Researchers at Woods Hole Oceanographic Institution (WHOI), the University of California Los Angeles (UCLA) and their colleagues used a new geochemical tool to shed light on the origin of nitrogen and other volatile elements on Earth, which may also prove useful as a way to monitor the activity of volcanoes. Their findings were published April 16, 2020, in the journal Nature.
Nitrogen is the most abundant gas in the atmosphere, and is the primary component of the air we breathe. Nitrogen is also found in rocks, including those tucked deep within the planet’s interior. Until now, it was difficult to distinguish between nitrogen sources coming from air and those coming from inside the Earth’s mantle when measuring gases from volcanoes.
“We found that air contamination was masking the pristine ‘source signature’ of many volcanic gas samples,” says WHOI geochemist Peter Barry, a coauthor of the study.
Without that distinction, scientists weren’t able to answer basic questions like: Is nitrogen left over from Earth’s formation or was it delivered to the planet later on? How is nitrogen from the atmosphere related to nitrogen coming out of volcanoes?
Barry and lead author Jabrane Labidi of UCLA, now a researcher at Institut de Physique du Globe de Paris, worked in partnership with international geochemists to analyze volcanic gas samples from around the globe — including gases from Iceland and Yellowstone National Park — using a new method of analyzing “clumped” nitrogen isotopes. This method provided a unique way to identify molecules of nitrogen that come from air, which allowed the researchers to see the true gas compositions deep within Earth’s mantle. This ultimately revealed evidence that nitrogen in the mantle has most likely been there since our planet initially formed.
“Once air contamination is accounted for, we gained new and valuable insights into the origin of nitrogen and the evolution of our planet,” Barry says.
While this new method helps scientists understand the origins of volatile elements on Earth, it may also prove useful as a way of monitoring the activity of volcanoes. This is because the composition of gases bellowing from volcanic centers change prior to eruptions. It could be that the mix of mantle and air nitrogen could one day be used as a signal of eruptions.
This study was supported by the Deep Carbon Observatory and the Alfred P. Sloan Foundation. The research team also included colleagues David Bekaert and Mark Kurz from WHOI, scientists from several other U.S.-based universities, and from France, Canada, Italy, the United Kingdom and Iceland.
Reference:
J. Labidi, P. H. Barry, D. V. Bekaert, M. W. Broadley, B. Marty, T. Giunta, O. Warr, B. Sherwood Lollar, T. P. Fischer, G. Avice, A. Caracausi, C. J. Ballentine, S. A. Halldórsson, A. Stefánsson, M. D. Kurz, I. E. Kohl, E. D. Young. Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen. Nature, 2020; 580 (7803): 367 DOI: 10.1038/s41586-020-2173-4
A new study finds volcanic activity played a direct role in triggering extreme climate change at the end of the Triassic period 201 million year ago, wiping out almost half of all existing species. The amount of carbon dioxide released into the atmosphere from these volcanic eruptions is comparable to the amount of CO2 expected to be produced by all human activity in the 21st century.
The end-Triassic extinction has long been thought to have been caused by dramatic climate change and rising sea levels. While there was large-scale volcanic activity at the time, known as the Central Atlantic Magmatic Province eruptions, the role it played in directly contributing to the extinction event is debated. In a study for Nature Communications, an international team of researchers, including McGill professor Don Baker, found evidence of bubbles of carbon dioxide trapped in volcanic rocks dating to the end of the Triassic, supporting the theory that volcanic activity contributed to the devastating climate change believed to cause the mass extinction.
The researchers suggest that the end-Triassic environmental changes driven by volcanic carbon dioxide emissions may have been similar to those predicted for the near future. By analysing tiny gas exsolution bubbles preserved within the rocks, the team estimates that the amount of carbon emissions released in a single eruption — comparable to 100,000 km3 of lava spewed over 500 years — is likely equivalent to the total produced by all human activity during the 21st century, assuming a 2C rise in global temperature above pre-industrial levels.
“Although we cannot precisely determine the total amount of carbon dioxide released into the atmosphere when these volcanoes erupted, the correlation between this natural injection of carbon dioxide and the end-Triassic extinction should be a warning to us. Even a slight possibility that the carbon dioxide we are now putting into the atmosphere could cause a major extinction event is enough to make me worried,” says professor of earth and planetary sciences Don Baker.
Reference:
Manfredo Capriolo, Andrea Marzoli, László E. Aradi, Sara Callegaro, Jacopo Dal Corso, Robert J. Newton, Benjamin J. W. Mills, Paul B. Wignall, Omar Bartoli, Don R. Baker, Nasrrddine Youbi, Laurent Remusat, Richard Spiess, Csaba Szabó. Deep CO2 in the end-Triassic Central Atlantic Magmatic Province. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-15325-6
Texas is a huge state with incredibly diverse geographical features, from sandy beaches and lush hill country to dry, scrubby desert. In all of Texas there are a wide range of gems and minerals and fossils. Remember that there are almost no public lands in Texas, so permission for gems to be excavated on private lands is necessary. Some digging sites require you to pay a day’s cost for digging different gems and minerals.
Where are Rare Gems & Minerals found in Texas?
Amber
Rich brown to yellowish amber has been found near Eagle Pass, Maverick County, in Cretaceous coal and on Terlingua Creek, Brewster County. Although much of this material is translucent and the quality suitable for lapidary purposes, the pieces are seldom more than a fraction of an inch in diameter.
Occasional finds of poor quality brownish amber have been reported from the
Tertiary formations of the Gulf Coastal Plain, but thus far no gem quality material has been found.
The softness of amber limits its use to brooches, necklaces,and other jewelry that is relatively safe from abrasion.
Augite
Augite of gem quality occurs near Eagle Flat, Hudspeth County, Texas. Although this material is very dark greenish brown and not commonly thought of as a gemstone, lapidaries have used it to fashion black faceted stones and cabochons that resemble obsidian. Most of the augite occurs as loose pieces and crystal fragments that have weathered out of nearby igneous rocks; the augite can also be found in situ in the igneous rocks.
Specimen sand pieces of cutting quality 1 inch in diameter are common, and fragments over 2 inches in diameter have been found. The augite is associated with black spinel and some dark gray to black pieces of natural glass. Although the faceted and cabochon-cut stones are not particularly attractive, some of the larger pieces of augite might be utilized for carving.
Beryl
Beryl crystals have been found in pegmatite dikes in Llano, Blanco, and Gillespie counties. These crystals are commonly several inches long and exceed 1 inch in diameter but are very badly fractured. Most of the beryl crystals do not approach gem quality and are entirely unsuitable for any lapidary use. The color of the crystals found thus far is bluish,greenish, pinkish brown, yellowish, and colorless. Some very tiny colorless beryl crystals have been found that are transparent,but thus far such crystals have been too small to be cut into gems.
Fine blue beryl crystals have been found in the Franklin Mountains near El Paso, Texas. Unfortunately, these crystals are so badly flawed and fractured that they are not suitable for lapidary use.
It seems likely that careful prospecting of Texas pegmatites will reveal at least some gem-quality beryl.
Celestite
Celestite is very seldom cut into gems. Being very soft, brittle, and having three cleavages, celestite is completely unsuitable for jewelry. These same properties make this mineral exceedingly difficult to facet; however, faceted stones are seen in large collections.
Fine crystals of colorless and blue gem quality celestite have been found at Mount Bonnell and other localities west of Austin, Travis County. The celestite crystals occur in vugs or geodes in limestone. The crystals are mostly white or colorless and fractured near the base or where attached, but the tips of the crystals are commonly clear celestine blue and completely free of flaws.
Crystals several inches in length have been found, but the average size is about 1 inch. The smaller crystals are frequently more transparent and consequently better suited for cutting. It is very difficult to obtain crystals that will allow the cutting of flaw less stones of more than 4 or 5 carats.
Bluish and colorless celestite of gem quality and fine crystals have been found near Lampasas, Lampasas County, and near Brown wood, Brown County, but neither of these localities has been very productive of good gem material.
Celestite geodes have been found in parts of Coke, Fisher,and Nolan counties, but these geodes contain little gem material.
Diamond
There is only one well-authenticated find of diamond in Texas. A small brownish diamond was found in1911on section 64, block 44, Foard County. The exact weight of the stone has not been recorded, but one authority estimated that it was of sufficient size and clarity to yield a cut stone of about one-quarter carat.
The only diamond-bearing rocks known in the United States are in Pike County, Arkansas. Although many other diamonds have been found in the United States, all were loose in gravels or streams except for some stones at the Arkansas locality. The fact that one diamond was found in Foard County does not mean that the prospects of finding more diamonds in Texas are much better there than anywhere else in the State. It is highly unlikely that more than a very few diamonds will ever be found in Texas, and any stones that may be found in the future are likely to be widely scattered.
