfortunately it appears that the “sweet spot” for hosting a rich Earth-like biosphere is not so wide.”

Future missions such as the James Webb Space Telescope (JWST), due for launch later this year, will have the sensitivity to look to distant worlds around other stars and shed new light on what it really takes for a planet to host life as we know it.

Reference:
Giovanni Covone, Riccardo M Ienco, Luca Cacciapuoti, Laura Inno. Efficiency of the oxygenic photosynthesis on Earth-like planets in the habitable zone. Monthly Notices of the Royal Astronomical Society, 2021; 505 (3): 3329 DOI: 10.1093/mnras/stab1357

Note: The above post is reprinted from materials provided by Royal Astronomical Society.

Analysing volcanoes to predict their awakening

June 26, 2021

One of the strombolian explosions that have occurred at Stromboli about every 10 minutes for at least 2000 years. © UNIGE, Luca Caricchi

Table of Contents

What causes an eruption? Why do some volcanoes erupt regularly, while others remain dormant for thousands of years? A team of geologists and geophysicists, led by the University of Geneva (UNIGE), Switzerland, has reviewed the literature on the internal and external mechanisms that lead to a volcanic eruption. Analyzing the thermo-mechanics of deep volcanic processes and magma propagation to the surface, together with magma chemistry, the geologists determined that most of the magma rising from depth actually does not cause a volcanic eruption. They also show that older volcanoes tend to produce less frequent, but larger and more dangerous eruptions. Their findings, published in Nature Reviews Earth and Environment, will help refine models of volcanic processes to reduce the impact of volcanic eruptions on the more than 800 million people living near active volcanoes.

Volcanic activity remains difficult to predict even when it is closely monitored. Why didn’t Mount Fuji erupt after the strong earthquake in Tohoku, Japan? Why did the eruption of Eyjafjallajökul generate such a large amount of volcanic ash? In order to determine the causes of volcanic eruptions, geologists and geophysicists led by Luca Caricchi, professor at the Department of Earth Sciences of the Faculty of Science of the UNIGE, have taken up the existing literature and analysed all the stages that precede an eruption.

The path of magma from the depths of the Earth

Magma is molten rock that comes from tens of kilometres depth and rises to the Earth’s surface. “During its journey, magma can get trapped in reservoirs within the Earth’s crust, where it may stagnate for thousands of years and potentially never erupt,” explains Meredith Townsend, a researcher at the Department of Earth Sciences of the University of Oregon (USA). Specialising in thermomechanical modelling, the American researcher focused on calculating the pressure required for the magma to break up the rocks surrounding the reservoir and rise to the surface. Eleonora Rivalta, a researcher at the Potsdam Research Centre for Geosciences (Germany) and the University of Bologna (Italy), studied the propagation of magma as it rises to the surface: “If it is runny enough, that is if it does not contain too many crystals, magma can rise very quickly by a sort of self-propelled fracking,” she continues. If magma crystallises more than 50%, it becomes too viscous and its march towards the surface stops. Magma can also take different paths, vertical, horizontal or inclined. Luca Caricchi specialises in magma chemistry, which provides vital information about the state of the magma before a volcanic eruption occurs. “The chemistry of magma and the crystals it contains provide vital information on the sequence of events leading to a volcanic eruption, which is valuable to better interpret the monitoring signals of active volcanoes and anticipate- whether an eruption might occur,” explains the Geneva-based researcher. Finally, Atsuko Namiki, a researcher at the Graduate School of Environmental Studies at Nagoya University (Japan), has analysed the external triggers of an eruption, such as earthquakes, tides or rain: “These alone cannot cause an eruption, the magma has to be ready and awaiting a trigger.”

“For an eruption to take place, several conditions must be met simultaneously. Magma with less than 50% crystals must be stored in a reservoir,” begins Luca Caricchi. Then this reservoir must be overpressurised. The overpressure can be the result of internal phenomena such as a renewed injection of magma or the exsolution of magmatic gases or it can rise to critical values because of external events such as earthquakes. Finally, once the pressure is sufficient for the magma to start rising, there are still many obstacles that can prevent the magma from erupting.

The age of the volcano as a primary criterion

This comprehensive analysis sheds a light on the behaviour of volcanoes that can change over their lifetime. “When a volcano is just starting to be active, its reservoir is rather small (a few km3) and the surrounding crust is relatively cold, which leads to many frequent, but small and rather predictable eruptions,” explains Luca Caricchi. It’s a different story with old volcanoes. “Their reservoir is bigger and the rocks around them are hotter. When new magma is injected, it does not generate much overpressure because the rocks around the reservoir deform and the growth continues,” says the geologist. As an example Mt St Helens (USA) started erupting 40’000 years ago (a time lapse by geological standards) and its last eruption in 2008 was small and not dangerous. On the contrary, Toba (Indonesia) started erupting explosively about 1.2 million years ago and its last eruption 74000 years ago was cataclysmic. It totally destroyed the surroundings and had an impact on global climate.

Eventually, the accumulation of large amounts of magma will lead to large eruptions. “Moreover, the warning signs are very difficult to detect because the high temperatures decrease seismic activity and the interaction between gases and magma modifies their composition, making it harder to understand what is going on underneath,” he says. The higher the rate of magma input, the faster the volcano ‘ages’.

Knowing the age of the volcano, which can be dated by analysing the zircon in the rocks, allows geologists to understand the stage of life of the volcanoes. “There are currently 1,500 active volcanoes, and about 50 of them erupt each year. Knowing whether or not to evacuate the population is crucial and we hope that our study will contribute to decrease the impact of volcanic activity on our society,” continues Luca Caricchi. “Hopefully our findings will be tested on volcanoes that have been studied extensively, such as those in Italy, USA and Japan, and transferred to other volcanoes for which there are less data, such as in Indonesia or South America.”

Reference:
Luca Caricchi, Meredith Townsend, Eleonora Rivalta, Atsuko Namiki. The build-up and triggers of volcanic eruptions. Nature Reviews Earth & Environment, 2021; DOI: 10.1038/s43017-021-00174-8

Note: The above post is reprinted from materials provided by Université de Genève.

Environmental impact of hydrofracking vs. conventional gas/oil drilling: Research shows the differences may be minimal

June 26, 2021

A new study led by A&S professor Tao Wen used a novel method of machine learning to explore the environmental impact of oil and gas drilling.

Crude oil production and natural gas withdrawals in the United States have lessened the country’s dependence on foreign oil and provided financial relief to U.S. consumers, but have also raised longstanding concerns about environmental damage, such as groundwater contamination.

A researcher in Syracuse University’s College of Arts and Sciences, and a team of scientists from Penn State, have developed a new machine learning technique to holistically assess water quality data in order to detect groundwater samples likely impacted by recent methane leakage during oil and gas production. Using that model, the team concluded that unconventional drilling methods like hydraulic fracturing — or hydrofracking — do not necessarily incur more environmental problems than conventional oil and gas drilling.

The two common ways to extract oil and gas in the U.S. are through conventional and unconventional methods. Conventional oil and gas are pumped from easily accessed sources using natural pressure. Conversely, unconventional oil and gas are acquired from hard-to-reach sources through a combination of horizontal drilling and hydraulic fracturing. Hydrofracking extracts natural gas, petroleum and brine from bedrock formations by injecting a mixture of sand, chemicals and water. By drilling into the earth and directing the high-pressure mixture into rock, the gas inside releases and flows out to the head of a well.

Tao Wen, assistant professor of earth and environmental sciences (EES) at Syracuse, recently led a study comparing data from different states to see which method might result in greater contamination of groundwater. They specifically tested levels of methane, which is the primary component of natural gas.

The team selected four U.S. states located in important shale zones to target for their study: Pennsylvania, Colorado, Texas and New York. One of those states — New York — banned the practice of hydrofracking in 2015 following a review by the NYS Department of Health which found significant uncertainties about health, including increased water and air pollution.

Wen and his colleagues compiled a large groundwater chemistry dataset from multiple sources including federal agency reports, journal articles, and oil and gas companies. The majority of tested water samples in their study were collected from domestic water wells. Although methane itself is not toxic, Wen says that methane contamination detected in shallow groundwater could be a risk to the relevant homeowner as it could be an explosion hazard, could increase the level of other toxic chemical species like manganese and arsenic, and would contribute to global warming as methane is a greenhouse gas.

Their model used sophisticated algorithms to analyze almost all of the retained geochemistry data in order to predict if a given groundwater sample was negatively impacted by recent oil and gas drilling.

The data comparison showed that methane contamination cases in New York — a state without unconventional drilling but with a high volume of conventional drilling — were similar to that of Pennsylvania — a state with a high volume of unconventional drilling. Wen says this suggests that unconventional drilling methods like fracking do not necessarily lead to more environmental problems than conventional drilling, although this result might be alternatively explained by the different sizes of groundwater chemistry datasets compiled for these two states.

The model also detected a higher rate of methane contamination cases in Pennsylvania than in Colorado and Texas. Wen says this difference could be attributed to different practices when drillers build/drill the oil and gas wells in different states. According to previous research, most of the methane released into the environment from gas wells in the U.S. occurs because the cement that seals the well is not completed along the full lengths of the production casing. However, no data exists to conclude if drillers in those three states use different technology. Wen says this requires further study and review of the drilling data if they become available.

According to Wen, their machine learning model proved to be effective in detecting groundwater contamination, and by applying it to other states/counties with ongoing or planned oil and gas production it will be an important resource for determining the safest methods of gas and oil drilling.

Wen and his colleagues from Penn State, including Mengqi Liu, a graduate student from the College of Information Sciences and Technology, Josh Woda, a graduate student from Department of Geosciences, Guanjie Zheng, former Ph.D. student from the College of Information Sciences and Technology, and Susan L. Brantley, distinguished professor in the Department of Geosciences and director of Earth and Environmental Systems Institute, recently had their findings published in the journal Water Research.

