Geology In

Giant 16-foot Long Dolphin Feasted on 'Killer Whale-size Prey'

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<tr><td class="tr-caption" style="text-align: center;">Photo: Nicholas D. Pyenson</td></tr>
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A giant 16-foot long dolphin has been discovered that lived 25 million years ago and was an apex predator. 
 
A report in the journal Current Biology on  offers a detailed description of the first nearly complete skeleton of an extinct large dolphin, discovered in what is now South Carolina. The 15-foot-long dolphin (Ankylorhiza tiedemani comb. n.) lived during the Oligocene—about 25 million years ago—and was previously known only from a partial rostrum (snout) fossil. 
 
The researchers say that multiple lines of evidence—from the skull anatomy and teeth, to the flipper and vertebral column—show that this large dolphin (a toothed whale in the group Odontoceti) was a top predator in the community in which it lived. They say that many features of the dolphin's postcranial skeleton also imply that modern baleen whales and modern toothed whales must have evolved similar features independently, driven by parallel evolution in the very similar aquatic habitats in which they lived. 
 
"The degree to which baleen whales and dolphins independently arrive at the same overall swimming adaptations, rather than these traits evolving once in the common ancestor of both groups, surprised us," says Robert Boessenecker of the College of Charleston in Charleston, South Carolina. "Some examples include the narrowing of the tail stock, increase in the number of tail vertebrae, and shortening of the humerus (upper arm bone) in the flipper. 
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"This is not apparent in different lineages of seals and sea lions, for example, which evolved into different modes of swimming and have very different looking postcranial skeletons," he adds. "It's as if the addition of extra finger bones in the flipper and the locking of the elbow joint has forced both major groups of cetaceans down a similar evolutionary pathway in terms of locomotion." 
 
Though first discovered in the 1880s from a fragmentary skull during phosphate dredging of the Wando River, the first skeleton of Ankylorhiza was discovered in the 1970s by then Charleston Museum Natural History curator Albert Sanders. The nearly complete skeleton described in the new study was found in the 1990s. A commercial paleontologist by the name of Mark Havenstein found it during construction of a housing subdivision in South Carolina. It was subsequently donated to the Mace Brown Museum of Natural History, to allow for its study. 
 
While there's much more to learn from this fossil specimen, the current findings reveal that Ankylorhiza was an ecological specialist. The researchers say the species was "very clearly preying upon large-bodied prey like a killer whale." 
 
Another intriguing aspect, according to the researchers, is that Ankylorhiza is the first echolocating whale to become an apex predator. When Ankylorhiza became extinct by about 23 million years ago, they explain, killer sperm whales and the shark-toothed dolphin Squalodon evolved and reoccupied the niche within 5 million years. After the last killer sperm whales died out about 5 million years ago, the niche was left open until the ice ages, with the evolution of killer whales about 1 or 2 million years ago. 
 
"Whales and dolphins have a complicated and long evolutionary history, and at a glance, you may not get that impression from modern species," Boessenecker says. "The fossil record has really cracked open this long, winding evolutionary path, and fossils like Ankylorhiza help illuminate how this happened." 
 
Boessenecker notes that more fossils of Ankylorhiza are awaiting study, including a second species and fossils of Ankylorhiza juveniles that can offer insight into the dolphin's growth. He says that there's still much to learn from fossilized dolphins and baleen whales from South Carolina. 
 
"There are many other unique and strange early dolphins and baleen whales from Oligocene aged rocks in Charleston, South Carolina," Boessenecker says. "Because the Oligocene epoch is the time when filter feeding and echolocation first evolved, and since marine mammal localities of that time are scarce worldwide, the fossils from Charleston offer the most complete window into the early evolution of these groups, offering unparalleled evolutionary insight." 
 
 
The above story is based on <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(20)30828-9" rel="nofollow" target="_blank">materials </a>provided by  <a href="https://www.cell.com/" rel="nofollow" target="_blank">Cell Press.</a></div>

Giant 16-foot Long Dolphin Feasted on 'Killer Whale-size Prey'

Photo: Nicholas D. Pyenson A giant 16-foot long dolphin has been discovered that lived 25 million years ago and was an apex predator....