Epidote
Llano County has furnished some green and brownish-green epidote that is suitable for cutting into cabochons. Most of the material that approaches gem quality has come from contact metamorphic zones and is associated with garnet,quartz,and some scheelite. Some small cavities in the rocks contain tiny transparent crystals of gem quality, but the largest obtainable flaw less faceted stones would probably be less than 15 points.
Faceted stones of epidote are sometimes known as pistacite owing to their common pistachio-green color.
Fluorite
Very fine green, transparent fluorite has been found near Voca, Mason County.The fluorite occurs as vug fillings in pegmatites, associated with crystals of pink microcline and colorless quartz. Most of the vugs have been completely filled by the fluorite; therefore, crystals of the fluorite are not too common. Masses of fluorite several pounds in weight, rich green, and quite transparent have been found near Voca. Transparent pieces an inch or more in diameter are common.
Fluorite is much too soft for everyday use in jewelry and because of the low refractive index does not yield brilliant faceted stones. The perfect four-directional cleavage, relative softness, and brittle tenacity of the mineral make it difficult to facet. Faceted stones are seldom seen outrside of collections. Cabochons are also difficult to cut from this material, but the rich color obtained is ample reward for the time and care necessary in cutting.
Fluorite occurs at several other localities in Texas, notably in Hudspeth, Brewster, Presidio, Llano, and Burnet counties, but not commonly in gem quality or colors that warrant its use as gem material.
Gadolinite
Gadolinite as a cut gemis not seen outside of large collections; however, it can be faceted into black opaque stones of little beauty but of great interest to collectors. The best known locality of this mineral in the United States is Baringer Hill,Llano County, Texas. Unfortunately, this locality was completely flooded by the completion of Buchanan Dam in 1938. Masses and rough crystals of gadolinite weighing over 100 pounds were mined from this locality.
The gadolinite occurred in a large, very coarse-grained pegmatite dike associated with quartz, microcline, and fluorite, as well as allanite, fergusonite, nivenite, cyrtolite, thorogummite, and various other rare minerals. Some of the minerals in the dike occurred in very large masses. One quartz mass over 40 feet in diameter was noted,and microcline masses up to 30 feet in diameter were not uncommon. Much of the gadolinite was used by industrial firms as a source of thorium compounds, although some specimen and gem material found its way into museums and private collections. Because the locality was worked mostly from 1910 to about 1925 and because since 1938 the waters of Lake Buchanan have completely flooded the entire area, material from this locality is now exceedingly difficult to obtain. The collection of the Smithsonian Institution, Washington, D.C., contains a cut and polished gem of Baringer Hill gadolinite that weighs 8.6 carats.
Garnet
The garnet group of minerals is variable in composition. Listed below are the pure members of this group, but garnets found in nature are usually a mixture of two or more of these end members.
Good crystals of gem-quality almandite garnet have been found in Llano, Blanco, Burnet, and Gillespie counties. In southeast Llano County, northwest Blanco County, and northeast Gillespie County, the stones mostly occur in stream gravels where they have collected after being weathered out of compact mica schists.
Owing to the fact that most of the garnets have not been transported very far from their source, the stones commonly show good crystal form. All of the garnets from one locality commonly do not have exactly the same crystal form. The garnets are mostly widely scattered in the stream gravels but can be found concentrated behind rocks and on small gravel bars.
Many of the crystals are less than one eighth inch in diameter; however, good crystals one-fourth to one-half inch in diameter are common.Most of the stones are too fractured or have too many inclusions to yield gems,but many transparent stones have been found. The transparent crystals usually yield flawless deep red faceted stones of 2 carats or less. Some of the stones that contain too many inclusions to facet are cut as cabochons and are then often known as carbuncle.
Small garnet fragments have been found in streams and in gneisses and pegmatites near Castell, Llano County, but they are not commonly of gem quality.
Occasional small gem-quality garnets have been found in pegmatites and contact metamorphic zones in Burnet County. Garnets have also been found in several other counties, notably Mason, El Paso, Hudspeth, and Culberson, but no stones of facet quality have been reported.
Labradorite
Very fine facet-quality labradorite has been found about 20 miles south of Alpine, Brewster County. The labradorite occurs loose in the soil as slightly weathered or frosted cleavage fragments, commonly showing one or more crystal faces. The pale-yellow or straw-yellow color of these fragments, as well as their lack of internal imperfections, makes these stones excellent gem material. Individual pieces that exceed three-fourths inch in their longest dimensions are rare. Cut stones of more than 5 or 6 carats from this locality are scarce. The source of this material is uncertain, but it is probably weathering out of an underlying igneous rock.
Microcline
Very fine crystals of blue microcline have been found east of Packsaddle Mountain and near Kings land in Llano County. Crystals exceeding 1foot in length have been found,although most are only a few inches long. The color of the microcline is mostly pale blue, but some crystals are darker. Microcline crystals associated with milky or vein quartz, smoky quartz, some biotite, and rarely cassiterite occur in pegmatite dikes which vary in size from a few inches to several feet in thickness.
The color of this microcline is pale in comparison to microcline from someother localities in the United States, but the Texas blue microcline does yield pleasing cabochons. Perfect crystals of this material are prized by collectors. Blue or greenish microcline is often called amazonite or amazon stone.
Bluish microcline associated with quartz and topaz has also been reported near Katemcy, Mason County.
Red microcline is common in several central Texas counties and is a primary constituent of many of the igneous rocks in those counties. Large crystals of perthitic red microcline occur in pegmatite dikes of Mason,Llano, Burnet,and Gillespie counties. Any feldspar quarry or other pegmatite mining operation in anyof these counties is likely to containlarge red microcline crystals and fragments. Unfortunately, the good crystals that may have been present are often shattered by blasting during quarrying operations.
Obsidian
Gem-quality black and dark-gray obsidian has been found in Presidio County associated with extrusive igneous rocks. The obsidian in this area is too opaque to serve as attractive faceted stones but is found in pieces of sufficient size and quality to yield nice cabochons. Some of the small weathered pieces of this material resemble tektite in out ward appearance; in fact, the “valverdites” mistaken originally for tektites are pebbles of weathered obsidian in terrace gravel of Val Verde County. Obsidian takes a high polish but is very sensitive to heat. Stones that are slightly over heated during grinding or sanding will quickly shatter. Obsidian of gem quality has been reported also in Brewster County.
Opal
Opal other than as fossil or opalized wood occurs at the following several localities in Texas. Approximately 16 miles southof Alpine, Brewster County, precious opal occurs in very small seams and as cavity fillings in very hard pinkish-brown rhyolite. This opal is milky or bluish and commonly exhibits small flashes of blue, green,red, and orange fire. Individual pieces of this opal are mostly quite small, rarely over one fourth inch in diameter, and very difficult to remove from the tough rhyolite matrix.
Pearl
Pearls are the result of the secretion of calcium carbonate by various shellfish around sand grains, parasitic organisms, shell fragments, or other foreign objects that have in some way entered the body cavity of the shellfish. Since the shellfish is unable to expel these irritating particles or organisms, it deposits successive layers of calcium carbonate around the foreign substance to make it smoother and less irritating. Although pearls are principally calcium carbonate, they also contain small amounts of an organic substance, called conchiolin,and water.Pearls are found in shellfish that live in either fresh or salt water
Quartz
The quartz family gemstones can be divided into two groups for purposes of description. The first group is the crystalline varieties,or those quartz varieties that commonly occur in distinct crystals. The second group is the cryptocrystalline varieties, or those quartz varieties that occur as irregular masses that are composed of many microscopic crystals. The crystalline varieties are usually much more transparent and are most often seen as faceted stones. The cryptocrystalline varieties vary from sub-transparent to opaque and are almost always cut as cabochrons.
Topaz
In central Texas, in the Llano River area, particularly near the city of Mason and in the hills of Mason County, many exceptional specimens of blue topaz are found.
The few areas where blue topaz takes place in Texas are private, but you can check for topace specimens for a small cost at several fee digging locations. The Lindsay Ranch, Seaquist Ranch and Bar M Ranch are among the most famous locations.
Topaz screens are usually available at prices between $15 and $25 a day.
The colorless crystals and light-blue shades of topaz are found. Most crystals are small, but over the years some of the better sites have recovered big, quality pieces.
Amethyst
The Amethyst Mountains are known to have a deposit of the crystal however the amount or quality of the amethyst found there has not been recorded. The name of the mountain was suggested by the Geological department of the United States after an expedition to its summit as amethyst was found there.
