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Enigmatic African fossils rewrite story of when lemurs got to Madagascar

Fossilized fragments of primate jaws and teeth from Africa are changing what researchers thought they knew about when lemurs made it to Madagascar.
Fossilized fragments of primate jaws and teeth from Africa are changing what researchers thought they knew about when lemurs made it to Madagascar. Shown here is Propotto leakeyi, which lived roughly 20 million years ago in Kenya. Original housed in the National Museums of Kenya. Credit: 3-D microCT scans and animation generated at Duke SMIF

Discovered more than half a century ago in Kenya and sitting in museum storage ever since, the roughly 20-million-year-old fossil Propotto leakeyi was long classified as a fruit bat.

Now, it’s helping researchers rethink the early evolution of lemurs, distant primate cousins of humans that today are only found on the island of Madagascar, some 250 miles off the eastern coast of Africa. The findings could rewrite the story of just when and how they got to the island.

In a study to be published August 21 in the journal Nature Communications, researchers have re-examined Propotto’s fossilized remains and suggest that the strange creature wasn’t a bat, but an ancient relative of the aye-aye, the bucktoothed nocturnal primate that represents one of the earliest branches of the lemur family tree.

The reassessment challenges a long-held view that today’s 100-some lemur species descended from ancestors that made their way to Madagascar in a single wave more than 60 million years ago, becoming some of the first mammals to colonize the island.

Instead, the study lends support to the idea that two lineages of lemurs split in Africa before coming to Madagascar. One lineage eventually led to the aye-aye, and the other to all other lemurs. There are no lemurs left on mainland Africa. These ancestors then colonized Madagascar independently, and millions of years later than once believed.

“One implication is that lemurs have had a much less extensive evolutionary history on Madagascar than was previously thought,” said study co-author Erik Seiffert, professor of anatomy at the University of Southern California.

When Propotto was first described in the 1960s, experts didn’t agree about what they were looking at. They didn’t have a lot to go on: just three lower jaw bones, each barely an inch long, and a handful of teeth less than three millimeters across.

In 1967, paleontologist George Gaylord Simpson inspected the fragments and classified the specimen as a previously unknown member of the loris family, nocturnal primates with enormous eyes. But a colleague named Alan Walker took a look and thought otherwise, eventually convincing Simpson that the bones belonged to a bat.

For nearly half a century the creature’s identity appeared to have been settled, until 2016, when another paleontologist, the late Gregg Gunnell of Duke University, began taking a fresh look at the fossil. To Gunnell’s eye, the creature’s hind teeth were more reminiscent of a primate than a bat. He also noted the stump of a broken front tooth, just visible in cross section, which would have jutted out from its mouth like a dagger — a trait only known in aye-ayes, the only living primates with rodent-like teeth.

“Gregg wrote to us and said, ‘Tell me I’m crazy,'” Seiffert said.

To verify Propotto’s place in the primate family tree, Seiffert and Steven Heritage of Duke’s Division of Fossil Primates analyzed more than 395 anatomical features and 79 genes for 125 mammal species, living and extinct.

With help from Doug Boyer, associate professor of evolutionary anthropology at Duke, the team also compiled microCT scans of the lower molars of 42 living and extinct mammal groups, including bats, treeshrews and primates. They then used a computer program to compare the bumps, pits and ridges on the scans of Propotto’s teeth to those of other animals.

The researchers found that Propotto shared a number of features with a similarly buck-toothed primate that lived 34 million years ago in Egypt called Plesiopithecus, and that both were ancient relatives of the aye-aye.

In the new study, Seiffert, Gunnell and colleagues propose that the ancestors of aye-ayes split from the rest of the lemur family tree roughly 40 million years ago, while still on the African continent, and the resulting two lineages didn’t make their separate ways to Madagascar until later.

The findings suggest they arrived around the same time as other mammals, such as rodents, Malagasy mongooses and hedgehog- and shrew-like animals called tenrecs. Frogs, snakes and lizards may have made the trip around the same time.

Lemurs can’t swim, so some scientists hypothesize that the small-bodied creatures crossed the 250-mile-wide channel that lies between Africa and Madagascar after being swept out to sea in a storm, by holding on to tree limbs or floating mats of vegetation before finally washing ashore.

But if the arrival were more recent, they might have had a shorter distance to travel, thanks to lower sea levels when the Antarctic ice sheet was much larger.

“It’s possible that lemurs weren’t in Madagascar at all until maybe the Miocene,” as recently as 23 million years ago, Boyer said.

“Some of the lowest sea levels were also during this time,” Heritage said.

Either way, “the fossils tell us something we never could have guessed from the DNA evidence about the history of lemurs on Madagascar,” Boyer said.

Reference:
Gregg F. Gunnell, Doug M. Boyer, Anthony R. Friscia, Steven Heritage, Fredrick Kyalo Manthi, Ellen R. Miller, Hesham M. Sallam, Nancy B. Simmons, Nancy J. Stevens, Erik R. Seiffert. Fossil lemurs from Egypt and Kenya suggest an African origin for Madagascar’s aye-aye. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05648-w

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

Study uses seismic noise to track water levels in underground aquifers

Earth
Earth. Credit: CC0 Public Domain

Seismic noise—the low-level vibrations caused by everything from subway trains to waves crashing on the beach—is most often something seismologists work to avoid. They factor it out of models and create algorithms aimed at eliminating it so they can identify the signals of earthquakes.

But Tim Clements thinks it might be tool to monitor one of the most precious resources in the world—water.

A graduate student working in the lab of Assistant Professor of Earth and Planetary Sciences Marine Denolle, Clements is the lead author of a recent study that used seismic noise to measure the size and the water levels in underground aquifers in California. The technique could even be used to track whether and how aquifers rebound following precipitation, and understand geological changes that might occur as water is pumped out. The study is described in a recently-published paper in Geophysical Research Letters.

“The way this would commonly be done today would be to take a measurement at a groundwater well,” Clements said. “And if you have a network of those wells, you can develop a model where you assume a number of hydrological parameters…and that allows you to measure the health of the aquifer.

“But what we showed is we can just directly measure these waves that are travelling through the entire aquifer,” he continued. “So we don’t have to make those assumptions, because we can directly measure the waves.”

Using those measurements, researchers were able to measure the water depth of the San Gabriel Valley aquifer, located just outside Los Angeles, to within a centimeter. Efforts to measure the size of the aquifer were limited by the existing seismic network, Clements said, and so were accurate only to about a kilometer.

“That gives us a way to begin thinking about volume,” Denolle said. “What we found is that using this method the volume we calculated as having been pumped out of the aquifer equaled the volume that was published.”

“We estimated it at about half a cubic kilometer,” Clements said. “And that’s exactly what the San Gabriel water master said they pumped out during the drought to meet demand.”

That drought, Clements said, was one reason researchers chose to focus on the San Gabriel Valley.

“They had experienced a massive drought over the last five years, and there are over 1 million people who live in this relatively small area outside Los Angeles who depend on the groundwater for all their water-use needs,” he said. “Over the past five years, they had lost a large amount of ground water, and there’s a large financial cost to that, so our goal was to understand if we can use seismic waves to understand what’s happening with the aquifer.”

The region is also already equipped with a network of seismographs, he said, making it relatively easy to obtain seismic noise data and use it to examine the aquifer.

While the study wasn’t the first to hit upon the idea of using seismic noise to study groundwater, Denolle said earlier efforts were hampered because they relied on a signal that was relatively weak in comparison to environmental factors like temperature and pressure.

“This was a large signal we looked at,” she said. “The aquifer oscillated with 20 meters of water-height changes in a couple years, so it’s a bigger signal than any environmental influence.”

The system could also be a useful tool for anyone involved in water resource management, Clements said, because it can give them a moment-to-moment view of precisely what is happening in an underground aquifer.

“This could be used for water management,” Clements said. “In this study, we looked at about 17 years of data, from 2000 to 2017, but going forward this could be used in a water management application, so you could get a picture of what’s happening with the aquifer on a daily basis.”

Aside from providing groundwater measurements, the technique can also be used to monitor the health of an aquifer over time.

“If we had the data, we may be able to use this technology to look back at what aquifers looked like the past and study the long-term evolution of an aquifer,” Denolle said. “One of the challenges for people who manage water resources is whether aquifers still respond elastically, meaning can we recharge it with the same storagage capacity or is it losing capacity over time as we pump water out? Using seismic waves, we can potentially find out whether these aquifers are elastic or not.”

Going forward, Clements said, he plans to pursue ways to improve the resolution of the system at both the micro and macro levels.

Working in collaboration with faculty at Tufts University, he installed wells and seismometers on campus to track changes as groundwater is pumped to the surface to irrigate sports fields. Other efforts are focused on using the existing seismometer network in California to improve ways to measure the overall size of aquifers.

Reference:
Timothy Clements et al, Tracking Groundwater Levels Using the Ambient Seismic Field, Geophysical Research Letters (2018). DOI: 10.1029/2018GL077706

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

Laughing Gas May Have Helped Warm Early Earth and Given Breath to Life

Ancient tiger eye BIF (banded iron formation)
Ancient tiger eye BIF (banded iron formation) rock with varying layers that include iron that fell out of ancient oceans. An eon ago, oceans appear to have been full of ferrous iron, which would have facilitated production of N2O (laughing gas). Credit: Georgia Tech / Allison Carter

More than an eon ago, the sun shone dimmer than it does today, but the Earth stayed warm due to a strong greenhouse gas effect, geoscience theory holds. Astronomer Carl Sagan coined this “the Faint Young Sun Paradox,” and for decades, researchers have searched for the right balance of atmospheric gases that could have kept early Earth cozy.

