Fig 1. Chronology of the Zipingpu reservoir sediment core based on the correlation between reservoir water level and sedimentary MS. Credit: Jin Zhangdong, et al.
The roles of “climate change” versus “tectonics” that dominate erosion and sediment transport over geological time scales have long been a hot topic in Earth science. How to effectively separate their respective roles is a big challenge, like the famous “chicken or egg” question.
A new study led by Prof. Jin Zhangdong from the Institute of Earth Environment (IEE) of the Chinese Academy of Sciences provided a new insight on the interplay between climate and tectonics from a sediment record in the Zipingpu Reservoir around the 2008 Wenchuan earthquake. The findings were published in Science Advances on June 12.
Infrequent extreme events such as large earthquakes pose hazards and have lasting impacts on landscapes and biogeochemical cycles. Sediments provide valuable records of past events, but unambiguously identifying event deposits is challenging because of nonlinear sediment transport processes and poor age control.
The Zipingpu Reservoir, with annually resolved sediments, provides a unique opportunity to document the link between a large earthquake and its sedimentary signature, because it was completed in September 2004 and is located downstream of the area impacted by the 2008 Wenchuan earthquake.
In October 2016, a 10.89-m sediment core back to the river bed was recovered from the Zipingpu Reservoir. An age model for the core was developed based on the correlation between sedimentary magnetic susceptibility and reservoir water level. The boundary of the 2008 Wenchuan earthquake was then assigned to the core depth of 6.20 m (Fig. 1). This is the first time that a 10-year sediment core was dated to annual resolution.
Based on the precise annual chronology, the roles of a single large earthquake and climate on erosion and sediment transfer were evaluated along with sedimentary and hydrometeorological data. The records demonstrated that the grain size and Rb/Sr ratios of the sediments in the Zipingpu Reservoir responded immediately to the earthquake. However, the changes were muted until two years after the event.
The most obvious seismic signals occurred in 2010 when intense monsoonal runoff facilitated fast material export and drove accumulation of coarser grains and lower Rb/Sr sediments, which were then sustained for several years (Fig. 2).
The results indicated that, although the earthquake mobilized very large amounts of sediment by landsliding, hydrological forcing was necessary to transport this debris from hillslopes to downstream sediment stores, even in a location proximal to the mountain front.
The delayed response highlighted the role of intense monsoonal rainfall in propagating tectonic signals into sedimentary archives.
This study provides direct evidence that can inform the interpretation of paleorecords and help to illuminate the ways in which sedimentary archives reflect the complex interaction of tectonics and climate in controlling sediment transfer in tectonically active mountain ranges.
Reference:
Fei Zhang et al, Monsoonal control on a delayed response of sedimentation to the 2008 Wenchuan earthquake, Science Advances (2019). DOI: 10.1126/sciadv.aav7110
Oarfish specimen, Natural History Museum of San Diego. | Patrick Emerson
The unusual appearance of deep-sea fish like the oarfish or slender ribbonfish in Japanese shallow waters does not mean that an earthquake is about to occur, according to a new statistical analysis.
The study published in the Bulletin of the Seismological Society of America contradicts long-held Japanese folklore that deep sea fish sightings are a sign of an imminent earthquake, say Yoshiaki Orihara of Tokai University in Japan and colleagues.
When the researchers examined the relationship between deep-sea fish appearances and earthquakes in Japan, however, they found only one event that could have been plausibly correlated, out of 336 fish sightings and 221 earthquakes.
“As a result, one can hardly confirm the association between the two phenomena,” the authors write in the BSSA paper.
The study included data from November 1928 to March 2011, looking at records of deep-sea fish appearances 10 and 30 days ahead of earthquakes that occurred 50 and 100 kilometers away from the fish sighting.
They confined their search to earthquakes of magnitude 6.0 or larger, since these are the earthquakes that have been linked to “precursor phenomena like unusual animal behavior in previous reports,” said Orihara.
There were no recorded deep-sea fish appearances before an earthquake of magnitude 7.0, and no earthquakes with a magnitude greater than 6.0 occurred within 10 days of a deep-sea fish appearance.
Orihara became interested in the deep-sea fish stories after the 2011 magnitude 9.0 Tohoku earthquake in Japan. If the stories were true, he said, deep-sea fish appearances could be used in disaster mitigation efforts.
“From this motivation, we started compiling the event catalog for statistical study,” said Orihara. “There were some previous papers to survey deep-sea fish appearances. However, their reports were insufficient for a statistical study. To collect a lot of events, we focused on local newspapers that have often reported the events.”
The researchers scoured a digitized database of newspaper articles to find mentions of the unusual appearance of deep-sea fish that folklore says will appear before an earthquake, including oarfish, several kinds of ribbonfish, dealfish and the unicorn crestfish.
Orihara said that he and his colleagues expect that their results “will have an influence on people who believe the folklore,” and they hope that their findings will be shared throughout Japan.
Reference:
Yoshiaki Orihara et al, Is Japanese Folklore Concerning Deep‐Sea Fish Appearance a Real Precursor of Earthquakes?, Bulletin of the Seismological Society of America (2019). DOI: 10.1785/0120190014
Research from the Wits School of Geoscience shows how platinum deposits form in the Bushveld Complex of South Africa.
Most of the world’s economically viable platinum deposits occur as “reefs” in layered intrusions—thin layers of silicate rocks that contain sulphides enriched in platinum group elements which are so vital for the sustainable development of modern human society.
There are two competing ideas of how platinum deposits formed: the first involves gravity-induced settling of crystals on the chamber floor, while the second idea implies that the crystals grow in situ, directly on the floor of the magmatic chamber.
Through examining the Merensky Reef of the Bushveld Complex in South Africa, which hosts the lion’s share of the world’s platinum and other noble metals, Dr. Sofya Chistyakova from the School of Geosciences of the University of the Witwatersrand and her collaborators have established that the crystals grow in situ, with its high platinum status being attained while all its minerals were crystallizing along the cooling margins of the magma chamber. Their research was published in a paper in Scientific Reports.
One of the remarkable features of the Bushveld Complex is that at the time when the Merensky Reef was forming, some portions of its chamber floor were highly irregular due to circular depressions (potholes). Such potholes with the Merensky Reef are best exposed in underground exposures of platinum mines.
“Our key discovery is that the entire Merensky Reef package in these potholes may develop as a ‘rind’ covering all the chamber floor depressions and culminations, even where these are vertical or overhanging” says Chistyakova.
This finding points to no possibility for the Merensky Reef to be formed by crystal settling on the chamber floor because sinking crystals cannot penetrate the solid rocks that form the pothole’s overhangs. This strongly supports the concept that the silicate minerals and sulphides of platinum deposits grow directly at the floor of magmatic chambers.
“This is the most fundamental conclusion of our work and it can probably be applied to platinum deposits in other layered intrusions as well as potentially extended to other types of magmatic deposits, for example, chromite and Fe-Ti-V magnetite ores in mafic-ultramafic complexes” says Chistyakova.
Reference:
Sofya Chistyakova et al. Merensky-type platinum deposits and a reappraisal of magma chamber paradigms, Scientific Reports (2019). DOI: 10.1038/s41598-019-45288-8
The outer layer of modern Earth is a collection of interlocking rigid plates, as seen in this illustration. These plates grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes. But new research suggests that plate tectonics did not begin until much later in Earth’s history. Credit: USGS
The quest to discover what drove one of the most important evolutionary events in the history of life on Earth has taken a new, fascinating twist.
A team of scientists have given a fresh insight into what may have driven the “Cambrian Explosion” — a period of rapid expansion of different forms of animal life that occurred over 500 million years ago.
While a number of theories have been put forward to explain this landmark period, the most credible is that it was fuelled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.
The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics.
During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism — chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.
This, the team calculated, led to an increase in atmospheric CO2 and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.
The study was led by Josh Williams, who began the research as an MSc student at the University of Exeter and is now studying for a PhD at the University of Edinburgh.
During his MSc project he used a sophisticated biogeochemical model to make the first quantification of changes in atmospheric oxygen levels just prior to this explosion of life.
Co-author and project supervisor Professor Tim Lenton, from the University of Exeter’s Global Systems Institute said: “One of the great dilemmas originally recognised by Darwin is why complex life, in the form of fossil animals, appeared so abruptly in what is now known as the Cambrian explosion.
“Many studies have suggested this was linked to a rise in oxygen levels — but without a clear cause for such a rise, or any attempt to quantify it.”
Not only did the model predict a marked rise in oxygen levels due to changes in plate tectonic activity, but that rise in oxygen — to about a quarter of the level in today’s atmosphere — crossed the critical levels estimated to be needed by the animals seen in the Cambrian explosion.