Zultanite: A Color Changing Stone

gemstones, Mineralogy 6:59 PM

Zultanite: A Color Changing Stone

Zultanite gemstones, rough and crystal form lighting Zultanite is a color change gemstone that is similar to alexandrite. Zultanite ...

Earth's Magnetic Field Can Change 10 Times Faster Than Thought

earth, Earth's magnetic field 8:11 PM

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Scientists using simulations in the lab have revealed that changes in the direction of the Earth's magnetic field may take place 10 times faster than previously thought. 
 
A new study by the University of Leeds and University of California at San Diego reveals that changes in the direction of the Earth's magnetic field may take place 10 times faster than previously thought. 
 
Their study gives new insight into the swirling flow of iron 2800 kilometres below the planet's surface and how it has influenced the movement of the magnetic field during the past hundred thousand years. 
 
Our magnetic field is generated and maintained by a convective flow of molten metal that forms the Earth's outer core. Motion of the liquid iron creates the electric currents that power the field, which not only helps guide navigational systems but also helps shield us from harmful extra terrestrial radiation and hold our atmosphere in place. 
 
The magnetic field is constantly changing. Satellites now provide new means to measure and track its current shifts but the field existed long before the invention of human-made recording devices. To capture the evolution of the field back through geological time scientists analyse the magnetic fields recorded by sediments, lava flows and human-made artefacts. Accurately tracking the signal from Earth's core field is extremely challenging and so the rates of field change estimated by these types of analysis are still debated. 
 
Now, Dr Chris Davies, associate professor at Leeds and Professor Catherine Constable from the Scripps Institution of Oceanography, UC San Diego, in California have taken a different approach. They combined computer simulations of the field generation process with a recently published reconstruction of time variations in Earth's magnetic field spanning the last 100,000 years 
 
Their study, published in Nature Communications, shows that changes in the direction of Earth's magnetic field reached rates that are up to 10 times larger than the fastest currently reported variations of up to one degree per year. 
 
They demonstrate that these rapid changes are associated with local weakening of the magnetic field. This means these changes have generally occurred around times when the field has reversed polarity or during geomagnetic excursions when the dipole axis -- corresponding to field lines that emerge from one magnetic pole and converge at the other -- moves far from the locations of the North and South geographic poles. 
 
The clearest example of this in their study is a sharp change in the geomagnetic field direction of roughly 2.5 degrees per year 39,000 years ago. This shift was associated with a locally weak field strength, in a confined spatial region just off the west coast of Central America, and followed the global Laschamp excursion -- a short reversal of the Earth's magnetic field roughly 41,000 years ago. 
 
Similar events are identified in computer simulations of the field which can reveal many more details of their physical origin than the limited paleomagnetic reconstruction. 
 
Their detailed analysis indicates that the fastest directional changes are associated with movement of reversed flux patches across the surface of the liquid core. These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas. 
 
Dr Davies, from the School of Earth and Environment, said: "We have very incomplete knowledge of our magnetic field prior to 400 years ago. Since these rapid changes represent some of the more extreme behaviour of the liquid core they could give important information about the behaviour of Earth's deep interior." 
 
Professor Constable said: "Understanding whether computer simulations of the magnetic field accurately reflect the physical behaviour of the geomagnetic field as inferred from geological records can be very challenging. 
 
"But in this case we have been able to show excellent agreement in both the rates of change and general location of the most extreme events across a range of computer simulations. Further study of the evolving dynamics in these simulations offers a useful strategy for documenting how such rapid changes occur and whether they are also found during times of stable magnetic polarity like what we are experiencing today." 
 
 
The above story is based on <a href="http://www.leeds.ac.uk/news/article/4623/earths_magnetic_field_changes_faster_than_previously_thought" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://www.leeds.ac.uk/" rel="nofollow" target="_blank">University of Leeds</a>.</div>

Earth's Magnetic Field Can Change 10 Times Faster Than Thought

Scientists using simulations in the lab have revealed that changes in the direction of the Earth's magnetic field may take place ...