A new study led by the Georgia Institute of Technology suggests that nitrous oxide, known for its use as the dental sedative laughing gas, may have played a significant role.

The research team carried out experiments and atmospheric computer modeling that in detail substantiated an existing hypothesis about the presence of nitrous oxide (N2O), a powerful greenhouse gas, in the ancient atmosphere. Established research has already pointed to high levels of carbon dioxide and methane, but they may not have been plentiful enough to sufficiently keep the globe warm without the help of N2O.

Jennifer Glass, an assistant professor at Georgia Tech, and Chloe Stanton, formerly an undergraduate research assistant in the Glass lab at Georgia Tech, published the study in the journal Geobiology on Wednesday, August 22, 2018. Their work was funded by the NASA Astrobiology Institute. Stanton is now a graduate research assistant at the Pennsylvania State University.

No ‘boring billion’

The study focused on the middle of the Proterozoic Eon, over a billion years ago. The proliferation of complex life was still a few hundred million years out, and the pace of our planet’s evolution probably appeared deceptively slow.

“People in our field often refer to this middle chapter in Earth’s history roughly 1.8 to 0.8 billion years ago as the ‘boring billion’ because we classically think of it as a very stable period,” said Stanton, the study’s first author. “But there were many important processes affecting ocean and atmospheric chemistry during this time.”

Chemistry in mid-Proterozoic ocean was heavily influenced by abundant soluble ferrous iron (Fe2+) in oxygen-free deep waters.

Ancient iron key

“The ocean chemistry was completely different back then,” said Glass, the study’s principal investigator. “Today’s oceans are well-oxygenated, so iron rapidly rusts and drops out of solution. Oxygen was low in Proterozoic oceans, so they were filled with ferrous iron, which is highly reactive.”

In lab experiments, Stanton found that Fe2+ in seawater reacts rapidly with nitrogen molecules, especially nitric oxide, to yield nitrous oxide in a process called chemodenitrification. This nitrous oxide (N2O) can then bubble up into the atmosphere.

When Stanton plugged the higher fluxes of nitrous oxide into the atmospheric model, the results showed that nitrous oxide could have reached ten times today’s levels if mid-Proterozoic oxygen concentrations were 10 percent of those today. This higher nitrous oxide would have provided an extra boost of global warming under the Faint Young Sun.

Breathing laughing gas

Nitrous oxide could have also been what some ancient life breathed.

Even today, some microbes can breathe nitrous oxide when oxygen is low. There are many similarities between the enzymes that microbes use to breathe nitric and nitrous oxides and enzymes used to breathe oxygen. Previous studies have suggested that the latter evolved from the former two.

The Georgia Tech model provides a plentiful source of nitrous oxide in ancient iron-rich seas for this evolutionary scenario. And prior to the Proterozoic, when oxygen was extremely low, early aquatic microbes could have already been breathing nitrous oxide.

“It’s quite possible that life was breathing laughing gas long before it began breathing oxygen,” Glass said. “Chemodenitrification might have supplied microbes with a steady source of it.”

Note: The above post is reprinted from materials provided by Georgia Institute of Technology.

99-million-year-old beetle trapped in amber served as pollinator to evergreen cycads

mid-Cretaceous beetle Cretoparacucujus cycadophilus
This image shows a dorsal view of the mid-Cretaceous beetle Cretoparacucujus cycadophilus, including the mandibular cavities it likely used for pollination. Credit: Chenyang Cai

Flowering plants are well known for their special relationship to the insects and other animals that serve as their pollinators. But, before the rise of angiosperms, another group of unusual evergreen gymnosperms, known as cycads, may have been the first insect-pollinated plants. Now, researchers reporting in the journal Current Biology on August 16 have uncovered the earliest definitive fossil evidence of that intimate relationship between cycads and insects.

The discovery came in the form of an ancient boganiid beetle preserved in Burmese amber for an estimated 99 million years along with grains of cycad pollen. The beetle also shows special adaptations, including mandibular patches, for the transport of cycad pollen.

“Boganiid beetles have been ancient pollinators for cycads since the Age of Cycads and Dinosaurs,” says Chenyang Cai, now a research fellow at the University of Bristol. “Our find indicates a probable ancient origin of beetle pollination of cycads at least in the Early Jurassic, long before angiosperm dominance and the radiation of flowering-plant pollinators, such as bees, later in the Cretaceous.”

When Cai’s supervisor Diying Huang at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, first showed him the beetle trapped in amber, he was immediately intrigued. He recognized that its large mandibles with bristly cavities might suggest the beetle was a pollinator of cycads.

After cutting, trimming, and polishing the specimen to get a better look under a microscope, Cai’s excitement only grew. The beetle carried several clumps of tiny pollen grains. Cai consulted Liqin Li, an expert in ancient pollen at the Chinese Academy of Sciences, who confirmed that the pollen grains belonged to a cycad.

The researchers also conducted an extensive phylogenetic analysis to explore the beetle’s family tree. Their analysis indicates the fossilized beetle belonged to a sister group to the extant Australian Paracucujus, which pollinate the relic cycad Macrozamia riedlei. The finding, along with the current disjunct distribution of related beetle-herbivore and cycad-host pairs in South Africa and Australia, support an ancient origin of beetle pollination of cycads, the researchers say.

Cai notes that the findings together with the distribution of modern boganiid beetles lead him to suspect that similar beetle pollinators of cycads are yet to be found. He’s been looking for them for the last five years. The challenge, he says, is that older Jurassic beetles are generally found as compression fossils not trapped in amber.

Reference:
Chenyang Cai, Hermes E. Escalona, Liqin Li, Ziwei Yin, Diying Huang, Michael S. Engel. Beetle Pollination of Cycads in the Mesozoic. Current Biology, 2018; DOI: 10.1016/j.cub.2018.06.036

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

Meteorite bombardment likely to have created the Earth’s oldest rocks

Oldest rock on Earth
Oldest rock on Earth: Acasta River gneiss (stock image). Credit: © Xenomanes / Fotolia

Scientists have found that 4.02-billion-year-old silica-rich felsic rocks from the Acasta River, Canada — the oldest rock formation known on Earth — probably formed at high temperatures and at a surprisingly shallow depth of the planet’s nascent crust. The high temperatures needed to melt the shallow crust were likely caused by a meteorite bombardment around half a billion years after the planet formed. This melted the iron-rich crust and formed the granites we see today. These results are presented for the first time at the Goldschmidt conference in Boston (14 August), following publication in the peer-reviewed journal Nature Geoscience.

The felsic rocks (rocks rich in silica/quartz) found at the Acasta River in Canada, are the Earth’s oldest rocks, although there are older mineral crystals*. Scientists have long known that the Acasta rocks are different to the majority of felsic rocks we see today, such as the granites widely used as a building or decorative material. Now a group of scientists from Australia and China have modelled the formation of the oldest Acasta felsic rocks and found that they could only have been formed at low pressures and very high temperatures.

Scientists believe that the primitive crust largely comprised dark, silica-poor mafic rocks, so there has been a question over how the Acasta River felsic rocks could have formed.

“Our modelling shows that the Acasta River rocks derived from the melting of pre-existing iron-rich basaltic rock, which formed the uppermost layers of crust on the primitive Earth,” said team leader Tim Johnson, from Curtin University, Perth.

“We used phase equilibria and trace element modelling to show that the Acasta River rocks were produced by partial melting of the original mafic rocks at very low pressures. It would have needed something special to produce the 900°C temperatures needed to generate these early felsic rocks at such low pressures, and that probably means a drastic event, most likely the intense heating caused by meteorite bombardment.

We estimate that rocks within the uppermost 3km of mafic crust would have been melted in producing the rocks we see today. We think that these ancient felsic rocks would have been very common, but the passage of 4 billion years, and the development of plate tectonics, means that almost nothing remains.

We believe that these rocks may be the only surviving remnants of a barrage of extraterrestial impacts which characterized the first 600 million years of Earth History.”

The Acasta River is part of the Slave Craton formation in Northern Canada, north of Yellowknife and the Great Slave Lake. The area is the homeland of the Tlicho people, which led to the geologists who discovered the rocks giving them the name “Idiwhaa,” derived from the Tlicho word for ancient.

Commenting, Dr Balz Kamber (Trinity College Dublin) said: “The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons. However, the implied pressure-temperature regime might also permit melting of shallow crust below a super-heated impact melt sea. In other words, an indirect consequence of the impact itself.”

* Rocks from Jack Hills in Australia contain zircon crystals from up to 4.4 billion years ago, embedded in younger rocks.

Reference:
Tim E. Johnson, Nicholas J. Gardiner, Katarina Miljković, Christopher J. Spencer, Christopher L. Kirkland, Phil A. Bland, Hugh Smithies. An impact melt origin for Earth’s oldest known evolved rocks. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0206-5

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

Rare teeth from ancient mega-shark found on Australia beach

shark tooth
Fossil enthusiast Philip Mullaly was strolling along an area known as a fossil hotspot at Jan Juc, on the country’s famous Great Ocean Road, when he spotted a giant shark tooth

A rare set of teeth from a giant prehistoric mega-shark twice the size of the great white have been found on an Australian beach by a keen-eyed amateur enthusiast, scientists said Thursday.