The team’s work was funded by National Science Foundation IIS-16-39150, US Geological Survey (104b award G16AP00079), and College of Earth and Mineral Sciences Dean’s Fund for Postdoc-Facilitated Innovation at Penn State.

Reference:
Tao Wen, Mengqi Liu, Josh Woda, Guanjie Zheng, Susan L. Brantley. Detecting anomalous methane in groundwater within hydrocarbon production areas across the United States. Water Research, 2021; 200: 117236 DOI: 10.1016/j.watres.2021.117236

Note: The above post is reprinted from materials provided by Syracuse University. Original written by Dan Bernardi.

Continuous activity of small earthquakes makes mountains grow

June 26, 2021

In the time between mega-earthquakes, smaller earthquakes continuously occur between oceanic and continental plates (background earthquakes). Where a lot of energy is released through these earthquakes, we observe coastal mountains that rise faster. In contrast, slow-uplifting coastal areas coincide with fewer background earthquakes. Credit: University of Tübingen

From a human perspective, earthquakes are natural disasters—in the past hundred years, they have caused more than 200,000 deaths and enormous economic damage. Mega-earthquakes with a magnitude of nine or higher on the Richter scale are considered a particular threat. Yet the inconceivable energy released in these events doesn’t seem to affect the uplift of mountains, according to a new study by geoscientists at the University of Tübingen. The energy of small earthquakes that work steadily in the background appears to play a far greater role in shaping the landscape. In Chile and Japan, Professor Todd Ehlers and Dr. Andrea Madella found parallels between seismic activity and the pattern and rate of mountain uplift. The results have been published in the journal Nature Geoscience.

Earthquakes generally occur in areas of the Earth where continental plates collide. Along the Chilean coast, for example, the Nazca plate is being pushed under the South American plate, causing the latter to be compressed and to accumulate elastic energy over hundreds of years. “The discharge of all that energy within a short time—often less than a minute—results in mega-earthquakes which can shake the ground in a terrifying way,” says Todd Ehlers, “and in that time, the oceanic Nazca plate slides under the continental one.”

Mountain ranges are pushed up at the edge of the compressed plate. In Peru and Chile, these are the Andes, which reach heights of more than 6,900 meters. In Japan, where several continental plates collide, mountains form a large part of the land mass.

Surprising patterns

In their study, the researchers examined records of earthquakes of various magnitudes along the fault lines in Chile and Japan and compared that data with the topographic patterns of the landscape. “Once we subtracted the mega-earthquakes and their smaller aftershocks from our calculations, we found that the energy released from the slow sustained activity of smaller earthquakes often matched the coastal uplift,” Andrea Madella reports.

These smaller earthquakes occur mainly at depths of 30 to 60 kilometers and have a magnitude of four to five. “The correlation surprised us. These smaller earthquakes have clearly been underestimated,” says Ehlers. “They occur constantly in the background without any particular spatial or temporal peaks. It seems to be their cumulative energy that makes the mountains grow over millions of years.” But what happens to the energy from mega-earthquakes? “It bends the whole landscape cyclically,” says Madella. “But that deformation is then reversed and often it causes no permanent uplift of mountains.”

Reference:
Andrea Madella et al, Contribution of background seismicity to forearc uplift, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00779-0

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

Rock crystals from the deep give microscopic clues to earthquake ground movements

June 26, 2021

Chunks of exotic green rocks from the mantle erupted from the San Carlos Volcanic Field, Arizona. Credit: James St John

Microscopic imperfections in rock crystals deep beneath Earth’s surface play a deciding factor in how the ground slowly moves and resets in the aftermath of major earthquakes, says new research involving the University of Cambridge.

The stresses resulting from these defects—which are small enough to disrupt the atomic building blocks of a crystal—can transform how hot rocks beneath Earth’s crust move and in turn transfer stress back to Earth’s surface, starting the countdown to the next earthquake.

The new study, published in Nature Communications, is the first to map out the crystal defects and surrounding force fields in detail. “They’re so tiny that we’ve only been able to observe them with the latest microscopy techniques,” said lead author Dr. David Wallis from Cambridge’s Department of Earth Sciences, “But it’s clear that they can significantly influence how deep rocks move, and even govern when and where the next earthquake will happen.”

By understanding how these crystal defects influence rocks in the Earth’s upper mantle, scientists can better interpret measurements of ground motions following earthquakes, which give vital information on where stress is building up—and in turn where future earthquakes may occur.

Earthquakes happen when pieces of Earth’s crust suddenly slip past each other along fault lines, releasing stored-up energy which propagates through the Earth and causes it to shake. This movement is generally a response to the build-up of tectonic forces in the Earth’s crust, causing the surface to buckle and eventually rupture in the form of an earthquake.

Their work reveals that the way Earth’s surface settles after an earthquake, and stores stress prior to a repeat event, can ultimately be traced to tiny defects in rock crystals from the deep.

“If you can understand how fast these deep rocks can flow, and how long it will take to transfer stress between different areas across a fault zone, then we might be able to get better predictions of when and where the next earthquake will strike,” said Wallis.

The team subjected olivine crystals—the most common component of the upper mantle—to a range of pressures and temperatures in order to replicate conditions of up to 100 km beneath Earth’s surface, where the rocks are so hot (roughly 1250oC) they move like syrup.

Wallis likens their experiments to a blacksmith working with hot metal—at the highest temperatures, their samples were glowing white-hot and pliable.

They observed the distorted crystal structures using a high-resolution form of electron microscopy, called electron backscatter diffraction, which Wallis has pioneered on geological materials.

Their results shed light on how hot rocks in the upper mantle can mysteriously morph from flowing almost like syrup immediately after an earthquake to becoming thick and sluggish as time passes.

This change in thickness—or viscosity—transfers stress back to the cold and brittle rocks in the crust above, where it builds up—until the next earthquake strikes.

The reason for this switch in behavior has remained an open question, “We’ve known that microscale processes are a key factor controlling earthquakes for a while, but it’s been difficult to observe these tiny features in enough detail,” said Wallis. “Thanks to a state-of-the-art microscopy technique, we’ve been able to look into the crystal framework of hot, deep rocks and track down how important these miniscule defects really are.”

Wallis and co-authors show that irregularities in the crystals become increasingly tangled over time; jostling for space due to their competing force fields—and it’s this process that causes the rocks to become more viscous.

Until now it had been thought that this increase in viscosity was because of the competing push and pull of crystals against each other, rather than being caused by microscopic defects and their stress fields inside the crystals themselves.

The team hope to apply their work to improving seismic hazard maps, which are often used in tectonically active areas like southern California to estimate where the next earthquake will occur. Current models, which are usually based on where earthquakes have struck in the past, and where stress must therefore be building up, only take into account the more immediate changes across a fault zone and do not consider gradual stress changes in rocks flowing deep within the Earth.

Working with colleagues at Utrecht University, Wallis also plans to apply their new lab constraints to models of ground movements following the hazardous 2004 earthquake which struck Indonesia, and the 2011 Japan quake—both of which triggered tsunamis and lead to the loss of tens of thousands of lives.

Reference:
David Wallis et al, Dislocation interactions in olivine control postseismic creep of the upper mantle, Nature Communications (2021). DOI: 10.1038/s41467-021-23633-8

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

New knowledge of Earth’s mantle helps to explain Indonesia’s explosive volcanoes

June 26, 2021

Agung, a volcano in Bali, had an explosive eruption in 2018. Credit: O.L. Andersen

Indonesia’s volcanoes are among the world’s most dangerous. Why? Through chemical analyses of tiny minerals in lava from Bali and Java, researchers from Uppsala University and elsewhere have found new clues. They now understand better how the Earth’s mantle is composed in that particular region and how the magma changes before an eruption. The study is published in Nature Communications.

Frances Deegan, the study’s first author and a researcher at Uppsala University’s Department of Earth Sciences, says, “Magma is formed in the mantle, and the composition of the mantle under Indonesia used to be only partly known. Having better knowledge of Earth’s mantle in this region enables us to make more reliable models for the chemical changes in magma when it breaks through the crust there, which is 20 to 30 kilometers thick, before an eruption.”

The composition of magma varies greatly from one geological environment to another, and has a bearing on the kind of volcanic eruption that occurs. The Indonesian archipelago was created by volcanism, caused by two of Earth’s continental tectonic plates colliding there. In this collision, Indo-Australian plate slides beneath the Eurasian plate at a speed of some 7 cm annually. This process, known as subduction, can cause powerful earthquakes. The tsunami disaster of 2004, for example, was caused by movements along this particular plate boundary.

Volcanism, too, arises in subduction zones. When the sinking tectonic plate descends into the mantle, it heats up and the water it contains is released, causing the surrounding rock to start melting. The result is volcanoes that are often explosive and, over time, build up arc-shaped groups of islands. Along the Sunda Arc, comprising Indonesia’s southern archipelago, several cataclysmic volcanic eruptions have taken place. Examples are Krakatoa in 1883, Mount Tambora in 1815 and Toba, which had a massive super-eruption some 72,000 years ago.

Magma reacts chemically with surrounding rock when it penetrates Earth’s crust before breaking out on the surface. It can therefore vary widely among volcanoes. To get a better grasp of the origin of volcanism in Indonesia, the researchers wanted to find out the composition of the “primary” magma, that is derived from the mantle itself. Since samples cannot be taken directly from the mantle, geologists studied minerals in lava recently ejected from four volcanoes: Merapi and Kelut in Java, and Agung and Batur in Bali.

Using the powerful ion beams from a secondary ion mass spectrometry (SIMS) instrument, an ultramodern form of mass spectrometer, the researchers examined crystals of pyroxene. This mineral is one of the first to crystallize from a magma. What they wanted to determine was the ratio of the oxygen isotopes 16O and 18O, which reveals a great deal about the source and evolution of magma.