Chalcedony
Two forms of chalcedony or cryptocrystalline formations are agate and jasper. In Brewster County, near the western town of Alpine, is available Moss agate that looks like a blue cheese, red and black agate. In the western central county of San Saba, in San McCulloch, and the north panhandle of the Moore County jasper, the shape of the jasper is typically red, green, yellow or gray.
Reference:
Texas Gemstones By Elbert A.King, Jr., The University of Texas at Austin, Austin,Texas.
Some of the world’s oldest known dinosaur eggs and embryos. The clutch of Massospondylus carinatus eggs discovered in 1976 in Golden Gate Highland National Park, South Africa. Credit: Brett Eloff
An international team of scientists led by the University of the Witwatersrand in South Africa, has been able to reconstruct, in the smallest details, the skulls of some of the world’s oldest known dinosaur embryos in 3D, using powerful and non-destructive synchrotron techniques at the ESRF, the European Synchrotron in France. They found that the skulls develop in the same order as those of today’s crocodiles, chickens, turtles and lizards. The findings are published today in Scientific Reports.
University of the Witwatersrand scientists publish 3D reconstructions of the ~2cm-long skulls of some of the world’s oldest dinosaur embryos in an article in Scientific Reports. The embryos, found in 1976 in Golden Gate Highlands National Park (Free State Province, South Africa) belong to South Africa’s iconic dinosaur Massospondylus carinatus, a 5-meter long herbivore that nested in the Free State region 200 million years ago.
The scientific usefulness of the embryos was previously limited by their extremely fragile nature and tiny size. In 2015, scientists Kimi Chapelle and Jonah Choiniere, from the University of Witwatersrand, brought them to the European Synchrotron (ESRF) in Grenoble, France for scanning. At the ESRF, an 844 metre-ring of electrons travelling at the speed of light emits high-powered X-ray beams that can be used to non-destructively scan matter, including fossils. The embryos were scanned at an unprecedented level of detail — at the resolution of an individual bone cell. With these data in hand, and after nearly 3 years of data processing at Wits’ laboratory, the team was able to reconstruct a 3D model of the baby dinosaur skull. “No lab CT scanner in the world can generate these kinds of data,” said Vincent Fernandez, one of the co-authors and scientist at the Natural History Museum in London (UK). “Only with a huge facility like the ESRF can we unlock the hidden potential of our most exciting fossils. This research is a great example of a global collaboration between Europe and the South African National Research Foundation,” he adds.
Up until now, it was believed that the embryos in those eggs had died just before hatching. However, during the study, lead author Chapelle noticed similarities with the developing embryos of living dinosaur relatives (crocodiles, chickens, turtles, and lizards). By comparing which bones of the skull were present at different stages of their embryonic development, Chapelle and co-authors can now show that the Massospondylus embryos were actually much younger than previously thought and were only at 60% through their incubation period.
The team also found that each embryo had two types of teeth preserved in its developing jaws. One set was made up of very simple triangular teeth that would have been resorbed or shed before hatching, just like geckos and crocodiles today. The second set were very similar to those of adults, and would be the ones that the embryos hatched with. “I was really surprised to find that these embryos not only had teeth, but had two types of teeth. The teeth are so tiny; they range from 0.4 to 0.7mm wide. That’s smaller than the tip of a toothpick!,” explains Chapelle.
The conclusion of this research is that dinosaurs developed in the egg just like their reptilian relatives, whose embryonic developmental pattern hasn’t changed in 200 million years. “It’s incredible that in more than 250 million years of reptile evolution, the way the skull develops in the egg remains more or less the same. Goes to show — you don’t mess with a good thing!,” concludes Jonah Choiniere, professor at the University of Witwatersrand and also co-author of the study.
The team hopes to apply their method to other dinosaur embryos to estimate their level of development. They will be looking at the rest of the skeleton of the Massospondylus embryos to see if it also shares similarities in development with today’s dinosaur relatives. The arms and legs of the Massospondylus embryos have already been used to show that hatchlings likely walked on two legs.
Main findings:
High powered X-rays were used to reconstruct the skulls of some of the world’s oldest known dinosaur embryos.
The skull could be seen in 3D at an unprecedented level of detail.
Dinosaur embryo skulls appear to develop in the same order as those of today’s crocodiles, chickens, turtles and lizards.
These dinosaur embryos appear to have been fossilised at approximately 60% through their incubation period. This is much earlier than previously thought.
The dinosaur embryos have two types of teeth that range in size from 0.4 to 0.7mm wide. One of these sets would have been shed or resorbed before hatching.
References:
Kimberley E. J. Chapelle, Vincent Fernandez, Jonah N. Choiniere. Conserved in-ovo cranial ossification sequences of extant saurians allow estimation of embryonic dinosaur developmental stages. Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-60292-z
Kimberley E. J. Chapelle, Roger B. J. Benson, Josef Stiegler, Alejandro Otero, Qi Zhao, Jonah N. Choiniere. A quantitative method for inferring locomotory shifts in amniotes during ontogeny, its application to dinosaurs and its bearing on the evolution of posture. Palaeontology, 2020; 63 (2): 229 DOI: 10.1111/pala.12451
Life restoration of Elessaurus gondwanoccidens, from the Sanga do Cabral Formation (Lower Triassic), Brazil. Credit: Márcio L. Castro
A new species of Triassic reptile from Brazil is a close cousin of a mysterious group called tanystropheids, according to a study published April 8, 2020 in the open-access journal PLOS ONE by Tiane De-Oliviera of the Federal University of Santa Maria, Brazil and colleagues.
After the Permian mass extinction, 250 million years ago, reptiles took over global ecosystems. Among the early groups to appear after this extinction event were the tanystropheids, a group of long-necked animals whose lifestyles are still mysterious, but who were nonetheless successful in the Triassic Period. However, the early evolution of this group is poorly understood, as their remains are very rare from the Early Triassic.
In this study, De-Oliviera and colleagues describe a new specimen of reptile from Early Triassic rocks of the Sanga do Cabral Formation in southern Brazil. Skeletal comparison indicates this specimen, known from remains of the hind leg, pelvis, and tail, is the closest known relative of tanystropheids. The researchers identified these remains as belonging to a new species, which they named Elessaurus gondwanoccidens. The name derives in part from the Elvish name (Elessar) of a character from Lord of the Rings also known as Aragorn or Strider, chosen as a reference to the fossil animal’s long legs.
Most tanystropheid fossils are found in Middle to Late Triassic rocks of Europe, Asia, and North America, and often in marine sediments. The presence of Elessaurus in continental deposits of Early Triassic South America suggests that the origins of this group may lie in the southern continents, and that their ancestors may have lived on land before later species adapted to aquatic life. A clearer view of the group’s origins will rely on more rare fossils from this early time in their evolution.
Reference:
Tiane M. De-Oliveira, Felipe L. Pinheiro, Átila Augusto Stock Da-Rosa, Sérgio Dias-Da-Silva, Leonardo Kerber. A new archosauromorph from South America provides insights on the early diversification of tanystropheids. PLOS ONE, 2020; 15 (4): e0230890 DOI: 10.1371/journal.pone.0230890
Note: The above post is reprinted from materials provided by PLOS.
The common name “coquí” describes various species of frogs in the genus Eleutherodactylus and is derived from two species’ distinctive chirping calls. The common coquí, Eleutherodactylus coquí, is the national symbol of Puerto Rico. Photo courtesy of Alberto Lopez Torres
The bright chirp of the coquí frog, the national symbol of Puerto Rico, has likely resounded through Caribbean forests for at least 29 million years.
A new study published in Biology Letters describes a fragmented arm bone from a frog in the genus Eleutherodactylus, also known as rain frogs or coquís. The fossil is the oldest record of frogs in the Caribbean and, fittingly, was discovered on the island where coquís are most beloved.
“It’s a national treasure,” said David Blackburn, Florida Museum curator of herpetology and the study’s lead author. “Not only is this the oldest evidence for a frog in the Caribbean, it also happens to be one of the frogs that are the pride of Puerto Rico and related to the large family Eleutherodactylidae, which includes Florida’s invasive greenhouse frogs.”
Jorge Velez-Juarbe, associate curator of marine mammals at the Natural History Museum of Los Angeles County, found the fossil on a river outcrop in the municipality of San Sebastian in northwestern Puerto Rico. Velez-Juarbe and his collaborators’ previous collecting efforts at the site uncovered fossil seeds, sea cows, side-necked turtles and the oldest remains of gharials and rodents in the Caribbean, dating to the early Oligocene Epoch, about 29 million years ago.
Still, “there have been many visits from which I have come out empty-handed over the last 14 years,” he said. “I’ve always kept my expectations not too high for this series of outcrops.”
On this trip in 2012, he combed the deposits for half a day without much luck when a small bone, partially exposed in the sediment, caught his eye. He examined it with his hand lens.