Philip Mullaly was strolling along an area known as a fossil hotspot at Jan Juc, on the country’s famous Great Ocean Road some 100 kilometres (60 miles) from Melbourne, when he made the find.

“I was walking along the beach looking for fossils, turned and saw this shining glint in a boulder and saw a quarter of the tooth exposed,” he said.

“I was immediately excited, it was just perfect and I knew it was an important find that needed to be shared with people.”

He told Museums Victoria, and Erich Fitzgerald, senior curator of vertebrate palaeontology, confirmed the seven centimetre-long (2.7 inch) teeth were from an extinct species of predator known as the great jagged narrow-toothed shark (Carcharocles angustidens).

The shark, which stalked Australia’s oceans around 25 million years ago, feasting on small whales and penguins, could grow more than nine metres long, almost twice the length of today’s great white shark.

“These teeth are of international significance, as they represent one of just three associated groupings of Carcharocles angustidens teeth in the world, and the very first set to ever be discovered in Australia,” Fitzgerald said.

He explained that almost all fossils of sharks worldwide were just single teeth, and it was extremely rare to find multiple associated teeth from the same shark.

This is because sharks, who have the ability to regrow teeth, lose up to a tooth a day and cartilage, the material a shark skeleton is made of, does not readily fossilise.

Fitzgerald suspected they came from one individual shark and there might be more entombed in the rock.

So he led a team of palaeontologists, volunteers, and Mullaly on two expeditions earlier this year to excavate the site, collecting more than 40 teeth in total.

Most came from the mega-shark, but several smaller teeth were also found from the sixgill shark (Hexanchus), which still exists today.

Museums Victoria palaeontologist Tim Ziegler said the sixgill teeth were from several different individuals and would have become dislodged as they scavenged on the carcass of the Carcharocles angustidens after it died.

“The stench of blood and decaying flesh would have drawn scavengers from far around,” he said.

“Sixgill sharks still exist off the Victorian coast today, where they live off the remains of whales and other animals. This find suggests they have performed that lifestyle here for tens of millions of years.”

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

Faster way to make mineral to remove carbon dioxide from atmosphere

Natural magnesite crystal (4 microns wide).
Natural magnesite crystal (4 microns wide). Credit: Ian Power

Scientists have found a rapid way of producing magnesite, a mineral which stores carbon dioxide. If this can be developed to an industrial scale, it opens the door to removing CO2 from the atmosphere for long-term storage, thus countering the global warming effect of atmospheric CO2. This work is presented at the Goldschmidt conference in Boston.

Scientists are already working to slow global warming by removing carbon dioxide from the atmosphere, but there are serious practical and economic limits on developing the technology. Now, for the first time, researchers have explained how magnesite forms at low temperature, and offered a route to dramatically accelerating its crystallization. A tonne of naturally-occurring magnesite can remove around half a tonne of CO2 from the atmosphere, but the rate of formation is very slow.

Project leader, Professor Ian Power (Trent University, Ontario, Canada) said: “Our work shows two things. Firstly, we have explained how and how fast magnesite forms naturally. This is a process which takes hundreds to thousands of years in nature at Earth’s surface. The second thing we have done is to demonstrate a pathway which speeds this process up dramatically.”

The researchers were able to show that by using polystyrene microspheres as a catalyst, magnesite would form within 72 days. The microspheres themselves are unchanged by the production process, so they can ideally be reused.

“Using microspheres means that we were able to speed up magnesite formation by orders of magnitude. This process takes place at room temperature, meaning that magnesite production is extremely energy efficient.”

“For now, we recognise that this is an experimental process, and will need to be scaled up before we can be sure that magnesite can be used in carbon sequestration (taking CO2 from the atmosphere and permanently storing it as magnesite). This depends on several variables, including the price of carbon and the refinement of the sequestration technology, but we now know that the science makes it do-able.”

Commenting, Professor Peter Kelemen at Columbia University’s Lamont Doherty Earth Observatory (New York) said: “It is really exciting that this group has worked out the mechanism of natural magnesite crystallization at low temperatures, as has been previously observed — but not explained — in weathering of ultramafic* rocks. The potential for accelerating the process is also important, potentially offering a benign and relatively inexpensive route to carbon storage, and perhaps even direct CO2 removal from air.”

Notes:

Professor Keleman was not involved in this work, this is an independent comment.

*Ultramafic rocks are rich in magnesium, with low silica content. Commercially, magnesite (MgCO3, magnesium carbonate) is used in the production of magnesium oxide mainly for the steel industry. It is also used as an inexpensive gemstone.

This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Reference:
I.M. Power, A.L. Harrison, P.A. Kenward, G.M. Dipple, S.A. Wilson. Magnesite formation at Earth’s surface. Goldschmidt Abstracts, 2018. https://goldschmidtabstracts.info/abstracts/abstractView?id=2018001242

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

Mantle xenon has a story to tell

Etna eruption
Etna eruption, Catania, Sicily. Credit: Wead / Fotolia

The Earth has been through a lot of changes in its 4.5 billion year history, including a shift to start incorporating and retaining volatile compounds from the atmosphere in the mantle before spewing them out again through volcanic eruptions.

This transport could not have begun much before 2.5 billion years ago, according to new research by Washington University in St. Louis, published in the August 9 issue of the journal Nature.

“Life on Earth cares about changes in the volatile budget of the surface,” said Rita Parai, assistant professor of geochemistry in Earth and Planetary Sciences in Arts & Sciences and first author of the study. “And there’s an interplay between what the deep Earth was doing and how the surface environment changed over billion-year timescales.”

Volatiles — such as water, carbon dioxide and the noble gases — come out of the mantle through volcanism and may be injected into the Earth’s interior from the atmosphere, a pair of processes called mantle degassing and regassing. The exchange controls the habitability of the planet, as it determines the surface availability of compounds that are critical to life — such as carbon, nitrogen and water.

The new model presented by Parai and collaborator Sujoy Mukhopadhyay, of the University of California, Davis, also establishes a range of dates during which the Earth shifted from a net degassing regime — again, think about those oozy volcanoes — to one that tilted the balance to net regassing potentially enabled by subduction, the conveyor-belt action of tectonic plates.

Mechanical properties change as water is added or removed from the mantle, so the onset of regassing had an important effect on the internal churning of the mantle, known as convection, which controls plate motions at the surface, Parai said.

Parai uses noble gases to address questions about how planetary bodies form and evolve over time. In this new research, she modeled the fate and transport of volatile compounds into the Earth’s mantle using xenon isotopes as tracers.

“Xenon is an excellent volatile tracer, because all minerals that carry water also carry xenon,” Parai said. “So if xenon regassing was negligible, water regassing must also have been negligible during the Archean (4 billion-2.5 billion years ago).”

Substantial regassing began sometime between a few hundred million to 2.5 billion years ago, the researchers found.

If plate tectonics and subduction began earlier than 2.5 billion years ago, then perhaps by then the Earth’s interior had cooled sufficiently for volatiles to remain in subducting plates, rather than getting released and percolating back to the surface through magmatism, Parai suggests.

“Most people rarely have an occasion to think about volatiles trapped in the Earth’s interior,” Parai said. “They’re present at low concentrations, but the mantle is huge in terms of mass. So for the Earth’s total volatile budget, the mantle is an important reservoir.”

She plans to focus her future research on pushing the limits of precision in xenon isotopic measurements in a variety of geological samples.

“The more observational constraints we have, the better,” she said.

Reference:
Rita Parai, Sujoy Mukhopadhyay. Xenon isotopic constraints on the history of volatile recycling into the mantle. Nature, 2018; 560 (7717): 223 DOI: 10.1038/s41586-018-0388-4

Note: The above post is reprinted from materials provided by Washington University in St. Louis. Original written by Talia Ogliore.

Study of material surrounding distant stars shows Earth’s ingredients ‘pretty normal’

Artists impression of white dwarf star (on right) showing dust disc, and surrounding planetary bodies.
Artists impression of white dwarf star (on right) showing dust disc, and surrounding planetary bodies. Credit: NASA/JPL-Caltech

The Earth’s building blocks seem to be built from ‘pretty normal’ ingredients, according to researchers working with the world’s most powerful telescopes. Scientists have measured the compositions of 18 different planetary systems from up to 456 light years away and compared them to ours, and found that many elements are present in similar proportions to those found on Earth.

This is amongst the largest examinations to measure the general composition of materials in other planetary systems, and begins to allow scientists to draw more general conclusions on how they are forged, and what this might mean for finding Earth-like bodies elsewhere.

“Most of the building blocks we have looked at in other planetary systems have a composition broadly similar to that of the Earth,” said researcher Dr Siyi Xu of the Gemini Observatory in Hawaii, who was presenting the work at the Goldschmidt conference in Boston.

The first planets orbiting other stars were only found in 1992 (this was orbiting a pulsar), since then scientists have been trying to understand whether some of these stars and planets are similar to our own solar system.