“Lava consists of roughly 50 percent oxygen, and Earth’s crust and mantle differ hugely in their oxygen isotope composition. So, to trace how much material the magma has assimilated from the crust after leaving the mantle, oxygen isotopes are very useful,” Deegan says.

The researchers found that the oxygen composition of pyroxene minerals from Bali had hardly been affected at all during their journey through Earth’s crust. Their composition was fairly close to their original state, indicating that a minimum of sediment had been drawn down into the mantle during subduction. An entirely different pattern was found in the minerals from Java.

“We were able to see that Merapi in Java exhibited an isotope signature very different from those of the volcanoes in Bali. It’s partly because Merapi’s magma interacts intensively with Earth’s crust before erupting. That’s highly important because when magma reacts with, for instance, the limestone that’s found in central Java right under the volcano, the magma becomes full to bursting point with carbon dioxide and water, and the eruptions get more explosive. That may be why Merapi’s so dangerous. It’s actually one of the deadliest volcanoes in Indonesia: it’s killed nearly 2,000 people in the past 100 years, and the most recent eruption claimed 400 lives,” says Professor Valentin Troll of Uppsala University’s Department of Earth Sciences.

The study is a collaboration among researchers at Uppsala University, the Swedish Museum of Natural History in Stockholm, the University of Cape Town in South Africa, the University of Freiburg in Germany and Vrije Universiteit (VU) Amsterdam in the Netherlands. The results of the study enhance our understanding of how volcanism in the Indonesian archipelago works.

“Indonesia is densely populated, and everything that gives us a better grasp of how these volcanoes work is valuable, and helps us to be better prepared for when the volcanoes erupt,” says Deegan.

Reference:
Frances M. Deegan et al, Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis, Nature Communications (2021). DOI: 10.1038/s41467-021-24143-3

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

Earth’s oldest minerals date onset of plate tectonics to 3.6 billion years ago

May 22, 2021

Zircons studied by the research team, photographed using cathodoluminescence, a technique that allowed the team to visualize the interiors of the crystals using a specialized scanning electron microscope. Dark circles on the zircons are the cavities left by the laser that was used to analyze the age and chemistry of the zircons.Scientists led by Michael Ackerson, a research geologist at the Smithsonian's National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, emerged roughly 3.6 billion years ago. The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to peer back into the planet's ancient past.The team tested more than 3,500 zircons, each just a couple of human hairs wide, by blasting them with a laser and then measuring their chemical composition with a mass spectrometer. These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were fit for study due to the ravages of the billions of years these minerals endured since their creation. Credit: Michael Ackerson, Smithsonian. — Zircons studied by the research team, photographed using cathodoluminescence, a technique that allowed the team to visualize the interiors of the crystals using a specialized scanning electron microscope. Dark circles on the zircons are the cavities left by the laser that was used to analyze the age and chemistry of the zircons.Scientists led by Michael Ackerson, a research geologist at the Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, emerged roughly 3.6 billion years ago. The study, published May 14 in the journal Geochemical Perspective Letters, uses zircons, the oldest minerals ever found on Earth, to peer back into the planet’s ancient past.The team tested more than 3,500 zircons, each just a couple of human hairs wide, by blasting them with a laser and then measuring their chemical composition with a mass spectrometer. These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were fit for study due to the ravages of the billions of years these minerals endured since their creation. Credit: Michael Ackerson, Smithsonian.

Scientists led by Michael Ackerson, a research geologist at the Smithsonian’s National Museum of Natural History, provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, emerged roughly 3.6 billion years ago.

Earth is the only planet known to host complex life and that ability is partly predicated on another feature that makes the planet unique: plate tectonics. No other planetary bodies known to science have Earth’s dynamic crust, which is split into continental plates that move, fracture and collide with each other over eons. Plate tectonics afford a connection between the chemical reactor of Earth’s interior and its surface that has engineered the habitable planet people enjoy today, from the oxygen in the atmosphere to the concentrations of climate-regulating carbon dioxide. But when and how plate tectonics got started has remained mysterious, buried beneath billions of years of geologic time.

The study, published May 14 in the journal Geochemical Perspectives Letters, uses zircons, the oldest minerals ever found on Earth, to peer back into the planet’s ancient past.

The oldest of the zircons in the study, which came from the Jack Hills of Western Australia, were around 4.3 billion years old — which means these nearly indestructible minerals formed when the Earth itself was in its infancy, only roughly 200 million years old. Along with other ancient zircons collected from the Jack Hills spanning Earth’s earliest history up to 3 billion years ago, these minerals provide the closest thing researchers have to a continuous chemical record of the nascent world.

“We are reconstructing how the Earth changed from a molten ball of rock and metal to what we have today,” Ackerson said. “None of the other planets have continents or liquid oceans or life. In a way, we are trying to answer the question of why Earth is unique, and we can answer that to an extent with these zircons.”

To look billions of years into Earth’s past, Ackerson and the research team collected 15 grapefruit-sized rocks from the Jack Hills and reduced them into their smallest constituent parts — minerals — by grinding them into sand with a machine called a chipmunk. Fortunately, zircons are very dense, which makes them relatively easy to separate from the rest of the sand using a technique similar to gold panning.

The team tested more than 3,500 zircons, each just a couple of human hairs wide, by blasting them with a laser and then measuring their chemical composition with a mass spectrometer. These tests revealed the age and underlying chemistry of each zircon. Of the thousands tested, about 200 were fit for study due to the ravages of the billions of years these minerals endured since their creation.

“Unlocking the secrets held within these minerals is no easy task,” Ackerson said. “We analyzed thousands of these crystals to come up with a handful of useful data points, but each sample has the potential to tell us something completely new and reshape how we understand the origins of our planet.”

A zircon’s age can be determined with a high degree of precision because each one contains uranium. Uranium’s famously radioactive nature and well-quantified rate of decay allow scientists to reverse engineer how long the mineral has existed.

The aluminum content of each zircon was also of interest to the research team. Tests on modern zircons show that high-aluminum zircons can only be produced in a limited number of ways, which allows researchers to use the presence of aluminum to infer what may have been going on, geologically speaking, at the time the zircon formed.

After analyzing the results of the hundreds of useful zircons from among the thousands tested, Ackerson and his co-authors deciphered a marked increase in aluminum concentrations roughly 3.6 billion years ago.

“This compositional shift likely marks the onset of modern-style plate tectonics and potentially could signal the emergence of life on Earth,” Ackerson said. “But we will need to do a lot more research to determine this geologic shift’s connections to the origins of life.”

The line of inference that links high-aluminum zircons to the onset of a dynamic crust with plate tectonics goes like this: one of the few ways for high-aluminum zircons to form is by melting rocks deeper beneath Earth’s surface.

“It’s really hard to get aluminum into zircons because of their chemical bonds,” Ackerson said. “You need to have pretty extreme geologic conditions.”

Ackerson reasons that this sign that rocks were being melted deeper beneath Earth’s surface meant the planet’s crust was getting thicker and beginning to cool, and that this thickening of Earth’s crust was a sign that the transition to modern plate tectonics was underway.

Prior research on the 4 billion-year-old Acasta Gneiss in northern Canada also suggests that Earth’s crust was thickening and causing rock to melt deeper within the planet.

“The results from the Acasta Gneiss give us more confidence in our interpretation of the Jack Hills zircons,” Ackerson said. “Today these locations are separated by thousands of miles, but they’re telling us a pretty consistent story, which is that around 3.6 billion years ago something globally significant was happening.”

This work is part of the museum’s new initiative called Our Unique Planet, a public-private partnership, which supports research into some of the most enduring and significant questions about what makes Earth special. Other research will investigate the source of Earth’s liquid oceans and how minerals may have helped spark life.

Ackerson said he hopes to follow up these results by searching the ancient Jack Hills zircons for traces of life and by looking at other supremely old rock formations to see if they too show signs of Earth’s crust thickening around 3.6 billion years ago.

Funding and support for this research were provided by the Smithsonian and the National Aeronautics and Space Administration (NASA).

Reference:
M.R. Ackerson, D. Trail, J. Buettner. Emergence of peraluminous crustal magmas and implications for the early Earth. Geochemical Perspectives Letters, 2021; 17: 50 DOI: 10.7185/geochemlet.2114

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

Clues from soured milk reveal how gold veins form

May 22, 2021

McGill Colloidal Au research team study a mineralized (gold-bearing) vein underground at the Brucejack mine. Credit: Duncan McLeish

Table of Contents

For decades scientists have been puzzled by the formation of rare hyper-enriched gold deposits in places like Ballarat in Australia, Serra Palada in Brazil, and Red Lake in Ontario. While such deposits typically form over tens to hundreds of thousands of years, these “ultrahigh-grade” deposits can form in years, month, or even days. So how do they form so quickly?

Studying examples of these deposits from the Brucejack Mine in northwestern British Columbia, McGill Professor Anthony Williams-Jones of the Department of Earth and Planetary Sciences and Ph.D. student Duncan McLeish have discovered that these gold deposits form much like soured milk. When milk goes sour, the butterfat particles clump together to form a jelly.

What did you set to find out?

Scientists have long known that gold deposits form when hot water flows through rocks, dissolving minute amounts of gold and concentrating it in cracks in the Earth’s crust at levels invisible to the naked eye. In rare cases, the cracks are transformed into veins of solid gold centimetres thick. But how do fluids with such low concentrations of gold produce rare ultrahigh-grade gold deposits?

What did you discover?

Our findings solve the paradox of “ultrahigh-grade” or “bonanza” gold formation, which has frustrated scientists for over a century. The paradox of bonanza gold deposits is that there is simply not enough time for them to form, they should not exist, but they do!