“At the moment, I couldn’t wrap my mind as to what it was,” Velez-Juarbe said. “Then once I got back home, cleaned around it with a needle to see it better and checked some references, I knew I had found the oldest frog in the Caribbean.”
The ancient coquí displaces an amber frog fossil discovered in the Dominican Republic in 1987 for the title of oldest Caribbean frog. While the amber fossil was originally estimated to be 40 million years old, scientists now date Dominican amber to about 20 million to 15 million years ago, Blackburn said.
Based on genetic data and family trees, scientists had hypothesized rain frogs lived in the Caribbean during the Oligocene, but lacked any fossil evidence. The small, lightweight bones of frogs often do not preserve well, especially when combined with the hot, humid climate of the tropics.
Matching a single bone fragment to a genus or species “is not always an easy process,” Velez-Juarbe said. It can also depend on finding the right expert. His quest for help identifying the fossil turned up empty until a 2017 visit to the Florida Museum where he had once been a postdoctoral researcher.
“I got to talk with Dave about projects, and the rest is now history,” he said.
Possibly first arriving in the Caribbean by rafting from South America, frogs in the genus Eleutherodactylus, which encompasses some 200 species, dominate the region today.
“This is the most diverse group by two orders of magnitude in the Caribbean,” Blackburn said. “They’ve diversified into all these different specialists with various forms and body sizes. Several invasive species also happen to be from this genus. All this raises the question of how they got to be this way.”
One partial arm bone may not tell the whole story of coquí evolution — but it’s a start.
“I am thrilled that, little by little, we are learning about the wildlife that lived in Puerto Rico 29-27 million years ago,” Velez-Juarbe said. “Finds like this help us unravel the origins of the animals we see in the Caribbean today.”
Reference:
David C. Blackburn, Rachel M. Keeffe, María C. Vallejo-Pareja, Jorge Vélez-Juarbe. The earliest record of Caribbean frogs: a fossil coquí from Puerto Rico. Biology Letters, 2020; 16 (4): 20190947 DOI: 10.1098/rsbl.2019.0947
These are figures from the Nature Geoscience groundwater aquifer paper. Credit: Wallis et al
Naturally occurring (geogenic) groundwater arsenic contamination is a problem of global significance, with noteworthy occurrences in large parts of the alluvial and deltaic aquifers in South and Southeast Asia. To address this problem tremendous research efforts have been dedicated over the last two decades to better understand the sources and distribution of arsenic-polluted groundwater. Now, an Australian team of scientists from Flinders University, CSIRO and the University of Western Australia, together with their colleagues at the Swiss Federal Institute of Aquatic Science and Technology (Eawag), have used computer modelling to integrate much of what has been learned over the years into computer simulations that mimic the complex interactions between groundwater flow, solute transport and geochemical reaction mechanisms. Such models are important to analyse field observations, to unravel which chemical and physical processes play a role, and to predict the behaviour of arsenic within aquifers — where and when pollution may occur in the future. The results of their study have now been published in the latest issue of Nature Geoscience.
Reconstructing the past to predict future arsenic behaviour
The research team selected a highly arsenic polluted site near Hanoi (Vietnam) to develop and test their computer model. In a first step they used the tiny concentrations of tritium that had entered the groundwater system from the atmosphere during the times of nuclear bomb testing, and its decay product helium, a noble gas, to reconstruct how fast and where the groundwater was moving over the last 5 decades. Once the model simulations were able to match the concentrations that were measured, additional complexity was added to the model in order to simulate how arsenic was mobilised and transported in the Holocene aquifer.
The river-groundwater interface acts as reaction hotspot
At the study site, changes in groundwater flow occurred over the past 50 years since the city of Hanoi markedly increased the extraction of groundwater to satisfy its steadily increasing water demand; this showed to be the main trigger for arsenic pollution in the aquifer. The computer modelling allowed the researchers to pinpoint the source of arsenic down to the river muds that are regularly deposited at the more slow-flowing zones of the Red River. The organic matter contained in those muds fuelled a biogeochemical reaction that led to the release of arsenic and its km-long transport into the aquifer underlying the Van Phuc village, a process that continues to this day. Employing their developed computer model in predictive mode the researchers were able to illustrate the interplay of four key factors on the evolution and longevity of arsenic release at surface water/groundwater interfaces, (i) the abundance of reactive organic matter; (ii) the abundance of iron oxides; (iii) the magnitude of groundwater flow; and (iv) river mud deposition rate.
Reference:
Ilka Wallis, Henning Prommer, Michael Berg, Adam J. Siade, Jing Sun, Rolf Kipfer. The river–groundwater interface as a hotspot for arsenic release. Nature Geoscience, 2020; DOI: 10.1038/s41561-020-0557-6
This visualization shows the magnetic field around Earth, or the magnetosphere. Earth’s magnetic field origins are still a mystery, a new MIT study finds. Credit: Greg Shirah and Tom Bridgman, The existence of a magnetic field beyond 3.5 billion years ago is still up for debateNASA/Goddard Space Flight Center Scientific Visualization Studio.
Microscopic minerals excavated from an ancient outcrop of Jack Hills, in Western Australia, have been the subject of intense geological study, as they seem to bear traces of the Earth’s magnetic field reaching as far back as 4.2 billion years ago. That’s almost 1 billion years earlier than when the magnetic field was previously thought to originate, and nearly back to the time when the planet itself was formed.
But as intriguing as this origin story may be, an MIT-led team has now found evidence to the contrary. In a paper published in Science Advances, the team examined the same type of crystals, called zircons, excavated from the same outcrop, and have concluded that zircons they collected are unreliable as recorders of ancient magnetic fields.
In other words, the jury is still out on whether the Earth’s magnetic field existed earlier than 3.5 billion years ago.
“There is no robust evidence of a magnetic field prior to 3.5 billion years ago, and even if there was a field, it will be very difficult to find evidence for it in Jack Hills zircons,” says Caue Borlina, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “It’s an important result in the sense that we know what not to look for anymore.”
Borlina is the paper’s first author, which also includes EAPS Professor Benjamin Weiss, Principal Research Scientist Eduardo Lima, and Research Scientist Jahandar Ramezan of MIT, along with others from Cambridge University, Harvard University, the University of California at Los Angeles, the University of Alabama, and Princeton University.
A field, stirred up
Earth’s magnetic field is thought to play an important role in making the planet habitable. Not only does a magnetic field set the direction of our compass needles, it also acts as a shield of sorts, deflecting away solar wind that might otherwise eat away at the atmosphere.
Scientists know that today the Earth’s magnetic field is powered by the solidification of the planet’s liquid iron core. The cooling and crystallization of the core stirs up the surrounding liquid iron, creating powerful electric currents that generate a magnetic field stretching far out into space. This magnetic field is known as the geodynamo.
Multiple lines of evidence have shown that the Earth’s magnetic field existed at least 3.5 billion years ago. However, the planet’s core is thought to have started solidifying just 1 billion years ago, meaning that the magnetic field must have been driven by some other mechanism prior to 1 billion years ago. Pinning down exactly when the magnetic field formed could help scientists figure out what generated it to begin with.
Borlina says the origin of Earth’s magnetic field could also illuminate the early conditions in which Earth’s first life forms took hold.
“In the Earth’s first billion years, between 4.4 billion and 3.5 billion years, that’s when life was emerging,” Borlina says. “Whether you have a magnetic field at that time has different implications for the environment in which life emerged on Earth. That’s the motivation for our work.”
“Can’t trust zircon”
Scientists have traditionally used minerals in ancient rocks to determine the orientation and intensity of Earth’s magnetic field back through time. As rocks form and cool, the electrons within individual grains can shift in the direction of the surrounding magnetic field. Once the rock cools past a certain temperature, known as the Curie temperature, the orientations of the electrons are set in stone, so to speak. Scientists can determine their age and use standard magnetometers to measure their orientation, to estimate the strength and orientation of the Earth’s magnetic field at a given point in time.
Since 2001, Weiss and his group have been studying the magnetization of the Jack Hills rocks and zircon grains, with the challenging goal of establishing whether they contain ancient records of the Earth’s magnetic field.
“The Jack Hills zircons are some of the most weakly magnetic objects studied in the history of paleomagnetism,” Weiss says. “Furthermore, these zircons include the oldest known Earth materials, meaning that there are many geological events that could have reset their magnetic records.”
In 2015, a separate research group that had also started studying the Jack Hills zircons argued that they found evidence of magnetic material in zircons that they dated to be 4.2 billion years old — the first evidence that Earth’s magnetic field may have existed prior to 3.5 billion years ago.
