The Ethiopian Rift Valley suffered colossal volcanic eruptions between about 320,000 and 170,000 years ago. Credit: David Pyle
The great Rift Valley that runs through Ethiopia has played a pivotal role in human evolution. It is both the location of the earliest fossils of anatomically modern humans and, later, become an important route for human migrations ‘out of Africa’.
Today, it is home to more than ten million people, a major hub for tourists, and the location of important transport links. The main Ethiopian Rift Valley is also one of the largest fields of volcanoes on Earth – although this status may not be obvious from the remnants of the sprawling tumbledown hills that break through the dusty flats of the rift valley floor. Here, Africa has been slowly pulling apart for millions of years. As the continent pulls apart, the crust extends and thins, promoting the rise of magma from the depths of the Earth’s mantle. None of these volcanoes is thought to have erupted since the early 19th century, and several are now the focus of development of geothermal energy potential.
In a new paper published in the journal Nature Communications, Will Hutchison, an Oxford DPhil student, and a team of collaborators from the UK, Ethiopia and the USA, shed a little more light on the violently explosive past of several of these rift volcanoes. Using a combination of field work (to reconstruct the deep history of the volcanoes) and isotopic age dating techniques, the researchers find that at least four of the volcanoes of the main Ethiopian Rift Valley suffered colossal eruptions between about 320,000 and 170,000 years ago. These were very significant eruptions – perhaps of the scale of the eruption of Krakatoa in Indonesia in 1883. They would have buried the rift floor in volcanic ejecta, disrupting water sources and habitats across wide areas, with the collapsed remnants of the volcanic edifices forming great ‘calderas’, or craters, in the rift floor.
This pulse in volcanism coincides with the arrival of Homo sapiens in the region around 200,000 years ago and raises the question of to what extent these changes in the landscape and environments occupied by our earliest human ancestors might have influenced human evolution and migration. The recognition that explosive volcanism in the rift occurs in bursts also poses some interesting geological questions, and future inter-disciplinary research is needed to understand the scale of eruptions at other large volcanoes of the rift, their causes, and their wider consequences.
Reference:
William Hutchison et al. A pulse of mid-Pleistocene rift volcanism in Ethiopia at the dawn of modern humans, Nature Communications (2016). DOI: 10.1038/ncomms13192
A Thunder Egg “Thunderegg” is a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. Thundereggs are rough spheres, most about the size of a baseball—though they can range from less than an inch to over a meter across. They usually contain centres of chalcedony which may have been fractured followed by deposition of agate, jasper or opal, either uniquely or in combination. Also frequently encountered are quartz and gypsum crystals, as well as various other mineral growths and inclusions. Thundereggs usually look like ordinary rocks on the outside, but slicing them in half and polishing them may reveal intricate patterns and colours. A characteristic feature of thundereggs is that (like other agates) the individual beds they come from can vary in appearance, though they can maintain a certain specific identity within them.
Thunder Egg is not synonymous with either geode or agate. A geode is a simple term for a rock with a hollow in it, often with crystal formation/growth. A thunderegg on the other hand is a specific geological structure. A thunderegg may be referred to as a geode if it has a hollow in it (see illustration of Gehlberg specimen), but not all geodes are thundereggs because there are many different ways for a hollow to form. Similarly, a thunderegg is just one of the forms that agate can assume.
Many thundereggs found at Rockhound State Park are spherical and consist of two distinct parts: a dark-gray to pinkish outer part and a white, blue, or gray inner part, or core, which is recognizable as agate, chalcedony, and quartz crystals, all forms of the compound SiO2. In many examples, these two parts can be described as a shell and a filling. However, some thundereggs, or spherulites, do not contain the filling; they are composed of solid dark-gray to pinkish shell material (Fig. 3) or are partly hollow. Geologically distinct processes form the two parts of the thundereggs. The outer part of the thundereggs is formed by complex magmatic processes (i.e. as spherulites), and then the inner part is formed and modified by multiple cycles of late-stage hydrothermal fluids. The processes that form geodes and thundereggs are complex and are controlled by constantly changing physical and chemical conditions, such as temperature, pressure, depth of formation, composition of the magma, composition of the ground water, and composition of the host rocks.
Occurrence
Thundereggs are found globally wherever conditions are right. In the USA, Oregon remains one of the most famous thunderegg locations. Germany is also an important center for thunderegg agates (especially sites like St Egidien and Gehlberg). Other countries known for their thundereggs include some places in Africa, Poland, Romania, Turkey, Mexico, Argentina, Canada, Australia and France.
Formation
Thundereggs are found in flows of rhyolite lava. They form in gas pockets in the lava, which act as molds, from the action of water percolating through the porous rock carrying silica in solution. The cooled bubbles were gradually filled by water percolating through the porous rock carrying rich quantities of silica (quartz). The deposits lined and filled the cavity, first with a darker matrix material, then an inner core of agate or chalcedony. The various colors come from differences in the minerals found in the soil and rock that the water has moved through.
The agate, chalcedony, and quartz veins and open-space-fillings within voids in the spherulites formed later by multiple cycles of hydrothermal fluids. Hydrothermal fluids are a mixture of late-stage fluids escaping the magma and local ground water. The fluids contain some elements from the original magma and also dissolved minerals from the country rock. The amount of ions that the fluid can dissolve depends upon pH, temperature, pressure, and composition of the fluid. The hydrothermal fluids move through fractures in the rocks, which crosscut the igneous textures, and form veins or banded agate, chalcedony, and quartz. Some of these fluids seep through microscopic pores and into spherulites and gas pockets in the volcanic rocks, and they precipitate crystals along the walls of the cavity, forming geodes and geode-like spherulites. Other fluids seep through fractures and gas and other void spaces in the spherulites. Because of their formation by multiple hydrothermal events, each thunderegg provides clues as to its unique formation.
Different temperatures and fluid compositions would account for the variety of textures found within any given thunderegg or geode. By carefully studying the crystal fill and textures in spherulites and geodes, geologists can piece together the different processes through time that formed them. The banding found within some spherulites and geodes consists of multiple layers of different colored agate, chalcedony, and locally quartz, and may have been formed by fluids supersaturated in silica (Fournier, 1985a). Supersaturated solutions are solutions that contain excessive silica in solution. The presence of silica minerals within the thundereggs and geodes indicates that the fluids were saturated in silica. Saturated fluids are fluids that contain enough silica in solution without precipitating silica minerals. When a silica-saturated solution cools slowly, crystalline quartz is deposited at approximately 200°–340° C (Fournier, 1985a). Rapid cooling of a silica-saturated fluid allows supersaturated solutions to form that precipitate chalcedony or amorphous silica. These supersaturated fluids are unstable and quickly deposit thin layers of chalcedony or amorphous silica, typically at lower temperatures (<200° C). The fluid loses silica due to precipitation and becomes saturated with silica but as the fluid continues to cool rapidly, it becomes supersaturated with silica again. An increase in salinity (such as NaCl) increases the solubility of silica at higher temperatures and also produces saturated silica solutions (Fournier, 1985a). Supersaturation of the fluids can also occur by mixing of different hydrothermal fluids, especially with different pHs, and by reaction of hydrothermal fluids with volcanic gases.
The different colors of the bands are a result of trace amounts of impurities, such as iron (red), manganese (black, pink), cobalt (blue, violet-red), copper (green, blue), chromium (orange-red), nickel (green), etc. Faceted quartz crystals indicate that the fluids were somewhat supersaturated with silica and that precipitation occurred under relatively slow-changing conditions (Fournier, 1985a).
Not all geodes are spherulites formed by magmatic processes; other natural processes form some geodes. Lower-temperature ground water percolates through the cooled volcanic rocks and dissolves additional minerals. These fluids are typically low temperature (<200° C), although locally higher-temperature (200°– 300° C) ground waters may be present, especially adjacent to the volcanic vents. These fluids move through microscopic pores in the rock by a process called “diffusion.” During diffusion, some ions in the fluid collect into void spaces and gas pockets in the rock, whereas other ions cannot pass through. This collection of ions surrounding these void spaces may actually, in some cases, form the hard outer shell that is characteristic of geodes. The outer shell may be strengthened by the precipitation of some ions that were excluded during crystallization of agate, chalcedony, and quartz and concentrated in the remaining fluid. Fluids also enter the void spaces through fractures. The void spaces may have originally formed by gas pockets within the magma or by prior dissolution of spherulites or other features within the volcanic rock.