As the concentration of gold in hot water is very low, very large volumes of fluid need to flow through the cracks in the Earth’s crust to deposit mineable concentrations of gold. This process would require millions of years to fill a single centimetre wide crack with gold, whereas these cracks typically seal in days, months, or years.

Using a powerful electron microscope to observe particles in thin slices of rock, we discovered that bonanza gold deposits form from a fluid much like milk. Milk consists of little butterfat particles that are suspended in water because they repel each other, like the negative ends of two magnets. When the milk goes sour the surface charge breaks down, and the particles clump together to form a jelly. It is the same with gold colloids, which consist of charged nanoparticles of gold which repel each other, but when the charge breaks down, they “flocculate” to form a jelly. This jelly gets trapped in the cracks of rocks to form the ultra high-grade gold veins. The gold colloids are distinctively red and can be made in the lab, whereas solutions of dissolved gold are colourless.

Why are the results important?

We produced the first evidence for gold colloid formation and flocculation in nature and the first images of small veins of gold colloid particles and their flocculated aggregates at the nano-scale. These images document the process by which the cracks are filled with gold and, scaled up through the integration of millions of these small veins, reveal how bonanza veins are formed.

How will this discovery impact the mining industry?

Our results are important to the mineral exploration and mining industry in Canada and around the world. Now that we finally understand how bonanza deposits form, mineral exploration companies will be able to use the results of our work to better explore for bonanza deposits as well as gold deposits. Genetic studies of Canada’s most fertile metallogenic districts—such as the one we have just completed at Brucejack—are required to improve our understanding of how world-class mineral deposits form, and thereby develop more effective strategies for their exploration.

What’s next for this research?

We suspect that the colloidal processes that operated at Brucejack and other bonanza gold systems may also have operated to form more typical gold deposits. The challenge will be to find suitable material to test this hypothesis. At Brucejack, the next step will be to better understand the reasons why colloid formation and flocculation occurred on the scale observed and reconstruct the geological environment of these processes. We have also been preparing gold colloids in the lab in an attempt to simulate what we discovered at Brucejack.

Reference:
Duncan F. McLeish et al, Colloidal transport and flocculation are the cause of the hyperenrichment of gold in nature, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073/pnas.2100689118

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

Where on Earth is all the water?

May 22, 2021

The quantitative model used in the study explains the enigmatic melt degrees and layered structures observed in most cratons on Earth.

High-temperature and high-pressure experiments involving a diamond anvil and chemicals to simulate the core of the young Earth demonstrate for the first time that hydrogen can bond strongly with iron in extreme conditions. This explains the presence of significant amounts of hydrogen in the Earth’s core that arrived as water from bombardments billions of years ago.

Given the extreme depths, temperatures and pressures involved, we are not physically able to probe very far into the earth directly. So, in order to peer deep inside the Earth, researchers use techniques involving seismic data to ascertain things like composition and density of subterranean material. Something that has stood out for as long as these kinds of measurements have been taking place is that the core is primarily made of iron, but its density, in particular that of the liquid part, is lower than expected.

This led researchers to believe there must be an abundance of light elements alongside the iron. For the first time, researchers have examined the behavior of water in laboratory experiments involving metallic iron and silicate compounds that accurately simulate the metal-silicate (core-mantle) reactions during Earth’s formation. They found that when water meets iron, the majority of the hydrogen dissolves into the metal while the oxygen reacts with iron and goes into the silicate materials.

“At the temperatures and pressures we are used to on the surface, hydrogen does not bond with iron, but we wondered if it were possible under more extreme conditions,” said Shoh Tagawa, a Ph.D. student at the Department of Earth and Planetary Science at the University of Tokyo during the study. “Such extreme temperatures and pressures are not easy to reproduce, and the best way to achieve them in the lab was to use an anvil made of diamond. This can impart pressures of 30-60 gigapascals in temperatures of 3,100-4,600 kelvin. This is a good simulation of the Earth’s core formation.”

The team, under Professor Kei Hirose, used metal and water-bearing silicate analogous to those found in the Earth’s core and mantle, respectively, and compressed them in the diamond anvil whilst simultaneously heating the sample with a laser. To see what was going on in the sample, they used high-resolution imaging involving a technique called secondary ion mass spectroscopy. This allowed them to confirm their hypothesis that hydrogen bonds with iron, which explains the apparent lack of ocean water. Hydrogen is said to be iron-loving, or siderophile.

“This finding allows us to explore something that affects us in quite a profound way,” said Hirose. “That hydrogen is siderophile under high pressure tells us that much of the water that came to Earth in mass bombardments during its formation might be in the core as hydrogen today. We estimate there might be as much as 70 oceans’ worth of hydrogen locked away down there. Had this remained on the surface as water, the Earth may never have known land, and life as we know it would never have evolved.”

Reference:
Shoh Tagawa, Naoya Sakamoto, Kei Hirose, Shunpei Yokoo, John Hernlund, Yasuo Ohishi, Hisayoshi Yurimoto. Experimental evidence for hydrogen incorporation into Earth’s core. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-22035-0

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

Discovery of new geologic process calls for changes to plate tectonic cycle

May 22, 2021

Elements of a newly discovered process in plate tectonics include a mass (rock slab weight), a pulley (trench), a dashpot (microcontinent), and a string (oceanic plate) that connects these elements to each other. In the initial state, the microcontinent drifts towards the subduction zone (Figure a). The microcontinent then extends during its journey to the subduction trench owing to the tensional force applied by the pull of the rock slab pull across the subduction zone (Figure b). Finally, the microcontinent accretes to the overriding plate and resists subduction due to its low density, causing the down-going slab to break off (Figure c). Credit: Erkan Gün/University of Toronto

Geoscientists at the University of Toronto (U of T) and Istanbul Technical University have discovered a new process in plate tectonics which shows that tremendous damage occurs to areas of Earth’s crust long before it should be geologically altered by known plate-boundary processes, highlighting the need to amend current understandings of the planet’s tectonic cycle.

Plate tectonics, an accepted theory for over 60 years that explains the geologic processes occurring below the surface of Earth, holds that its outer shell is fragmented into continent-sized blocks of solid rock, called “plates,” that slide over Earth’s mantle, the rocky inner layer above the planet’s core. As the plates drift around and collide with each other over million-years-long periods, they produce everything from volcanoes and earthquakes to mountain ranges and deep ocean trenches, at the boundaries where the plates collide.

Now, using supercomputer modelling, the researchers show that the plates on which Earth’s oceans sit are being torn apart by massive tectonic forces even as they drift about the globe. The findings are reported in a study published this week in Nature Geoscience.

The thinking up to now focused only on the geological deformation of these drifting plates at their boundaries after they had reached a subduction zone, such as the Marianas Trench in the Pacific Ocean where the massive Pacific plate dives beneath the smaller Philippine plate and is recycled into Earth’s mantle.

The new research shows much earlier damage to the drifting plate further away from the boundaries of two colliding plates, focused around zones of microcontinents — continental crustal fragments that have broken off from main continental masses to form distinct islands often several hundred kilometers from their place of origin.

“Our work discovers that a completely different part of the plate is being pulled apart because of the subduction process, and at a remarkably early phase of the tectonic cycle,” said Erkan Gün, a PhD candidate in the Department of Earth Sciences in the Faculty of Arts & Science at U of T and lead author of the study.

The researchers term the mechanism a “subduction pulley” where the weight of the subducting portion that dives beneath another tectonic plate, pulls on the drifting ocean plate and tears apart the weak microcontinent sections in an early phase of potentially significant damage.

“The damage occurs long before the microcontinent fragment reaches its fate to be consumed in a subduction zone at the boundaries of the colliding plates,” said Russell Pysklywec, professor and chair of the Department of Earth Sciences at U of T, and a coauthor of the study. He says another way to look at it is to think of the drifting ocean plate as an airport baggage conveyor, and the microcontinents are like pieces of luggage travelling on the conveyor.

“The conveyor system itself is actually tearing apart the luggage as it travels around the carousel, before the luggage even reaches its owner.”

The researchers arrived at the results following a mysterious observation of major extension of rocks in alpine regions in Italy and Turkey. These observations suggested that the tectonic plates that brought the rocks to their current location were already highly damaged prior to the collisional and mountain-building events that normally cause deformation.

“We devised and conducted computational Earth models to investigate a process to account for the observations,” said Gün. “It turned out that the temperature and pressure rock histories that we measured with the virtual Earth models match closely with the enigmatic rock evolution observed in Italy and Turkey.”

According to the researchers, the findings refine some of the fundamental aspects of plate tectonics and call for a revised understanding of this fundamental theory in geoscience.

“Normally we assume — and teach — that the ocean plate conveyor is too strong to be damaged as it drifts around the globe, but we prove otherwise,” said Pysklywec.

The findings build on the legacy of J. Tuzo Wilson, also a U of T scientist, and a renowned figure in geosciences who pioneered the idea of plate tectonics in the 1960s.

The research was made possible with support from SciNet and Compute Canada, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Scientific and Technological Research Council of Turkey.

Reference:
Erkan Gün, Russell N. Pysklywec, Oğuz H. Göğüş, Gültekin Topuz. Pre-collisional extension of microcontinental terranes by a subduction pulley. Nature Geoscience, 2021; DOI: 10.1038/s41561-021-00746-9

Note: The above post is reprinted from materials provided by University of Toronto. Original written by Sean Bettam.

Yellowstone National Park is hotter than ever

May 22, 2021

Karen Heeter overlooks Yellowstone from Republic Pass on a tree coring excursion in July 2018. Credit: Grant L. Harley

Yellowstone National Park is famous for harsh winters but a new study shows summers are also getting harsher, with August 2016 ranking as one of the hottest summers in the last 1,250 years.