Williams added: “What is particularly compelling about this research is that not only does the model predict a rise in oxygen to levels estimated to be necessary to support the large, mobile, predatory animal life of the Cambrian, but the model predictions also show strong agreement with existing geochemical evidence.”
“It is remarkable to think that our oldest animal ancestors — and therefore all of us — may owe our existence, in part, to an unusual episode of plate tectonics over half a billion years ago” said Professor Lenton.
Reference:
Joshua J. Williams, Benjamin J. W. Mills, Timothy M. Lenton. A tectonically driven Ediacaran oxygenation event. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-10286-x
The fossilized remains of Dickinsonia found at the Nilpena Heritage site in Australia. Credit: Scott Evans / UCR
New UC Riverside-led research settles a longstanding debate about whether the most ancient animal communities were deliberately mobile. It turns out they were, because they were hungry.
“This is the first time in the fossil record we see an animal moving to get food,” said study lead Scott Evans, a UCR paleontology doctoral candidate.
Evans’ team demonstrated that the 550-million-year-old ocean-dwelling creatures moved on their own rather than being pushed around by waves or weather. The research answers questions about when, why and how animals first developed mobility.
The team searched for evidence of movement in more than 1,300 fossils of Dickinsonia, dinner-plate-shaped creatures up to a meter long that lived and fed on a layer of ocean slime.
Details of the team’s analysis were published this month in the journal Geobiology. It found that Dickinsonia move like worms, constricting and relaxing their muscles to go after their next meal of microorganisms.
Dickinsonia were first discovered in the 1940s and since then, scientists have debated whether the fossils showed evidence of self-directed movement. To test this, it was crucial that Evans be able to analyze how multiple creatures living in the same area behaved relative to one another.
Evans and study co-author Mary Droser, a UCR professor of paleontology, reasoned that if Dickinsonia were riding waves or caught in storms, then all the individuals in the same area would have been moved in the same direction. However, that isn’t what the evidence shows.
“Multiple fossils within the same community showed random movement not at all consistent with water currents,” Evans said.
Critically, Evans was able to use fossil communities in the Australian outback unearthed by Droser and paper co-author James Gehling of the South Australian Museum. The duo systematically excavated large bed surfaces containing as many as 200 Dickinsonia fossils, allowing Evans to test whether the groups of the animals moved in the same or different directions, Evans said.
The team also analyzed the directions traveled by individual Dickinsonia.
“Something being transported by current should flip over or be somewhat aimless,” Evans said. “These movement patterns clearly show directionality based on the animals’ biology, and that they preferred to move forward.”
Future studies at UCR will try to determine what Dickinsonia bodies were made of. “The tissues of the animals are not preserved, so it’s not possible to directly analyze their body composition,” he said. “But we will look at other clues they left behind.”
Understanding Dickinsonia’s capabilities offers insight not only into the evolution of animal life on Earth, but also about the Earth itself and possibly about life on other planets.
“If we want to search for complex life on other planets, we need to know how and why complex life evolved here,” Evans said. “Knowing the conditions that enabled large mobile organisms to move during the Ediacaran era, 550 million years ago, gives us a clue about the habitable zone elsewhere.”
That Dickinsonia could move helps confirm a large amount of oxygen was available in Earth’s oceans during that time period, since it would have been required to fuel their movement. In a related study, Evans explored a spike in ocean oxygen levels during the Ediacaran period. Later, when oxygen levels dropped, Evans said that Dickinsonia — and things like them — went extinct.
Reference:
Scott D. Evans, James G. Gehling, Mary L. Droser. Slime travelers: Early evidence of animal mobility and feeding in an organic mat world. Geobiology, 2019; DOI: 10.1111/gbi.12351
The team studied nearly 3000 fossils. Photo credit: Rowan Whittle
A new study shows how marine life around Antarctica returned after the extinction event that wiped out the dinosaurs.
A team led by British Antarctic Survey studied just under 3000 marine fossils collected from Antarctica to understand how life on the sea floor recovered after the Cretaceous-Paleogene (K-Pg) mass extinction 66 million years ago. They reveal it took one million years for the marine ecosystem to return to pre-extinction levels. The results are published today (19 June 2019) in the journal Palaeontology.
The K-Pg extinction wiped out around 60% of the marine species around Antarctica, and 75% of species around the world. Victims of the extinction included the dinosaurs and the ammonites. It was caused by the impact of a 10 km asteroid on the Yucatán Peninsula, Mexico, and occurred during a time period when the Earth was experiencing environmental instability from a major volcanic episode. Rapid climate change, global darkness, and the collapse of food chains affected life all over the globe.
The K-Pg extinction fundamentally changed the evolutionary history of life on Earth. Most groups of animals that dominate modern ecosystems today, such as mammals, can trace the roots of their current success back to the aftermath of this extinction event.
A team of scientists from British Antarctic Survey, the University of New Mexico and the Geological Survey of Denmark & Greenland show that in Antarctica, for over 320,000 years after the extinction, only burrowing clams and snails dominated the Antarctic sea floor environment. It then took up to one million years for the number of species to recover to pre-extinction levels.
Author Dr Rowan Whittle, a palaeontologist at British Antarctic Survey says:
“This study gives us further evidence of how rapid environmental change can affect the evolution of life. Our results show a clear link in the timing of animal recovery and the recovery of Earth systems.”
Author Dr James Witts, a palaeontologist at University of New Mexico says:
“Our discovery shows the effects of the K-Pg extinction were truly global, and that even Antarctic ecosystems, where animals were adapted to environmental changes at high latitudes like seasonal changes in light and food supply, were affected for hundreds of thousands of years after the extinction event.”
Reference:
Rowan J. Whittle, James D. Witts, Vanessa C. Bowman, J. Alistair Crame, Jane E. Francis, Jon Ineson. Nature and timing of biotic recovery in Antarctic benthic marine ecosystems following the Cretaceous-Palaeogene mass extinction. Palaeontology, 2019; DOI: 10.1111/pala.12434
Scientists believe they have discovered the site of the biggest meteorite impact ever to hit the British Isles.
Evidence for the ancient, 1.2 billion years old, meteorite strike, was first discovered in 2008 near Ullapool, NW Scotland by scientists from Oxford and Aberdeen Universities. The thickness and extent of the debris deposit they found suggested the impact crater — made by a meteorite estimated at 1km wide — was close to the coast, but its precise location remained a mystery.
In a paper published today in Journal of the Geological Society, a team led by Dr Ken Amor from the Department of Earth Sciences at Oxford University, show how they have identified the crater location 15-20km west of a remote part of the Scottish coastline. It is buried beneath both water and younger rocks in the Minch Basin.
Dr Ken Amor said: ‘The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery. It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.
‘The next step will be a detailed geophysical survey in our target area of the Minch Basin.’
Using a combination of field observations, the distribution of broken rock fragments known as basement clasts and the alignment of magnetic particles, the team was able to gauge the direction the meteorite material took at several locations, and plotted the likely source of the crater.
Dr Ken Amor said: ‘It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area.’
1.2 billion years ago most of life on Earth was still in the oceans and there were no plants on the land. At that time Scotland would have been quite close to the equator and in a semi-arid environment. The landscape would have looked a bit like Mars when it had water at the surface.
Earth and other planets may have suffered a higher rate of meteorite impacts in the distant past, as they collided with debris left over from the formation of the early solar system.
However, there is a possibility that a similar event will happen in the future given the number of asteroid and comet fragments floating around in the solar system. Much smaller impacts, where the meteorite is only a few meters across are thought to be relatively common perhaps occurring about once every 25 years on average.
It is thought that collisions with an object about 1 km (as in this instance) across occur between once every 100,000 years to once every one million years — but estimates vary.
One of the reasons for this is that our terrestrial record of large impacts is poorly known because craters are obliterated by erosion, burial and plate tectonics.
Reference:
Kenneth Amor, Stephen P. Hesselbo, Don Porcelli, Adam Price, Naomi Saunders, Martin Sykes, Jennifer Stevanović, Conal MacNiocaill. The Mesoproterozoic Stac Fada proximal ejecta blanket, NW Scotland: constraints on crater location from field observations, anisotropy of magnetic susceptibility, petrography and geochemistry. Journal of the Geological Society, 2019; jgs2018-093 DOI: 10.1144/jgs2018-093
Chemical analyses of meteorites allow for a better estimation of the chemical composition of the Earth and its potential building blocks. That is the result of a study conducted by a research team from the Institutes of Geology and Mineralogy at the Universities of Cologne and Bonn. The results have appeared in the current issue of Nature Geoscience.