How do the Thunder Egg/spherulites become hollow?
this is difficult to demonstrate directly, we speculate that the hollow centers of spherulites are formed by nucleation, coalescence, and expansion of vapor bubbles at high temperature, resulting in a hollow center that can be filled later by silica. The vapor bubbles would have formed as a result of crystallization of quartz, feldspar, and magnetite, which contain no water, from rhyolitic magma, which contains a small amount of dissolved water at atmospheric pressure (Taylor, 1986). Calculations of the volume of water vapor that could have formed from anhydrous crystallization suggest that the volume would be more than enough to generate the size of hollow cavities seen in spherulites. The reason that some spherulites are hollow and others are not may be related to the rate and depth of crystallization and to the resultant ability or inability of vapor bubbles to nucleate and coalesce.
These fiery images offer a glimpse inside the ‘Gateway To Hell’ – the world’s oldest continuously active lava lake. Travel photographer Joel Santos, 38, piloted a drone low over the bubbling lake, which reaches temperatures exceeding 1,100 degrees celsius.
The lake, which has had a continuous flow since 1906, is situated inside the Erta Ale volcano, otherwise known as Smoking Mountain, in the Afar region of northeastern Ethiopia. The volcano’s last major eruption occurred in 2005, killing 250 livestock and forcing thousands of nearby residents to flee. And the Portuguese photographer remained acute aware of the hazards posed by filming such a potentially devastating natural phenomenon at such close quarters.”
An extremely well-preserved footprint in Denali National Park reveals a meat-eating dinosaur’s claws, fleshy toe pads and pebbly skin texture. Credit: Pat Druckenmiller
Paleontologists from the University of Alaska Fairbanks and the National Park Service found the first dinosaur bones in Denali National Park during an expedition in July. They also discovered several new dinosaur trackways, which are fossilized impressions left by ancient animals walking through mud that eventually became rock.
Pat Druckenmiller, curator of Earth sciences at the University of Alaska Museum of the North, is leading a collaborative project with Denali National Park over the next several years to explore additional areas and make new discoveries.
“This marks the beginning of a multi-year project to locate, document and study dinosaur fossils in Denali National Park,” Druckenmiller said. “This is a world-class site for tracks of dinosaurs and other animals that lived in Alaska during the Cretaceous Period. Now that we have found bones, we have another way to understand the dinosaurs that lived here 70 million years ago.”
The research team found four different fragments, including one ossified tendon. The largest is a few inches long. They are clearly parts of bigger bones from a large animal. This rules out other animals with a backbone known from this geological period, including mammals, birds and even flying reptiles. Because they are parts of much bigger bones, Druckenmiller expects more complete remains may be found in the park.
“Finding these bones opens a new chapter in the story of Denali dinosaurs,” he said. “That story is still being written as we find new sites, new kinds of dinosaurs and evidence of their behavior.”
Before 2005, there was no known dinosaur record in Denali. That year, UAF students discovered the first track in the Cantwell Formation near Igloo Creek. Since then paleontologists have catalogued thousands of tracks. Still, this is the first time scientists have found identifiable bones left by animals that populated the area during the Late Cretaceous Period.
Park geologist Denny Capps said Denali National Park was created to protect the present intact ecosystem 99 years ago.
“We now know that it protects an ancient ecosystem, as well,” Capps said. “Visitors could discover a fresh bear track next to a 70-million-year-old dinosaur track or potentially even a bone. Thankfully, these resources are protected within the Denali wilderness for all to enjoy.”
Heather MacFarlane, a UA Museum of the North research assistant, discovered the first bone. She and other researchers recognized the fragments as bones rather than sedimentary material based on the surface and internal structure. These fossils closely resemble other plant-eating dinosaur bones found in Alaska.
Paleontologist Cassi Knight, physical science technician for Denali National Park, was with MacFarlane when the discovery was made.
“It is significant because it answers a question that has been standing for the past 11 years; ‘Are there dinosaur bones preserved in the Cantwell Formation?'” Knight said. “We have a great record of dinosaurs inhabiting this area, and now we finally know that their bones are preserved, too.”
Gregory Erickson, a Florida State University researcher who specializes in the use of bone and tooth histology to interpret the paleobiology of dinosaurs, was also part of the discovery team. He is preparing thin sections of some of the fossils. Scientists can examine these delicate slices under high-powered microscopes to determine the type of animal that left the bones behind. Annual growth lines and other patterns can also reveal the animal’s age.
Based on the shape and structure of the fossilized tendon discovered by the team, Erickson and Druckenmiller determined that it is from a large ornithopod dinosaur, probably a hadrosaur. These duck-billed, herbivorous dinosaurs were probably the most abundant large animals in Alaska. They were also the primary track-makers in the park during this time period.
Another larger fragment is composed of spongy bone originating from the end of a large animal’s limb. This microstructure shows the bone didn’t come from a crocodile or other slow-growing, cold-blooded animal. It is clearly from a medium-sized to large dinosaur, they said.
Druckenmiller and Erickson previously published documentation suggesting that during this time period, a distinct, polar fauna existed in what is now Alaska. Then, a polar forest covered the Arctic because the climate was much warmer. The dinosaurs had to contend with months of winter darkness and cooler temperatures than environments typically associated with dinosaurs.
Zircon crystals examined with an electron microscope. The brighter and more concentrically zoned crystals with nice straight edges are the volcanic zircons. Credit: Milo Barham
Australia could have been home to some of Earth’s largest ever volcanic eruptions more than 100 million years ago.
A Curtin University team looking at core samples from the Nullarbor’s Madura Shelf found volcanic zircon crystals similar to those found in the volcanic region of eastern Australia that existed more than 100 million years ago.
Curtin University Institute for Geoscience Research geologist Dr Milo Barham led the research and says the super-eruptions that occurred to transport material from the east to the west coast of Australia would have been bigger than anything in recorded history.
“Our work has now shown that there must have been these large volcanic events, these magnitude eight volcanoes that were projecting material thousands of kilometres away,” he says.
“It’s the first evidence of it occurring here and also some of the oldest evidence of being able to trace and prove one of these cases.”
“The one we’re suggesting is bigger than anything that’s occurred during human history, it’s bigger than Krakatoa.”
Dr Barham says the zircon crystals would have been transported from a huge eruption column tens of kilometres high coupled with strong polar winds in the troposphere.
“Reconstructions of the climate at the time suggest that we had these winds. Australia was further south back then and we would’ve been subjected to these polar easterly winds,” he says.
“That would’ve pushed this eruption material all the way across to Western Australia.”
He says if an explosion like this happened today, there would be massive devastation.
“You’d be putting out maybe a thousand cubic kilometres of material during the eruption, so nearby it’s going to be blanketed in hundreds of metres thick of material.”
“You’re going to have a shockwave that propagates out and knocks down trees, destroys houses and cities and kills people for hundreds of kilometres.”
“Mt St Helen’s was on such a small scale relatively. If you scale that up by several orders of magnitude then you can start getting a sense the biggest impact would be the particulate matter that you put up into the atmosphere.”
“It would cool the climate by blocking sunlight and basically scattering the suns energy. You’d have several years without a decent summer.”
Dr Barham’s says the next step is to see if they pinpoint the exact time of the eruptions as well as find more matching volcanic material further west.
The Director of Earth Science Museum Diogenes de Almeida Campos shows the biggest piece of fossil of the Austroposeidon magnificus dinosaur’s neck.
Sometimes the greatest dinosaur discoveries are just lying waiting to be found in a museum cupboard.
Titanosaurs were some of the most enormous animals to have ever strode the Earth, moving in enormous herds and thundering across the land, devouring any forests in their path. They reached a near-global distribution during their time, even reaching Antarctica and Australia, and recent discoveries have revealed an amazing species diversity for the group.
In South America, titanosaurs truly reached their zenith in both size and biodiversity. Nonetheless, new species keep becoming known to science through numerous discoveries, both old and new! Recently, yet another new species has been named based on series of fossilised vertebra after being locked away for more than 60 years in a museum basement.
The fossils were actually originally discovered back in 1953 by Brazilian palaeontologist Llewllyn Ivor Price, but remained hidden in storage at the Museum of Earth Sciences in Rio de Janeiro due to the lack of proper tools or finances to study it further.
The new species is named Austroposeidon magnificus, and comes from a place in São Paulo State of southeast Brazil called the Paraná Basin. It hails from right near the end of the Cretaceous, when the truly gigantic dinosaurs were roaming the lands, just before many went extinct. The name, Austroposeidon, comes from “Austro” meaning southern, and refers to Poseidon, the Greek god for causing earthquakes, as the beast would have shook the very ground it walked on!