The new study drew upon samples of living and dead Engelmann spruce trees collected at high elevations in and around Yellowstone National Park to extend the record of maximum summer temperatures back centuries beyond instrumental records. The findings were published in Geophysical Research Letters, AGU’s journal for high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

The team, led by Karen Heeter, a dendrochronologist at the University of Idaho in Moscow, found that the 20th and 21st centuries, and especially the past 20 years, are the hottest in the new 1,250-year record. Previously, temperature records for the Yellowstone region were only available going back to 1905.

The climate data gleaned from the tree ring samples fits closely with the instrumental record over the past 100 years. The team was also able to identify several known periods of warming in the tree ring record, including the Medieval Climate Anomaly that occurred between 950 and 1250, as well as several multidecadal periods of cooling that occurred prior to 1500.

“If we can find historical analogs to the warming conditions we’re seeing now, that’s really valuable,” Heeter said. “The records show that the 1080s were extremely warm and in the 16th century, there was a period of prolonged warmth for about 130 years.”

The warm periods of the past were characterized by substantial multidecadal temperature variability, markedly different from the prolonged, intense warming trends seen over the past 20 years. Today’s unprecedented warming may spell trouble for the Greater Yellowstone Ecosystem, the pride of the US National Park system, by exacerbating droughts, wildfires, and other types of ecosystem stress.

The new record provides crucial data for scientists seeking to better understand the relationships between increasing temperatures and environmental factors like fire regimes, seasonal snowpack, and vegetation changes, Heeter said. “The warming trend we see beginning around 2000 is the most intense in the record. The rate of warmth over a relatively short period of time is alarming and has important implications for ecosystem health and function,” she said.

In addition to providing one of the few millennial-length temperature records for North America, the study identified summer surface temperature trends using a new tree ring technique called Blue Intensity, Heeter said.

“Unlike traditional tree ring methods where we just measure annual or sub-annual growth rings, Blue Intensity gives us a representation of ring density,” Heeter said. Density of the outermost part of annual growth rings, called the latewood, has been shown to correlate closely with maximum summer temperatures, she said.

Developed in Europe in the early 2000s, Blue Intensity has been shown to be a more cost effective method of assessing tree ring density than other methods, says Robert Wilson, a dendrochronologist at the University of St. Andrews in Scotland, who was not involved in the new study.

Engelmann spruce trees, found throughout North America from Canada to Mexico, are the “perfect species for BI methods due to their uniformly light-colored wood,” Wilson said, helping to assuage the main drawback of the Blue Intensity method, which can be biased by color variations in wood samples. Engelmann spruce also live between 600 and 800 years and rot relatively slowly. The pristine setting of Yellowstone National Park provided an opportunity to source samples from living and downed trees dating back 1,250 years.

Heeter and colleagues are also working on applying Blue Intensity methods to more locations across North America, particularly in southern states, where obtaining a strong temperature signal from traditional tree ring data can be difficult. The team has already made the new Greater Yellowstone dataset available to other researchers by adding it to the International Tree-Ring Data Bank, which is publicly available from NOAA.

“I have all these things I’d like to do with [the Yellowstone dataset], such as looking at periods of drought through time or temperature and fire trends,” Heeter said. “But I hope that it might also be useful to other researchers who are studying other aspects of the ecosystem. Honestly, I think the [research] possibilities are endless.”

Reference:
Karen J. Heeter, Maegen L. Rochner, Grant L. Harley. Summer Air Temperature for the Greater Yellowstone Ecoregion (770–2019 CE) Over 1,250 Years. Geophysical Research Letters, 2021; 48 (7) DOI: 10.1029/2020GL092269

Note: The above post is reprinted from materials provided by American Geophysical Union.

A closer look at the creation of a metamorphic sole

May 22, 2021

This study site was used by researchers to examine a portion of the Oman–United Arab Emirates ophiolite’s metamorphic sole. Credit: Tyler Ambrose

When two of Earth’s tectonic plates collide, the heavier plate is forced underneath and back into the mantle in a process called subduction. During the early stages of newly initiated subduction zones, the uppermost part of the downward traveling plate can detach and accrete to the base of the overriding (upper) plate. Later, these slices can be exposed at Earth’s surface and are known as metamorphic soles.

Soles provide direct evidence of conditions in the subduction zone; however, their interpretation is clouded by uncertainties surrounding how the sole accretes to the base of the upper plate and the process by which it is then exhumed from within the subduction zone. Ambrose et al. attempt to trace this sequence of events by mapping the evolution of the sole’s texture, the arrangement and orientation of a rock’s component minerals. They do so in a region of well-exposed oceanic crust in the United Arab Emirates.

The authors extracted 16 thin sections distributed across a 250-meter exposed section of the sole. The scientists then performed extensive laboratory testing on 10 of the samples. Using the observed mineral distribution and composition, they deduced a gradient in temperature but not pressure across the sole. This gradient implies that the sole attached to the upper plate in layers as the region cooled but that the entire accretion of the sole occurred at depths of 30–40 kilometers.

The study concludes by outlining a three-step sequence for the evolution of the metamorphic sole. At the onset of subduction, the oceanic crust sinks to a depth of 30–40 kilometers and is heated to temperatures of 700°C–900°C. Then, during peak metamorphic conditions, increased viscosity during the formation of a granulite facies (a kind of metamorphic rock that contains minerals) assemblage causes the subduction plate boundary to migrate deeper into the slab, leaving behind the high-temperature portion of the sole. Finally, as the region cools, the sole grows with layers at similar pressures but increasingly lower temperatures.

Reference:
T. K. Ambrose et al, Burial, Accretion, and Exhumation of the Metamorphic Sole of the Oman‐UAE Ophiolite, Tectonics (2021). DOI: 10.1029/2020TC006392

Note: The above post is reprinted from materials provided by Eos, hosted by the American Geophysical Union.

Mammals in the time of dinosaurs held each other back

May 22, 2021

Early lineages of mammal like this large Gobiconodon from Mongolia, outcompeted the ancestors of modern mammals in the time of dinosaurs. Credit: Corbin Rainbolt

A new study led by researchers from the Oxford University Museum of Natural History, University of Oxford and the University of Birmingham for Current Biology has used new methods to analyse the variability of mammal fossils, revealing extraordinary results: it was not dinosaurs, but possibly other mammals, that were the main competitors of modern mammals before and after the mass extinction of dinosaurs.

The study challenges old assumptions about why mammals only seemed to diversify, becoming larger and exploring new diets, locomotion and ways of life, after the extinction of the non-bird dinosaurs. It points to a more complex story of competition between distinct mammal groups. The new research also highlights the importance of testing old and established ideas about evolution using the latest statistical tools.

“There were lots of exciting types of mammals in the time of dinosaurs that included gliding, swimming and burrowing species, but none of these mammals belonged to modern groups, they all come from earlier branches in the mammal tree.” said Dr Elsa Panciroli, a researcher from the Oxford University Museum of Natural History and a co-author of the study. “These other kinds of mammals mostly became extinct at the same time as the non-avian dinosaurs, at which point modern mammals start to become larger, explore new diets and ways of life. From our research it looks like before the extinction it was the earlier radiations of mammals that kept the modern mammals out of these exciting ecological roles by outcompeting them.”

Most of the mammal species alive today trace their origins to groups that expanded explosively 66 million years ago, when a mass extinction killed all non-bird dinosaurs. It was traditionally thought that, before the extinction, mammals lived in the shadow of the dinosaurs. They were supposedly prevented from occupying the niches that were already occupied by the giant reptiles, keeping the mammals relatively small and unspecialised in terms of diet and lifestyle. It appeared that they were only able to flourish after the dinosaurs’ disappearance left these niches vacant.

However, new statistical methods were used to analyse how constrained different groups of mammals were in their evolution before and after the mass extinction. These methods identified the point where evolution stopped producing new traits and started producing features that had already evolved in other lineages. This allowed the researchers to identify the evolutionary “limits” placed on different groups of mammals, showing where they were being excluded from different niches by competition with other animals. The results suggest that it may not have been the dinosaurs that were placing the biggest constraints on the ancestors of modern mammals, but their closest relatives.

The study looked at the anatomy of all the different kinds of mammals living alongside dinosaurs, including the ancestors of modern groups, also known as therians. By measuring how frequently new features appeared, such as changes in the size and shape of their teeth and bones, and the pattern and timing of their appearance before and after the mass extinction, the researchers determined that the modern mammals were more constrained during the time of the dinosaurs than their close relatives. This meant that while their relatives were exploring larger body sizes, different diets, and novel ways of life such as climbing and gliding, they were excluding modern mammals from these lifestyles, keeping them small and generalist in their habits.

“This result makes very little sense if you assume that it was the dinosaurs constraining the therians” said Dr Neil Brocklehurst of the University of Oxford, who led the research. “There is no reason why the dinosaurs would be selectively competing with just these mammals and allowing others to prosper. It instead appears that the therians were being held back by these other groups of mammals.”

The researchers suggest the extinction of other mammal groups was more important in paving the way for modern mammal success. As further evidence for this, the researchers looked at body size in different mammal groups. They discovered that both the smallest and largest mammals showed the same release from constraints following the dinosaur extinction, suggesting that size made little difference to their success.

Co-author Dr Gemma Benevento of the University of Birmingham said, “Most of the mammals that lived alongside the dinosaurs were less than 100g in body mass — that’s smaller than any non-bird dinosaur. Therefore, these smallest mammals would probably not have been directly competing with dinosaurs. Despite this, small mammals show diversity increases after the extinction which are just as profound as those seen in larger mammals.”

Dr Brocklehurst added, “Palaeontology is undergoing a revolution. We have greatly expanded the toolkit available to analyse large datasets and directly test our ideas about evolution. Most studies of the mammal radiation have focused on how fast they evolved, but analysing what limits there were on the evolution provides new perspectives. We have had to rethink many of our theories using these state-of-the-art approaches.”