Dazzling Colors of 99-Million-Year-Old Insects Preserved in Amber

amber, Earth History 8:07 PM

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<tr><td class="tr-caption" style="text-align: center;">Diverse structural-colored insects in mid-Cretaceous amber from northern Myanmar. 
CREDIT: NIGPAS</td></tr>
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Nature is full of colors, from the radiant shine of a peacock's feathers or the bright warning coloration of toxic frogs to the pearl-white camouflage of polar bears. 
 
Usually, fine structural detail necessary for the conservation of color is rarely preserved in the fossil record, making most reconstructions of the fossil based on artists' imagination. 
 
A research team from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has now unlocked the secrets of true coloration in the 99-million-year-old insects. 
 
Colors offer many clues about the behaviour and ecology of animals. They function to keep organisms safe from predators, at the right temperature, or attractive to potential mates. Understanding the coloration of long-extinct animals can help us shed light on ecosystems in the deep geological past. 
 
The study, published in Proceedings of the Royal Society B on July 1, offers a new perspective on the often overlooked, but by no means dull, lives of insects that co-existed alongside dinosaurs in Cretaceous rainforests. 
 
Researchers gathered a treasure trove of 35 amber pieces with exquisitely preserved insects from an amber mine in northern Myanmar. 
 
"The amber is mid-Cretaceous, approximately 99 million years old, dating back to the golden age of dinosaurs. It is essentially resin produced by ancient coniferous trees that grew in a tropical rainforest environment. Animals and plants trapped in the thick resin got preserved, some with life-like fidelity," said Dr. CAI Chenyang, associate professor at NIGPAS who lead the study. 
 
The rare set of amber fossils includes cuckoo wasps with metallic bluish-green, yellowish-green, purplish-blue or green colors on the head, thorax, abdomen, and legs. In terms of color, they are almost the same as cuckoo wasps that live today, said Dr. CAI. 
 
The researchers also discovered blue and purple beetle specimens and a metallic dark-green soldier fly. "We have seen thousands of amber fossils but the preservation of color in these specimens is extraordinary," said Prof. HUANG Diying from NIGPAS, a co-author of the study. 
 
"The type of color preserved in the amber fossils is called structural color. It is caused by microscopic structure of the animal's surface. The surface nanostructure scatters light of specific wavelengths and produces very intense colors. This mechanism is responsible for many of the colors we know from our everyday lives," explained Prof. PAN Yanhong from NIGPAS, a specialist on palaeocolor reconstruction. 
 
To understand how and why color is preserved in some amber fossils but not in others, and whether the colors seen in fossils are the same as the ones insects paraded more than 99 million years ago, the researchers used a diamond knife blades to cut through the exoskeleton of two of the colorful amber wasps and a sample of normal dull cuticle. 
 
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<tr><td class="tr-caption" style="text-align: center;">Diverse structural-colored insects in mid-Cretaceous amber from northern Myanmar. 
CREDIT: NIGPAS</td></tr>
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Using electron microscopy, they were able to show that colorful amber fossils have a well-preserved exoskeleton nanostructure that scatters light. The unaltered nanostructure of colored insects suggested that the colors preserved in amber may be the same as the ones displayed by them in the Cretaceous. But in fossils that do not preserve color, the cuticular structures are badly damaged, explaining their brown-black appearance. 
 
What kind of information can we learn about the lives of ancient insects from their color? Extant cuckoo wasps are, as their name suggests, parasites that lay their eggs into the nests of unrelated bees and wasps. Structural coloration has been shown to serve as camouflage in insects, and so it is probable that the color of Cretaceous cuckoo wasps represented an adaptation to avoid detection. "At the moment we also cannot rule out the possibility that the colors played other roles besides camouflage, such as thermoregulation," adds Dr. CAI. 
 