Austraoposeidon would have been a pretty magnificent sight to behold, coming in at around 25 metres (about 82 feet) in length when fully grown, placing it way up in the heavyweight category. That’s about the same as two buses back to front, and makes it the largest known dinosaur from Brazil! So far..
Kamila Bandeira and colleagues were able to even use 3-D CT scanning to show that, similarly to other titanosaurs, the vertebral bones were pneumatised – possessing numerous internal air pockets. These would have considerably lightened the enormous skeleton, much as we see in modern birds. The researchers went back to the original place of discovery to try and find more of the animal, but unfortunately the area has been urbanised now, rendering finding the final resting place nigh impossible.
Austroposeidon wouldn’t have been alone in its adventures. Other sauropods, albeit much smaller sized ones, are known from the same rocks, including Brasilotitan and Gondwanatitan. Similar to other regions were multiple giant herbivores co-existed, it is likely that these animals had certain very specific feeding styles in order to efficiently maximise the use of limited vegetation resources. The latter two might have fed on plants closer to the ground, while Austraoposeidon towered above them, gracefully grazing from the treetops.
The deserts of South America are revealing new dinosaur species to us at an astonishing rate, and the future of discovery there is truly exciting!
Reference:
Kamila L. N. Bandeira et al. A New Giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil, PLOS ONE (2016). DOI: 10.1371/journal.pone.0163373
A new study led by UAlbany researchers tracks the heavy influence of massive volcanic eruptions on the intertropical convergence zone that is home to some of the most intense rainfall on the planet. Credit: University at Albany
Volcanic eruptions over the last 1,000 years have exacted a heavy influence on global climate, according to a new study led by researchers at the University at Albany. The impact is felt most dramatically near the equator, where eruptions have led to reduced rainfall in both the summer monsoon and winter seasons, as well as a cooling trends across entire continents.
Writing in Earth System Dynamics, UAlbany researchers Christopher Colose and Mathias Vuille, along with Allegra LeGrande of the NASA Goddard Institute for Space Studies, document the influence of large, explosive (Plinian) volcanic eruptions during the last millennium. They found that the narrow precipitation belt in the deep tropics – the intertropical convergence zone (ITCZ) would shift following massive eruptions.
The ITCZ is a critical resource, producing some of the most intense rainfall on the planet, providing water for ecosystems and agriculture, and affecting hundreds of millions of people. The monsoons, linked to the ITCZ, equally provide vital rainwater used for sanitation, drinking water, hydropower production and irrigation in tropical countries all over the world, from India to Bolivia.
“We looked at how volcanic eruptions in one hemisphere impact the tropical rain belt and found that it tends to move toward the opposite hemisphere,” said Colose, a graduate researcher who is completing his Ph.D. in atmospheric and environmental sciences at UAlbany.
It has long been known that volcanic eruptions cool the planet and reduce rainfall averaged across the entire globe. “However, following Plinian eruptions, the rain belt moves away from the hemisphere where the volcano is located. So if you’re sitting somewhere south of the equator in South America, and an eruption goes off in Iceland, the tropical rain belt may move southward a bit, and actually give you a bit more rain,” said Colose. “This is a fascinating example of how an event can trigger changes in the atmosphere that modify the climate thousands of miles away.”
The findings may help scientists better understand the dynamics at work during monsoon seasons across the planet, and to create a prediction model for the climatic impact following a massive volcanic eruption.
“Plinian volcanic eruptions are a dominant driver of naturally forced climate change during the last millennium,” said Colose. “For instance, the effect of the Mount Pinatubo eruption in 1991was felt worldwide, with the average temperature dropping for the next three years.”
On a global scale, the climate during the 1,000 years prior to the industrial revolution was quite stable, but volcanic eruptions had the largest external influence on the changes that did occur. Other smaller factors include subtle fluctuations in the Sun’s output, wobbles in the Earth’s orbit, and land-use change caused by humans across Europe and North America.
Plinian eruptions thrust massive volumes of aerosols into the atmosphere, blocking the sunlight Earth absorbs and resulting in a widespread cooling effect. Although the Earth is currently warming due to large-scale greenhouse gas emissions, a large volcanic eruption like Mt. Pinatubo would suppress the temperature rise for a couple of years. However, it is only a temporary effect.
Reference:
Christopher M. Colose et al. Hemispherically asymmetric volcanic forcing of tropical hydroclimate during the last millennium, Earth System Dynamics (2016). DOI: 10.5194/esd-7-681-2016
The pXRF was used on islets across the site of Nan Madol and intensively on the islet of Nandauwas. Credit: Mark McCoy
New dating on the stone buildings of Nan Madol suggests the ancient coral reef capital in the Pacific Ocean was the earliest among the islands to be ruled by a single chief.
The discovery makes Nan Madol a key locale for studying how ancient human societies evolved from simple societies to more complex societies, said archaeologist Mark D. McCoy, Southern Methodist University, Dallas. McCoy led the discovery team.
McCoy deployed uranium series dating to determine that when the tomb was built it was one-of-a-kind, making it the first monumental scaled burial site on the remote islands of the Pacific.
The discovery enables archaeologists to study more precisely how societies transform to more and more complex and hierarchical systems, said McCoy, an expert in landscape archaeology and monumental architecture and ideology in the Pacific Islands.
“The kind of society that we live in today, it wasn’t born last year, or even 100 years ago,” McCoy said. “It has its roots in a pre-modern era like Nan Madol where you have a king or chief. These islanders invented a new kind of society — that is a socially creative achievement. The idea of chiefs, someone in charge, is not a new thing, but it’s an extremely important precursor. We know tribes and bands predate chiefdoms and states. But it’s not a straight line. By looking at these intermediate stages we get insight into that social phenomenon.”
The analysis is the first time uranium-thorium series dating, which is significantly more precise than previously used radiocarbon dating, was deployed to calculate the age of the stone buildings that make up the famous site of Nan Madol (pronounced Nehn Muh-DOLL) — the former capital of the island of Pohnpei.
“The thing that makes this case special is Nan Madol happened in isolation, it happened very recently, and we have multiple lines of evidence, including oral histories to support the analysis,” McCoy said. “And because it’s an island we can be much more specific about the natural resources, the population, all the things that are more difficult when people are on a continent and all connected. So we can understand it with a lot more precision.”
Nan Madol, which UNESCO this year named a World Heritage Site, was previously dated as being established in A.D. 1300. McCoy’s team narrowed that to just a 20-year window more than 100 years earlier, from 1180 to 1200.
The finding pushes back even earlier the establishment of the powerful dynasty of Saudeleur chiefs who asserted authority over the island society for more than 1,000 years.
First chief was buried in Pohnpei tomb by A.D. 1200
An ancient city built atop a coral reef, Nan Madol has been uninhabited for centuries now. Located in the northwestern Pacific on the remote island of Pohnpei, it’s accessible via a 10-hour flight from Hawaii interspersed with short hops from atoll to atoll, including a stop at a U.S. military installation. Nan Madol is the largest archaeological site in Micronesia, a group of islands in the Caroline Archipelago of Oceania.
Uranium dating indicates that by 1180, massive stones were being transported from a volcanic plug on the opposite side of the island for construction of the tomb. And by 1200, the burial vault had its first internment, the island’s chief. Manipulate two 3D models of the burial monument, one with foliage and one without, at https://skfb.ly/StXA and https://skfb.ly/S9LF.
Construction of monumental buildings followed over the next several centuries on other islands not in the Saudeleur Dynasty across Oceania.
McCoy, an associate professor in the SMU Department of Anthropology, and his team reported their discovery in the journal Quaternary Research in “Earliest direct evidence of monument building at the archaeological site of Nan Madol identified using 230Th/U coral dating and geochemical sourcing of megalithic architectural stone.”
Co-authors include Helen A. Alderson, University of Cambridge, U.K., Richard Hemi, University of Otago, New Zealand, Hai Cheng, Xi’an Jiaotong University, China, and R. Lawrence Edwards, University of Minnesota.
An inactive volcano that hasn’t erupted in at least one million years, Pohnpei Island is much larger than its neighboring atolls at 128 square miles (334 square kilometers), making it about the physical size of Columbia, S.C.
Now part of the 607-island nation of the Federated States of Micronesia, Pohnpei Island and its nearby atolls have a population of 34,000.
Pohnpei monument indicates invention of a new kind of society
How Nan Madol was built remains an engineering mystery, much like Egypt’s Pyramids.