“It is difficult to examine these remote bodies directly. Because of the huge distances involved, their nearby star tends to drown out any electromagnetic signal, such as light or radio waves” said Siyi Xu. “So we needed to look at other methods.”

Because of this, the team decided to look at how the planetary building blocks affect signals from white dwarf stars. These are stars which have burnt off most of their hydrogen and helium, and shrunk to be very small and dense — it is anticipated that our Sun will become a white dwarf in around 5 billion years.

Dr Xu continued, “White dwarfs’ atmospheres are composed of either hydrogen or helium, which give out a pretty clear and clean spectroscopic signal. However, as the star cools, it begins to pull in material from the planets, asteroids, comets and so on which had been orbiting it, with some forming a dust disk, a little like the rings of Saturn. As this material approaches the star, it changes how we see the star. This change is measurable because it influences the star’s spectroscopic signal, and allows us to identify the type and even the quantity of material surrounding the white dwarf. These measurements can be extremely sensitive, allowing bodies as small as an asteroid to be detected.”

The team took measurements using spectrographs on the Keck telescope in Hawaii, the world’s largest optical and infrared telescope, and on the Hubble Space Telescope.

Siyi Xu continued, “In this study, we have focused on the sample of white dwarfs with dust disks. We have been able to measure calcium, magnesium, and silicon content in most of these stars, and a few more elements in some stars. We may also have found water in one of the systems, but we have not yet quantified it: it’s likely that there will be a lot of water in some of these worlds. For example, we’ve previously identified one star system, 170 light years away in the constellation Boötes, which was rich in carbon, nitrogen and water, giving a composition similar to that of Halley’s Comet. In general though, their composition looks very similar to bulk Earth.

This would mean that the chemical elements, the building blocks of earth are common in other planetary systems. From what we can see, in terms of the presence and proportion of these elements, we’re normal, pretty normal. And that means that we can probably expect to find Earth-like planets elsewhere in our Galaxy.”

Dr Xu continued “This work is still on-going and the recent data release from the Gaia satellite, which so far has characterized 1.7 billion stars, has revolutionized the field. This means we will understand the white dwarfs a lot better. We hope to determine the chemical compositions of extrasolar planetary material to a much higher precision”

Professor Sara Seager, Professor of Planetary Science at Massachusetts Institute of Technology, is also the deputy science director of the recently-launched TESS (Transiting Exoplanet Survey Satellite) mission, which will search for exoplanets. She said:

“It’s astonishing to me that the best way to study exoplanet interiors is by planets ripped apart and absorbed by their white dwarf host star. It is great to see progress in this research area and to have solid evidence that planets with Earth-like compositions are common — fueling our confidence that an Earth-like planet around a very nearby normal star is out there waiting to be found.”

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

New research predicts landslide boundaries two weeks before they happen

Credit: CC0 Public Domain

University of Melbourne researchers have developed a software tool that uses applied mathematics and big data analytics to predict the boundary of where a landslide will occur, two weeks in advance.

Professor Antoinette Tordesillas from the School of Mathematics and Statistics said there are always warning signs in the lead up to a collapse or ‘failure’, the tricky part is identifying what they are.

“These warnings can be subtle. Identifying them requires fundamental knowledge of failure at the microstructure level—the movement of individual grains of earth,” Professor Tordesillas said.

“Of course, we cannot possibly see the movement of individual grains in a landslide or earthquake that stretches for kilometres, but if we can identify the properties that characterise failure in the small-scale, we can shed light on how failure evolves in time, no matter the size of the area we are observing.”

These early clues include patterns of motion that change over time and become synchronised.

“In the beginning, the movement is highly disordered,” said Professor Tordesillas. “But as we get closer to the point of failure—the collapse of a sand castle, crack in the pavement or slip in an open pit mine—motion becomes ordered as different locations suddenly move in similar ways.

“Our model decodes this data on movement and turns it into a network, allowing us to extract the hidden patterns on motion and how they are changing in space and time. The trick is to detect the ordered motions in the network as early as possible, when movements are very subtle.”

Professor Robin Batterham from the Department of Chemical and Biomolecular Engineering said the new software focuses on turning algorithms and big data into risk assessment and management actions that can save lives.

“People have gone somewhat overboard on so-called data analytics, machine learning and so on,” said Professor Batterham.

“While we’ve been doing this sort of stuff for 40 years, this software harnesses the computer power and memory available to look not just at the surface movement, but extract the relevant data patterns. We’re able to do things that were just unimaginable in a mathematical sense 30 years ago.

“We can now predict when a rubbish landfill might break in a developing country, when a building will crack or the foundation will move, when a dam could break or a mudslide occur. This software could really make a difference.”

Reference:
Antoinette Tordesillas et al, A data-driven complex systems approach to early prediction of landslides, Mechanics Research Communications (2018). DOI: 10.1016/j.mechrescom.2018.08.008

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

Maya rituals unearthed

The Valley of Peace Archaeology project team explore an ancient Maya site in central Belize.
The Valley of Peace Archaeology project team explore an ancient Maya site in central Belize. Credit: Jeannie Larmon

Deep in the untamed lowlands, we search for artifacts buried under hundreds of years of sediment. We are excavating two ancient Maya sites nestled in the sacred landscape of Cara Blanca in central Belize. Both date to A.D. 800-900, when prolonged and severe droughts struck this region, disrupting the daily life of the Maya.

These two structures – a platform teetering on the edge of a 60-meter-deep pool and a sweatbath compound – were part of a ritual pilgrimage circuit traversed by the ancient Maya to pay tribute to the rain god Chahk during the extended droughts.

Openings in the earth like this pool were thought to be portals to the underworld, places where deities and ancestors resided. In previous years studying this poolside platform, we discovered a massive burning event and thousands of ceramic sherds purposely placed on the plaster floor.

Burnings and offerings of this nature were a common practice with the ancient Maya. These were part of termination rituals, meant to “deanimate” objects or spaces and remove them from the life cycle. Everything was believed to contain a life force, making deanimation a critical process for the Maya.

Our aim this year is to garner a deeper understanding of this ritual space. We scrape away at the soil, trowel by trowel, filling buckets and sifting each one to avoid missing any bit of data. The deeper we go, the harder it becomes to hoist the dirt out of this trench.

It isn’t long before we unexpectedly uncover another platform. The ceramics at this layer seem to be from a much earlier time period – about A.D. 600! This suggests the Maya were ritually engaging with the Cara Blanca landscape before the drought period began – much earlier than we anticipated.

This older, deeper platform has thin floors and few walls. No human remains are buried here. This might reflect a wetter, less socially trying time.

As we walk from the trench to a sweatbath compound 10 minutes away, tiny pink petals fallen from flowering trees paint the walkways. The sweatbath appears heavily looted; our goal is to salvage whatever information remains. But when we start to excavate, we find no looters’ debris. We also find no large stones, which are usually present in a building collapse. This suggests the Maya dismantled this structure themselves during a termination ritual prior to their total abandonment of the area.

As we leave the site, driving off-road for 20 minutes down a rocky ravine, we ponder the importance of Cara Blanca to the ancient Maya. The intense effort they made to build and terminate these structures may reflect just how dire their circumstances were in the time of the droughts.

Note: The above post is reprinted from materials provided by University of Illinois at Urbana-Champaign.

200-million year old Pterosaur ‘built for flying’

Caelestiventus hanseni
Factfile on Caelestiventus hanseni a new species of flying reptiles, known as Pterosaurs, discovered in US state of Utah.

Scientists on Monday unveiled a previously unknown species of giant pterosaur, the first creatures with a backbone to fly under their own power.

Neither dino nor bird, pterosaurs—more commonly known as pterodactyls—emerged during the late Triassic period more than 200 million years ago and lorded over primeval skies until a massive space rock slammed into Earth, wiping out the dinosaurs and most other forms of life some 65 million years ago.

The newly discovered member of the family, identified through remains found in northeastern Utah, had a wing-span of 1.5 metres (five feet) and 112 teeth, including fang-like spikes sticking out near the snout.

A jutting lower jaw suggests a pelican-like pouch, perhaps to scoop up fish and unsuspecting small reptiles.

“They are delicately framed animals that are built for flying,” said Brooks Britt, a paleontologist at Brigham Young University in Utah and lead author of a study in Nature Ecology & Evolution.

Caelestiventus hanseni—roughly, “heavenly wind”—is probably the most complete skeletal remains of a pterosaur ever found.

“Most pterosaurs bones look like road-kill,” Britt told AFP, noting that there are only 30-odd specimens worldwide from the Triassic period which lasted some 51 million years.

By contrast, the new specimen comprises dozens of intact bones and teeth, along with an entire brain casing.

The wings are in fact skin membranes largely held up by the fourth “finger”, or digit, of their forelimbs. Huge sockets suggest C. hanseni had “fantastic eyesight”, said Britt.

Saints & Sinners

When not soaring in search of a meal, it walked on all fours with its wings folded vertically.

The fossil remains are still encased in sandstone, but scientists generated accurate 3-D images and models of each bone using CAT-scan technology.

The site where C. hanseni was unearthed, known to fossil hunters as Saints & Sinners, reveals a dramatic story of survival and local extinction in the face of climate change, the researchers said.

The rocks it was found in were part of an oasis in a two-million square kilometre (775,000 square mile) desert covered with giant sand dunes.