But Borlina notes that the team did not confirm whether the magnetic material they detected actually formed during or after the zircon crystal formed 4.2 billion years ago — a goal that he and his team took on for their new paper.
Borlina, Weiss, and their colleagues had collected rocks from the same Jack Hills outcrop, and from those samples, extracted 3,754 zircon grains, each around 150 micrometers long — about the width of a human hair. Using standard dating techniques, they determined the age of each zircon grain, which ranged from 1 billion to 4.2 billion years old.
Around 250 crystals were older than 3.5 billion years. The team isolated and imaged those samples, looking for signs of cracks or secondary materials, such as minerals that may have been deposited on or within the crystal after it had fully formed, and searched for evidence that they were significantly heated over the last few billion years since they formed. Of these 250, they identified just three zircons that were relatively free of such impurities and therefore could contain suitable magnetic records.
The team then carried out detailed experiments on these three zircons to determine what kinds of magnetic materials they might contain. They eventually determined that a magnetic mineral called magnetite was present in two of the three zircons. Using a high-resolution quantum diamond magnetometer, the team looked at cross-sections of each of the two zircons to map the location of the magnetite in each crystal.
They discovered magnetite lying along cracks or damaged zones within the zircons. Such cracks, Borlina says, are pathways that allow water and other elements inside the rock. Such cracks could have let in secondary magnetite that settled into the crystal much later than when the zircon originally formed. Either way, Borlina says the evidence is clear: These zircons cannot be used as a reliable recorder for Earth’s magnetic field.
“This is evidence we can’t trust these zircon measurements for the record of the Earth’s magnetic field,” Borlina says. “We’ve shown that, before 3.5 billion years ago, we still have no idea when Earth’s magnetic field started.”
Despite these new results, Weiss stresses that previous magnetic analyses of these zircons are still highly valuable.
“The team that reported the original zircon magnetic study deserves a lot of credit for trying to tackle this enormously challenging problem,” Weiss says. “As a result of all the work from both groups, we now understand much better how to study the magnetism of ancient geological materials. We now can begin to apply this knowledge to other mineral grains and to grains from other planetary bodies.”
This research was supported, in part, by NASA.
Reference:
Cauê S. Borlina, Benjamin P. Weiss, Eduardo A. Lima, Fengzai Tang, Richard J. M. Taylor, Joshua F. Einsle, Richard J. Harrison, Roger R. Fu, Elizabeth A. Bell, Ellen W. Alexander, Heather M. Kirkpatrick, Matthew M. Wielicki, T. Mark Harrison, Jahandar Ramezani and Adam C. Maloof. Reevaluating the evidence for a Hadean-Eoarchean dynamo. Science Advances, 2020 DOI: 10.1126/sciadv.aav9634
The ash plume from the Kilauea volcano on the big island of Hawaii was pictured May 12, 2018, from the International Space Station. Credit: NASA
Instead of looking up to the sky for bright bursts of fiery color, a research team spent Fourth of July 2018 peering down at fiery globs of molten lava from a sky-diving airplane. Bolted to their plane was a new NASA instrument designed to detect each time the volcano took a breath, as its caldera swelled and deflated.
The team flew multiple flights above the Kīlauea Volcano in Hawaii Volcanoes National Park from July 3 to 5, 2018, to demonstrate how a new instrument could pave the way for a future constellation of small satellites dedicated to monitoring impacts from volcanic activity, earthquakes and changes in land surfaces, said Lauren Wye, the principal investigator who led and recently concluded the instrument’s development at SRI International in Menlo Park, California.
A global map detailing land elevation changes over time can help scientists pinpoint ground motion before, during and following earthquakes and volcanic eruptions, and help identify impacts from floods and groundwater pumping. “The CubeSat Imaging Radar for Earth Sciences, or CIRES, can help decision-makers and emergency managers obtain observations sooner after a hazardous event so that they are better prepared to deal with disaster relief,” Wye said.
Although Kīlauea’s eruption impacted over 50 square miles of land, ground deformation, or a change in land elevation, is not always perceptible to the human eye. Highly specialized technology like Wye’s new instrument can pinpoint and record these changes.
CIRES is equipped with an S-band Interferometric Synthetic Aperture Radar (InSAR). The S-band radar is able to penetrate through vegetation and reach the ground. CIRES takes two radar images of a specific area from approximately the same position in space at two different times and then processes the two images to determine the difference between them.
The National Academies of Sciences, Engineering and Medicine’s 2017 Decadal Survey, “Thriving on Our Changing Planet: A Decadal Strategy for Earth Observations from Space,” recommends that NASA use InSAR measurements to help address the dynamics of earthquakes, volcanoes, landslides, glaciers, groundwater and Earth’s interior.
A constellation of small InSAR satellites could work in tandem with the NASA-ISRO SAR Mission (NISAR), which is NASA’s first dedicated InSAR satellite currently in development. Multiple small satellites could collect frequent data over rapidly evolving processes, like volcanic eruptions, earthquakes and landslides, adding to NISAR’s systematic global data.
Once upon a radar
Traditionally, researchers monitor ground deformation with on-the-ground sensors and the Global Positioning System (GPS). InSAR measurements are complementary to ground measurements and can often guide how ground sensors are installed. “InSAR data have revolutionized how we look at earthquakes and volcanoes,” Kyle Anderson, a geophysicist at the U.S. Geological Survey, said.
In orbit, a series of small InSAR satellites could peer down and record changes in ground deformation. “Volcanoes will often inflate with magma before they erupt,” Anderson said. Anderson worked with the CIRES team at Kīlauea. “Although it’s difficult to predict how big or how long the eruption will be, we can say, this volcano started inflating and there’s a higher probability of it erupting.”
The CIRES project began in January 2015 at SRI International with funding from NASA’s Earth Science Technology Office to develop the instrument’s radar electronics hardware over two years. It then received an additional three years of funding to prepare the radar for space, demonstrate the imaging capabilities via aircraft, including both on-board and remotely piloted aircraft, and advance a space-deployable antenna to complete the instrument.
“InSAR has been particularly useful for better understanding volcanoes in remote areas,” Anderson said. For example, the technology helped scientists notice deformation near the Three Sisters cluster of volcanoes in central Oregon from 1997 to 2001. InSAR pinpointed deformation in an area that last saw an eruption 1,500 years ago. Because of the observed changes, the USGS installed seismometers, GPS stations and gas-monitoring equipment to check for other signs of activity. In 2004, those instruments detected a swarm of 300 small earthquakes.
“InSAR allows you to get wide areas of coverage and see how one part of the volcano’s caldera is changing relative to another part,” Patrick Rennich, the CIRES signal processing and experiment design lead, said. Typically, researchers place a limited number of GPS sensors on specific parts of the volcano to monitor any movement. “CIRES should be able to cover the entire caldera,” Rennich said.
Steps to space
During development, “the team ran into a lot of hiccups,” Wye said. However, with each hiccup, like a delayed test flight, the team got innovative. “It led to a lot of fun exercises,” Wye said.
One of those exercises saw the team strapping the instrument to a moving car. They drove the car, which they dubbed “CarSAR,” along elevated roads in the Bay Area of Northern California in early 2018 to see how CIRES would pick up information in a valley below. “But we really needed to get higher to test our data,” Wye said.
When the Kīlauea Volcano started erupting in May 2018, they saw their opportunity. On July 4, 2018, lava was flowing and the volcano’s caldera was collapsing. CIRES successfully obtained SAR, or snapshot imagery, but wasn’t able to obtain InSAR, or comparison images, over Kīlauea, in part because, “It was difficult to fly on the exact same path every day,” Rennich said.
The flights over Kīlauea, among other field tests, helped the team learn what worked and didn’t work as they developed the instrument. They were able to optimize CIRES to improve its power management, size, sensor capabilities and ability to withstand heat.
In December 2019, the team again strapped CIRES, with updated hardware and software, to an airplane usually reserved for commercial skydiving and flew 10,000 feet above an army training facility in Indiana. “It turns out that skydiving operators are very comfortable flying with an open door,” Rennich said.
The team flew CIRES above a simulated flooded village at the Muscatatuck Urban Training Center to better understand radar signatures in a flooded urban environment. The flight also produced data that could improve algorithms that quantify the extent of flooding and related damage. NASA’s Earth Science Technology Office and Disasters Program helped fund the flights and analysis of the CIRES data.
“By mounting CIRES on an airplane, we could fly at different angles and see how different building orientations affect how they appear in radar images due to flooding,” Sang-Ho Yun, a geophysicist and coinvestigator of this project at NASA’s Jet Propulsion Laboratory in Pasadena, California, said. “Flooding is like a ghost,” Yun said; its ephemeral nature makes it difficult to assess the accuracy of flood mapping techniques.