“It’s a fair comparison to the Pyramids, because the construction, like the Pyramids, didn’t help anyone — it didn’t help society be fairer, or to grow crops or to provide any social good. It’s just a really big place to put a dead person,” McCoy said.
It’s important to document such things, he said, because this architectural wonder indicates that independently of Egypt, another group of people put effort into building a monument.
“And we think that’s associated with the invention of a new kind of society, a new kind of chiefdom that ruled the entire island,” McCoy said.
Unlike Egypt and the Pyramids however, Nan Madol was invented much more recently in the big story of human prehistory, he said.
“At A.D. 1200 there are universities in Europe. The Romans had come and gone. The Egyptians had come and gone,” he said. “But when you’re looking at Pohnpei, it’s very recent, so we still have the oral histories of the descendants of the people who built Nan Madol. There’s evidence that you just don’t have elsewhere.”
Monumental city built of coral and stone
Pohnpei was originally settled in A.D. 1 by islanders from the Solomon or Vanuatu island groups. According to local oral history, the Saudeleur Dynasty is estimated to have begun its rule around 1160 by counting back generations from the modern day.
To build the tomb and other structures, naturally formed boulders of basalt, each weighing tons, were somehow transported far from existing quarries on the other side of the island to a lagoon overgrown with mangrove and stretching across 205 acres (83 hectares).
The basalt blocks formed when hot lava cooled and adopted the shape of long, column-shaped boulders and cobbles. Formed from 1 million to 8 million years ago, they came from a number of possible quarry locations on the island.
The city’s stone structures were built atop 98 shallow artificial coral reef islets, each one built by the Saudeleur people. The structures were constructed about three feet above waterline by laying down framing stones, filling the void between them with crushed coral, then laying up double parallel walls and again filling the gap between with crushed coral. The islets are separated by tidal canals and protected from the ocean by 12 sea walls, making Nan Madol what many consider the Venice of the Pacific.
“The structures are very cleverly built,” said McCoy. “We think of coral as precious, but for the architects of Nan Madol it was a building material. They were on a little island surrounded by huge amounts of coral reef that grows really quickly in this environment, so they could paddle out at low tide and mine the coral by smashing some off and breaking it up into rubble.”
The largest and most elaborate architecture in the city is the tomb of the first Saudeleur, measuring 262 feet by 196 feet (80 meters by 60 meters), basically the size of a football field. It is more than 26 feet (8 meters) tall, with exterior walls about six feet to 10 feet (1.8 to 3 meters) thick. A maze of walls and interior walkways, it includes an underground crypt capped with basalt.
“The architecture is meant to be extremely impressive, and it is,” McCoy said. “The structures were built to last — this is one of the rainiest places on earth, so it can be muddy and slippery and wet, but these islets on the coral reef are very stable.”
Portable X-ray technology provides clue to source of megalithic stones
McCoy and his team used portable X-ray fluorescence (XRF) to geochemically match the columnar-shaped basalt stones to natural sources on the island. The uranium-thorium technique calculates a date based on characteristics of the radioactive isotope thorium-230 and its radioactive parent uranium-234.
That enabled them to determine the construction chronology of a tomb that oral histories identify as the resting place of the first chief to rule the entire island.
“We used an X-ray gun, which looks like a 1950s-styled ray gun,” McCoy said. “It allows you — at a distance and without destroying the thing you’re interested in — to bounce X-rays off it and work out what the chemistry is. The mobile technology has gotten much more affordable, making this kind of study feasible.”
Using uranium series dating on coral emerged in the last decade. Accuracy — superior to radiocarbon — is plus or minus a few years of when the coral died. A very good radiocarbon date only will get within 100 years.
“That’s a monumental shift in terms of the precision with which we talk about things,” McCoy said. “If Nan Madol had not been made of the kind of stone we could source, if the architects hadn’t chosen to use coral, we wouldn’t have been able to get this date. So it’s a happy coincidence that the evidence at the site came together.”
McCoy suggests that future research look at finding the cause for this major turning point on Pohnpei, and what sparked this new hierarchy of rule and monumental building in this society.
Reference:
Mark D. McCoy, Helen A. Alderson, Richard Hemi, Hai Cheng, R. Lawrence Edwards. Earliest direct evidence of monument building at the archaeological site of Nan Madol (Pohnpei, Micronesia) identified using 230Th/U coral dating and geochemical sourcing of megalithic architectural stone. Quaternary Research, 2016; DOI: 10.1016/j.yqres.2016.08.002
Representative Image: Exceedance probability within 30 years considering all earthquakes (JMA seismic intensity: 6 Lower or more; average case; period starting Jan. 2010)
In Japan, Taiwan and New Zealand, one of the largest driving forces behind earthquakes is the active convergence of tectonic plates at rates of four to eight centimeters per year. The plate boundaries in each region are complex throughout the length of each plate margin. Destructive earthquakes like the 2011 Tohoku-Oki earthquake and tsunami in Japan, the Canterbury Earthquake Sequence in New Zealand that began in 2010, and the 2016 Meinong, Taiwan earthquake caused significant loss of life and billions of dollars in property damage, making it essential that these countries refine their seismic hazard models to prepare for future earthquakes.
Since 2014, research groups in these regions have been collaborating on research topics and sharing expertise to help develop national seismic hazard models. In a focus section published October 19 in Seismological Research Letters, the scientists describe their work for the Joint Japan-Taiwan-New Zealand National Seismic Hazard Model Collaboration.
The eight papers in the section discuss the different modeling approaches taken by each country, and the primary audiences for the resulting seismic hazard models–from governments who enforce building codes to insurers and energy and manufacturing industries. The section is edited by seismologists Matthew Gerstenberger and Bill Fry at GNS Science, New Zealand.
“By combining our efforts we are able to benefit from this experience to make what will hopefully be substantial improvements in the seismic hazard models for each region,” Gerstenberger and Fry write in the preface to the focus section.
Topics in the eight papers of the focus section include:
The Japanese National Seismic Hazard Model was updated in 2014 with several key changes made in the wake of the 2011 Tohoku-Oki earthquake, with special attention given to revising the probability of large earthquakes occurring in the country; including in the model “outer-rise” earthquakes that arise within a subducting plate before it enters the subduction zone; and revising earthquake rates along the eastern margin of the Sea of Japan.
What lessons might the Tohoku-Oki earthquake in Japan hold for understanding the consequences of similar megathrust earthquakes along New Zealand’s Hikurangi and Taiwan’s Ryukyu subduction zones? In a region where few historical earthquakes of that size can be compared, the Tohoku quake has offered insight into the magnitude, ground motion, and redistribution of seismic stress that might occur with similar quakes in the region.
The Tohoku-Oki earthquake also prompted a reevaluation of long-period ground motion hazard, which can affect high-rise buildings, among other large structures. A new study adds a complex computer simulation model to other long-period ground motion simulations already in use for seismic hazard modeling of megathrust earthquakes in Japan.
A new seismic hazard model for Canterbury, New Zealand can be used to provide earthquake hazard on a scale from one day to fifty years in the future, used by engineers and others involved in revising the seismic hazard design standards that are being applied to the rebuilding of Christchurch after two major earthquakes in 2010 and 2011.
Some of the Canterbury earthquakes occurred along faults that were not known to be active. A new historical analysis looks at how complete the fault model is in New Zealand National Seismic Hazard Model, and concludes that about half of the largest New Zealand quakes occurring after 1800 would not be included in a fault source model with the largest discrepancy for slow moving faults.
Using GPS data to investigate seismic potential on known active faults in Taiwan, researchers have created a new model that highlights known faults in central and eastern Taiwan that could be capable of generating earthquakes of magnitude 6.0 to 7.3 in the next decades.
Researchers investigated the sensitivity of Taiwan’s national seismic hazard model, with an eye toward how each seismic source used in the model contributes to hazards in six metropolitan areas. Subduction zone sources, they conclude, should be taken into account when assessing hazards in Northern Taiwan.
A final study in the focus section uses the OpenQuake-engine to review the main characteristics of earthquake source models used to calculate the most recent seismic hazard maps for Japan, Taiwan and New Zealand. Despite some tectonic similarities among these regions, the hazard models differ in the modeling options used to create them. Researchers in the collaboration will continue to discuss these similarities and differences and look for new ways to work together to improve all national models.