“During droughts, large numbers of animals—including pterosaurs, predatory dinosaurs and crocodylomorphs—were drawn to the pond in the middle of the oasis, where they died as water dried up,” said Britt.

The result was a treasure trove of more than 18,000 bones and fragments from dozens of water-starved animals.

C. hanseni is not the biggest pterosaur ever found, but was likely the largest of its era, especially for a desert environment.

It also predates other desert-dwelling specimens by about 65 million years. Pterosaurs from the same period found so far came from ancient coastal areas in what is now Europe and Greenland.

That the high-flying creatures were spread across much of the globe may have helped them survive the end-of-Triassic mass extinction, which wiped out half of the species on land and in the sea.

Reference:
Brooks B. Britt et al. Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0627-y

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

Those fragrances you enjoy? Dinosaurs liked them first

Glandular laurel in amber.
Glandular laurel in amber. Credit: Image courtesy of Oregon State University

The compounds behind the perfumes and colognes you enjoy have been eliciting olfactory excitement since dinosaurs walked the Earth amid the first appearance of flowering plants, new research reveals.

Oregon State University entomologist George Poinar Jr. and his son Greg, a fragrance collector, found evidence that floral scents originated in primitive flowers as far back as 100 million years ago as pollinator attractants — a role they still play even though today’s flowers also have colorful petals for luring pollinators.

“I bet some of the dinosaurs could have detected the scents of these early flowers,” George Poinar said. “In fact, floral essences from these early flowers could even have attracted these giant reptiles.”

The Poinars examined amber flowers from Burma, including the now extinct glandular laurel flower (Cascolaurus burmensis) and veined star flower (Tropidogyne pentaptera).

The research revealed that the flower-based chemical compounds that are the basis for the perfumes and colognes we use today have been providing olfactory excitement to pollinating insects and other animals since the mid-Cretaceous Period.

Without colorful petals, flowers from that period had to rely solely on scents to attract pollinators.

“You can’t detect scents or analyze the chemical components of fossil flowers, but you can find the tissues responsible for the scents,” said George Poinar, professor emeritus in the OSU College of Science.

The floral secretory tissues producing these scents include nectaries, glandular trichomes, eliaphores and osmophores.

Nectaries are glands that produce fragrances and sweet deposits that insects love. Glandular trichomes are hairs with cells that make and send out scented secretory products. Eliaphores are stalked aromatic oil glands. oOsmophores, also known as floral fragrance glands, are cell clusters specializing in scent emission.

The study also found that secretory tissues of these Cretaceous flowers are similar in structure to those of their modern descendants. That suggests modern and ancient flowers of the same lineages produced similar essences.

Some of flowers studied were even in the process of emitting compounds at the time they were engulfed by the tree resin that later became amber.

The study also included a milkweed flower (Discoflorus neotropicus) and an acacia flower (Senegalia eocaribbeansis) in 20- to 30-million-year-old Dominican Republic amber.

The anther glands on the fossil acacia flower were especially attractive to bees, one of which was fossilized while visiting the stamens. Today, honeybees are still visiting acacia flowers that have the same type of flora glands that existed in the ancient past.

“It’s obvious flowers were producing scents to make themselves more attractive to pollinators long before humans began using perfumes to make themselves more appealing to other humans,” George Poinar said.

Reference:
George Poinar, Greg Poinar. The antiquity of floral secretory tissues that provide today’s fragrances. Historical Biology, 2018; 1 DOI: 10.1080/08912963.2018.1502288

Note: The above post is reprinted from materials provided by Oregon State University. Original written by Steve Lundeberg.

First North American co-occurrence of Hadrosaur and Therizinosaur tracks found in Alaska

therizinosaurs and hadrosaurs at Alaska's Denali National Park during the Cretaceous Period.
Artist’s rendering of therizinosaurs and hadrosaurs at Alaska’s Denali National Park during the Cretaceous Period. Credit: Illustration by Masato Hattori

An international team of paleontologists and other geoscientists has discovered the first North American co-occurrence of hadrosaur and therizinosaur tracks in the lower Cantwell Formation within Denali National Park, suggesting that an aspect of the continental ecosystem of central Asia was also present in this part of Alaska during the Late Cretaceous.

This comprehensive cross-disciplinary effort has resulted in a paper — entitled “An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska” — published in Scientific Reports, an online open access scientific mega journal published by the Nature Publishing Group, covering all areas of the natural sciences.

Anthony R. Fiorillo, Ph.D., chief curator and vice president of research and collections at the Perot Museum of Nature and Science in Dallas, Texas, is the lead author. Co-authors are Paul J. McCarthy, Ph.D., University of Alaska, Department of Geosciences; Yoshitsugu Kobayashi, Ph.D., Hokkaido University Museum, Sapporo, Hokkaido, Japan; Carla S. Tomsich, graduate student, University of Alaska, Department of Geosciences; Ronald S. Tykoski, Ph.D., director of paleontology lab, Perot Museum of Nature and Science; Yuong-Nam Lee, Ph.D., School of Earth and Environmental Sciences, Seoul National University, South Korea; Tomonori Tanaka, graduate student, Hokkaido University Museum, Sapporo, Hokkaido, Japan; and Christopher R. Noto, Ph.D., Department of Biological Sciences, University of Wisconsin-Parkside, Kenosha, Wisconsin.

Fiorillo and a colleague published on a distinct single footprint in Denali National Park in 2012 that they determined to be made by a therizinosaur, an unusual predatory dinosaur thought to have become an herbivore. Therizinosaurs are best known from Asia. Upon his return in 2013 and 2014, they conducted a more detailed analysis of the area, and he and his colleagues unearthed dozens more tracks of therizinosaurs. What surprised Fiorillo and his team most was the co-occurrence of dozens of hadrosaurs, also known as duck-bill dinosaurs.

“Hadrosaurs are very common and found all over Denali National Park. Previously, they had not been found alongside therizinosaurs in Denali. In Mongolia, where therizinosaurs are best known — though no footprints have been found in association — skeletons of hadrosaurs and therizinosaurs have been found to co-occur from a single rock unit so this was a highly unusual find in Alaska, and it prompted my interest,” said Fiorillo. “From our research, we’ve determined that this track association of therizinosaurs and hadrosaurs is currently the only one of its kind in North America.”

The plant-eating therizinosaurs are rare and unusual creatures in the fossil record. The strange-looking dinosaurs had long skinny necks, little teeth, a small beak for cropping plants, and big torsos accompanied by large hind feet and long arms with “hands like Freddy Krueger.”

Though therizinosaurs are known from Asia and North America, the best and most diverse fossil record is from Asia — even up to the time of extinction — and therein is the connection. Fiorillo has long postulated that

Cretaceous Alaska could have been the thoroughfare for fauna between Western North America and Asia — two continents that shared each other’s fauna and flora in the latest stages of the Cretaceous.

“This study helps support the idea that Alaska was the gateway for dinosaurs as they migrated between Asia and North America,” said Dr. Kobayashi.

To support the theory, Fiorillo’s international team of scientists from across the U.S., Japan and South Korea worked to establish if the tracks were those of a therizinosaur and to study any unique aspects of the ecosystem. The members — including a sedimentologist, geologist, paleobotanist, paleoecologist and additional paleontologists including an expert on therizinosaurs — determined that this particular area of Denali was a wet, marsh-like environment and that one fossil in particular looked like a water lily, which supported the theory that there were ponds and standing water nearby. They suspect that both therizinosaurs and hadrosaurs liked these wetter locations.

Fiorillo believes that this Alaskan discovery may connect these animals environmentally and perhaps behaviorally to other therizinosaurs in central Asia. An Asian report of these animals being associated also came from an interval of rocks that was unusually ‘wet’ at the time, relative to rocks above and below it.

“This discovery provides more evidence that Alaska was possibly the superhighway for dinosaurs between Asia and western North America 65-70 million years ago,” added Fiorillo.

Reference:
Anthony R. Fiorillo, Paul J. McCarthy, Yoshitsugu Kobayashi, Carla S. Tomsich, Ronald S. Tykoski, Yuong-Nam Lee, Tomonori Tanaka, Christopher R. Noto. An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-30110-8

Note: The above post is reprinted from materials provided by Perot Museum of Nature and Science.

Size matters: If you are a bubble of volcanic gas

Kilauea eruption, 2018.
Kilauea eruption, 2018. Credit: Clive Oppenheimer

The chemical composition of gases emitted from volcanoes — which are used to monitor changes in volcanic activity — can change depending on the size of gas bubbles rising to the surface, and relate to the way in which they erupt. The results, published in the journal Nature Geoscience, could be used to improve the forecasting of threats posed by certain volcanoes.

A team of scientists, including a volcanologist and mathematician from the University of Cambridge, discovered the phenomenon through detailed observations of gas emissions from Kīlauea volcano in Hawaii.

At many volcanoes around the world, gas emissions are monitored routinely to help with forecasting eruptions. Changes in the output or proportions of different gases — such as carbon dioxide and sulphur dioxide — can herald shifts in the activity of a volcano. Volcanologists have considered that these chemical changes reflect the rise and fall of magma in the Earth’s crust but the new research reveals that the composition of volcanic gases depends also on the size of the gas bubbles rising up to the surface.