The study focuses on the distribution and origin of so-called volatile elements such as zinc, lead and sulphur, which have low boiling temperatures in space. The newly determined distribution of these volatile elements in the Earth shows that some of these building blocks have a chemical composition similar to carbonaceous chondrites, an aqueous group of primitive meteorites. These meteorites come closest to the composition of the original solar nebula from which our solar system formed. Thus, the study also indirectly provides another valuable indication of the source of vital components such as water, carbon and nitrogen on Earth.
The chemical composition of the Earth is not easy to determine. Geological processes such as the formation of the metallic core and the outer crust led to a redistribution of the elements composing our planet. For example, elements attracted to iron have migrated into the Earth’s core, while elements attracted to silicate compose the rocks of the Earth’s mantle and crust. ‘Today, we only have access to samples from the silicate part of the Earth, which is why we can only estimate the chemical composition of the entire Earth through the additional analysis of primitive meteorites — the potential building blocks of the Earth,’ said Professor Carsten Münker from the University of Cologne. The recent publication makes an important contribution to understanding the chemical composition of the deeper layers of the Earth.
The research team focused on the distribution of volatile trace elements such as the rare metals indium, cadmium and tellurium. This is a particular challenge since a proportion of these metals was lost already at the beginning of the solar system due to their volatility. Today, they are extremely rare both in meteorites and in the Earth — less than one gram per ton of rock. ‘So far, we have always assumed that the distribution of these elements decreases linearly the more volatile they are,’ said the geochemist Dr Frank Wombacher, one of the initiators of the study.
By using high-precision methods, however, the scientists arrived at a surprising result. ‘While the frequencies initially decrease linearly, contrary to expectations the most volatile elements are all equally depleted,’ explains Ninja Braukmüller, a doctoral researcher who carried out the study in Cologne. Indium and zinc, the volatile elements attracted to silicate in the Earth’s mantle, also show this pattern. ‘This seems to be unique among the potential building blocks of the Earth,’ says Dr Claudia Funk, a co-author of the study. The results allow the scientists to conclude that the building blocks that have brought volatile elements to Earth are similar in their chemical composition to that of primitive carbonaceous chondrites.
Reference:
Ninja Braukmüller, Frank Wombacher, Claudia Funk, Carsten Münker. Earth’s volatile element depletion pattern inherited from a carbonaceous chondrite-like source. Nature Geoscience, 2019; DOI: 10.1038/S41561-019-0375-X
Superheated, iron-rich fluid gushes from a hydrothermal vent more than 2,500 meters deep in the Southern Ocean. The iron spewing from deep water vents like this one may fuel phytoplankton blooms on the surface. Photo credit: NERC/NSF Chesso Consortium
Researchers at Stanford University say they have found an aquatic highway that lets nutrients from Earth’s belly sweep up to surface waters off the coast of Antarctica and stimulate explosive growth of microscopic ocean algae.
Their study, published June 5 in the journal Nature Communications, suggests that hydrothermal vents — openings in the seafloor that gush scorching hot streams of mineral-rich fluid — may affect life near the ocean’s surface and the global carbon cycle more than previously thought.
Mathieu Ardyna, a postdoctoral scholar and the study’s lead author, said the research provides the first observed evidence of iron from the Southern Ocean’s depths turning normally anemic surface waters into hotspots for phytoplankton — the tiny algae that sustain the marine food web, pull heat-trapping carbon dioxide out of the air and produce a huge amount of the oxygen we breathe. “Our study shows that iron from hydrothermal vents can well up, travel across hundreds of miles of open ocean and allow phytoplankton to thrive in some very unexpected places,” he said.
Kevin Arrigo, a professor of Earth system science and senior author of the paper, called the findings “important because they show how intimately linked the deep ocean and surface ocean can be.”
Mysterious blooms
Phytoplankton need iron to thrive, and that limits their abundance in vast swaths of the ocean where concentrations of the nutrient are low. But when conditions are right, phytoplankton can also grow explosively, blooming across thousands of square miles in a matter of days.
That’s what Ardyna noticed recently as he looked at data recorded in 2014 and 2015 by a fleet of floating robots outfitted with optical sensors in the Southern Ocean. More than 1,300 miles off the coast of Antarctica and 1,400 miles from the African continent, two unexpectedly large blooms cropped up in an area known for severe iron shortages and low concentrations of chlorophyll, an indicator of phytoplankton populations.
Massive blooms in this region could only be possible with an influx of iron. Ardyna and Arrigo quickly ruled out the ocean’s most common sources, including continental shelves, melting sea ice and atmospheric dust, which were simply too far away to have much influence.
That led them to suspect that the nutrient must be welling up from below, possibly from a string of hydrothermal vents that dot a mid-ocean ridge 750 miles from where the massive blooms had inexplicably appeared. To help test their hypothesis, they recruited an international team of collaborators specialized in various aspects of oceanography and modeling.
“It has long been known that hydrothermal vents create unique and profound oases of life,” Ardyna said. Until recently, scientists generally believed those nourishing effects remained fairly local. But a growing amount of evidence from computer simulations of ocean dynamics has hinted that iron and other life-sustaining elements spewed from hydrothermal vents may in fact fuel planktonic blooms over much wider areas.
However, direct measurements have been lacking.
In the Southern Ocean, that’s partly due to the remote location, extreme cold and rough seas, which make it difficult to study up close or collect accurate data. “Your sensors have to be in the right place at the right time to see these blooms,” Ardyna said. “Satellites can underestimate intensity or miss them altogether because of bad coverage or strong mixing of the water column, which pushes phytoplankton down too deep for satellites to see.”
Clues from space, floating robots
To track the flow of particles from the vents on the mid-ocean ridge, the scientists analyzed data from satellites measuring chlorophyll and from autonomous, sensor-laden buoys known as Argo floats. As they dive and drift along ocean currents, some of these buoys detect chlorophyll and other proxies for phytoplankton biomass. “The floats give us precious and unique data, covering a large section of the water column down to 1,000 meters deep during an entire annual cycle,” Ardyna said.
The scientists couldn’t directly measure iron in the water, but instead analyzed measurements of helium collected by scientific cruises in the 1990s. The presence of helium signals waters influenced by hydrothermal vents, which funnel large amounts of primordial helium from beneath Earth’s crust.
The chlorophyll, phytoplankton and helium data suggest that a powerful current circling Antarctica grabs nutrients rising up from vents. Two turbulent, fast-moving branches of the current then shuttle the nutrients eastward for a month or two before serving them like a banquet to undernourished phytoplankton. Together with the arrival of spring sunshine that phytoplankton need for photosynthesis, the delivery triggers a massive bloom that can likely absorb and store significant amounts of carbon from the atmosphere, said Arrigo, who is also the Donald and Donald M. Steel Professor in Earth Sciences.
Over time, the blooms drift eastward toward the current racing around Antarctica and fade as sea creatures devour them. “We suspect these hotspots are either consumed or exported to deep waters,” Ardyna said.
Each bloom lasts little more than a month, but the mechanisms that trigger them are likely to be more common in the global ocean than scientists previously suspected.
“Hydrothermal vents are scattered all over the ocean floor,” Ardyna said. Knowing about the pathways that bring their nutrients up to surface waters will help researchers make more accurate calculations about the flow of carbon in the world’s oceans. “Much remains to be done to reveal other potential hotspots and quantify how this mechanism is altering the carbon cycle.”
Reference:
Mathieu Ardyna, Léo Lacour, Sara Sergi, Francesco d’Ovidio, Jean-Baptiste Sallée, Mathieu Rembauville, Stéphane Blain, Alessandro Tagliabue, Reiner Schlitzer, Catherine Jeandel, Kevin Robert Arrigo, Hervé Claustre. Hydrothermal vents trigger massive phytoplankton blooms in the Southern Ocean. Nature Communications, June 5, 2019; DOI: 10.1038/s41467-019-09973-6
This is what the Earth inside looks like: Deep down lies the core of the Earth, followed by the Earth’s mantle. The Earth’s crust begins 35 kilometres below the surface. Credit: Peter Eggermann / Adobe Stock
The huge magnetic field which surrounds the Earth, protecting it from radiation and charged particles from space — and which many animals even use for orientation purposes — is changing constantly, which is why geoscientists keep it constantly under surveillance. The old well-known sources of the Earth’s magnetic field are the Earth’s core — down to 6,000 kilometres deep down inside the Earth — and the Earth’s crust: in other words, the ground we stand on. The Earth’s mantle, on the other hand, stretching from 35 to 2,900 kilometres below the Earth’s surface, has so far largely been regarded as “magnetically dead.” An international team of researchers from Germany, France, Denmark and the USA has now demonstrated that a form of iron oxide, hematite, can retain its magnetic properties even deep down in the Earth’s mantle. This occurs in relatively cold tectonic plates, called slabs, which are found especially beneath the western Pacific Ocean.