Flight of marine terraces on the south coastline of Crete, Greece, eastern Mediterranean. The lower prominent paleoshoreline (indicated by the red-line) records tectonic rock uplift during the 365 AD M>8 earthquake. The higher marine terraces (indicated by the yellow-lines) record cumulative uplift over many earthquake-cycles that occurred during the last 125 thousand years. Credit: V. Mouslopoulou/GFZ
A new mechanism may explain how great earthquakes with magnitudes larger than M7 are linked to coastal uplift in many regions worldwide. This has important implications for the seismic hazard and the tsunami risk along the shores of many countries. The mechanism is proposed by an international team of scientists led by Vasiliki Mouslopoulou of the GFZ German Research Centre for Geosciences in the journal Tectonics. The idea is that series of severe earthquakes within a geologically short period of time cause the rising of the land where one tectonic plate slips beneath another slab of Earth’s crust in a process called subduction.
To test their hypothesis, the scientists investigated ancient coastlines that were preserved over time, so-called paleoshorelines, to determine the rate of uplift over past millennia. Vasiliki Mouslopoulou says: “It is not unlikely that coastlines along active subduction margins with no detectable tectonic uplift over the last 10,000 years will accommodate bigger than M7 earthquakes in the near future.”
Uplift is common along the coastlines of continents at subduction systems worldwide (e.g., Kamchatka, Japan, New Zealand and Papua New Guinea) with rates of vertical uplift accrued over the last 10,000 years being generally higher — up to ten times more than for time intervals larger than 125,000 years.
This rate variability is odd and requires explanation. The origins and the magnitude of these rate variations were examined by German (GFZ) and New Zealand (University of Canterbury) scientists using a global data set of 282 uplifted paleoshorelines from eight subduction margins globally (Italy, Greece, New Zealand, Japan, Papua New Guinea, Iran-Pakistan, Chile) and 2D numerical models.
Paleoshorelines are a useful tool to constrain the magnitude and mechanisms of this uplift, as they are often spectacularly preserved as wave-cut platforms, benches and sea-notches, providing a geological record of the interplay between sea-level changes and rock uplift.
Data analysis and modelling suggest that varying uplift rates along subduction margins are mainly a short-term phenomenon. For geologists, short term means shorter than 20,000 years. These uplift rates cannot be accounted for by plate-boundary processes, as previously thought. Instead, they reflect a propensity for natural temporal variations in uplift rates where recent (not more than 10,000 years ago) uplift has been greatest due to temporal clustering of large-magnitude (bigger than M7) earthquakes on upper-plate faults.
Given the size and geographical extent of the analyzed dataset the conclusions of this work are likely to have wide applications.
Asked what’s new with these findings Vasiliki Mouslopoulou explains: “For the first time temporal clustering of great-earthquakes is shown on active subduction margins, indicating an intense period of strain release due to successive earthquakes, followed by long periods of seismic quiescence.” This finding has applications to the seismic hazard of these regions, as it highlights the potential for future damaging earthquakes and tsunamis at active subduction margins with no measurable recent uplift. In such cases, paleoshorelines older than 10,000 years could provide an important constraint for hazard analysis. In other words: To assess the likelihood of future great quakes it will help to look at paleoshorelines.
Further, it alerts scientists that earthquake clustering may not only characterise shallow faulting and smaller-sized earthquakes with magnitudes lower than M7 but it is a property of large subduction earthquakes.
This work presents a conceptual model in which strain is released by temporally clustered great-earthquakes that rupture faults within the upper-plate as opposed to the zone where the tectonic plates meet (plate-interface). Onno Oncken of GFZ comments: “This is an intriguing finding that changes the stereotype view that all or most great subduction earthquakes occur along the active contact, i.e. plate-interface, of the two converging plates. We hope that this new finding will promote the mapping and discovery of such faults along active subduction margins and will also help explain the variability in the recurrence of great-earthquakes encountered on many subductions globally.”
Reference:
Vasiliki Mouslopoulou, Onno Oncken, Sebastian Hainzl, Andrew Nicol. Uplift rate transients at subduction margins due to earthquake clustering. Tectonics, 2016; DOI: 10.1002/2016TC004248
In a paper published in Nature, a team of researchers from Uppsala University and the ESRF in France apply synchrotron x-ray tomography to a tiny jawbone of a 424 million year old fossil fish in order to illuminate the origin of this strange system of tooth replacement. Credit: Henning Blom
Remember dropping your milk teeth? After a lot of wiggling the tooth finally dropped out. But in your hand was only the enamel-covered crown: the entire root of the tooth had somehow disappeared. In a paper published in Nature, a team of researchers from Uppsala University and the ESRF in France apply synchrotron x-ray tomography to a tiny jawbone of a 424 million year old fossil fish in order to illuminate the origin of this strange system of tooth replacement.
Teeth are subject to a lot of wear and tear, so it makes sense to be able to replace them during the lifetime of the animal. Surprisingly, however, the teeth of the earliest jawed vertebrates were fixed to the jaw bones and could not be shed. Tooth shedding eventually evolved independently on two occasions, using two quite different processes. In sharks and rays, the fibres that anchor the tooth to the skin of the jaw dissolve and the whole tooth simply falls out. In bony fish and land vertebrates, the developing tooth becomes attached directly to the jaw bone by a special tissue known as “bone of attachment”, and when it is time for the tooth to be shed this attachment must be severed; specialized cells come in and resorb the dentine and bone of attachment until the tooth comes loose. That’s why our milk teeth loose their roots before they are shed. But when did this process evolve?
The authors of the new study decided to investigate a jaw bone of the 424 million year old fossil fish Andreolepis from Gotland in Sweden, close to the common ancestor of all living bony fish and land vertebrates. The jaw is a tiny thing, less than a centimetre in length, but it hides a wonderful secret: the internal microstructure of the bone is perfectly preserved and contains a record of its growth history. Until recently it has only been possible to see internal structures by physically cutting thin sections from the fossil and viewing them under the microscope, but this destroys the specimen and provides only a two-dimensional image that is hard to interpret.
However, at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, it is now possible to make tomographic scans that capture the same level of microscopic detail, in three dimensions, without damaging the specimen. Donglei Chen, first author of the study, has spent several years painstakingly ‘dissecting’ the scan data on the computer screen, building up a three-dimensional map of the entire sequence of tooth addition and loss – the first time an early fossil dentition has been analyzed in such detail.
“Every time a tooth was shed, the resorption process created a hollow where it had been attached. When the succeeding replacement tooth was cemented in place by bone of attachment, the old resorption surface remained as a faint buried scar within the bone tissue. I found up to four of these buried resorption surfaces under each tooth, stacked on top of each other like plates in a cupboard. This shows that the teeth were replaced again and again during the life of the fish,” explains Donglei Chen.
This is the earliest known example of tooth shedding by basal resorption, and it seems to be most similar to the process of tooth replacement seen today in primitive bony fish such as gar (Lepisosteus) and bichir (Polypterus). Like in these fish, new replacement teeth developed alongside the old ones, rather than underneath them like in us.
“The amount of biological information we get from the scans is simply astonishing. We can follow the process of growth and resorption right down to cellular level, almost like in a living animal. As we apply this technique to more early vertebrates, we will come to understand their life processes much better – and no doubt we will be in for some major surprises,” says Per Ahlberg, one of the leaders of the project.
Reference:
Donglei Chen, Henning Blom, Sophie Sanchez, Paul Tafforeau & Per E. Ahlberg (2016) The stem osteichthyan Andreolepis and the origin of tooth replacement, Nature, DOI: 10.1038/nature19812
A volcano in southwestern Japan erupted early on Saturday, spewing a plume of ash 6.8 miles into the sky, according to the Japanese Meteorological Agency. Japanese broadcaster NHK captured the moment on video when Mount Aso erupted. (Oct. 8, 2016)
Many thousands of years ago, as the world slowly began to thaw at the end of the last ice age, the landscapes of southern Peru were quite different than the ones University of Maine’s Gordon Bromley finds himself wandering about these days.
Large domes of ice, blanketing the high and jagged peaks of ancient cordilleras, spilled down through steep Andean valleys like giant rivers of ice and carved across the high-altitude plateaus.
Today, these once grand ice formations are all but gone, yet the geological echoes of the last great global glaciation still remain.
When Bromley, a research assistant professor in the School of Earth and Climate Sciences and Climate Change Institute, looks out over the wide and barren vistas of the Peruvian altiplano, he reads the landscape like a long-lost tome recording the story of our planet’s ice-age past.
Bromley is a glacial geologist working to understand the chronology of late-Quaternary glacial events in the remote Andes of southern Peru.
In a new paper published in the journal Quaternary Science Reviews, Bromley and a research team present a new glacial chronology from two ancient moraine systems in southern Peru.