Until the latest spectacular eruption opened up fissures on the flank of the volcano, Kīlauea held a vast lava lake in its summit crater. The behaviour of this lava lake alternated between phases of fiery ‘spattering’ powered by large gas bubbles bursting through the magma, and more gentle gas release, accompanied by slow and steady motion of the lava.

In the past, volcanic gases have been sampled directly from steaming vents and openings called fumaroles. But this is not possible for the emissions from a lava lake, 200 metres across, and at the bottom of a steep-sided crater. Instead, the team used an infrared spectrometer, which is employed for routine volcano monitoring by co-authors of the study, Jeff Sutton and Tamar Elias from the Hawaiian Volcano Observatory (US Geological Survey).

The device was located on the edge of the crater, pointed at the lava lake, and recorded gas compositions in the atmosphere every few seconds. The emissions of carbon- and sulphur-bearing gases were measured during both the vigorous and mild phases of activity.

Each individual measurement was used to compute the temperature of the volcanic gas. What immediately struck the scientists was that the gas temperatures ranged from 1150 degrees Celsius — the temperature of the lava — down to around 900 degrees Celsius. “At this temperature, the lava would freeze,” said lead author Dr Clive Oppenheimer, from Cambridge’s Department of Geography. “At first, we couldn’t understand how the gases could emerge much colder than the molten lava sloshing in the lake.”

The clue to this puzzle came from the variation in calculated gas temperatures — they were high when the lava lake was placid, and low when it was bubbling furiously. “We realised it could be because of the size of the gas bubbles,” said co-author Professor Andy Woods, Director of Cambridge’s BP Institute. “Larger bubbles rise faster through the magma and expand rapidly as the pressure reduces, just like bubbles rising in a glass of fizzy drink; the gas cools down because of the expansion.” Larger bubbles form when smaller bubbles bump into each other and merge.

Woods and Oppenheimer developed a mathematical model to account for the process, which showed a very good fit with the observations.

But there was yet another surprising finding from the gas observations from Hawaii. As well as being cooler, the emissions from the large gas bubbles were more oxidised than expected — they had higher proportions of carbon dioxide to carbon monoxide.

The chemical balance of volcanic gases such as carbon dioxide and carbon monoxide (or sulphur dioxide and hydrogen sulphide) is generally thought to be controlled by the chemistry of the surrounding liquid magma but what the new findings showed is that when bubbles get large enough, most of the gas inside follows its own chemical pathway as the gas cools.

The ratio of carbon dioxide to carbon monoxide when the lava lake was in its most energetic state was six times higher than during the most stable phase. The scientists suggest this effect should be taken into account when gas measurements are being used to forecast major changes in volcanic activity.

“Gas measurements are critical to our monitoring and hazard assessment; refining our understanding of how magma behaves beneath the volcano allows us to better interpret our observations,” said co-author Tamar Elias from the Hawaiian Volcano Observatory.

And there is another implication of this discovery — not for eruptions today but for the evolution of the Earth’s atmosphere billions of years ago. “Volcanic emissions in Earth’s deep past may have made the atmosphere more oxidising than we thought,” said co-author Bruno Scaillet. “A more oxygen-rich atmosphere would have facilitated the emergence and viability of life on land, by generating an ozone layer, which shields against harmful ultraviolet rays from the sun.”

Reference:
Clive Oppenheimer, Bruno Scaillet, Andrew Woods, A. Jeff Sutton, Tamar Elias, Yves Moussallam. Influence of eruptive style on volcanic gas emission chemistry and temperature. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0194-5

Note: The above post is reprinted from materials provided by University of Cambridge. The original story is licensed under a Creative Commons License.

Iron-silica particles unlock part of the mystery of Earth’s oxygenation

Iron-silica particles helped shield cyanobacteria like these, which played a key role in the oxygenation of Earth's atmosphere according to new research from UAlberta.
Iron-silica particles helped shield cyanobacteria like these, which played a key role in the oxygenation of Earth’s atmosphere according to new research from UAlberta. Credit: George Owttrim

The oxygenation of Earth’s atmosphere was thanks, in part, to iron and silica particles in ancient seawater, according to a new study by geomicrobiologists at the University of Alberta. But these results solve only part of this ancient mystery.

Early organisms called cyanobacteria produced oxygen through oxygenic photosynthesis, resulting in the oxygenation of Earth’s atmosphere. But cyanobacteria needed protection from the sun’s UV radiation in order to evolve. That’s where iron and silica particles in ancient seawater come in, according to Aleksandra Mloszewska, a former PhD student who conducted this research under the supervision of Kurt Konhauser, professor in the Department of Earth and Atmospheric Sciences, and George Owttrim, professor in the Department of Biological Sciences.

The research team characterized the effect of UV stress on cyanobacteria and the degree of radiation through the seawater medium through a combination of microbiological, spectroscopic, geochemical and modelling techniques. Their results show that the presence of high silica and iron concentrations in early sea water allowed for the formation of iron-silica precipitates that remained suspended in the ocean for extended periods of time.

“In effect, the iron-silica particles acted as an ancient ‘sunscreen’ for the cyanobacteria, protecting them from the lethal effects of direct UV exposure,” said Konhauser, the senior author from UAlberta. “This was critical on the early Earth before a sufficiently thick ozone layer was established that could enable marine plankton to spread across the globe, as is the case today.”

More missing pieces

But, the researchers explain, the iron-silica rich precipitates tell only part of the story.

“The accumulation of atmospheric oxygen from cyanobacterial facilitated the evolution of oxygen-based respiration and multicellular organisms,” says Owttrim. But the reason for the large amount of time that it took for free oxygen to accumulate permanently in the atmosphere after the initial evolution of cyanobacteria remains a mystery.

While iron-silica precipitates would have allowed early cyanobacteria to survive, UV radiation would still have prevented their widespread growth.

“It is likely that early cyanobacteria would not have been as productive as they are today because of the effects of UV stress. Until the accumulation of sufficient cyanobacteria-derived oxygen allowed a more permanent means of protection to develop, such as an ozone layer, UV stress may have played an even more important role in shaping the structure of the earliest ecosystems,” explained Mloszewska.

These new findings are helping researchers to understand not only how early cyanobacteria were affected by the high level of radiation on the early Earth but also the environmental dynamics that affected the oxygenation history of our atmosphere.

“These findings could also be used as a case study to help us understand the potential for the emergence of life on other planets that are affected by elevated UV radiation levels, for example Earth-sized rocky planets within the habitable zones of nearby M-dwarf star systems like TRAPPIST-1, Proxima Centauri, LHS 1140 and Ross 128 among others,” said Mloszewska.

The research was conducted in collaboration with colleagues at the University of Tuebingen and Yale University and was supported by the National Science and Research Council of Canada, and by the NASA Alternative Earths Astrobiology Institute. The paper, “UV radiation limited the expansion of cyanobacteria in early marine photic environments” is published in Nature Communications.

Reference:
Aleksandra M. Mloszewska, Devon B. Cole, Noah J. Planavsky, Andreas Kappler, Denise S. Whitford, George W. Owttrim, Kurt. O Konhauser. UV radiation limited the expansion of cyanobacteria in early marine photic environments. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05520-x

Note: The above post is reprinted from materials provided by University of Alberta. Original written by Katie Willis.

Chemical footprint in present-day atmosphere mimics that observed in ancient rock

Artistic depiction of early Earth blasted by solar system debris.
Artistic depiction of early Earth blasted by solar system debris. Credit: NASA/Goddard Image Lab

Early Earth was a hot, gaseous, dusty and dynamic planet with an atmosphere and an ocean. Then its surface cooled and stabilized enough for clouds, landmasses and early life to form about four billion years ago, during what’s called the isotopic age of rocks, or the Archean Period. Atmospheric chemical byproducts from that time traveled through the air and deposited inside the planet’s oldest rock, recording life’s earliest activities like photosynthesis and oxygen production.

Sulfur isotopes can serve as tracers of atmospheric oxygen, and new data collected from the present-day atmosphere in China by an international team of researchers, led by the University of California San Diego, indicate remarkable similarity to the isotopic footprint found in ancient rocks. This opens up new interpretations of the Archean Period’s sulfur isotope sedimentary signature—a proxy for the origins and evolution of atmospheric oxygen and early life on Earth.

The study led by Mark Thiemens, distinguished professor of chemistry and biochemistry; Mang Lin, a recent Ph.D. graduate from UC San Diego and Yanan Shen, a professor at the University of Science and Technology of China, is published in the current issue of the Proceedings of the National Academy of Sciences. Their research involved taking current sulfate aerosol measurements of five sulfur isotopes from samples of atmospheric aerosols collected at Mount Wuyi, a remote site in China, and Guangzhou, a megacity. The isotope measurements, performed at UC San Diego and the University of Science and Technology of China resolved the chemical mechanisms and transport of atmospheric aerosols at a new scientific level.

“By using the stable and radioactive isotopes, we were able to zero in on new sources of the isotope effect today and better define the early atmosphere and evolution of life,” Thiemens said.

Thiemens explained that in the Archean atmosphere the oxygen and ozone levels were low enough that ultraviolet (UV) light penetrated the Earth’s surface and dissociated sulfur dioxide, forensically producing a specific isotopic pattern. The study reveals that stable sulfur isotope compositions are anomalous and mimic measurements of ancient sulfur isotopes.