“This new knowledge about the Earth’s mantle and the strongly magnetic region in the western Pacific could throw new light on any observations of the Earth’s magnetic field,” says mineral physicist and first author Dr. Ilya Kupenko from the University of Münster (Germany). The new findings could, for example, be relevant for any future observations of the magnetic anomalies on the Earth and on other planets such as Mars. This is because Mars has no longer a dynamo and thus no source enabling a strong magnetic field originating from the core to be built up such as that on Earth. It might, therefore, now be worth taking a more detailed look on its mantle. The study has been published in the “Nature” journal.
Background and methods used:
Deep in the metallic core of the Earth, it is liquid iron alloy that triggers electrical flows. In the outermost crust of the Earth, rocks cause magnetic signal. In the deeper regions of the Earth’s interior, however, it was believed that the rocks lose their magnetic properties due to the very high temperatures and pressures.
The researchers now took a closer look at the main potential sources for magnetism in the Earth’s mantle: iron oxides, which have a high critical temperature — i.e. the temperature above which material is no longer magnetic. In the Earth’s mantle, iron oxides occur in slabs that are buried from the Earth’s crust further into the mantle, as a result of tectonic shifts, a process called subduction. They can reach a depth within the Earth’s interior of between 410 and 660 kilometres — the so-called transition zone between the upper and the lower mantle of the Earth. Previously, however, no one had succeeded in measuring the magnetic properties of the iron oxides at the extreme conditions of pressure and temperature found in this region.
Now the scientists combined two methods. Using a so-called diamond anvil cell, they squeezed micrometric-sized samples of iron oxide hematite between two diamonds, and heated them with lasers to reach pressures of up to 90 gigapascal and temperatures of over 1,000 °C (1,300 K). The researchers combined this method with so-called Mössbauer spectroscopy to probe the magnetic state of the samples by means of synchrotron radiation. This part of the study was carried out at the ESRF synchrotron facility in Grenoble, France, and this made it possible to observe the changes of the magnetic order in iron oxide.
The surprising result was that the hematite remained magnetic up to a temperature of around 925 °C (1,200 K) — the temperature prevailing in the subducted slabs beneath the western part of Pacific Ocean at the Earth’s transition zone depth. “As a result, we are able to demonstrate that the Earth’s mantle is not nearly as magnetically ‘dead’ as has so far been assumed,” says Prof. Carmen Sanchez-Valle from the Institute of Mineralogy at Münster University. “These findings might justify other conclusions relating to the Earth’s entire magnetic field,” she adds.
Relevance for investigations of the Earth’s magnetic field and the movement of the poles
By using satellites and studying rocks, researchers observe the Earth’s magnetic field, as well as the local and regional changes in magnetic strength. Background: The geomagnetic poles of the Earth — not to be confused with the geographic poles — are constantly moving. As a result of this movement they have actually changed positions with each other every 200,000 to 300,000 years in the recent history of the Earth. The last poles flip happened 780,000 years ago, and last decades scientists report acceleration in the movement of the Earth magnetic poles. Flip of magnetic poles would have profound effect on modern human civilisation. Factors which control movements and flip of the magnetic poles, as well as directions they follow during overturn are not understood yet.
One of the poles’ routes observed during the flips runs over the western Pacific, corresponding very noticeably to the proposed electromagnetic sources in the Earth’s mantle. The researchers are therefore considering the possibility that the magnetic fields observed in the Pacific with the aid of rock records do not represent the migration route of the poles measured on the Earth’s surface, but originate from the hitherto unknown electromagnetic source of hematite-containing rocks in the Earth’s mantle beneath the West Pacific.
“What we now know — that there are magnetically ordered materials down there in the Earth’s mantle — should be taken into account in any future analysis of the Earth’s magnetic field and of the movement of the poles,” says co-author Prof. Leonid Dubrovinsky at the Bavarian Research Institute of Experimental Geochemistry and Geophysics at Bayreuth University.
Reference:
I. Kupenko, G. Aprilis, D. M. Vasiukov, C. McCammon, S. Chariton, V. Cerantola, I. Kantor, A. I. Chumakov, R. Rüffer, L. Dubrovinsky, C. Sanchez-Valle. Magnetism in cold subducting slabs at mantle transition zone depths. Nature, 2019; 570 (7759): 102 DOI: 10.1038/s41586-019-1254-8
Yunfeng Chen (L) and Jeffrey Gu (R) working in the field at a seismic station in the Canadian Rocky Mountains.
The Canadian Rocky Mountains were formed when the North American continent was dragged westward during the closure of an ocean basin off the west coast and collided with a microcontinent over 100 million years ago, according to a new study by University of Alberta scientists.
The research, based on high resolution data of Earth’s subsurface at the Alberta-British Columbia (BC) border, favours an interpretation different from the traditional theory of how the Canadian Rocky Mountains formed. The traditional theory, known as the accretion model, suggests that a gradual accumulation of additional matter eventually formed the Canadian Rockies — unlike the sudden collision event proposed by this research.
“This research provides new evidence that the Canadian section of this mountain range was formed by two continents colliding,” said Jeffrey Gu, professor in the Department of Physics and co-author on the study. “The proposed mechanism for mountain building may not apply to other parts of the Rocky Mountains due to highly variable boundary geometries and characteristics from north to south.”
The study involved seismic data collected from a dense network of seismic stations in western Alberta and eastern BC, combined with geodynamic calculations and geological observations. The results suggest that an ocean basin off North America’s west coast descended beneath the ribbon-shaped microcontinent, dragging North America westward, where it collided with the microcontinent.
“This study highlights how deep Earth images from geophysical methods can help us to understand the evolution of mountains, one of the most magnificent processes of plate tectonics observed at the Earth’s surface,” said Yunfeng Chen, who conducted this research during his PhD studies under the supervision of Gu. Chen received the Faculty of Science Doctoral Dissertation Award in 2018.
“There are other mountain belts around the world where a similar model may apply,” said Claire Currie, associate professor of physics and co-author on the study. “Our data could be important for understanding mountain belts elsewhere, as well as building our understanding of the evolution of western North America.”
Alberta and British Columbia communities supported these research efforts by hosting seismic stations on their land. This research is also supported by the Alberta Energy Regulator.
Reference:
Yunfeng Chen, Yu Jeffrey Gu, Claire A. Currie, Stephen T. Johnston, Shu-Huei Hung, Andrew J. Schaeffer, Pascal Audet. Seismic evidence for a mantle suture and implications for the origin of the Canadian Cordillera. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-09804-8
Pterosaurs were flying reptiles of the extinct clade or order Pterosauria. For most of the Mesozoic, they persisted: from the early Triassic to the end of the Cretaceous (228 to 66 million years old). Pterosaurs are the oldest vertebrate flight recognized to have developed. Their wings were created by a skin, muscle, and other tissue membrane that stretched from the knees to a fourth finger dramatically extended.
Early species had long, completely dented jaws and lengthy bodies, while subsequent types had a sharply decreased tail and teeth were missing from some. Many sported furry coats consisting of hair-like filaments known as pycnofibers that coated their heads and wing components. Pterosaurs ranged from the very tiny anurognathides to the biggest recognized flying animals of all time, including Quetzalcoatlus and Hatzegopteryx, to a broad spectrum of adult dimensions.
Pterosaurs are often referred to in the famous press and by the general public as ‘ flying animals, ‘ but the word ‘ homo ‘ is limited to those reptiles that came from the last common ancestor of the communities Saurischia and Ornithischia (clad Dinosaur, which contains animals), and the current scientific consensus is that this category excludes pterosaurs as well as the multiple types of ex-patriarchs.
However, pterosaurs, unlike these other reptiles, are closer to birds and dinosaurs than to crocodiles or any other living reptiles. Also known informally as pterodactyls are pterosaurs, especially in fiction and reporters. However, technically, pterodactyl only refers to members of the genus Pterodactylus, and more broadly to members of the suborder Pterodactyloidea of the pterosaurs.
When was pterosaur fossil Discovered?
In 1784, the Italian naturalist Cosimo Alessandro Collini defined the first pterosaur fossil. Collini misunderstood his sample as a seagoing animal that used as paddles its lengthy front legs. Even until 1830, when German zoologist Johann Georg Wagler proposed that Pterodactylus use its legs as flippers, a few researchers persisted to promote aquatic interpretation. In 1801, Georges Cuvier first proposed that pterosaurs were floating beasts and created the word “Ptero-dactyle” for the sample retrieved in Germany in 1809.