Reference:
Neil Brocklehurst, Elsa Panciroli, Gemma Louise Benevento, Roger B.J. Benson. Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals. Current Biology, 2021; DOI: 10.1016/j.cub.2021.04.044

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

18.5 million year old vine fossil identified as new species

May 8, 2021

A cross-section of an 18.5 million-year-old fossil of Ampelorhiza heteroxylon. Credit: Nathan Jud/Provided

An 18.5 million-year-old fossil found in Panama provides evidence of a new species and is the oldest reliable example of a climbing woody vine known as a liana from the soapberry family. The discovery sheds light on the evolution of climbing plants.

The new species, named Ampelorhiza heteroxylon, belongs to a diverse group of tropical lianas called Paullinieae, within the soapberry family (Sapindaceae). More than 475 species of Paullinieae live in the tropics today.

Researchers identified the species from fossilized roots that revealed features known to be unique to the wood of modern climbing vines, adaptations that allow them to twist, grow and climb.

The study, “Climbing Since the Early Miocene: The Fossil Record of Paullinieae (Sapindaceae),” was published April 7 in the journal PLOS ONE.

“This is evidence that lianas have been creating unusual wood, even in their roots, as far back as 18 million years ago,” said wood anatomist Joyce Chery ’13, assistant research professor in the School of Integrative Plant Science, Plant Biology Section, in the College of Agriculture and Life Sciences, and a corresponding author of the paper.

“Before this discovery, we knew almost nothing about when or where these lianas evolved or how rapidly they diversified,” said first author Nathan Jud, assistant professor of plant biology at William Jewell College and a former Cornell postdoctoral researcher.

Panama was a peninsula 18.5 to 19 million years ago, a volcanic landscape covered with tropical forest in North America and separated from South America by a Central American seaway. While these forests contained North American animals, the plants mostly descended from South American tropical plants that had dispersed across the seaway, Jud said.

“The fossil we described is the oldest macrofossil of these vines,” he said, “and they were among the plants that made it to North America long before the Great American Biotic Interchange when large animals moved between the continents some 3 million years ago.”

In the study, the researchers made thin slices of the fossil, examined the arrangements and dimensions of tissues and water conducting vessels under a microscope and created a database of all the features. They then studied the literature to see how these features matched up with the living and fossil records of plants.

“We were able to say, it really does look like it’s a fossil from the Paullinieae group, given the anatomical characteristics that are similar to species that live today,” Chery said.

During their analyses, the researchers identified features that are characteristic of lianas. Most trees and shrubs have water-conducting tissues (which transport water and minerals from roots to leaves) that are all roughly the same size when viewed in a cross-section; in vines, these conduits come in two sizes, big and small, which is exactly what the researchers discovered in the fossil.

“This is a feature that is pretty specific to vines across all sorts of families,” Chery said.

The two vessel sizes provide insurance for a twisting and curving plant, as large vessels provide ample water flow, but are also vulnerable to collapse and develop cavities that disrupt flow. The series of smaller vessels offers a less vulnerable backup water transport system, Chery said.

Also, cross-sections of the wood in trees and shrubs are circular, but in the fossil, and in many living vines, such cross-sections are instead irregular and lobed.

Thirdly, on the walls of those vascular vessels, they found long horizontal perforations that allow for water to flow in lateral directions. That is a distinguishing feature of lianas in the soapberry family, Chery said.

In future work, now that they can place the lianas of Sapindaceae to 18.5 million years ago, the researchers intend to continue their investigation of the evolutionary history and diversification of this family. Chery also plans to investigate how wood has evolved in this group of vines, including identifying the genes that contribute to lobe-shaped stems.

The study was partly funded by the National Science Foundation.

Reference:
Nathan A. Jud, Sarah E. Allen, Chris W. Nelson, Carolina L. Bastos, Joyce G. Chery. Climbing since the early Miocene: The fossil record of Paullinieae (Sapindaceae). PLOS ONE, 2021; 16 (4): e0248369 DOI: 10.1371/journal.pone.0248369

Note: The above post is reprinted from materials provided by Cornell University. Original written by Krishna Ramanujan.

A deep reservoir of primordial helium in the Earth

May 8, 2021

The Earth has a layered internal structure with the crust, upper mantle, mantle transition zone, lower mantle, outer core, and inner core from the surface to the center. In the Earth’s formation stage at approximately 4.6 billion years ago, the heavy metal components were separated from silicates and sank in the magma ocean, and a core formed at the center of the Earth. In this core-mantle separation process, partitioning of noble gases between the core and mantle occurred. Credit: Taku Tsuchiya, Ehime University

Noble gases, including helium, neon, and argon, are characterized by high chemical inertness which causes low reactivity with other materials and high volatility. Among them, ³He, ²⁰Ne, and ³⁶Ar are particular isotopes which were components of the primordial solar nebula existing in space before the Earth had formed. ³He is also known to have been produced by the Big Bang and a substantial amount is contained in ocean island basalts, e.g., Loihi Seamount, Hawaii (e.g., Dixon et al., 2000). Such basalts are hot spot rocks which originated in the Earth’s deep interior, indicating that ³He was stored somewhere in the deep Earth. It is surprising that such primordial helium has been confined in the Earth’s interior for 4.6 billion years, from the time of the Earth’s formation to now, even though noble gases are highly volatile. Considering the vigorous mantle convection throughout the geological time scale (e.g., Van der Hilst et al., 1997; Wang et al., 2015), it would seem unlikely that noble gases would be trapped inside the Earth so long. Although it has been suggested that the candidates for the location of the reservoir of primordial helium are the deepest mantle and the core (image 1), its location remains unclear. This is one of the biggest mysteries in deep Earth science and still under intense debate.

The outer core, composed mainly of liquid iron, is a candidate for the reservoir of primordial helium, and there is a possibility that helium is supplied from this area to the mantle. Such noble gases could be carried up to the surface with upwelling mantle plumes. This seems a reasonable scenario to explain the fact that rocks collected in the active hot spot areas, such as in Loihi Seamount and Iceland, contain high concentrations of primordial noble gases. If the outer core is the reservoir of noble gases, the necessary amounts would have to be dissolved in liquid iron under high pressure. However, previous experimental studies reported that at relatively low pressures from 1 atm to 20 GPa, noble gases generally prefer silicates (the mantle) to metals (the core) (e.g., Bouhifd et al., 2013). (The property by which a particular solute is dissolved into different coexisting solvents in different amounts is called element partitioning.) On the other hand, there exists no study so far which has investigated the property of metal/silicate partitioning of noble gases at pressures of 10 GPa to 100 GPa, corresponding to the conditions where the Earth’s proto core reacted with the magma ocean in the early stage of the Earth’s formation. Therefore, it is hard to exclude the possibility that the core is a reservoir of noble gases. If noble gases change to prefer metals with increasing pressure (a property called siderophile), more could be dissolved into the core, and it is important to clarify the partitioning properties of noble gases.

Precise experimental measurements of elements partitioning under high pressure are quite difficult, so in this study, by means of the quantum mechanical computer simulation technology called the ab initio method, the partitioning properties of helium and argon between liquid iron and molten silicate (magma) were investigated in the wide pressure range of 20 GPa to 135 GPa. Computer simulations of element partitioning were conducted by calculating the reaction energies when noble gases are dissolved into liquid iron and molten silicate. By comparing these reaction energies, the relative differences in the equilibrium of the noble gas concentrations in coexisting liquid iron and molten silicate could be estimated. Based on the fundamental principle of thermodynamics, noble gases are dissolved more into a solvent with a smaller reaction energy, and thus larger differences in the reaction energies more greatly enhance the contrast in the noble gas concentrations in liquid iron and molten silicate. Special techniques are required to compute the reaction energies of noble gases with liquids such as liquid iron and molten silicate. In this study, this was conducted by combining a method called the thermodynamic integration method, authorized by statistical mechanics, with the ab initio molecular dynamics method.

The calculations of the partitioning properties of noble gases between liquid iron and molten silicate obtained by these original techniques indicate for the first time in the world that noble gases remain, preferring molten silicate to liquid iron up to the core-mantle boundary pressure (135 GPa), and there is no distinct increase in their siderophility. The amount of helium dissolved in the core in the early stage of the Earth’s formation is considered to be approximately 1/100 of the amount dissolved in the mantle. (In contrast, argon is found to become more siderophile with increasing pressure. The different high-pressure behaviors are caused by the different atomic sizes of helium and argon.) This result, showing no considerable pressure effects, suggests that the core is unsuitable as the primordial reservoir, but the estimated total amount of 3He stored in the core is, even if only 1/100, enough to explain the 3He flux measured in the present hot spots.

Even though 100 times more helium was dissolved into the magma ocean, most of it would have evaporated into the air while it solidified and only marginal amounts would be left due to its high volatility. In contrast, helium dissolved in the core during the proto core formation in the magma ocean was confined to the core after the magma ocean solidified. It is considered that such helium has been gradually seeping into the mantle across the core-mantle boundary and ascending to the surface with upwelling plumes over a long period of time. It can be measured in the hot spot rocks even now. These results provide conclusive support showing that the 3He reservoir is at the core. This is an important insight for the location of the primordial reservoir, one of the long-standing mysteries in geoscience.

Reference:
Zhihua Xiong et al. Helium and Argon Partitioning Between Liquid Iron and Silicate Melt at High Pressure, Geophysical Research Letters (2020). DOI: 10.1029/2020GL090769

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

What can a dinosaur’s inner ear tell us? Just listen

May 7, 2021

Hesperornis image provided by the Yale Peabody Museum of Natural History. (Photo: Robert Lorenz)Hesperornis image provided by the Yale Peabody Museum of Natural History. (Photo: Robert Lorenz) — Hesperornis image provided by the Yale Peabody Museum of Natural History. (Photo: Robert Lorenz)

If paleontologists had a wish list, it would almost certainly include insights into two particular phenomena: how dinosaurs interacted with each other and how they began to fly.