Additionally, Thiemens explained that the photo destruction of sulfur dioxide by UV light in the early Earth’s atmosphere provides a measure of oxygen levels. He said that the levels of oxygen and ozone levels of early Earth were sufficiently low so that UV light reached the Earth’s surface, dissociating the sulfur dioxide and producing the anomalies.

Measurement of sulfur anomalies in the oldest rocks as a measure of oxygen levels was discovered at the Thiemens Research Group laboratory at UC San Diego with James Farquhar and Huiming Bao. The method is widely used to track oxygen levels before around 2.2 billion years ago, when oxygen and ozone levels rose to such levels that UV light was filtered out and the anomaly disappeared from the rock record.

“A surprise from Mang Lin’s measurements was that with combined stratospheric tracer Sulfur-35 (a radioactive sulfur isotope), and another stable isotope of stable sulfur, there is no correlation,” said Thiemens. “It was demonstrated by correlation with known combustion products that the processes of biomass burning and combustion produce this specific isotope anomaly, which had not been known before, providing new interpretation of early Earth chemistry and suggesting there are other processes that occur in the early Earth, such as volcanoes, that could produce the anomalies along with UV light photolysis.”

According to Thiemens, this study provides “yet another quiver in the arrow” of parsing out processes that occur in the early Earth and defining both life’s origin and change.

Reference:
Mang Lin et al. Five-S-isotope evidence of two distinct mass-independent sulfur isotope effects and implications for the modern and Archean atmospheres, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1803420115

Note: The above post is reprinted from materials provided by University of California – San Diego.

New understanding of deep earthquakes

Earth
Earth. Photo credit: Pr3t3nd3r/Getty Images Plus

Researchers have known for decades that deep earthquakes — those deeper than 60 kilometers, or about 37 miles below the Earth’s surface — radiate seismic energy differently than those that originate closer to the surface. But a systematic approach to understanding why has been lacking.

Now a team of researchers from the University of Houston has reported a way to analyze seismic wave radiation patterns in deep earthquakes to suggest global deep earthquakes are in anisotropic rocks, something that had not previously been done. The rock anisotropy refers to differences in seismic wave propagation speeds when measured along different directions.

Their findings were published Monday, July 30, by the journal Nature Geoscience.

Most earthquakes occur at shallow depths, according to the U.S. Geological Survey, and they generally cause more damage than deeper earthquakes. But there are still substantial questions about the causes of deep earthquakes.

Normal rocks are ductile, or pliable, at these great depths because of high temperature and thus aren’t able to rupture in an abrupt fashion to produce deep earthquakes, which occur below subduction zones where two tectonic plates collide at ocean trenches. The plate being pushed under is referred to as the subducting slab. The fact that deep earthquakes occur only in these slabs suggests some unusual process is happening within the slab.

Yingcai Zheng, assistant professor of seismic imaging in the UH College of Natural Sciences and Mathematics and corresponding author for the paper, said seismologists have sought to understand deep earthquakes since the phenomenon was discovered in 1926. Hypotheses include the effect of fluids, runaway thermal heating or solid-phase change due to sudden collapse of the mineral crystal structure.

In addition to Zheng, researchers involved in the work include the first author Jiaxuan Li, a Ph.D. candidate in the Department of Earth and Atmospheric Sciences; Leon Thomsen, research professor of geophysics; Thomas J. Lapen, professor of geology; and Xinding Fang, adjunct professor at UH and concurrently associate professor at the Southern University of Science and Technology China.

“Over the past 50 years, there has been growing evidence that a large proportion of deep earthquakes do not follow the double-couple radiation pattern seen in most shallow earthquakes,” Zheng said. “We set out to look at why that happens.” The double-couple pattern is caused by a shear rupture of a pre-existing fault.

The work, funded by the National Science Foundation, looked at potential reasons for the differing radiation patterns; Zheng said earlier theories suggest that deep earthquakes stem from a different rupture mechanism and possibly different physical and chemical processes than those that spark shallow earthquakes.

But after studying the radiation patterns of 1,057 deep earthquakes at six subduction zones worldwide, the researchers determined another explanation. They found that the surrounding rock fabric enclosing the deep quake alters the seismic radiation into a non-double-couple pattern. “Both the common double-couple radiation patterns and uncommon patterns of deep earthquakes can be explained simultaneously by shear rupture in a laminated rock fabric,” Li said.

Before the subducting plate enters the trench, it can absorb sea water to form hydrated anisotropic minerals. As the slab descends in the Earth’s mantle, the water can be expelled due to high pressure and high temperature conditions, a process known as dehydration. The dehydration and strong shearing along the slab interface can make the rock brittle and lead to rupture in intermediate-depth earthquakes, defined as those between 60 kilometers and 300 kilometers deep (37 miles to 186 miles).

“We found at these depths that the anisotropic rock fabric is always parallel to the slab surface, although the slab can change directions greatly from place to place,” Li said.

Anisotropy is also found in rocks at even greater depths, which suggests materials such as magnesite or aligned carbonatite melt pockets may be involved in generating the deep ruptures, the researchers said. Because the inferred anisotropy is high — about 25 percent — the widely believed meta-stable solid phase change mechanism is not able to provide the needed anisotropy inferred by the researchers.

Reference:
Jiaxuan Li, Yingcai Zheng, Leon Thomsen, Thomas J. Lapen, Xinding Fang. Deep earthquakes in subducting slabs hosted in highly anisotropic rock fabric. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0188-3

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

Platinum is key in ancient volcanic related climate change

biotite
SEM micrograph of the volcanic mineral biotite, found in ancient pottery from the Hopewell site at Shawnee Lookout.

Supervolcanoes are one of Mother Nature’s deadliest phenomena, and when they erupt, they can change the climate of the entire planet.

To get a glimpse for how future catastrophic volcanic events might alter our lives, scientists at the University of Cincinnati dug deep into the past to find new evidence for volcanic related climate change.

The results of the study are published in the July issue of Scientific Reports titled “Positive platinum anomalies at three late holocene high magnitude volcanic events in Western Hemisphere sediments.”

“We looked at platinum particles as an indicator for how far volcanic ash has traveled,” says Kenneth Tankersley, UC associate professor of anthropology and geology and lead author on the study.

“The age of the sediment containing the platinum allowed our interdisciplinary team of anthropologists, geologists, geographers and biologists to directly pinpoint radical change in climate for eight different Western hemisphere archeological sites to three major catastrophic volcanoes from the beginning of the little ice age and Medieval Warming. The most recent dated to the 18th-century.”

Why is this important? Tankersley and the researchers hope studies like this can help the world better prepare for the next major eruption. As he says, “It’s not ‘if’ these catastrophic volcanic events will return, it’s ‘when.'”

“Can you imagine a year or even a decade with no summer?” asks Tankersley. “This happened consistently throughout the past 10,000 years.”

For example, Tankersley explains the Eldgjá eruption of (CE 934) as producing so much dust in the atmosphere, it filtered enough sun and heat to lower global temperatures significantly for a couple of years. What ensued were severe winters contributing to famine, epidemics, and loss of many lives. Over 900 years later a volcanic event on the Pacific island of Krakatoa caused Cincinnati to have an extremely cold winter and a very cool summer in the late 1800s.

Not all explosive volcanic eruptions result in the global distribution of particle spread, such as the most recent Kilauea volcano in Hawaii. However, Tankersley notes, there is a definite link between significant changes in climate conditions outside regular climate cycles and the high magnitude volcanic events explored in this research.

PLATINUM VALUE

A key player in this investigation is Platinum. According to the researchers, the rare element doesn’t occur naturally on the Earth’s surface. Instead, it occurs after a cosmic impact like a meteor, asteroid or a slice of a comet hits the earth.

Or, as in this case, platinum is revealed when volcanic ash spews along with fountains of incandescent lava and cow-pie shaped molten rock bombs. The resulting ash clouds contain platinum, evidence for the far-reaching effects of major volcanic eruptions.

The study looked at sediment samples from eight Western hemisphere archeological sites in the Ohio valley, the American southwest, the Caribbean and the Maya Lowland in Guatemala.

The interdisciplinary researchers from across UC’s campus and Kongju National University were able to successfully connect the radical climate change patterns from each of those sites to one or more of three high magnitude volcanic events including the Eldgjá volcano (CE 934) and the Laki volcano (CE 1783) in Iceland and Kuwae volcano on the island of Vanuatu off the coast of Eastern Africa (CE 1452).

All three catastrophic volcanic eruptions happened within the last 1,000 years or the late Holocene — the geological period we live in currently.

DATING SEDIMENT

Among UC’s research team is first-year anthropology grad student Dominique Sparks-Stokes who retrieved deep sediment samples from two of the Ohio Valley sites and identified botanical remains for radiocarbon dating.

After teasing out carbonized plants from the deep core samples, Sparks-Stokes and the researchers were able to count the number of carbon atoms — a process Tankersley says helps geochronologists put a precise date on where they are within the core.

In the lab, Sparks-Stokes works on trays filled with sandy colored dust and flakes. “See those tiny sparkling particles in this dust that looks like shiny sand? Much of that shiny material is quartz, feldspar and mica from volcanic dust preserved in the baked pottery.