However, the formal title for this genus became Pterodactylus owing to the standardization of scientific names, although the word “pterodactyl” continued to be given popularly and wrongly to all Pterosaurian representatives. Now, palaeontologists prevent using “pterodactyl” and prefer “pterosaur.” They relegate the word “pterodactyl” specifically for Pterodactylus genus representatives or more widely for Pterodactyloidea suborder representatives.
Pterosaur Evolution
Scientists have long discussed where the evolutionary tree is fitted with pterosaurs. Today’s major hypothesis is that pterosaurs, reptiles, and crocodiles are strongly linked to each other and belong to a community called archosaurs.
Pterosaurs have been an incredibly effective reptile community. Throughout the dinosaur era they flourished, a span of over 150 million years. The oldest pterosaurs, relatively tiny flying reptiles with sturdy bodies and lengthy tails, evolved over moment into a wide range of species. Some had long, slim jaws, sophisticated head crests, or customized teeth, and some were extremely big.
Pterosaur Extinction
It was once believed that rivalry with early bird species could have brought many of the pterosaurs to extinction. Part of this is because it was believed that only big species of pterosaurs were present by the end of the Cretaceous (not correct anymore; see below). It was believed that the lower species had become extinct, their niche filled with birds. However, the decrease of pterosaurs (if current) tends to be irrelevant to the variety of birds, as the ecological overlap between the two communities seems minimal.
In reality, pterosaurs had recovered at least some avian niches before the KT case. The Cretaceous–Paleogene extinction incident, which also wiped out all non-avian dinosaurs and most avian species, and many other creatures, appears to have hit the pterosaurs at the end of the Cretaceous Period.
In the early 2010s, several new pterosaur taxa, such as the ornithocheirids Piksi and “Ornithocheirus,” possible pteranodontides and nyctosaurides, several tapejarids and indeterminate non-azhdarchid Navajodactylus, have been discovered dating to the Campanian / Maastrichtian. In the Campanian there were also small azhdarchoid pterosaurs. This indicates that late Cretaceous pterosaur faunas have been much more varied than earlier assumed, potentially not even substantially declining from the early Cretaceous. Piksi, however, is no longer regarded as a pterosaur.
Apparently there were small size pterosaur species in the Csehbánya Formation, suggesting a greater variety of Late Cretaceous pterosaur ##s than earlier reported. The latest results of a tiny cat-sized adult azhdarchid further show that tiny pterosaurs from the Late Cretaceous may, in reality, have been scarcely maintained in the fossil record, assisted by the reality that there is a powerful bias against tiny terrestrial vertebrates such as juvenile animals, and that their variety may effectively have been much greater than earlier assumed.
Late Cretaceous maintained at least some non-pterodactylod pterosaurs, postulating a rock taxa scenario for late Cretaceous pterosaur faunas.
How Did Pterosaurs Fly?
Flight enabled pterosaurs to move lengthy distances, utilize fresh environments, evade predators, and take their prey from above. They distributed throughout the globe and branched out into a huge variety of species, including the largest animals ever to wing.
Built to Fly
Pterosaurs produced lift with their wings like other flying animals. They required the same types of movements as birds and bats, but their wings developed separately and developed their own separate aerodynamic framework.
With their forelimbs, Pterosaurs moved. Their lengthy wings developed from the same portion of the body as our arms. As the arm and leg bones of pterosaurs developed for floating, they lengthened, and one finger’s bones— our ring finger’s equal — became extraordinarily lengthy. These bones, like the mast on a boat, backed the top of the wing, a slim skin flap formed like a flag.
Wing Bones
Although there are many creatures that can glide through the air, pterosaurs, birds, and bats are the only vertebrates that have developed to move through their bones. All three organizations came down from creatures living on the floor, and their wings developed in a comparable manner: their forelimbs gradually became lengthy, bladelike, and aerodynamic.
In order to get off the floor, large pterosaurs required powerful limbs, but dense bones would have rendered them too heavy. The answer? The wing bones of a pterosaur were hollow pipes, with no bigger walls than a play board. They were versatile and lightweight like bird bones, while reinforced by inner struts.
Inside the Wings
Recent findings indicate that wing membranes of pterosaurs were more than just skin flaps. Long strands stretched from the front to the back of the bones forming a sequence of stabilizing bases so that the membranes could be spread tight or folded as a fan. Separate muscle fibers assisted pterosaurs to change their wings ‘ strain and shape, and veins and arteries maintained blood-fed wings.
The exhibition includes a remarkable Rhamphorhynchus muensteri fossil, discovered in Germany in 2001, featuring wing tissues so well preserved that scientists could see fine details in their structure. Researchers identified skin cells lined with blood vessels, muscles, and lengthy fibers that strengthened the wing under ultraviolet light. Paleontologists call this fossil Dark Wing due to the shadowy shape of the wing membrane.
The sluglike mollusk Wiwaxia was among the trove of fossils dating back to the Middle Ordovician. Credit: Julien Kimmig.
A clutch of marine fossil specimens unearthed in northern Portugal that lived between 470 and 459 million years ago is filling a gap in understanding evolution during the Middle Ordovician period.
The discovery, explained in a new paper just published in The Science of Nature, details three fossils found in a new “Burgess Shale-type deposit.” (The Burgess Shale is a deposit in Canada renowned among evolutionary biologists for excellent preservation of soft-bodied organisms that don’t have a biomineralized exoskeleton.)
“The paper describes the first soft-body fossils preserved as carbonaceous films from Portugal,” said lead author Julien Kimmig, collections manager at the University of Kansas Biodiversity Institute and Natural History Museum. “But what makes this even more important is that it’s one of the few deposits that are actually from the Ordovician period — and even more importantly, they’re from the Middle Ordovician, a time were very few soft-bodied fossils are known.”
Kimmig and his KU Biodiversity Institute colleagues, undergraduate researcher Wade Leibach and senior curator Bruce Lieberman, along with Helena Couto of the University of Porto in Portugal (who discovered the fossils), describe three marine fossil specimens: a medusoid (jellyfish), possible wiwaxiid sclerites and an arthropod carapace.
“Before this, there had been nothing found on the Iberian Peninsula in the Ordovician that even resembled these,” Kimmig said. “They close a gap in time and space. And what’s very interesting is the kind of fossils. We find Medusozoa — a jellyfish — as well as animals which appear to be wiwaxiids, which are sluglike armored mollusks that have big spines. We found these lateral sclerites of animals which were actually thought to have gone extinct in the late Cambrian. There might have been some that survived into the Ordovician in a Morocco deposit, but nothing concrete has been ever published on those. And here we have evidence for the first ones actually in the middle of the Ordovician, so it extends the range of these animals incredibly.”
Kimmig said the discovery of uncommon wiwaxiids fossils in this time frame suggests the animals lived on Earth for a far greater span of time than previously understood.
“Especially with animals that are fairly rare that we don’t have nowadays like wiwaxiids, it’s quite nice to see they lived longer than we ever thought,” he said. “Closely after this deposit, in the Upper Ordovician, we actually get a big extinction event. So, it’s likely the wiwaxiids survived up to that big extinction event and didn’t go extinct earlier due to other circumstances. But it might have been whatever caused the big Ordovician extinction event killed them off, too.”
According to the researchers, the soft-bodied specimens fill a gap in the fossil record for the Middle Ordovician and suggest “many soft-bodied fossils in the Ordovician remain to be discovered, and a new look at deep-water shales and slates of this time period is warranted.”
“It’s a very interesting thing with these discoveries — we’re actually getting a lot of information about the distribution of animals chronologically and geographically,” Kimmig said. “Also, this gives us a lot of information on how animals adapted to different environments and where they actually managed to live. With these soft-body deposits, we get a much better idea of how many animals there were and how their environment changed over time. It’s something that applies to modern days, with changing climate and changing water temperatures, because we can see how animals over longer periods of time in the geologic record have actually adapted to these things.”
Co-author Couto discovered the fossils in the Valongo Formation in northern Portugal, an area famed for containing trilobites. When the animals were alive, the Valongo Formation was part of a shallow sea on the margin of northern Gondwana, the primeval supercontinent.
“Based on the shelly fossils, the deposit looks like it was a fairly common Ordovician community,” Kimmig said. “And now we know that in addition to those common fossils jellyfish were floating around, we had sluglike mollusks roaming on the ground, too, and we had bigger arthropods, which might have been predatory animals. So, in that regard, we’re getting a far better image with these soft-bodied fossils of what these communities actually looked like.”