The paper reports the results of a seven-year interdisciplinary project that included researchers from the University of Maine, Columbia University’s Lamont-Doherty Earth Observatory, Pacific Lutheran University and Dartmouth College.
The new chronologies suggests that the glaciers of the southern Peruvian Andes reached their maximum extent between 28,000 and 26,000 years ago—earlier than the last glacial maximum (LGM) is recognized in other parts of the globe—and about 19,000 years ago they began their final recession with a very brief period of advance 16,100 thousand years ago.
Tropical glaciers are particularly sensitive to changes in climate and, like many other glaciers around the world, have undergone series of major retreats and minor advances since the LGM. However, the role the ocean and atmosphere play in this ebb and flow are far less understood. This is the overarching question Bromley and his team hope to address.
While few equate glaciers with the tropics, Bromley is particularly interested in what the glaciers of these areas and the landforms they’ve left behind can tell us about the dynamics of the global climate system as the world began to warm after its near 100,000-year-long hibernation during the last ice age.
Glacial geologists, like Bromley, use moraines to study long-vanished glaciers. Moraines are relics of the ice’s movement and spatial extent. Just as bulldozers push material forward and aside as they move through construction debris, advancing glaciers transport soil and rocks as they slowly scrape across the landscape. When they recede, this material is left behind in distinctive patterns and piles called moraines.
Bromley and the researchers use a geochemical technique called cosmogenic surface-exposure dating to ascertain exactly when each moraine was formed. As glaciers retreat, the surfaces of rocks, which had been frozen in ice for millennia, are uncovered and newly exposed to the sky and the flux of cosmic radiation.
Born from distant supernova, cosmic rays hurtle through space at near the speed of light until they enter Earth’s atmosphere and collide with the freshly exposed boulders. And while these particles glide through our bodies on a near constant basis, they interact with the quartz inside the rocks, blasting apart oxygen and silicon atoms, creating the rare isotope beryllium-10. Over time the amount of the isotope builds up inside the rock which compose each moraine.
By measuring the amount of beryllium-10 in a sample of the exposed moraine boulder, geoscientists like Bromley can determine precisely when it was abandoned on the landscape by a receding glacier.
In the Cordillera Carabaya, a subrange of the East Andes in far southern Peru, approximately 75 miles from the Bolivian border and at an altitude straddling 15,000 feet, Bromley and his team surveyed and sampled the complex moraine systems from two remote valley systems.
Surface exposure data garnered from the moraines in this region provided great insight into the glacial dynamics of the southern Peruvian Andes.
The results suggest that the atmosphere in the tropics warmed quickly at the end of the last ice age and that this warming appears to be in step with changes in the tropical Pacific Ocean.
“I think we have an impression now that the tropical climate is extremely sensitive, it dominates global climate and its extremely dynamic,” says Bromley.
Bromley and the research team suggest that a warm sea surface temperature (SST) anomaly the Equatorial Pacific, which persisted for nearly 3,000 years, as well as a southward displacement of the Inter Tropical Convergence Zone potentially played a key role in this reversal.
Similar to a modern El Nino event, changes in ocean and atmospheric circulation in the tropical Pacific may have allowed for the extended expansion of the Pacific Warm Pool.
The warm pool is an area of particularly warm ocean generally confined to the waters surrounding Indonesia. However with the breakdown of the influx of cooler waters into the eastern Pacific and a weakening of the offshore winds of South America, the warm pool is allowed to reach its full potential and expands to the length of the equatorial Pacific.
“As the energetic powerhouse of the globe, the tropics are the principal source of heat energy and water vapor for the climate system and thus represent a fundamental and dynamic component of global climate,” says Bromley.
When the Pacific warm pool expands, it drastically increases convection and brings large amounts of warm moist air high into the troposphere where it affects these high altitude tropical glaciers.
“The tropical atmosphere seems to be set by the Pacific Ocean as a whole,” says Bromley. “And the warming of the tropical Pacific has a rapid and global effect throughout the atmosphere.”
Like a global thermostat the tropical atmosphere sets the tone for the general temperature throughout the globe. As the tropics warm as a result of the growth of warm SST anomalies in the Pacific, so do global temperatures.
This type of atmospheric heating on a smaller scale was seen during the last and particularly strong El Nino event and contributed to the record-setting average global temperatures of 2015 and 2016.
The rapid decline of glaciers throughout the tropics may herald the very beginnings of the atmospheric change that drove global deglaciation at the end of the last ice age.
In addition to SST anomalies in the Pacific Ocean, the team is also investigating how the tropical temperature record aligns with atmospheric carbon dioxide concentrations to determine the greenhouse gas’s role in the termination of these tropical glaciers.
The team suggests that other high resolution moraine records like the one presented in this study are needed to further understand the variability of the tropical atmosphere and its implication on both past, and present, global climates.
Miners in Burma have unearthed one of the world’s most valuable pieces of jade -it worth £140million.
It was found in a mine in the jade-producing Kachin state, in the north of the country.
Workers were excavating rare gems at a remote mine when they stumbled across the gem stone.
The rock, weighing 175 tonnes and measuring 9ft high and 18ft long, is second only in size to the carved statue at the Jade Buddha Palace in China which weighs 260 tonnes.
Burma – or Myanmar – is the world’s largest producer of jadeite – and the 50 billion dollar a year industry represents half of the country’s GDP , where it is known as the “stone of heaven”.
SUE the Dinosaur’s forearm came to the Advanced Photon Source for its most detailed scan ever, which could shed light on why the large dinosaur had such small arms. Credit: Field Museum of Natural History
The tiny arms on the otherwise mighty Tyrannosaurus rex are one of the biggest and most enduring mysteries in paleontology.
But researchers will soon get more insight as an arm bone from the most famous T. rex in history — the Field Museum’s SUE — was studied at the Advanced Photon Source at the U.S. Department of Energy’s Argonne National Laboratory, where the most detailed scan ever taken of that skeleton occurred earlier this month.
The extremely bright X-rays from the Advanced Photon Source, a giant synchrotron light source nearly a mile around, will give scientists an unprecedented look inside the arm bones of SUE, which is the largest and best-preserved T. rex skeleton ever found.
“These X-rays will give us a map of the blood vessels and muscle attachments in the bone, which have never been seen before,” said Carmen Soriano, a paleontologist and beamline scientist with the Advanced Photon Source. “This data could provide new insight into dinosaur biology, as well as clues to how SUE lived her life.”
Peter Makovicky, the Field Museum’s Curator of Dinosaurs, added, “It’s wonderful to have access to this tool that allows us to examine the structure of the bones in unprecedented detail without harming them fossil — and it’s just down the road.”
During the recent experiments, researchers directed intense X-rays — about a million times more powerful than an X-ray at a doctor’s office — at the fossil.
They scanned an area about three inches square and one to two inches deep on both bones of SUE’s forelimb, which is about the same length as a human arm, but much more robust.
Based on the ways the beams scatter from the rock, researchers can reconstruct the locations of different anatomical elements in the bones and the tiny holes deep inside that were once blood vessels and cells.
“Understanding the fine internal morphology of the skeleton will give us clues about how the arm could move and what it was used for,” Soriano said.
Even bare bones contain hints at what they were used for in life. For example, the bones of birds are hollow and less calcified for flying, while heavier, denser bones might indicate bones were used for tasks of strength. Patterns revealed by these intense scans will give scientists more information to decode what SUE might have used her arms for.
The study was performed in collaboration with Paul Tafforeau of the European Synchrotron Radiation Facility in France. The collaboration began when he and Soriano met at a conference in Chicago as the only paleontologists-in-residence at X-ray light sources in the world.
“Paleontologists really love any high tech we can use,” Soriano said, “since it’s the closest we can get to time travel.”
The experiments took place at the X-ray Science Division’s beamline 2-BM. The arm was returned to display at the Field October 11 while the data is analyzed.
Assistant Professor Mainak Mookherjee found that the mineral feldspar became softer under extreme pressure. Credit: Mainak Mookherjee
A Florida State University geology researcher is going deep below the Earth’s surface to understand how some of the most abundant minerals that comprise the Earth’s crust change under pressure.
In a paper published today in Scientific Reports, Assistant Professor of Geology Mainak Mookherjee explores how feldspar, one of the most important minerals in the Earth’s crust, changes under pressure. Typically, materials become stiffer when pressure is applied, but Mookherjee found that these pale-colored crystals actually become softer under extreme pressures.
“I am interested in exploring these materials at extreme conditions,” Mookherjee said. “Feldspar is very abundant in the earth’s crust so we need to understand its elastic property.”