 
 
The above story is based on <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2020.0301" rel="nofollow" target="_blank">materials </a>provided by <a href="http://english.cas.cn/" rel="nofollow" target="_blank">Chinese Academy of Sciences Headquarters.</a></div>

Dazzling Colors of 99-Million-Year-Old Insects Preserved in Amber

Diverse structural-colored insects in mid-Cretaceous amber from northern Myanmar. CREDIT: NIGPAS Nature is full of colors, from the ...

Asteroid Impact, Not Volcanic Activity, Killed the Dinosaurs, Study Finds

dinosaur, Earth History 8:06 PM

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Around 66 million years ago, an enormous asteroid smashed into the Earth off the coast of what is now Mexico in a catastrophic event that famously led to the demise of the non-avian dinosaurs. According to a first-of-its-kind study, this impact created the climatic conditions to wipe out nearly all viable dinosaur habitats. Modelling of the Chicxulub asteroid impact 66 million years ago shows it created a world largely unsuitable for dinosaurs to live in. The asteroid, which struck the Earth off the coast of Mexico at the end of the Cretaceous era 66 million years ago, has long been believed to be the cause of the demise of all dinosaur species except those that became birds. However, some researchers have suggested that tens of thousands of years of large volcanic eruptions may have been the actual cause of the extinction event, which also killed off almost 75% of life on Earth. Now, a research team from Imperial College London, the University of Bristol and University College London has shown that only the asteroid impact could have created conditions that were unfavourable for dinosaurs across the globe. They also show that the massive volcanism could also have helped life recover from the asteroid strike in the long term. Their results are published today in Proceedings of the National Academy of Sciences. Lead researcher Dr. Alessandro Chiarenza, who conducted this work whilst studying for his Ph.D. in the Department of Earth Science and Engineering at Imperial, said: "We show that the asteroid caused an impact winter for decades, and that these environmental effects decimated suitable environments for dinosaurs. In contrast, the effects of the intense volcanic eruptions were not strong enough to substantially disrupt global ecosystems. "Our study confirms, for the first time quantitatively, that the only plausible explanation for the extinction is the impact winter that eradicated dinosaur habitats worldwide." The asteroid strike would have released particles and gases high into the atmosphere, blocking out the Sun for years and causing permanent winters. Volcanic eruptions also produce particles and gases with Sun-blocking effects, and around the time of the mass extinction there were tens of thousands of years of eruptions at the Deccan Traps, in present-day India. To determine which factor, the asteroid or the volcanism, had more climate-changing power, researchers have traditionally used geological markers of climate and powerful mathematical models. In the new paper, the team combined these methods with information about what kinds of environmental factors, such as rainfall and temperature, each species of dinosaur needed to thrive. They were then able to map where these conditions would still exist in a world after either an asteroid strike or massive volcanism. They found that only the asteroid strike wiped out all potential dinosaur habitats, while volcanism left some viable regions around the equator. Co-lead author of the study Dr. Alex Farnsworth, from the University of Bristol, said: "Instead of only using the geologic record to model the effect on climate that the asteroid or volcanism might have caused worldwide, we pushed this approach a step forward, adding an ecological dimension to the study to reveal how these climatic fluctuations severely affected ecosystems." Co-author Dr. Philip Mannion, from University College London, added: "In this study we add a modelling approach to key geological and climate data that shows the devastating effect of the asteroid impact on global habitats. Essentially, it produces a blue screen of death for dinosaurs." Although volcanoes release Sun-blocking gases and particles, they also release carbon dioxide, a greenhouse gas. In the short term after an eruption, the Sun-blockers have a larger effect, causing a 'volcanic winter'. However, in the longer term these particles and gases drop out of the atmosphere, while carbon dioxide stays around and builds up, warming the planet. After the initial drastic global winter caused by the asteroid, the team's model suggests that in the longer term, volcanic warming could have helped restore many habitats, helping new life that evolved after the disaster to thrive. Dr. Chiarenza said: "We provide new evidence to suggest that the volcanic eruptions happening around the same time might have reduced the effects on the environment caused by the impact, particularly in quickening the rise of temperatures after the impact winter. This volcanic-induced warming helped boost the survival and recovery of the animals and plants that made through the extinction, with many groups expanding in its immediate aftermath, including birds and mammals." 
 