According to the KU researcher, scientists didn’t grasp until recently that deposits from this period could preserve soft-bodied specimens.
“For a long time, it was just not known that these kinds of deposits survived in to the Ordovician,” Kimmig said. “So, it is likely these deposits are more common in the Ordovician than we know of, it’s just that people were never looking for them.”
Kimmig led analysis of the fossils at KU’s Microscopy and Analytical Imaging Laboratory to ensure the fossils were made of organic material. Leibach, the KU undergraduate researcher, conducted much of the lab work.
“We analyzed the material and looked at the composition because sometimes you can get pseudo fossils — minerals that create something that looks like a fossil,” Kimmig said. “We had to make sure that these fossils actually had an organic origin. And what we found is that they contain carbon, which was the big indication they would actually be organic.”
Reference:
Julien Kimmig, Helena Couto, Wade W. Leibach, Bruce S. Lieberman. Soft-bodied fossils from the upper Valongo Formation (Middle Ordovician: Dapingian-Darriwilian) of northern Portugal. The Science of Nature, 2019; 106 (5-6) DOI: 10.1007/s00114-019-1623-z
Reconstruction of the studied pterosaur, with four different feather types over its head, neck, body, and wings, and a generally ginger-brown colour. Credit: Reconstruction by Yuan Zhang.
New research, led by the University of Bristol, suggests that feathers arose 100 million years before birds — changing how we look at dinosaurs, birds, and pterosaurs, the flying reptiles.
It also changes our understanding of feathers themselves, their functions and their role in some of the largest events in evolution.
The new work, published in the journal Trends in Ecology & Evolution combines new information from palaeontology and molecular developmental biology.
The key discovery came earlier in 2019, when feathers were reported in pterosaurs — if the pterosaurs really carried feathers, then it means these structures arose deep in the evolutionary tree, much deeper than at the point when birds originated.
Lead author, Professor Mike Benton, from the University of Bristol’s School of Earth Sciences, said: “The oldest bird is still Archaeopteryx first found in the Late Jurassic of southern Germany in 1861, although some species from China are a little older.
“Those fossils all show a diversity of feathers — down feathers over the body and long, vaned feathers on the wings. But, since 1994, palaeontologists have been contending with the perturbing discovery, based on hundreds of amazing specimens from China, that many dinosaurs also had feathers.”
Co-author, Baoyu Jiang from the University of Nanjing, added: “At first, the dinosaurs with feathers were close to the origin of birds in the evolutionary tree.
“This was not so hard to believe. So, the origin of feathers was pushed back at least to the origin of those bird-like dinosaurs, maybe 200 million years ago.”
Dr Maria McNamara, co-author from University College Cork, said: “Then, we had the good fortune to work on a new dinosaur from Russia, Kulindadromeus.
“This dinosaur showed amazingly well-preserved skin covered with scales on the legs and tail, and strange whiskery feathers all over its body.
“What surprised people was that this was a dinosaur that was as far from birds in the evolutionary tree as could be imagined. Perhaps feathers were present in the very first dinosaurs.”
Danielle Dhouailly from the University of Grenoble, also a co-author, works on the development of feathers in baby birds, especially their genomic control. She said: “Modern birds like chickens often have scales on their legs or necks, and we showed these were reversals: what had once been feathers had reversed to be scales.
“In fact, we have shown that the same genome regulatory network drives the development of reptile scales, bird feathers, and mammal hairs. Feathers could have evolved very early.”
Baoyu Jiang continued: “The breakthrough came when we were studying two new pterosaurs from China.
“We saw that many of their whiskers were branched. We expected single strands — monofilaments — but what we saw were tufts and down feathers. Pterosaurs had feathers.”
Professor Benton added: “This drives the origin of feathers back to 250 million years ago at least.
“The point of origin of pterosaurs, dinosaurs and their relatives. The Early Triassic world then was recovering from the most devastating mass extinction ever, and life on land had come back from near-total wipe-out.
“Palaeontologists had already noted that the new reptiles walked upright instead of sprawling, that their bone structure suggested fast growth and maybe even warm-bloodedness, and the mammal ancestors probably had hair by then.
“So, the dinosaurs, pterosaurs and their ancestors had feathers too. Feathers then probably arose to aid this speeding up of physiology and ecology, purely for insulation. The other functions of feathers, for display and of course for flight, came much later.”
Reference:
Michael J. Benton, Danielle Dhouailly, Baoyu Jiang, Maria McNamara. The Early Origin of Feathers. Trends in Ecology & Evolution, 2019; DOI: 10.1016/j.tree.2019.04.018
This view of the Grand Canyon shows the Great Unconformity, a boundary where as much as a billion years’ worth of sedimentary deposits are missing from the geologic record. The boundary can be seen at roughly the middle of this image, separating the older, lumpy and angular rocks below from the younger horizontal layers above. New research suggests that the missing sediments, likely scrubbed away by glaciers during the global “snowball Earth” that ended roughly 635 million years ago, washed away to the oceans, where they lubricated subduction faults and kick-started the modern age of plate tectonics. Image credit: USGS/Alex Demas
Earth’s outer layer is composed of giant plates that grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes. These plates also separate at undersea mountain ridges, where molten rock spreads from the centers of ocean basins.
But this was not always the case. Early in Earth’s history, the planet was covered by a single shell dotted with volcanoes — much like the surface of Venus today. As Earth cooled, this shell began to fold and crack, eventually creating Earth’s system of plate tectonics.
According to new research, the transition to plate tectonics started with the help of lubricating sediments, scraped by glaciers from the slopes of Earth’s first continents. As these sediments collected along the world’s young coastlines, they helped to accelerate the motion of newly formed subduction faults, where a thinner oceanic plate dips beneath a thicker continental plate.
The new study, published June 6, 2019 in the journal Nature, is the first to suggest a role for sediments in the emergence and evolution of global plate tectonics. Michael Brown, a professor of geology at the University of Maryland, co-authored the research paper with Stephan Sobolev, a professor of geodynamics at the GFZ German Research Centre for Geosciences in Potsdam.
The findings suggest that sediment lubrication controls the rate at which Earth’s crust grinds and churns. Sobolev and Brown found that two major periods of worldwide glaciation, which resulted in massive deposits of glacier-scrubbed sediment, each likely caused a subsequent boost in the global rate of plate tectonics.
The most recent such episode followed the “snowball Earth” that ended sometime around 635 million years ago, resulting in Earth’s modern plate tectonic system.
“Earth hasn’t always had plate tectonics and it hasn’t always progressed at the same pace,” Brown said. “It’s gone through at least two periods of acceleration. There’s evidence to suggest that tectonics also slowed to a relative crawl for nearly a billion years. In each case, we found a connection with the relative abundance — or scarcity — of glacial sediments.”
Just as a machine needs grease to keep its parts moving freely, plate tectonics operates more efficiently with lubrication. While it may be hard to confuse the gritty consistency of clay, silt, sand and gravel with a slippery grease, the effect is largely the same at the continental scale, in the ocean trenches where tectonic plates meet.
“The same dynamic exists when drilling Earth’s crust. You have to use mud — a very fine clay mixed with water or oil — because water or oil alone won’t work as well,” Brown said. “The mud particles help reduce friction on the drill bit. Our results suggest that tectonic plates also need this type of lubrication to keep moving.”
Previous research on the western coast of South America was the first to identify a relationship between sediment lubrication and friction along a subduction fault. Off the coast of northern Chile, a relative lack of sediment in the fault trench creates high friction as the oceanic Nazca plate dips beneath the continental South America plate. This friction helped to push the highest peaks of the central Andes Mountains skyward as the continental plate squashed and deformed.
In contrast, further south there is a higher sediment load in the trench, resulting in less friction. This caused less deformation of the continental plate and, consequently, created smaller mountain peaks. But these findings were limited to one geographic area.
For their study, Sobolev and Brown used a geodynamic model of plate tectonics to simulate the effect of sediment lubrication on the rate of subduction. To verify their hypothesis, they checked for correlations between known periods of widespread glaciation and previously published data that indicate the presence of continental sediment in the oceans and trenches. For this step, Sobolev and Brown relied on two primary lines of evidence: the chemical signature of the influence of continental sediments on the chemistry of the oceans and indicators of sediment contamination in subduction-related volcanoes, much like those that make up today’s “ring of fire” around the Pacific Ocean.
According to Sobolev and Brown’s analysis, plate tectonics likely emerged on Earth between 3 and 2.5 billion years ago, around the time when Earth’s first continents began to form. This time frame also coincides with the planet’s first continental glaciation.