Mookherjee’s work shows that at a depth of about 30 kilometers from the Earth’s surface, feldspar decomposes to denser mineral phases such as pyroxene and quartz. The densification of feldspar could partially explain a scientific observation called seismic discontinuity across the Earth’s crust and mantle.
This seismic discontinuity, also called Mohorovicic discontinuity, is the boundary between the Earth’s crust and mantle. It was first observed in 1909 by a Croatian scientist Andrija Mohorovicic who realized that seismograms from shallow-focus earthquakes had two sets of waves—one that followed a direct path near the Earth’s surface, i.e., crust, and the other arriving faster and probably refracted from the underlying higher-velocity medium mantle.
“This is the first study of the elastic properties of feldspar at high pressure,” Mookherjee said. “And it provides very new insight and a novel way of accounting for the sharp Mohorovicic discontinuity.”
Scientists have been working since the late 1950s to understand the Mohorovicic discontinuity that separates the Earth’s outermost layer—oceanic and continental crust—with the underlying mantle. Last year, researchers from the drill ship JOIDES Resolution made attempts to drill a bore hole across the discontinuity, but fell short. Further drilling attempts are planned for future.
“We care about the mineral structures in the deep Earth and how they transform to denser crystal structures within the Earth,” Mookherjee said. “Through a thorough understanding of the atomic scale structures at extreme conditions and how they influence the properties of the Earth materials, it is possible to gain valuable insight into deep Earth dynamics.”
Dinosaur skin impression on rock. Credit: Víctor Fondevilla/UAB
Researchers from the Universitat Autònoma de Barcelona (UAB) in collaboration with the Institut Català de Paleontologia Miquel Crusafont (ICP), have discovered in Vallcebre (Barcelona) an impression fossil with the surface of the skin of a dinosaur from the Late Cretaceous, a period right before their extinction. Its characteristics make it a unique discovery in Europe.
A geological research conducted in the village of Vallcebre, near Barcelona, to study the origins of rock sediments from the Late Cretaceous period (approx. 66 million years ago) has revealed an extraordinary artefact. Researchers discovered the impression of skin scales left by a dinosaur which had lain down in the mud. During that period, the area was a muddy region corresponding to the banks of a river. As chance had it, that muddy region where the animal’s scales had left their mark was later covered with sand which, in the course of thousands of years, finally petrified to form sandstone and thus become the sedimentary rock which preserves the impression recently discovered by the researchers. The sand acted as a mould and therefore, what actually can be seen on the rock is not really the impression, but the relief of the animal’s original skin.
The characteristics of the discovery are unique, given that the Late Cretaceous period corresponds to the moment short before dinosaurs became extinct, there are few places on Earth containing sandstone from this period, and characterising these dinosaurs is very important in order to understand how and why they disappeared. “This is the only registry of dinosaur skin from this period in all of Europe, and it corresponds to one of the most recent specimens, closer to the extinction event, in all of the world,” highlights UAB researcher Victor Fondevilla, main author of the research. “There are very few samples of fossilised skin registered, and the only sites with similar characteristics can be found in United States and Asia,” Fondevilla states. He goes on to say: “Other dinosaur skin fossils have been found in the Iberian Peninsula, in Portugal and Asturias, but they correspond to other more distant periods.”
The shape of the scales observed on the rock show a pattern characteristic of the skin of some dinosaurs: in a form of a rose with a central bump in the shape of a polygon, surrounded by five or six more bumps. However, the scales are large, too large for the typical size of carnivorous dinosaurs and hadrosaurs roaming this area 66 million years ago. “The fossil probably belongs to a large herbivore sauropod, maybe a titanosaurus, since we discovered footprints from the same species very close to the rock with the skin fossil” Fondevilla says.
In fact, two skin impressions were found, one measuring approximately 20 centimetres wide, and the other slightly smaller, measuring only 5 centimetres wide, separated by a 1.5 metre distance and probably made by the same animal. “The fact that they are impression fossils is evidence that the animal is from the sedimentary rock period, one of the last dinosaurs to live on the planet. When bones are discovered, dating is more complicated because they could have moved from the original sediment during all these millions of years,” Fondevilla states.
The finding verifies the excellent fossil registry of the Pyrenees in terms of dinosaurs living in Europe little before they became extinct throughout the planet. “The sites in Berguedà, Pallars Jussà, Alt Urgell and La Noguera, in Catalonia, have provided proof of five different groups of dinosaurs: titanosaurs, ankylosaurids, theropods, hadrosaurs and rhabdodontids,” explains Àngel Galobart, head of the Mesozoic research group at the ICP and director of the Museum of Conca Dellà in Isona. “The sites in the Pyrenees are very relevant from a scientific point of view, since they allow us to study the cause of their extinction in a geographic point far away from the impact of the meteorite,” Galobart explains.
The research, published in Geological Magazine, was led by Víctor Fondevilla and Oriol Oms from the UAB Department of Geology, in collaboration with Bernat Vila and Àngel Galobart, both from the Institut Català de Paleontologia Miquel Crusafont (ICP) and the Museum of Conca Dellà.
Reference:
VÍCTOR FONDEVILLA, BERNAT VILA, ORIOL OMS, ÀNGEL GALOBART. Skin impressions of the last European dinosaurs. Geological Magazine, 2016; 1 DOI: 10.1017/S0016756816000868
Study of the first fossil vocal organ from the Mesozoic provides insight into the evolution of bird calls and song. The fossil syrinx is from the late Cretaceous of Antarctica. Within dinosaurs there was a transition from a vocal organ present in the larynx (present in crocodiles) to one uniquely developed deep in the chest in birds. Credit: Nicole Fuller/Sayo Art for UT Austin.
The oldest known vocal organ of a bird has been found in an Antarctic fossil of a relative of ducks and geese that lived more than 66 million years ago during the age of dinosaurs.
The discovery of the Mesazoic-era vocal organ — called a syrinx — and its apparent absence in nonavian dinosaur fossils of the same age indicate that the organ may be have originated late in the evolution of birds and that other dinosaurs may not have been able to make noises similar to the bird calls we hear today, according to findings published in Nature on Oct 12. Birds are direct descendants of dinosaurs and are considered living dinosaurs by scientists.
“This finding helps explain why no such organ has been preserved in a nonbird dinosaur or crocodile relative,” said Julia Clarke, a paleontologist at The University of Texas at Austin Jackson School of Geosciences who discovered the fossil syrinx and led the analysis. “This is another important step to figuring out what dinosaurs sounded like as well as giving us insight into the evolution of birds.”
The syrinx is made of stiff, cartilage rings that support soft tissues that vibrate to produce the complex songs and calls of modern birds. Cartilage does not fossilize as well as hard tissues such as bone. But the high mineral content in the syrinx’s rings sometimes allows for fossilization. All other known examples of fossilized syrinxes occur in birds that lived well after nonavian dinosaurs went extinct.
The syrinx was found in a fossil of Vegavis iaai, a bird that lived during the Cretaceous. Clarke described the species in 2005. It was discovered on Antarctica’s Vega Island in 1992 by a team from the Argentine Antarctic Institute. However, it wasn’t until 2013 that Clarke noticed that the Vegavis fossil included a syrinx. During the past two years, the team searched the dinosaur fossil record for other examples of a syrinx, but so far has found none.
The asymmetrical shape of the syrinx indicates that the extinct species could have made honking noises via two sound sources in the right and left parts of the organ. The researchers also scanned syrinxes of other birds to compare with the Vegavis syrinx. This included 12 syrinxes from living birds and the next oldest fossilized syrinx, which had not yet been studied.
Franz Goller, a co-author and physiologist at the University of Utah, said the study is the beginning of the work to determine what the fossilized organ can tell us about the sounds of early birds.
“Here, we begin to outline how fossilizable characteristics of the syrinx may inform us about sound features, but we need a lot more data on living birds,” Goller said. “Remarkably, prior to this work, there is almost no discussion of these important questions.”
This study follows research that Clarke and other collaborators published in July 2016 that found some dinosaurs would likely have made closed-mouth vocalizations akin to ostrich booms that don’t require a syrinx. Together, the two studies have major implications for dinosaur sound-making throughout time, Clarke said.
In addition, the evolution of vocal behavior can give insights into other anatomical features, Clarke said, such as the appearance of bigger brains.
“The origin of birds is about so much more than the evolution of flight and feathers,” Clarke said.
To study sound production in more detail, part of the team is working with engineers to model sound-producing organs, a project funded by the Gordon and Betty Moore Foundation.