The above story is based on <a href="https://www.pnas.org/content/early/2020/06/23/2006087117" rel="nofollow" target="_blank">materials </a>provided by  <a href="https://www.imperial.ac.uk/" rel="nofollow" target="_blank">Imperial College London.</a></div>

Asteroid Impact, Not Volcanic Activity, Killed the Dinosaurs, Study Finds

Around 66 million years ago, an enormous asteroid smashed into the Earth off the coast of what is now Mexico in a catastrophic event th...

A Billion Years Missing From Geologic Record

Earth History, Geology 7:40 PM

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<tr><td class="tr-caption" style="text-align: center;">A hiker walks along a road near Manitou Springs, Colorado, where an exposed outcrop shows a feature known as the “Great Unconformity.”Credit: Rebecca Flowers</td></tr>
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The geologic record is exactly that: a record. The strata of rock tell scientists about past environments, much like pages in an encyclopedia. Except this reference book has more pages missing than it has remaining. So geologists are tasked not only with understanding what is there, but also with figuring out what's not, and where it went. One omission in particular has puzzled scientists for well over a century. First noticed by John Wesley Powell in 1869 in the layers of the Grand Canyon, the Great Unconformity, as it's known, accounts for more than one billion years of missing rock in certain places. Scientists have developed several hypotheses to explain how, and when, this staggering amount of material may have been eroded. Now, UC Santa Barbara geologist Francis Macdonald and his colleagues at the University of Colorado, Boulder and at Colorado College believe they may have ruled out one of the more popular of these. Their study appears in the Proceedings of the National Academy of Sciences. "There are unconformities all through the rock record," explained Macdonald, a professor in the Department of Earth Science. "Unconformities are just gaps in time within the rock record. This one's called the Great Unconformity because it was thought to be a particularly large gap, maybe a global gap." A leading thought is that glaciers scoured away kilometers of rock around 720 to 635 million years ago, during a time known as Snowball Earth, when the planet was completely covered by ice. This hypothesis even has the benefit of helping to explain the rapid emergence of complex organisms shortly thereafter, in the Cambrian explosion, since all this eroded material could have seeded the oceans with tremendous amounts of nutrients. Macdonald was skeptical of this reasoning. Although analogues of the Great Unconformity appear throughout the world -- with similar amounts of rock missing from similar stretches of time -- they don't line up perfectly. This casts doubt as to whether they were truly eroded by a global event like Snowball Earth. Part of the challenge of investigating the Great Unconformity is that it happened so long ago, and the Earth is a messy system. "These rocks have been buried and eroded multiple times through their history," Macdonald said. Fortunately, the team was able to test this hypothesis using a technique called thermochronology. A few kilometers below the Earth's surface, the temperature begins to rise as you get closer to the planet's hot mantle. This creates a temperature gradient of roughly 50 degrees Celsius for every kilometer of depth. And this temperature regime can become imprinted in certain minerals. As certain radioactive elements in rocks break down, Helium-4 is produced. In fact helium is constantly being generated, but the fraction retained in different minerals is a function of temperature. As a result, scientists can use the ratio of helium to thorium and uranium in certain minerals as a paleo-thermometer. This phenomenon enabled Macdonald and his coauthors to track how rock moved in the crust as it was buried and eroded through the ages. "These unconformities are forming again and again through tectonic processes," Macdonald said. "What's really new is we can now access this much older history." The team took samples from granite just below the boundary of the Great Unconformity at Pikes Peak in Colorado. They extracted grains of a particularly resilient mineral, zircon, from the stone and analyzed the radio nucleotides of helium contained inside. The technique revealed that several kilometers of rock had been eroded from above this granite between 1,000 and 720 million years ago. Importantly, this stretch of time definitively came before the Snowball Earth episodes. In fact, it lines up much better with the periods in which the supercontinent Rodinia was forming and breaking apart. This offers a clue to the processes that may have stricken these years from the geologic record. "The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents," Macdonald said. The Earth's cycle of supercontinent formation and separation uplifts and erodes incredible extents of rock over long periods of time. And because supercontinent processes, by definition, involve a lot of land, their effects can appear fairly synchronous across the geologic record. However, these processes don't happen simultaneously, as they would in a global event like Snowball Earth. "It's a messy process," Macdonald said. "There are differences, and now we have the ability to perhaps resolve those differences and pull that record out." While Macdonald's results are consistent with a tectonic origin for these great unconformities, they don't end the debate. Geologists will need to complement this work with similar studies in other regions of the world in order to better constrain these events. The mystery of the Great Unconformity is inherently tied to two of geology's other great enigmas: the rise and fall of Snowball Earth and the sudden emergence of complex life in the Ediacaran and Cambrian. Progress in any one could help researchers finally crack the lot. "The Cambrian explosion was Darwin's dilemma," Macdonald remarked. "This is a 200-year old question. If we can solve that, we would definitely be rock stars." 
 