The problem is, using fossils to deduce such behavior is a tricky business. But a new, Yale-led study offers a promising entry point — the inner ear of an ancient reptile.

According to the study, the shape of the inner ear offers reliable signs as to whether an animal soared gracefully through the air, flew only fitfully, walked on the ground, or sometimes went swimming. In some cases, the inner ear even indicates whether a species did its parenting by listening to the high-pitched cries of its babies.

“Of all the structures that one can reconstruct from fossils, the inner ear is perhaps that which is most similar to a mechanical device,” said Yale paleontologist Bhart-Anjan Bhullar, senior author of the new study, published in the journal Science.

“It’s so entirely dedicated to a particular set of functions. If you are able to reconstruct its shape, you can reasonably draw conclusions about the actual behavior of extinct animals in a way that is almost unprecedented,” said Bhullar, who is an assistant professor of earth and planetary sciences and an assistant curator at the Yale Peabody Museum of Natural History.

Working with colleagues at the American Museum of Natural History, Bhullar and first author Michael Hanson of Yale compiled a matrix of inner ear data for 128 species, including modern-day animals such as birds and crocodiles, along with dinosaurs such as Hesperornis, Velociraptor, and the pterosaur Anhanguera.

Hesperornis, an 85-million-year-old bird-like species that had both teeth and a beak, was the inspiration for the research. The Yale Peabody Museum of Natural History has the world’s only three-dimensional fossil that preserves a Hesperornis inner ear.

“I was aware of literature associating cochlear dimensions with hearing capability, and semicircular canal structure with locomotion in reptiles and birds, so I became curious as to how Hesperornis would fit into the picture,” said Hanson, a graduate student at Yale.

Hanson and Bhullar analyzed the Hesperornis inner ear with CT scanning technology to determine its three-dimensional shape.

Next, the researchers conducted the same analysis with a variety of other fossils — and current species — to determine whether the inner ear provided strong indications of behavior. In many cases, the researchers created 3D models from crushed or partially-crushed skull fossils.

After assembling the data, the researchers found clusters of species with similar inner ear traits. The clusters, they said, correspond with the species’ similar ways of moving through and perceiving the world.

Several clusters were the result of the structure of the top portion of the inner ear, called the vestibular system. This, said Bhullar, is “the three-dimensional structure that tells you about the maneuverability of the animal. The form of the vestibular system is a window into understanding bodies in motion.”

One vestibular cluster corresponded with “sophisticated” fliers, species with a high level of aerial maneuverability. This included birds of prey and many songbirds.

Another cluster centered around “simple” fliers like modern fowl, which fly in quick, straight bursts, and soaring seabirds and vultures. Most significantly, the inner ears of birdlike dinosaurs called troodontids, pterosaurs, Hesperornis, and the “dino-bird” Archaeopteryx fall within this cluster.

The researchers also identified a cluster of species which had a similar elongation of the lower portion of the inner ear — the cochlear system — that has to do with hearing range. This cluster featured a fairly large group of species, including all modern birds and crocodiles, which together form a group called archosaurs, the “ruling reptiles.”

Bhullar said the data suggest that the cochlear shape’s transformation in ancestral reptiles coincided with the development of high-pitched location, danger, and hatching calls in juveniles.

It implies that adults used their new inner ear feature to parent their young, the researchers said.

“All archosaurs sing to each other and have very complex vocal repertoires,” Bhullar said. “We can reasonably infer that the common ancestors of crocodiles and birds also sang. But what we didn’t know was when that occurred in the evolutionary line leading to them. We’ve discovered a transitional cochlea in the stem archosaur Euparkeria, suggesting that archosaur ancestors began to sing when they were swift little predators a bit like reptilian foxes.”

Co-authors of the study are Mark Norell and Eva Hoffman of the American Museum of Natural History.

The Yale Department of Earth & Planetary Sciences, the Yale Institute for Biospheric Studies, the American Museum of Natural History, and the National Science Foundation funded the research.

Reference:
Michael Hanson, Eva A. Hoffman, Mark A. Norell, Bhart-Anjan S. Bhullar. The early origin of a birdlike inner ear and the evolution of dinosaurian movement and vocalization. Science, 2021; 372 (6542): 601 DOI: 10.1126/science.abb4305

Note: The above post is reprinted from materials provided by Yale University. Original written by Jim Shelton.

Most human origins stories are not compatible with known fossils

May 7, 2021

The last common ancestor of chimpanzees and humans represents the starting point of human and chimpanzee evolution. Fossil apes play an essential role when it comes to reconstructing the nature of our ape ancestry. Printed with permission from © Christopher M. Smith — The last common ancestor of chimpanzees and humans represents the starting point of human and chimpanzee evolution. Fossil apes play an essential role when it comes to reconstructing the nature of our ape ancestry.
Printed with permission from © Christopher M. Smith

In the 150 years since Charles Darwin speculated that humans originated in Africa, the number of species in the human family tree has exploded, but so has the level of dispute concerning early human evolution. Fossil apes are often at the center of the debate, with some scientists dismissing their importance to the origins of the human lineage (the “hominins”), and others conferring them starring evolutionary roles. A new review out on May 7 in the journal Science looks at the major discoveries in hominin origins since Darwin’s works and argues that fossil apes can inform us about essential aspects of ape and human evolution, including the nature of our last common ancestor.

Humans diverged from apes — specifically, the chimpanzee lineage — at some point between about 9.3 million and 6.5 million years ago, towards the end of the Miocene epoch. To understand hominin origins, paleoanthropologists aim to reconstruct the physical characteristics, behavior, and environment of the last common ancestor of humans and chimps.

“When you look at the narrative for hominin origins, it’s just a big mess — there’s no consensus whatsoever,” said Sergio Almécija, a senior research scientist in the American Museum of Natural History’s Division of Anthropology and the lead author of the review. “People are working under completely different paradigms, and that’s something that I don’t see happening in other fields of science.”

There are two major approaches to resolving the human origins problem: “Top-down,” which relies on analysis of living apes, especially chimpanzees; and “bottom-up,” which puts importance on the larger tree of mostly extinct apes. For example, some scientists assume that hominins originated from a chimp-like knuckle-walking ancestor. Others argue that the human lineage originated from an ancestor more closely resembling, in some features, some of the strange Miocene apes.

In reviewing the studies surrounding these diverging approaches, Almécija and colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the hominin origins problem. “Top-down” studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are just the survivors of a much larger, and now mostly extinct, group. On the other hand, studies based on the “bottom-up”approach are prone to giving individual fossil apes an important evolutionary role that fits a preexisting narrative.

“In The Descent of Man in 1871, Darwin speculated that humans originated in Africa from an ancestor different from any living species. However, he remained cautious given the scarcity of fossils at the time,” Almécija said. “One hundred fifty years later, possible hominins — approaching the time of the human-chimpanzee divergence — have been found in eastern and central Africa, and some claim even in Europe. In addition, more than 50 fossil ape genera are now documented across Africa and Eurasia. However, many of these fossils show mosaic combinations of features that do not match expectations for ancient representatives of the modern ape and human lineages. As a consequence, there is no scientific consensus on the evolutionary role played by these fossil apes.”

Overall, the researchers found that most stories of human origins are not compatible with the fossils that we have today.

“Living ape species are specialized species, relicts of a much larger group of now extinct apes. When we consider all evidence — that is, both living and fossil apes and hominins — it is clear that a human evolutionary story based on the few ape species currently alive is missing much of the bigger picture,” said study co-author Ashley Hammond, an assistant curator in the Museum’s Division of Anthropology.

Kelsey Pugh, a Museum postdoctoral fellow and study co-author adds, “The unique and sometimes unexpected features and combinations of features observed among fossil apes, which often differ from those of living apes, are necessary to untangle which features hominins inherited from our ape ancestors and which are unique to our lineage.”

Living apes alone, the authors conclude, offer insufficient evidence. “Current disparate theories regarding ape and human evolution would be much more informed if, together with early hominins and living apes, Miocene apes were also included in the equation,” says Almécija. “In other words, fossil apes are essential to reconstruct the ‘starting point’ from which humans and chimpanzees evolved.”

Reference:
Sergio Almécija, Ashley S. Hammond, Nathan E. Thompson, Kelsey D. Pugh, Salvador Moyà-Solà, David M. Alba. Fossil apes and human evolution. Science, 2021; 372 (6542): eabb4363 DOI: 10.1126/science.abb4363

Note: The above post is reprinted from materials provided by American Museum of Natural History.

Microfossil found in Scottish Highlands could be a new insight into animal evolution

May 7, 2021

An enhanced image of Bicellum showing an outer wall of sausage-shaped cells enclosing an inner cell mass. Credit: Boston College

The billion-year-old fossil of an organism, exquisitely preserved in the Scottish Highlands, reveals features of multicellularity nearly 400 million years before the biological trait emerged in the first animals, according to a new report in the journal Current Biology by an international team of researchers, including Boston College paleobotanist Paul K. Strother.

The discovery could be the “missing link” in the evolution of animals, according to the team, which included scientists from the U.S., United Kingdom, and Australia. The microfossil, discovered at Loch Torridon, contains two distinct cell types and could be the earliest example of complex multicellularity ever recorded, according to the researchers.

The fossil offers new insight into the transition of single celled organisms to complex, multicellular animals. Modern single-celled holozoa include the most basal living animals and the fossil discovered shows an organism which lies somewhere between single cell and multicellular animals, or metazoa.