A major boost in plate tectonics then occurred between 2.2 to 1.8 billion years ago, following another global ice age that scrubbed massive amounts of sediments into the fault trenches at the edges of the continents.
The next billion years, from 1.75 billion to 750 million years ago, saw a global reduction in the rate of plate tectonics. This stage of Earth’s history was so sedate, comparatively speaking, that it earned the nickname “the boring billion” among geologists.
Later, following the global “snowball Earth” glaciation that ended roughly 635 million years ago, the largest surface erosion event in Earth’s history may have scrubbed more than a vertical mile of thickness from the surface of the continents. According to Sobolev and Brown, when these sediments reached the oceans, they kick-started the modern phase of active plate tectonics.
Reference:
Stephan V. Sobolev, Michael Brown. Surface erosion events controlled the evolution of plate tectonics on Earth. Nature, 2019; 570 (7759): 52 DOI: 10.1038/s41586-019-1258-4
During the Early Cretaceous period (145-100 million years ago), nonavian dinosaurs likely migrated between Africa and Europe. Image adapted from research figure originally published in Systematic Biology, DOI: 10.1093/sysbio/syz024, CC-BY
One researcher at the University of Tokyo is in hot pursuit of dinosaurs, tracking extinct species around ancient Earth. Identifying the movements of extinct species from millions of years ago can provide insights into ancient migration routes, interaction between species, and the movement of continents.
“If we find fossils on different continents from closely related species, then we can guess that at some point there must have been a connection between those continents,” said Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo.
A map of life — biogeography
Previous studies in biogeography — the geographic distribution of plants and animals — had not considered the evolutionary relationships between ancient species. The new method that Kubo designed, called biogeographical network analysis, converts evolutionary relationships into geographical relationships.
For example, cats and dogs are more closely related to each other than to kangaroos. Therefore, a geographical barrier must have separated the ancestors of kangaroos from the ancestors of cats and dogs well before cats and dogs became separate species.
Most fossils are found in just a few hot-spot locations around the world and many ancient species with backbones (vertebrates) are known from just one fossil of that species. These limitations mean that a species’ fossils cannot reveal the full area of where it was distributed around the world.
“Including evolutionary relationships allows us to make higher resolution maps for where species may have migrated,” said Kubo.
The analysis used details from evolutionary studies, the location of fossil dig sites, and the age of the fossils. Computer simulations calculated the most likely scenarios for the migration of species between continents on the Cretaceous-era Earth, 145 to 66 million years ago.
North and south divide
This new analysis verified what earlier studies suggested: nonavian dinosaurs were divided into a group that lived in the Northern Hemisphere and another that lived in the Southern Hemisphere, and that those two groups could still move back and forth between Europe and Africa during the Early Cretaceous period (145 to 100 million years ago), but became isolated in the Late Cretaceous period (100 to 66 million years ago).
During the Early Cretaceous period, there were three major supercontinents: North America-Europe-Asia, South America-Africa, and Antarctica-India-Australia.
By the Late Cretaceous period, only the North America-Europe-Asia supercontinent remained. The other supercontinents had separated into the continents we know today, although they had not yet drifted to their current locations.
“During the Late Cretaceous period, high sea levels meant that Europe was a series of isolated islands. It makes sense that nonavian dinosaur species differentiated between Africa and Europe during that time,” said Kubo.
Kubo plans to complete additional biogeographical analyses for different time periods to continue tracking extinct species around the world and through time.
Reference:
Tai Kubo. Biogeographical Network Analysis of Cretaceous Terrestrial Tetrapods: A Phylogeny-Based Approach. Systematic Biology, 2019; DOI: 10.1093/sysbio/syz024
Google Earth is a free program from Google that allows you to “fly” over a virtual globe and view the Earth through high-resolution graphics and satellite images.
Google Earth is a computer program based mainly on satellite imagery that makes a 3D representation of Earth. By superimposing satellite images, aerial photography, and GIS data onto a 3D globe, the program maps the Earth, enabling users to see towns and landscapes from different perspectives. By entering addresses and coordinates, or using a keyboard or mouse, users can explore the globe.
The program can also be downloaded using a touch screen or stylus to navigate on a smartphone or tablet. Users can use the program to use Keyhole Markup Language to add their own information and upload it through multiple sources, such as forums or blogs. Google Earth can display multiple types of overlaid pictures on the Earth’s surface and is also a Web Map Service customer.
In relation to Earth navigation, through the desktop application, It offers a number of other instruments. There are additional globes accessible for the Moon and Mars, as well as a night sky viewing instrument. It also includes a flight simulator match. Other characteristics enable consumers to view pictures uploaded to Panoramio from multiple locations, data given on some locations by Wikipedia, and graphics from Street View. Google Earth’s web-based edition also involves Voyager, a function that brings in-program trips on a regular basis, often provided by researchers and documentaries.
Versions
On macOS, Linux, iOS, and Android, Google Earth has been published. The Linux variant started with Google Earth’s version 4 beta, using the Qt toolkit as a indigenous port. The Free Software Foundation considers it a high priority free software project to develop a free compliant client for Google Earth. Google Earth came out on February 22, 2010 for Android, and on October 27, 2008 for iOS. Google Earth’s portable variants can use multi-touch controls to shift, zoom, or spin the perspective around the globe, allowing the present place to be selected.
Currently 32 different mineral species of the “tourmaline group” are delineated by the distribution of the major elements of which they are comprised. So, a single shard of tourmaline with slight variations in chemistry often contains multiple species of the mineral, even if they all formed in the same geologic event. Credit: Public domain
The first minerals to form in the universe were nanocrystalline diamonds, which condensed from gases ejected when the first generation of stars exploded. Diamonds that crystallize under the extreme pressure and temperature conditions deep inside of Earth are more typically encountered by humanity. What opportunities for knowledge are lost when mineralogists categorize both the cosmic travelers and the denizens of deep Earth as being simply “diamond“?
Could a new classification system that accounts for minerals’ distinct journeys help us better understand mineralogy as a process of universal and planetary evolution?
The current system for classifying minerals—developed by James Dwight Dana in the 1850s—categorizes more than 5,400 mineral “species” based on their dominant chemical compositions and crystalline structures. This is an unambiguous, robust, and reproducible designation scheme.
Carnegie’s Robert Hazen suggests an additional classification system, which could amplify existing knowledge of how minerals evolve over time without superseding the existing designations. In American Mineralogist’s Roebling Medal Paper, Hazen argues for categories that reflect a deeper, more-modern understanding of planetary scale transformation over time.
A system grouping minerals and non-crystalline natural solids—which are not currently classified by the existing system—into what Hazen calls “natural kind clusters” would better reflect the inherent messiness of planetary evolution, he explains.
“For maximum efficacy, scientific classification systems must not just organize and define, but also reflect current theory, and allow it to expand and guide us to new conclusions,” Hazen says.
He pioneered the concept of mineral evolution—linking an explosion in mineral diversity to the rise of life on Earth and the resulting oxygen-rich atmosphere. Hazen then added another layer to his vision by introducing mineral ecology—which analyzes the spatial distribution of Earth’s minerals to predict which ones remain undiscovered and to assert our planet’s mineralogical uniqueness.
A system of categorization that reflects not just a mineral’s chemistry and crystalline structure, but also the physical, chemical, or biological processes by which it formed, would be capable of recognizing that nanodiamonds from space are fundamentally different to diamonds formed in Earth’s depths.
The existing classification system groups some minerals with disparate formation histories together in one category, while splitting others with similar origin stories into separate mineral species.
Another example: currently 32 different mineral species of the “tourmaline group” are delineated by the distribution of the major elements of which they are comprised. So, a single shard of tourmaline with slight variations in chemistry often contains multiple species of the mineral, even if they all formed in the same geologic event.
A natural kind classification system would rectify that problem, and allow for the inclusion of non-crystalline materials, such as volcanic glass, amber, and coal, which currently aren’t counted as minerals, but can offer knowledge about our evolving planet.
“Earth’s mineralogy tells vivid stories, revealing how eons of geologic activity and the rise of life facilitated novel combinations of elements,” Hazen argues. “But to glean every nuance of this mineralogical text, we must embrace a new language for describing the creation of minerals that reflects the passage of time.”
The location of the two largest earthquakes are shown with place markers along with their magnitudes determined in this study. Credit: University of Melbourne
On 19th June 2012 at 8:53 pm local time, a moment magnitude-4.9 earthquake rattled the residents in and around the small town of Thorpdale in eastern Victoria. Moment magnitude measures the size or strength of an earthquake based on how much energy is released, which differs from the better known Richter scale.