The team also performed an experiment where they controlled motion on the ground to test CIRES. During the Indiana flight, “One of our colleagues on the ground would raise silvery metal reflectors by half a centimeter to a centimeter to show that we can detect that level of change,” Rennich said. This helped prove that CIRES collected accurate InSAR data.
The flights were successful in part because the team was able to fly CIRES along the same path multiple times in a row, which they weren’t able to do in Hawaii. “We implemented a better pilot navigation system,” Rennich said, which allowed the team to fly within a few feet of where they had flown the previous day. In Hawaii, the they flew approximately 500 feet from the previous day’s course.
“When you’re in space, trajectory is much more repeatable,” Rennich said, because each satellite is on a predictable, traceable course.
For the team to make CIRES, or a CIRES-like instrument work in space, they would need to significantly extend its antenna, from two feet across to 10 feet across, Rennich said. “Everything else pretty much stays the same,” he said.
“Small satellites, similar in scope to CIRES, can be a dream system from a rapid disaster response point of view,” Yun said. Although small satellites, like CIRES, won’t be able to obtain the same accuracy as larger systems, they could obtain data more frequently when a disaster hits. “With small satellites, we can cost effectively achieve that goal,” Yun said.
Over the last two decades there has been a revolution in the study of dinosaurs after it was discovered that some of these extinct animals were feathered.
Exactly how many species had feathers has been contentious, but a new study has shown that feathers were likely restricted to just a small proportion of the non-bird dinosaurs.
When the first perfectly preserved specimens of feathered dinosaurs were found in China in the 1990s, it was proved beyond doubt that these ancient animals were the ancestors of modern-day birds.
Since then, more and more species of dinosaur have been revealed to have been covered in feather-like structures. But how common these structures were, and how many different groups were feathered, is still being debated today.
Prof Paul Barrett, a dinosaur researcher at the Museum, has conducted an analysis of all the known specimens of dinosaur skin and mapped them onto evolutionary trees to see how they relate. The study was carried out with Nicolás Campione and David Evans and published as a contribution to a new book The Evolution of Feathers.
‘To date, most examples of dinosaur feathers have been found in the meat-eating dinosaurs, known as theropods, which is the group that also includes birds,’ explains Paul. ‘So that is not too much of a surprise.
‘But there’s been speculation as to how far back feathers appear in meat-eating dinosaur evolution, and whether feathers might also have been seen in all other dinosaurs.’
This is because there are a couple of examples of other dinosaurs from completely unrelated groups with feather-like coverings, most notably the herbivorous dinosaurs Kulindadromeus, Psittacosaurus and Tianyulong. In addition, it is also thought that some pterosaurs, which are the next closest relatives to dinosaurs, may also have been covered in feather-like structures.
This has led to speculation that feathers were not just concentrated in the meat-eaters, but that many other groups, like the horned ceratopsians such as Triceratops, may also have had a smattering of feathers.
But the analysis by Paul and his colleagues shows that this was unlikely, and it supports the idea that true feathers were concentrated only in the group closest to living birds. The few other specimens with feather-like features may instead be examples of convergent evolution.
What is a feather?
One of the biggest challenges when it comes to determining whether or not a dinosaur had feathers is the definition of a feather itself.
Skin can do lots of strange things. Crocodiles have ossified parts of their skin into armour plates, mammals developed fur from theirs, while tortoises evolved beak sheaths. Feathers are just another example of what animals have done with the structure of skin.
To be a true feather, there are characteristics that need to be fulfilled. The structures must be made from a protein called beta-keratin, they must be branched, and finally they must originate from a follicle.
While these are obviously easy characteristics to ascertain in living species, when it comes to the fossil record things start to get a little trickier. Aspects like their physical structure might be discernible from well preserved specimens but figuring out what protein they were made from and whether or not they originated from a follicle is far less straightforward.
‘Most of the occurrences of feathers that we know about in the fossil record are all very heavily concentrated in the meat-eating dinosaurs that are closely related to birds,’ explains Paul. ‘The dinosaurs that are furthest away from birds that all scientists agree had feathers are actually animals like tyrannosaurs and comsognathids, which although they look very different from birds are not actually that distantly related.’
We can’t be certain that the feather-like structures seen on theropods like the tyrannosaurs originated from a follicle in the skin because these microscopic structures are not preserved. But the fact that these animals are so closely related to birds, on the basis of numerous features seen throughout their skeletons, means these structures are considered to be true feathers.
In fact, most dinosaurs with strong evidence of feathers come from within a very select group of theropods known as the Coelurosauria. This includes not only tyrannosaurs and birds, but also the ornithomimosaurs, therizinosaurs and compsognathids.
Going further back in time, things get rapidly murkier. ‘We have very little evidence of feathers in earlier meat-eating dinosaurs,’ says Paul. ‘The further down the theropod dinosaur family tree we go, the evidence for feathers gets thinner and thinner.’
Mostly scaly
This could be for one of two reasons: either the animals simply did not have feathers, or these earlier dinosaurs have been fossilised in rocks that are not conducive for the preservation of soft tissues.
For those 77 dinosaur species where skin has been preserved, Paul and his colleagues were able to map them onto evolutionary trees to see how feathers were distributed across dinosaurs and their close relatives.
‘We have really strong evidence that animals like the duck-billed dinosaurs, horned dinosaurs and armoured dinosaurs did not have feathers because we have lots of skin impressions of these animals that clearly show they had scaly coverings,’ says Paul. ‘We also have zero evidence of any feather like structures in the long-necked dinosaurs, the sauropodomorphs.
‘If we look at the evidence that we do have, and we combine that with evolutionary trees, what we find is that there is no evidence for the first dinosaurs being feathered.’
Instead, it seems to indicate that feathers were an important part of the theropod story but not necessarily so for dinosaurs as a whole. Similarly, it might suggest that some feather-like structures could have appeared in some other dinosaur groups once or twice independently.
The major implication of this research is that the earliest dinosaurs were probably primitively scaly like other reptiles. Even when feathered pterosaurs are added to the evolutionary trees, it doesn’t alter these conclusions.
This could have an impact on why we think feathers evolved, as this means that although they were were almost certainly giving some benefits to meat-eating dinosaurs, maybe in helping them to stay warm or in display, these were seemingly less important in the other dinosaur groups.
It also suggests that perhaps dinosaurs had the underlying genetic ability to produce feathers from the start, but that they didn’t always develop them, or maybe some groups even lost them.
‘Some people might be disappointed that we don’t think we should be putting feathers on dinosaurs other than the meat-eaters,’ says Paul. ‘But this work raises a lot of other interesting questions. If all dinosaurs did possess the possibility of making feathers, then why didn’t they?
One of the biggest gaps in the arthropod fossil record was what the ancestors to millipedes and centipedes looked like, but now that gap has been filled. Credit: Katja Schulz/Wikimedia Commons
Insects, spiders and millipedes make up the majority of all animals on land. While today not many of them live in the water, their ancestors were once aquatic.
A 411-million-year-old fossil shows us what one of these groups looked like when they still spent their days in the water.
The ancestors to modern-day arthropods, the vastly successful group that includes insects, spiders, millipedes and crabs, originated during the Cambrian Period about 541 million years ago.
These creatures were small and fully aquatic, living in the oceans and freshwater at the same time as most other major lineages of animals were also starting to appear. But at what point these early arthropods then began to split into the major land-living groups we see today has not been well established.
One of the biggest holes in the fossil record of arthropods has been the origin of the centipedes and millipedes, known collectively as the Myriapoda. No aquatic form of this lineage has ever been identified, until now.
Looking at fossils found within a rock formation known as the Rhynie Chert that date to about 410 million years old, researchers have been able to look in exquisite detail at some of the tiny arthropods preserved within. They found that some of these creatures were aquatic myriapods.
Dr. Greg Edgecombe, a palaeontologist at the Museum who studies arthropods, has been working with colleagues to describe these tiny early relatives to centipedes and millipedes.
“It’s something I have been wrestling with for a couple of decades now, and is one of the great holes in the arthropod fossil records,” says Greg. “This it is the first opportunity to see what the animals looked like in that gap.”
The description has now been published in the Proceedings of the National Academy of Sciences of the U.S..
The first animals on land
Arthropods are the most successful groups of animals on the planet, accounting for roughly 80% of all animals currently alive.
They are one of a few groups of animals that successfully made the transition from the oceans to land, one of the others being amniotes, and were the first to do so by at least some 420 million years ago.
Generally, the terrestrial arthropods can be broken up in three main groups: the hexapods (which includes insects), the arachnids (spiders and their kin) and the myriapods (centipedes and millipedes).
But rather that this occurring as a single event, each separate group of arthropods made the transition on their own.