“Our findings show that the genetic underpinnings of cell-to-cell cohesion and segregation — the ability for different cells to sort themselves into separate regions within a multicellular mass — existed in unicellular organisms a billion years ago, some 400 million years before such capabilities were incorporated into the first animals,” said Strother, a research professor in the Department of Earth and Environmental Sciences at Boston College.

The fossil’s discovery in an inland lake shifts the focus on the first forms of early life from the ocean to freshwater.

Animals, or etazoa, are one of only five groups of organisms that have evolved complex multicellularity — organisms that grow from a single cell that develops into a myriad of different cells and tissues. Animals probably evolved from unicellular ancestors that went through multicellular stages during their life cycles, said Strother, an expert in paleobotany and palynology, the study of fossil spores and pollen. Land plants, too, achieved complex multicellularity when they evolved from simpler algal ancestors some time during the early Paleozoic from about 500 to 400 million years ago..

“We describe here a new fossil that is similar to living unicellular relatives of animals, belonging to the group Ichthyosporea,” said Strother. “Our fossil shows life-cycle stages with two different kinds of cells, which could be the first step toward the evolution of complex multicellularity in the evolutionary lineage leading to the Metazoa.”

The study was based on populations of cells preserved in the mineral phosphate that were collected from billion-year-old lake deposits found in the northwest Scottish Highlands, Strother said. Samples are prepared in rock thin sections which allow microfossils to be seen under the light microscope or with a focused ion beam microscope.

The microfossils were discovered as part of an ongoing project to describe life living in freshwater lakes one billion years ago, using samples collected in Scotland and Michigan by Strother beginning in 2008, with support from NASA and the National Geographic Society, and now the Natural Environment Research Council in the UK.

The new fossil has been described and formally named Bicellum brasieri in the new report.

Strother said the discovery has the potential to change the way scientists look at the earliest forms of life on Earth.

“Our study of life in billion-year-old lakes is challenged by our ability to determine which kinds of organisms are represented in these deposits,” he said. “Previously we have assumed that most of what we see in these deposits are various kinds of extinct algae, but the morphological features of Bicellum really are more like those of modern-day unicellular relatives of animals. This is causing us to broaden our approach to reconstructing the diversity and ecology of life on Earth one billion years ago.”

The discovery will allow researchers to expand upon a more thorough reconstruction of the life-cycle of Bicellum, Strother said.

“Armed with comparative morphology with modern day Ichthyosporeans, we may be able to recognize additional morphogenic stages and determine how a single generative cell divides to become a multicellular cell mass,” he said.

Reference:
Paul K. Strother, Martin D. Brasier, David Wacey, Leslie Timpe, Martin Saunders, Charles H. Wellman. A possible billion-year-old holozoan with differentiated multicellularity. Current Biology, 2021; DOI: 10.1016/j.cub.2021.03.051

Note: The above post is reprinted from materials provided by Boston College. Original written by Ed Hayward.

Previously unrecognized tsunami hazard identified in coastal cities

May 7, 2021

Researchers also want to encourage the locals to develop practical evacuation plans to help them feel less pessimistic about their survival odds. Credit: Katsushika Hokusai

A new study found overlooked tsunami hazards related to undersea, near-shore strike-slip faults, especially for coastal cities adjacent to faults that traverse inland bays. Several areas around the world may fall into this category, including the San Francisco Bay area, Izmit Bay in Turkey and the Gulf of Al-Aqaba in Egypt.

The study led by University of Illinois Urbana-Champaign civil and environmental engineering professor Ahmed Elbanna and professor Ares Rosakis of the California Institute of Technology used the Blue Waters supercomputer at the National Center for Supercomputing Applications to model tsunami hazards related to strike-slip faults around the globe. The results are published in the Proceedings of the National Academy of Sciences.

“Whenever we saw large tsunamis triggered by earthquakes along strike-slip faults, people assumed that perhaps the earthquake had caused an undersea landslide, displacing water that way,” Rosakis said.

The researchers said that a strike-slip fault exists when two blocks of rock on the fault line slide horizontally past one another. The San Andreas Fault is an example of a strike-slip fault.

In September 2018, a moderate 7.5 magnitude earthquake and unexpectedly powerful tsunami swept through Palu, a city situated on the inland side of Palu Bay on the Indonesian island of Sulawesi. The quake occurred along a northwest-southeast trending strike-slip fault that runs through the city and plunges below the bay along Palu’s northwest shore.

“It looked like a bulldozer had come in and leveled the town,” said co-author Costas Synolakis, the president of Athens College and a professor of civil engineering at the University of Southern California, who surveyed the area following the devastating event. “This is why it is so important that we try to understand what really happened.”

Studies exploring connections between strike-slip faulting and tsunamis exist. However, they focus on specific fault systems or geographic locations, obscuring the complex details of the fault geometry and bathymetry, the study reports.

“What is unique about our study is that instead of considering a location-specific event, we focused on the fundamentals of a strike-slip fault system interacting within the boundaries of a narrow bay,” Elbanna said. “We opted to simulate a very basic planar fault passing through a very simplified smooth-bottomed bay, similar to a bathtub. Having this simplified baseline model allows us to generalize to any place on the planet that may be at risk.”

Intersonic earthquakes are fault ruptures that happen so quickly that their movement outpaces the seismic shear waves they generate — like a sonic boom, but with the shock wave moving through the earth’s crust. The simulations found that intersonic earthquakes can provide enough energy and large enough horizontal displacements to trigger large tsunami waves.

When such earthquakes occur within a narrow bay, the researchers reported three distinct phases that can lead to a tsunami: the initial fault movement and shockwave causing almost instantaneous shaking of the coastal land; the displacement of water while the earthquake is occurring; and gravity-driven motion of the tsunami wave after the ground motion has subsided that carries the wave to shore.

“Each of these phases will have a different effect depending on the unique geography of the surrounding land and bathymetry of the bay,” Elbanna said. “And, unlike the earthquakes and subsequent water displacement that occur many miles offshore, an earthquake and tsunami that occurs within the narrow confines of a bay will allow for very little warning time for the coast.”

Elbanna compares the effect of horizontal strike-slip fault displacements to holding a water cup in your hand and shaking it horizontally.

“The sloshing motion is a result of the horizontal shaking. When an earthquake occurs along a strike-slip fault in a narrow bay, the horizontal ground motion pushes and pulls the boundaries of the bay leading to displacement of water in the vertical direction and initiation of the tsunami,” he said.

“The physics-based model used in this study provides critical insight about the hazard associated with strike-slip faulting, particularly, the need to account for such risk to mitigate future damage to other bays traversed by strike-slip faults,” said Illinois graduate student Mohamed Abdelmeguid, who conducted the simulations along with former graduate student Xiao Ma, currently a senior research scientist at Exxon Mobil.

The at-risk regions identified by the team — Northern California, Turkey and Egypt — have experienced intersonic earthquakes in the past, and the researchers recommend revisiting the tsunami hazard rating of underwater strike-slip faults, particularly those traversing narrow bays.

“It may not look like the tsunami scene from Dwayne Johnson’s ‘San Andreas’ movie, but the tsunami risk for Northern California and several places worldwide need to be seriously revisited,” Elbanna said.

Reference:
Ahmed Elbanna et al. Anatomy of strike-slip fault tsunami-genesis. PNAS, 2021 DOI: 10.1073/pnas.2025632118

Note: The above post is reprinted from materials provided by University of Illinois at Urbana-Champaign, News Bureau. Original written by Lois Yoksoulian.

New research uncovers continental crust emerged 500 million years earlier than thought

May 7, 2021

A close-up image of bladed barite crystals in the Mapepe Formation in the Barberton Greenstone Belt of South Africa. Credit: Desiree Roerdink

The first emergence and persistence of continental crust on Earth during the Archaean (4 billion to 2.5 billion years ago) has important implications for plate tectonics, ocean chemistry, and biological evolution, and it happened about half a billion years earlier than previously thought, according to new research being presented at the EGU General Assembly 2021.

Once land becomes established through dynamic processes like plate tectonics, it begins to weather and add crucial minerals and nutrients to the ocean. A record of these nutrients is preserved in the ancient rock record. Previous research used strontium isotopes in marine carbonates, but these rocks are usually scarce or altered in rocks older than 3 billion years.

Now, researchers are presenting a new approach to trace the first emergence of old rocks using a different mineral: “barite.”

Barite forms from a combination of sulfate coming from ocean water mixing with barium from hydrothermal vents. Barite holds a robust record of ocean chemistry within its structure, useful for reconstructing ancient environments. “The composition of the piece of barite we pick up in the field now that has been on Earth for three and a half billion years, is exactly the same as it was when it when it actually precipitated,” says Desiree Roerdink, a geochemist at University of Bergen, Norway, and team leader of the new research. “So in essence, it is really a great recorder to look at processes on the early Earth.”

Roerdink and her team tested six different deposits on three different continents, ranging from about 3.2 billion to 3.5 billion years old. They calculated the ratio of strontium isotopes in the barite, and from there, inferred the time where the weathered continental rock made its way to the ocean and incorporated itself into the barite. Based on the data captured in the barite, they found that weathering started about 3.7 billion years ago — about 500 million years earlier than previously thought.

“That is a huge time period,” Roerdink says. “It essentially has implications for the way that we think about how life evolved.” She added that scientists usually think about life starting in deep sea, hydrothermal settings, but the biosphere is complex. “We don’t really know if it is possible that life could have developed at the same time on land,” she noted, adding “but then that land has to be there.”

Lastly, the emergence of land says something about plate tectonics and the early emergence of a geodynamic Earth. “To get land, you need processes operating to form that continental crust, and form a crust that is chemically different from the oceanic crust,” Roerdink says.

Note: The above post is reprinted from materials provided by European Geosciences Union.

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