The quake was felt more than 100 kilometers away in Melbourne’s CBD and in other parts of the state.
Then, nearly a month later, on 20th July at 7:11 pm, another magnitude-4.3 seismic shock jolted the region.
A second earthquake like this is normal because, usually, the release of residue stress on a fault produces smaller aftershocks in the days following a mainshock.
But, in fact, our new research suggests that these earthquakes broke not one, but two adjacent faults. And it’s likely that the seismic slip on the first fault activated the second one; which means that the first earthquake communicated with the second one in a language that only the Earth understands.
A quake conversation
Two days after the first quake, the University of Melbourne seismology group deployed 13 temporary seismic stations on a rolling basis in Thorpdale.
These stations are designed to pick up any distinct signals of seismic waves emanating from tiny aftershocks following the first earthquake.
But the stations then picked up signals from the second earthquake that people felt along with the aftershocks.
Because the first earthquake was of reasonable size, permanent—more distant seismic stations maintained by the University of Melbourne along with other agencies like Geoscience Australia and the Seismology Research Centre—picked up its seismic signals.
These signals consist of three main types:
Primary (or P) waves are the fastest seismic waves and will be picked up by a station first
The Secondary (S) waves travel at a slower speed than the P waves. Both these wave types are called body waves because they travel inside the Earth. In Victoria, P and S waves travel at speeds, respectively, of about 20,000 kilometers an hour and 12,600 kilometers an hour
Surface waves, on the other hand, travel along the surface of the Earth and are the slowest, traveling at around 10,000 kilometers per hour but produce the most shaking.
To give you an idea of how fast this is, the speed of sound sits at around 1200 kilometers per hour.
Using these P waveforms, our research team accurately estimated the first earthquake as 4.9 magnitude and the second July one to be 4.3.
The energy released in the first earthquake was about 27 petajoules (PJ) and it released eight times more energy than the second one. In terms of strength, 27 PJ could power the state of Victoria for an entire week.
By accurately timing the arrival of P and S waves at the stations, our team then worked to precisely triangulate the locations of the earthquakes in Thorpdale.
And this is when things got interesting.
More than a single fault
If these earthquakes (including aftershocks) occurred on a single fault, all the earthquakes should have clustered in one place.
But, the two earthquakes had their own separate clusters, and the second earthquake was located roughly seven kilometers to the northwest of the first one. So, it became clear that these earthquakes were two separate mainshocks—which was confirmed by additional projections of fault plane analysis.
There were forty-four aftershocks in the first 24 hours following the first mainshock.
A week later, the aftershock rate diminished to about one a day, and after 18 days, none were recorded. Then, five days before the second mainshock, that aftershock rate picked up.
Three days prior to the second main event, four aftershocks were recorded, and a day after that, another twelve occurred.
A day before the second mainshock, six aftershocks were detected. It appears that the aftershocks—or the geologic conditions that produce them—were gradually moving towards the location of the second, magnitude 4.3 earthquake.
And on the day of the second mainshock, forty-one aftershocks occurred.
Stress transfer
One way that an earthquake can trigger another is as a result of a mechanism known as Coulomb stress transfer. That is, an earthquake can change stress conditions in the surrounding Earth’s crust in a way that could bring nearby faults either closer to or away from failure.
Testing this condition showed us that the first mainshock slightly relieved stress at the location of the second mainshock. This may have contributed to the nearly 30-day delay in the second mainshock.
In addition, any water trapped in the crust’s pores under high compression near the second mainshock may have played a role. It’s possible that this water seeped into the fault plane, triggering the second mainshock, as a result of shaking and aftershocks from the first quake.
Seeping water can act as a lubricant for an otherwise locked fault interface, reducing the frictional strength that holds a fault together.
This process is similar to the way in which man-made earthquakes (known as induced seismicity) are triggered from reservoir impoundment and waste water injections.
Victoria’s Thomson Reservoir, which sits about 200 kilometers east of Melbourne, is one example of seeping fluid triggering an earthquake.
In this instance, a swarm of earthquakes occurred, that included one in 1996 with a local magnitude of five.
Predicting quakes?
One of the most famous examples of “communicating earthquakes” are the ones that occurred along the 1500-kilometer-long North Anatolian Fault, which sits in modern-day Turkey.
This fault separates two tectonic plates—the Eurasian plate to the north and the Anatolian plate to the south. From 1939 until around 1999, twelve earthquakes with magnitudes exceeding 6.7 have marched westward along the fault line.
So, does this information help us predict earthquakes? Does it help us foretell the size, location and the time of an earthquake?
The short answer is no.
Professor Charles Richter, who developed the Richter magnitude scale which quantifies the size of earthquakes, once famously said: “Journalists and the general public rush to any suggestion of earthquake prediction like hogs toward a full trough, [prediction] provides a happy hunting ground for amateurs, cranks, and outright-publicity seeking fakers.”
All that is possible is an earthquake forecast that gives a probability of occurrence of an earthquake with a certain size in a region over decadal time-scales.
Even this process has large uncertainties especially in places like Australia where our historical earthquake record is poor.
But what these two earthquakes talking to each other does tell us, is that earthquakes are not isolated events. Instead, they can interact with each other and increase damage by prolonging earthquake activity in a region.
Researchers at The Ohio State University have created high-resolution maps of points around the globe where groundwater meets the oceans—the first such analysis of its kind, giving important data points to communities and conservationists to help protect both drinking water and the seas.
In a study published June 3 in the journal Geophysical Research Letters, the team showed that nearly half of fresh submarine groundwater discharge flows into the ocean near the tropics. They also found that regions near active fault lines—the area around the San Andreas Fault in California, for example—send greater volumes of groundwater into the ocean than regions that are tectonically stable. And, they found that dry, arid regions have very little groundwater discharge, opening the limited groundwater supplies in those parts of the world to saltwater intrusion.
The Ohio State team worked with researchers at NASA’s Jet Propulsion Laboratory and the University of Saskatchewan to combine topographical data from satellites and climate models to show the flow of groundwater around the world’s coasts.
The findings could help coastal communities better protect and manage their drinking water.
“Freshwater-groundwater discharge is a natural line of defense against saltwater intrusion,” said Audrey Sawyer, assistant professor of earth sciences at Ohio State and a co-author of the study. “And saltwater intrusion is a concern in places like Miami, Georgia, Cape Cod—it’s up and down the coast. It’s a problem that dry regions have as little groundwater discharge as they do because these are also the places where people are going to tend to look for groundwater to meet their freshwater needs.”
Their work, the first near-global and spatially distributed high-resolution map of fresh groundwater flow to the coast, could give scientists better clues about where to monitor groundwater discharge. Such monitoring is more challenging than monitoring the water quality of a river or stream, because groundwater, by its nature, enters oceans and lakes under water—people can’t see it from land.
When researchers think about coastal water quality and the way water affects the biochemical makeup of the world’s lakes and oceans, they typically think about rivers and streams—and for good reason. Most of the water that gets to lakes and oceans comes from surface water sources. But groundwater plays and important role, too, carrying minerals and, in some cases, pollutants, to surface bodies of water.
“If you’ve ever been swimming in a lake or in the ocean in the summertime and you go through a cold patch, that is probably a place where groundwater is coming out,” Sawyer said. “And that’s just one way that groundwater affects surface water—in that case, it’s affecting temperature, but it also affects the chemistry of the water. These effects can be hard to measure over large scales.”
That’s why Sawyer’s team started building these images: The research group focuses on groundwater, and realized that there was limited information showing—in detail—where groundwater was most likely to flow into the oceans.
The study found that in some parts of the world, groundwater could be polluting oceans and lakes with nutrients and other chemicals.
Groundwater, for example, can carry higher concentrations of nitrates—a key contributor of the types of harmful algal blooms that have caused problems for both fish and drinking water in Lake Erie, the Chesapeake Bay and the Gulf of Mexico—as well as high concentrations of mercury. Understanding how and where groundwater gets to surface water could help policymakers create better plans to improve those bodies of water.
The study also found that climate heavily influences groundwater flow, and that cities in dry areas are especially vulnerable to saltwater contamination of aquifers.
“This study draws attention to the idea that surface water and groundwater are all connected, and if you start to extract groundwater, you’re affecting that connection to our surface water bodies, and that can affect surface water quality, too,” Sawyer said. “There is competition between the outward push of groundwater towards the coast and the saltwater that wants to come in, and if we don’t have as much of an outward push because we’re taking that fresh groundwater out of the ground instead of letting it flow to the coast, it puts us in a more vulnerable position. It’s not that we can’t use groundwater, but we need to monitor our impact and remember that groundwater is not an inexhaustible resource.”