“There were three major independent terrestrialisation events in Arthropoda,” explains Greg. “All of them had to deal with the same basic challenges because land was a hostile environment.” Each group had to figure out how to prevent drying out, how to support their own bodies and walk, how to excrete and not least how to breathe.
We know that the first arthropods appeared during the Early Cambrian some 541 million years ago, as their fossils have been found in deposits such as the Burgess Shale, and we know that by the Early Devonian they were well established on land.
It is what happened in between these events that has been less certain.
The first terrestrial ecosystems
The Rhynie Chert is a deposit found in Aberdeen, Scotland. It preserves one of the earliest terrestrial ecosystems, containing some of the first plants and animals that colonised the land.
When the rocks were being formed, the region would have been a system of pools and springs not unlike what is seen in Yellowstone National Park today, although not quite as extreme. Within these pools freshwater plants and animals were thriving, and around the margins they were beginning to explore the surrounding land.
It is within these rocks that Greg’s colleague Dr. Christine Strullu-Derrien was able to identify the tiny fossil arthropods. By using innovative microscopy methods, Christine managed to image these animals in astonishing detail, showing the fine anatomy of their mouth parts.
“These little details allow us to see that there are a set of organs in the head of the fossils that correspond to what we see in the mouth regions of living myriapods,” says Greg. This has confirmed that they were likely the early, aquatic-living ancestors to all living centipedes and millipedes.
What is interesting about this is that this is not the first time that these early myriapods have been found in the fossil record.
Known as euthycarcinoids, the bodies of these creatures are known in rocks dating from the Cambrian to the Triassic, while their trackways have been found on ancient tidal flats and coastal sand dunes. It’s just that these fossils were not detailed enough and had previously been misidentified as being early crustacean or arachnid relatives.
Now, Greg and his colleagues have been able to show that this interpretation was wrong, and that they actually belong to an entirely different groups of arthropods and help to plug this long-standing gap in the fossil record.
The work is also helping to show how the use of modern technology can give new insights into old specimens.
“To be honest, they’re just seriously beautiful fossils,” says Greg. “We can tell more about the shape of these animals than I could even have imagined would have been possible.
“That one image of the specimen is one of the most sublime fossils that I will ever have the opportunity to work on.”
Reference:
Gregory D. Edgecombe et al. Aquatic stem group myriapods close a gap between molecular divergence dates and the terrestrial fossil record, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.1920733117
In a ground-breaking first University of New England (UNE) researchers have produced the only fully online human skeleton, propelling a traditionally lab-based science into the digital cloud.
The physical skeleton was gifted by Rowan Webb, a UNE archaeology technician who passed away from cancer in 2010 and who wanted his remains to be used for scientific research.
Inspired by his story, a team of UNE researchers and technical specialists dedicated two years to realise Rowan’s aspiration using digitisation and rendering technology only widely available since his death.
UNE Anatomy will begin teaching with the online 3-D models this week.
“Rowan had no idea about the technology that we would have at our disposal, and that it could make his gift available to the whole world so that anybody could learn from him,” says UNE zooarchaeologist Dr. Melanie Fillios, who initiated and led the digital project.
“His family and those who knew him say he would be absolutely ecstatic. In a way, he lives on,” she said.
The digitisation project using 3-D photogrammetry was only made possible by a team of specialists willing to jump through administrative, legal and funding hoops, and with the support of the Shellshear Museum at the University of Sydney, which kindly provided access to Rowan’s physical skeleton.
UNE palaeontology Ph.D. candidate Michael Curry photographed each bone for the project, which has required nothing short of technical perfection.
“In the end I think I took around 30,000 photos of Rowan’s skeleton to get the most detailed images we could. It’s taken almost a year to take those images, reconstruct them and tweak them so they’re showing exactly what we want to see,” Mr Curry said.
And Mr Curry’s photography work was just the start of the digitisation process. Weeks of photography were followed by over a year spent creating and refining 3-D models from the images.
“We also needed to find a stable, publicly accessible digital platform, consider storage of the models and photos and prepare the metadata,” he said.
The new digital resource will be used for the first time in UNE’s zooarchaeology unit this year, but will also be available as a resource for anyone with an internet connection anywhere in the world.
“Rowan’s skeleton will be used to teach the critical skill of human bone identification across a range of applications, from introductory human anatomy to forensic work,” Dr. Fillios said.
“We’re looking into cross-disciplinary collaborations with UNE’s rural criminology units, and potentially offering short courses to benefit the Australian Federal Police (AFP), using Rowan’s skeleton to teach the basics of bone identification. But the sky is the limit for its possible uses,” she said.
UNE archaeologist Associate Professor Peter Grave describes the work as “absolutely cutting-edge”.
“I think we got the jump on the technology by about six months, thanks to Melanie’s initiative. Others are starting to catch up, so our current focus is to now develop applications for Rowan’s virtual skeleton in a learning and research environment,” he said.
As the appetite for online learning grows, 3-D models made available online are becoming an essential teaching resource. The UNE Archaeology team hopes their growing collection of online 3-D digital models will one day become part of a worldwide, freely accessible resource for teaching and research to benefit a range of disciplines.
“We think it’s important these resources are publicly available,” Dr. Grave said.
“We’d like to have a database that crosses disciplinary boundaries, where all universities and museums can pitch in to contribute models into the public sphere where it can be used for research worldwide.”
Although turtles belong to the reptiles, their skulls differs markedly from those of other members of this group. Credit: I. Werneburg
The origin of turtles is among the most debated topics in evolutionary biology. In a recently published study in the journal Nature Scientific Reports, Senckenberg scientist Ingmar Werneburg, in cooperation with an international research team, refutes existing hypotheses and sheds a new light on the evolution of the skull architecture. The results indicate a close link between skull evolution and the highly flexible neck of these armored reptiles.
In addition to their shell, turtles are characterized by their flexible necks and small heads. “Although turtles belong to the reptiles, their skulls differs markedly from those of other members of this group, which—together with their unique armored skeleton—makes it difficult to assess their phylogenetic origin,” explains PD Dr. Ingmar Werneburg of the “Senckenberg Centre for Human Evolution and Palaeoenvironment (SHEP) an der Universität Tübingen.”
Fossils suggest that several modifications during turtle evolution drove the initially mobile skull to transform to a rigid structure. In this process, the temporal openings behind the eyes closed as well, forming a so-called anapsid skull, which is not found in any other living reptile.
At the same time, the animals developed a unique arrangement of their jaw muscles, comparable to a pulley system. “Until now, it was assumed that these modifications led to an increased bite force in turtles, and that this development constituted a functional adaptation to a modified feeding behavior,” adds Werneburg.
This hypothesis was now tested for the first time under biomechanical aspects by an international research team led by Werneburg. The scientist from Tübingen comments as follows: “To our surprise, the results do not show any support for an increased bite force—neither due to the skull’s rigidity nor caused by the rearranged jaw musculature.” However, the analyses reveal that the evolutionary innovations led to an optimized skull structure, which can withstand higher stress loads while requiring less bone material.
“We combined our new findings with the previous paleontological and anatomical knowledge, allowing us to develop a new scenario,” explains Werneburg. The key feature in this scenario is the close link between the evolution of the skull and the highly flexible neck. “We assume that the skull of modern turtles is the result of a complex process that has been taking place since the emergence of the shell.” On the one hand, the neck movement facilitates a general increase in the animal’s mobility, which counteracts its otherwise rigid body. On the other hand, the option of retracting the neck serves as an additional protective mechanism in dangerous situations.
Moreover, the modifications in the turtles’ skull may not only have led to an improved stress distribution but may also have paved the way for the evolution of new species. “The evolutionary potential for a novel skull architecture and longer, more flexible necks enabled the development of a larger diversity among turtles during and after the Jurassic period,” adds Werneburg in closing.
Reference:
Gabriel S. Ferreira et al. Feeding biomechanics suggests progressive correlation of skull architecture and neck evolution in turtles, Scientific Reports (2020). DOI: 10.1038/s41598-020-62179-5
Holotype of calamitalean sphenopsid Annularia paisii sp. nov. showing an insect-induced gall
Evolutionary history of ecological interactions between terrestrial arthropods and vascular plants
The interactions between the terrestrial arthropods and vascular plants comprise one of more complex and intriguing terrestrial ecosystems that have persisted from Early Devonian times until today. These interactions are diverse, with multiple species of arthropods, mainly insects, and host-plants interacting over a range of trophic levels through predation (i.e. herbivory), parasitism, and pollination. The features, intensity and diversity of these interactions are mainly influenced by climatic and environmental conditions. Galling represents the most biologically complex of all major arthropod–plant interactions, consisting of parasitic relationships, which are characterized by the endophytic insect-induced plant tissue damage that can occur on all major plant organs. The insect-induced galling damage consists of atypically enlarged plant structures, three-dimensional, conspicuous, generally of bilateral or radial symmetry and externally hardened, that offers to the encapsulated insect larvae a microclimate, nutrition, and protection from natural enemies. The insect galls affect usually the plants only locally, but in some instances can cause systemic effects.