 The above story is based on <a href="https://www.news.ucsb.edu/2020/019892/great-unconformity" rel="nofollow" target="_blank">Materials</a> provided by <a href="http://www.ucsb.edu/" rel="nofollow" target="_blank">University of California - Santa Barbara</a>. Original written by Harrison Tasoff. <span style="-webkit-text-stroke-width: 0px; background-color: white; color: #333333; display: inline !important; float: none; font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 14px; font-style: normal; font-variant-caps: normal; font-variant-ligatures: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-decoration-color: initial; text-decoration-style: initial; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px;"> </div>

A Billion Years Missing From Geologic Record

A hiker walks along a road near Manitou Springs, Colorado, where an exposed outcrop shows a feature known as the “Great Unconformity.”Cre...

Geochemists Solve Mystery of Earth's Vanishing Crust

earth, Geochemistry, Geology 6:52 PM

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<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-7Fvk82aIAXM/XvdqrV5-UtI/AAAAAAAASWU/XEiPprha9h44Yx3Uxw5WU5B2d4NGdsxoQCLcBGAsYHQ/s1600/RecycledCrust_withlabels_WEB-1%2B%25281%2529.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img alt="Geochemists Solve Mystery of Earth's Vanishing Crust" border="0" data-original-height="798" data-original-width="1197" height="425" src="https://1.bp.blogspot.com/-7Fvk82aIAXM/XvdqrV5-UtI/AAAAAAAASWU/XEiPprha9h44Yx3Uxw5WU5B2d4NGdsxoQCLcBGAsYHQ/s640/RecycledCrust_withlabels_WEB-1%2B%25281%2529.jpg" title="" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Recycled ancient crust returns to the oceanic ridges. Credit: Caroline McNiel/National MagLab </td></tr>
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Thank goodness for the Earth's crust: It is, after all, that solid, outermost layer of our planet that supports everything above it. But much of what happens below that layer remains a mystery, including the fate of sections of crust that vanish back into the Earth. Now, a team of geochemists based at the Florida State University-headquartered National High Magnetic Field Laboratory has uncovered key clues about where those rocks have been hiding. The researchers provided fresh evidence that, while most of the Earth's crust is relatively new, a small percentage is actually made up of ancient chunks that had sunk long ago back into the mantle then later resurfaced. They also found, based on the amount of that "recycled" crust, that the planet has been churning out crust consistently since its formation 4.5 billion years ago—a picture that contradicts prevailing theories. "Like salmon returning to their spawning grounds, some oceanic crust returns to its breeding ground, the volcanic ridges where fresh crust is born," said co-author Munir Humayun, a MagLab geochemist and professor at Florida State's Department of Earth, Ocean and Atmospheric Science (EOAS). "We used a new technique to show that this process is essentially a closed loop, and that recycled crust is distributed unevenly along ridges." In addition to Humayun, the research team included MagLab postdoctoral researcher Shuying Yang, lead author on the paper, and MagLab Geochemistry Group Director and EOAS Chair Vincent Salters. The Earth's oceanic crust is formed when mantle rock melts near fissures between tectonic plates along undersea volcanic ridges, yielding basalt. As new crust is made, it pushes the older crust away from the ridge toward continents, like a super slow conveyer belt. Eventually, it reaches areas called subduction zones, where it is forced under another plate and swallowed back into the Earth. Scientists have long theorized about what happens to subducted crust after being reabsorbed into the hot, high-pressure environment of the planet's mantle. It might