Reference:
Julia A. Clarke, Sankar Chatterjee, Zhiheng Li, Tobias Riede, Federico Agnolin, Franz Goller, Marcelo P. Isasi, Daniel R. Martinioni, Francisco J. Mussel and Fernando E. Novas. Fossil evidence of the avian vocal organ from the Mesozoic. Nature, 2016 DOI: 10.1038/nature19852
Microtektites as first seen in a sediment sample from the onset of the Paeocene-Eocene Thermal Maximum. Credit: Rensselaer Polytechnic Institute
A comet strike may have triggered the Paleocene-Eocene Thermal Maximum (PETM), a rapid warming of Earth caused by an accumulation of atmospheric carbon dioxide 56 million years ago, which offers analogs to global warming today. Sorting through samples of sediment from the time period, researchers at Rensselaer Polytechnic Institute discovered evidence of the strike in the form of microtektites — tiny dark glassy spheres typically formed by extraterrestrial impacts. The research will be published in the journal Science.
“This tells us that there was an extraterrestrial impact at the time this sediment was deposited — a space rock hit the planet,” said Morgan Schaller, an assistant professor of earth and environmental sciences at Rensselaer, and corresponding author of the paper. “The coincidence of an impact with a major climate change is nothing short of remarkable.” Schaller is joined in the research by Rensselaer professor Miriam Katz and graduate student Megan Fung, James Wright of Rutgers University, and Dennis Kent of Columbia University.
Schaller was searching for fossilized remains of Foraminifera, a tiny organism that produces a shell, when he first noticed a microtektite in the sediment he was examining. Although it is common for researchers to search for fossilized remains in PETM sediments, microtektites have not been previously detected. Schaller and his team theorize this is because microtektites are typically dark in color, and do not stand out on the black sorting tray researchers use to search for light-colored fossilized remains. Once Schaller noticed the first microtektite, the researchers switched to a white sorting tray, and began to find more.
At peak abundance, the research team found as many as three microtektites per gram of sediment examined. Microtektites are typically spherical, or tear-drop shaped, and are formed by an impact powerful enough to melt and vaporize the target area, casting molten ejecta into the atmosphere. Some microtektites from the samples contained “shocked quartz,” definitive evidence of their impact origin, and exhibited microcraters or were sintered together, evidence of the speed at which they were traveling as they solidified and hit the ground.
Atmospheric carbon dioxide increased rapidly during the PETM, and an accompanying spike in global temperatures of about 5 to 8 degrees Celsius lasted for about 150,000 years. Although this much is known, the source of the carbon dioxide had not been determined, and little is known about the exact sequence of events — such as how rapidly carbon dioxide entered the atmosphere, how quickly and at what rate temperatures began to rise, and how long it took to reach a global high temperature.
One clue can be found in a sudden shift in the ratio of carbon isotopes (atoms containing a number of neutrons unequal to the protons in their nucleus) in certain fossils from the time period. In particular, Foraminifera, or “forams,” produce a shell whose chemistry is representative of atmospheric and ocean carbon isotopes. The research team initially set out to examine the ratio of carbon isotopes in Foraminifera fossils over time, to more closely pinpoint events during the PETM.
“In sediment records, when you look at the ratio of carbon-12 to carbon-13 in a particular species, you see that it’s stable and then it abruptly shifts, wiggles back and forth and slowly returns to pre-event values over hundreds of thousands of years,” Schaller said. “This evidence defines the event, and tells us that the atmosphere changed, in particular adding carbon from a source depleted in carbon-13. A comet impact on its own may have contributed carbon to the atmosphere, but is too small to explain the whole event and more likely acts as a trigger for additional carbon releases from other sources.” As a source of fossils, the team used sediment cores — cylinders of sediment extracted vertically from sediment deposits with a hollow bit — known to correspond to the time period of the PETM. Sediments near the top are more recent, those further down are older, and signature layers indicating known events are used to calibrate the timescale represented in the sample. The team chose cores from three sites — Wilson Lake and Millville in New Jersey, and Blake Nose, an underwater site east of Florida — known for a rich sedimentary record of the time period.
As Schaller tells it, the discovery of microtektites was “completely by accident.” Ordinarily, the team passes samples through sieves of various sizes, to isolate samples most likely to contain forams. The tektites, which are smaller than most forams, would have been largely removed in this process.
“We were having lousy luck looking for forams, and I was frustrated. I went to the lab and dumped a sample on the sorting tray without sieving it, and there it was,” Schaller said. “It was a stunning moment. I knew what I was looking at was not normal.”
Once the team made the discovery, they obtained a sample from a fourth site — Medford — where the unit is naturally exposed at the surface, to rule out the possibility that the samples had been contaminated by the drilling process. The Medford samples also contained microtektites.
Reference:
Dennis V. Kent et al. Impact ejecta at the Paleocene-Eocene boundary. Science, October 2016 DOI: 10.1126/science.aaf5466
A new model of canyon-forming floods from UMass Amherst and CalTech researchers suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. Credit: UMass Amherst/Isaac Larsen
Geomorphologists who study Earth’s surface features and the processes that formed them have long been interested in how floods, in particular catastrophic outbursts that occur when a glacial lake ice dam bursts, for example, can change a planet’s surface, not only on Earth but on Mars.
Now geoscience researchers Isaac Larsen at the University of Massachusetts Amherst and Michael Lamb at the California Institute of Technology have proposed and tested a new model of canyon-forming floods which suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. They point out that “reconstructing the magnitude of the canyon-forming floods is essential for understanding how floods modify planetary surfaces, the hydrology of early Mars, and abrupt climate change.”
Larsen and Lamb apply their new model to the “channeled scablands” in eastern Washington State, an area that, like some on Mars, has very deep canyons cut into fractured basalt bedrock. The researchers say their results suggest “there may be a rich imprint of both the history and discharge of flooding in the morphology of canyons” such as terraces, valley shapes and slope profiles on Earth and on Mars “that warrant further investigation.” Details appear in the current issue of Nature.
The researchers say channels in the scablands today, which are up to 650 feet (200 meters) deep and 3 miles (5 km) wide, were likely formed by flood discharges five- to tenfold smaller than brimful estimates, that is by “significantly lower megaflood discharges than previously thought. The channeled scablands are a classic landscape in the history of geomorphology and we’re bringing new views of how it was formed.”
Until the 1920s, scientists did not understand what could have formed the tortured landscape of eastern Washington studied for decades by J Harlen Bretz, a giant figure in geosciences, Larsen recalls. Bretz was the first to suggest that they were formed by catastrophic flooding of unknown origin. His views were dismissed for years, but Bretz was later vindicated when glacial Lake Missoula was identified as the floodwater source.
As most scientists came to accept the catastrophic flood explanation for the canyons and then tried to estimate floodwater discharges, they assumed that floods filled canyons to the brim, a huge amount of water. But an alternate hypothesis proposed and now tested by Lamb and and Larsen posits that as floodwater cuts into bedrock, the canyon deepens, meaning less water is required to shape it.
In areas underlain by fractured bedrock, Larsen says, “our general concept is that the channel floor was being cut and lowered as the floods were happening, and you need to account for that when reconstructing the scenario of flood magnitude. This applies to the scablands, to Mars and other areas where there have been catastrophic outburst floods.”
He and Lamb combine numerical flood models with estimates of the force required to erode basalt bedrock to show that for Moses Coulee, a canyon carved by catastrophic Lake Missoula floods in eastern Washington when an ice dam repeatedly broke and reformed around 15,000 years ago, their “threshold shear stress model” explains the shape and depth of currently observed channels better than the brimful model.
“We numerically routed floods through the canyon in different states, from current configuration and at four different past scenarios,” Larsen notes. “We predicted the discharge from two models and tested which one is most reasonable, based on the depositional evidence from the current bars seen today in the canyons. The size of floods our model predicts from the basalt erosion better match locations of depositional flood bars in the canyon than the brimful model predicts.”
Larsen and Lamb’s new model also works better to explain observed canyon-cutting mechanics and outflow channels observed on Mars, they point out, “supporting the notion of a multi-flood or low-magnitude flood origin for the Mars outflow channels. ” Larsen adds, “There are very similar but larger canyons on the surface of Mars. These outflow channels are much bigger than the ones on Earth, but they look very similar and the assumption is they formed by similar processes. We know in most cases there were not canyons before these floods happened. They had to be carved, so the bottoms were getting lower and lower with each flood. We believe in the final phases of floods, they were not filled to the brim.”
Reference:
Progressive incision of the Channeled Scablands by outburst floods, Nature, DOI:10.1038/nature19817