“We have perfect conditions in these pocketed and protected environments where winds have little effect from erosion,” adds Sparks-Stokes, referring to the sinkholes in Serpent Mound and the Wynema site in the Ohio Valley areas.

“We dated the preserved sediments containing platinum and compared those dates to Western Hemisphere volcanic activity from the same era and associated that with erratic climate change patterns during that time as a result of those volcanic events.”

Identifying platinum particles within ancient volcanic ash is the first step. Dating the sediment using geochronology is the next, which is where UC geologist Lewis Owen comes in.

“In addition to radiocarbon dating, Owen added his optically stimulated luminescence expertise to a suite of scientific technology referred to as chronometric dating,” notes Tankersley. “We compared these findings to our typologically and temporally distinctive artifacts, which allowed us to pin down volcanic events that were already known from those epochs in time.”

BETWEEN A ROCK AND A “HOT” PLACE

Regular volcanoes eject millions of cubic feet of ash and debris over an entire state. But as Tankersley points out, supervolcanoes can devastate a whole continent, and half of the Earth’s super volcanoes happened in North America.

The last high magnitude eruption created a mini ice age that led to dramatic climate change. The greatest impact from another catastrophic event would come months after the explosion, however, as the deadliest result of these events is not so much the ash that falls to the ground but the gases that stay in the air, adds Tankersley.

“Explosive volcanoes blow materials up into the stratosphere,” explains research team member Warren Huff, UC professor emeritus of geology. “The explosion releases sulfur dioxide gas, which converts into sulfuric acid aerosol droplets that then travel through the earth’s atmosphere on wind currents.

“More than 200-million tons of sulfur dioxide, thrust into the air and spread worldwide by the stratospheric winds, can produce a veil covering the earth cutting out much of the sunlight. When the shade dims the heat from the sun for long periods of time the earth cools down.”

Volcanologists currently find an active supervolcano brewing under 3,400 square miles of protected wilderness in Northwest Wyoming’s Yellowstone National Park. It has exploded several times between 2.1 million years and 830,000 years ago.

“The concentrations of platinum from well-dated and well-stratified late Holocene sites provide an opportunity for more vigorous scientific evaluations of the impact of future high magnitude volcanic eruptions on climate change and society,” adds Tankersley.

Reference:
Kenneth Barnett Tankersley, Nicholas P. Dunning, Lewis A. Owen, Warren D. Huff, Ji Hoon Park, Changjoo Kim, David L. Lentz, Dominique Sparks-Stokes. Positive Platinum anomalies at three late Holocene high magnitude volcanic events in Western Hemisphere sediments. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-29741-8

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

Icy Greenland’s heated geologic past

Continental plates around Greenland.
This is a visualization of the continental plates around Greenland. Credit: NASA’s Goddard Space Flight Center

By mapping the heat escaping from below the Greenland Ice Sheet, a NASA scientist has sharpened our understanding of the dynamics that dominate and shape terrestrial planets.

Dr. Yasmina M. Martos, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, mined publicly available magnetic field, gravity and other geologic information for clues about the amount and distribution of heat beneath the portion of the North American continent that is Greenland.

Her resulting heat map exposed a thermal track beneath Greenland that records the movement of a continent through Earth’s history.

Greenland is thought to have slowly moved over a mantle plume, a source of great heat, which left a diagonal scar of warm, dense rock below the surface as the tectonic plate shifted. Greenland moved from a more southern latitude toward the Arctic over 100 million years, a period when the supercontinent Pangaea was breaking up into the drifting continents of today. Eventually, the plume is thought to have formed Iceland above the surface of the ocean through countless volcanic eruptions — a visible trace of the plume’s existence, in contrast to Greenland’s hidden scar.

“I don’t think there is any other place on Earth where a plume history has been recorded by a piece of continent that hasn’t been affected by it at the surface,” Martos said. “But it’s there, so we can use thermal heat to understand the history of the region.”

Tracking these geodynamics of planets helps scientists understand their evolution. But more immediately, the heat information feeds sea-level-change models on Earth by helping scientists predict the behavior of ice. This is particularly important for the surface of land that, in the case of Greenland, is buried below kilometers of ice and so is hard to get to. More than 80 percent of the Greenland is covered by ice.

Where there’s heat, there might be a plume

In an Aug. 1 Geophysical Research Letters paper, Martos and her team mapped the geothermal heat flux, or rate of heat escape, in Greenland. Their models, surprisingly, showed regional variations, plus a path of heat along a peculiar route from the northwest to the southeast of the island.

“We would expect Greenland to have a more uniform signal of geothermal heat flow in its interior, but that’s not the case,” said Martos, the lead author on the paper.

Other authors include Tom A. Jordan and David G. Vaughan from the British Antarctic Survey; Manuel Catalán from the Royal Institute and Observatory of the Spanish Navy; Thomas M. Jordan from Stanford University and University of Bristol, and Jonathan L. Bamber, also from the University of Bristol.

The team suggests the scar was created as the tectonic plate, which includes Greenland, moved through the millennia over a mantle plume that is active below the lithosphere. The lithosphere is Earth’s outer layer; it includes the crust and upper part of the mantle. This plume is a channel of hot rock that starts hundreds of kilometers below the surface. It rises through the mantle and reaches the bottom of the lithosphere. The heat is then transported up through the lithosphere and alters its chemical composition, which thickens the crust.

Because the northwest region of Greenland moved off the plume earlier it appears in Martos’ models to be significantly cooler than the southeast. Though the southern region is slowly cooling off.

“The nice thing is that the heat is recorded there now, but probably in a hundred million years we’re not going to see that anymore,” Martos said.

A similar plume formed the Hawaiian Islands and is currently fueling the K?lauea volcano eruptions. The Hawaiian chain of islands and seamounts that were created when the Pacific Plate moved over the plume in the middle of the Pacific Ocean is a visible representation of the type of scar that Martos found beneath Greenland.

The heat beneath Earth’s surface

Plumes are one of several geothermal heat-transporting phenomena on Earth; their number is uncertain, but scientists think there could be as many as 20. Otherwise, the inner planet is heated evenly throughout by decaying radioactive elements in Earth’s top layers. There’s also primordial warmth left over from the formation of our planet 4.5 billion years ago, and from the meteorites that pummeled it. The team considered these heat sources, Martos said, but ruled out their role in producing the scar because they would have formed a uniform heat pattern across Greenland.

Another factor that can increase heat in a specific location is tectonic activity. This activity includes rifting — or the breaking apart of continental plates, which creates space for warmer mantle to bubble to the surface — and volcanic eruptions. But these phenomena also didn’t square with the team’s findings, said Martos, given that Greenland is a craton, or an ancient piece of continent with no major tectonic events on record there.

Measuring heat without touching the surface

Because Greenland is covered by an ice sheet that is up to 1.8 miles (3 kilometers) thick in the center, getting physical samples from the ground below the ice is nearly as difficult as getting them from the Moon. Remotely sensed data offers virtually the only window to Greenland’s subsurface dynamics.

Martos’s team decided to look at magnetic field information collected by magnetometers, instruments flown by airplanes that measure the strength of the magnetic field of Earth. The data revealed anomalies in the magnetism of rocks below Greenland.

Magnetism is related to temperature, thus rocks heated to certain temperatures lose their magnetism. This typically happens deep inside Earth. Because magnetite is the most abundant magnetic mineral in the lower part of the crust, the researchers studied that mineral exclusively. Magnetite loses its ferromagnetic properties, or magnetism, when heated to 1,076 degrees Fahrenheit (580 degrees Celsius), a point known as the Curie temperature. Accounting for this temperature’s effect on magnetite allowed the team to find the base of magnetism in the crust of Greenland. From there, they observed the depth variations of the location of the Curie temperature for magnetite to map the heat released all over the island.

Along the plume’s path, the team found that the Curie temperature occurred closer to the surface. This offered evidence that the plume had heated the bottom of the lithosphere, and that the heat was still there.

The team also used gravity data to model the features of the lithosphere and confirm the plume’s effect on crustal thickness.

In the central part of the island, the team estimated geothermal heat flux values around 60 to 70 milliwatts per meter squared, or up to 50 percent higher than the heat escaping parts of the island not affected by the plume. This is a tiny amount; a 100-watt light bulb, by comparison, generates three orders of magnitude — or 1,000 times — more heat.

Still, said Martos and her co-authors, the heat they found can melt ice at the base of the Greenland Ice Sheet. It does not, however, contribute to the accelerated melting of Greenland’s glaciers. Because the geothermal heat declines over such huge periods of time — tens of millions of years — there has likely been no change in heat flux since the ice fully formed on Greenland about 3 million years ago.

Martos’ modeling tools will help scientists better understand the effect of below-surface heat on things like melt or breakage at the base of ice sheets and glaciers on Earth. It will also help them study remote locations on Earth and other rocky bodies in our solar system.

Martos began this research while she was a Marie Curie fellow of the European Union at the British Antarctic Survey.

Reference:
Yasmina M. Martos Tom A. Jordan Manuel Catalan Thomas M. Jordan Jonathan L. Bamber David G. Vaughan. Geothermal heat flux reveals the Iceland hotspot track underneath Greenland. Geophysical Research Letters, 2018 DOI: 10.1029/2018GL078289

Note: The above post is reprinted from materials provided by NASA/Goddard Space Flight Center. Original written by Lonnie Shekhtman.

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