sink deeper into the mantle and settle there, or rise back to the surface in plumes, or swirl through the mantle, like strands of chocolate through a yellow marble cake. Some of that "chocolate" might eventually rise up, re-melt at mid-ocean ridges, and form new rock for yet another millions-year-long tour of duty on the sea floor. This new evidence supports the "marble cake" theory. Scientists had already seen clues supporting the theory. Some basalts collected from mid-ocean ridges, called enriched basalts, have a higher percentage of certain elements that tend to seep from the mantle into the melt from which basalt is formed; others, called depleted basalts, had much lower levels. To shed more light on the mystery of the disappearing crust, the team chemically analyzed 500 samples of basalt collected from 30 regions of ocean ridges. Some were enriched, some were depleted and some were in between. Early on, the team discovered that the relative proportions of germanium and silicon were lower in melts of recycled crust than in the "virgin" basalt emerging from melted mantle rock. So they developed a new technique that used that ratio to identify a distinct chemical fingerprint for subducted crust. They devised a precise method of measuring that ratio using a mass spectrometer at the MagLab. Then they crunched the numbers to see how these ratios differed among the 30 regions sampled, expecting to see variations that would shed light on their origins. At first the analysis revealed nothing of note. Concerned, Yang, a doctoral candidate at the time, consulted with her adviser. Humayun suggested looking at the problem from a wider angle: Rather than compare basalts of different regions, they could compare enriched and depleted basalts. After quickly re-crunching the data, Yang was thrilled to see clear differences among those groups of basalts. "I was very happy," recalled Yang, lead author on the paper. "I thought, 'I will be able to graduate!'" The team had detected lower germanium-to-silicon ratios in enriched basalts—the chemical fingerprint for recycled crust—across all the regions they sampled, pointing to its marble cake-like spread throughout the mantle. Essentially, they solved the mystery of the vanishing crust. It was a lesson in missing the forest for the trees, Humayun said. "Sometimes you're looking too closely, with your nose in the data, and you can't see the patterns," he said. "Then you step back and you go, 'Whoa!'" Digging deeper into the patterns they found, the scientists unearthed more secrets. Based on the amounts of enriched basalts detected on global mid-ocean ridges, the team was able to calculate that about 5 to 6 percent of the Earth's mantle is made of recycled crust, a figure that sheds new light on the planet's history as a crust factory. Scientists had known the Earth cranks out crust at the rate of a few inches a year. But has it done so consistently throughout its entire history? Their analysis, Humayun said, indicates that, "The rates of crust formation can't have been radically different from what they are today, which is not what anybody expected." 
 
 The above story is based on <a href="https://news.fsu.edu/news/science-technology/2020/06/26/fsu-maglab-geochemists-solve-mystery-of-earths-vanishing-crust/" rel="nofollow" target="_blank">materials </a>provided by <a href="https://news.fsu.edu/" rel="nofollow" target="_blank">Florida State University.</a></div>

Geochemists Solve Mystery of Earth's Vanishing Crust

Recycled ancient crust returns to the oceanic ridges. Credit: Caroline McNiel/National MagLab Thank goodness for the Earth's crus...

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Tanzanian Miner Finds World's Biggest Gemstone Worth $3.3 Million

famous, Mining 8:52 PM

Tanzanian Miner Finds World's Biggest Gemstone Worth $3.3 Million

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