The insect galls have a long evolutionary history and earliest fossil records are known from the Pennsylvanian strata. These earliest insect galls occurred on stems of arborescent ferns and calamitalean sphenopsids. Although insect galls have been well-documented in a wide range of host-plant species, about 80% of extant galls occur on leaves. The Pennsylvanian-age galls are very poorly known because they are rarely found and only occasionally reported in the fossil record.
Host ancient “horsetail” shows insect gall preserved in situ
The horsetails are plants with a very old historical lineage, with fossil record from the Late Devonian to the present day, existing in abundance in Portugal today. The new species hosted Annularia paisii shows an insect gall induced by parasitoid insects (popularly known as galling insects), which is an ichnospecies until now unknown for science that received a name of Paleogallus carpannularites. This shows the existence of complex insect-plant relationships 303 million years ago and reiterates the importance of the fossil record of the Portuguese Carboniferous. The patterns of herbivory of insects and other arthropods on horsetails are little known. In our paper, recently published in the International Journal of Plant Sciences, we addresses this subject, in which they document 315 million years of sphenophyte herbivory relationships by arthropod.
Ecological adaptation of Annularia paisii
The arrangement of the leaves of Annularia paisii appears anomalous for a species of Annularia. Its leaves are arranged in cup-shaped whorls, a typical characteristic of other calamitalean sphenopsid like fossil genus Asterophyllites. Several explanations can account for this condition. The leaves of Annularia paisii perhaps were retracted into a cup shape during their burial. Alternatively, the cup shape could have been an induced feature resulting from their sensitivity to sunlight or an external tactile stimulus similar to the modern sensitive plant, Mimosa pudica. Another possibility is a physiological reaction from an herbivorous insect, such as a gall antagonism. Annularia paisii is named in honor of the Portuguese paleobotanist João Pais (1949–2016) from Nova University in Lisbon (Portugal).
Reference:
Pedro Correia, Arden R. Bashforth, Zbynĕk Šimůnek, Christopher J. Cleal, Artur A. Sá, and Conrad C. Labandeira, “The History of Herbivory on Sphenophytes: A New Calamitalean with an Insect Gall from the Upper Pennsylvanian of Portugal and a Review of Arthropod Herbivory on an Ancient Lineage,” International Journal of Plant Sciences. DOI: 10.1086/707105
Flake of clear yellow amber from Anglesea, Victoria containing a new, beautifully preserved biting midge ca. 41 million years old. Credit: Enrique Peñalver.
The oldest known animals and plants preserved in amber from Southern Gondwana are reported in Scientific Reports this week. Gondwana, the supercontinent made up of South America, Africa, Madagascar, India, Antarctica and Australia, broke away from the Pangea supercontinent around 200 million years ago. The findings further our understanding of ecology in Australia and New Zealand during the Late Triassic to mid-Paleogene periods (230-40 million years ago).
Jeffrey Stilwell and colleagues studied more than 5,800 amber pieces from the Macquarie Harbour Formation in Western Tasmania, dating back to the early Eocene Epoch (~54-52 million years ago) and Anglesea Coal Measures in Victoria, Australia, from the late middle Eocene (42-40 million years ago). The authors report a rare “frozen behaviour” of two mating long-legged flies (Dolichopodidae). The specimens also include the oldest known fossil ants from Southern Gondwana and the first Australian fossils of ‘slender springtails’, a tiny, wingless hexapod. Other organisms preserved in the amber include a cluster of juvenile spiders, biting midges (Ceratopogonidae), two liverwort and two moss species.
The authors also studied deposits found at locations in southeastern Australia, Tasmania and New Zealand. These include the oldest reported amber from Southern Pangea dating back to 230 million years ago, 96-92 million year old deposits from forests near the South Pole and an intact fossil of an insect called a felt scale (Eriococcidae) from 54-52 million years ago.
The findings provide new insights into the ecology and evolution of Southern Gondwana and indicate that there may be a vast potential for future, similar finds in Australia and New Zealand.
Reference:
Amber from the Triassic to Paleogene of Australia and New Zealand as exceptional preservation of poorly known terrestrial ecosystems, Scientific Reports (2020). DOI: 10.1038/s41598-020-62252-z
Minoan eruption of Thera. Satellite image of Thera, November 21, 2000. Credit: NASA, public domain
Charlotte Pearson’s eyes scanned a palm-sized chunk of ancient tree. They settled on a ring that looked “unusually light,” and she made a note without giving it a second thought. Three years later, and armed with new methodology and technology, she discovered that the light ring might mark the year that the Thera volcano on the Greek island of Santorini erupted over the ancient Minoan civilization. The date of the eruption, which is one of the largest humanity has ever witnessed, has been debated for decades.
Pearson, a University of Arizona assistant professor of dendrochronology and anthropology, is lead author of a paper, published in the Proceedings of the National Academy of Sciences, in which she and her colleagues have used a new hybrid approach to assign calendar dates to a sequence of tree rings, which spans the period during which Thera erupted, to within one year of a calendar date. This allows them to present new evidence that could support an eruption date around 1560 B.C.
Filling the Gaps
“In every tree ring, you have this time capsule that you can unpack,” Pearson said.
Trees grow in accordance with the conditions of their local environment. Each year, trees produce a new layer of concentric growth, called a tree ring, which can record information about rainfall, temperature, wildfires, soil conditions and more. Trees can even record solar activity as it waxes and wanes.
When a sequence of rings from trees of various ages are overlapped and added together, they can span hundreds or thousands of years, providing insight about past climate conditions and context for concurrent civilizations.
“The longest chronology in the world stretches back 12,000 years. But in the Mediterranean, the problem is that we don’t have a full, continuous record going back to the time of Thera,” Pearson said. “We have recorded the last 2,000 years very well, but then there’s a gap. We have tree rings from earlier periods, but we don’t know exactly which dates the rings correspond to. This is what’s called a ‘floating chronology.'”
Filling this gap could help pin down the Thera eruption date and paint a climatic backdrop for the various civilizations that rose and fell during the Bronze and Iron ages, which together spanned between 5,000 and 2,500 years ago.
“Until you can put an exact year on events on a scale that makes sense to people—one year—it’s not quite as powerful,” Pearson said. “This study is really about taking (my co-author and tree ring lab research professor) Peter Kuniholm’s chronology that he’s put together over 45 years of work and dating it in a way not possible before. Most importantly, it is fixed in time, just as if we had filled our tree ring gap.”
A Hybrid Approach
Since the inception of the UArizona Laboratory of Tree-Ring Research in 1937, an assortment of tree ring samples from all over the world accumulated in less-than-ideal conditions beneath Arizona Stadium. But since the completion of the university’s upgraded Bryant Bannister Tree Ring Building in 2013, the curation team, led by Peter Brewer, has been relocating, organizing and preserving samples for future research.
“This is the collection that founded the field of tree ring research, and it’s by far the world’s largest,” Brewer said. “Researchers come from all over to use our collection.”
“It’s just crammed full of the remains of ancient forests and archaeological sites, which no longer exist, and it contains wood samples that were fundamental in the growth of the discipline of dendrochronology,” Pearson said.
The collection includes timbers from the Midas Mound Tumulus at Gordion in Turkey—a giant tomb of a man that was likely Midas’ father or grandfather. From timbers like these, Kuniholm has been building a tree ring chronology from the Mediterranean for nearly a half century. Together, Kuniholm’s record from the B.C. period spans over 2,000 years, including trees growing downwind of the Thera eruption, making it key to the team’s research.
Despite the length of this chronology, it remained undated. To pin it down, the team decided to try something new.
When cosmic rays from space enter the Earth’s atmosphere, neutrons collide with nitrogen atoms to create a radioactive version of carbon, called carbon-14, which spreads around the planet. All other life on Earth, including tree rings, pick up the carbon-14, and because tree-rings lock away a measurement of carbon-14 for each year that they grow, they hold patterns showing how it changed over time. These patterns of carbon-14 in tree rings around the world should match.
Pearson and her team used the patterns of carbon-14 captured in the Gordion tree rings to anchor the floating chronology to similar patterns from other calendar dated tree ring sequences.
“It’s a new way to anchor floating tree ring chronologies that makes use of the annual precision of tree rings,” Pearson said.
To validate their findings, the team turned to the calendar-dated rings of high-elevation bristlecone pines from western North America that lived at the same time as the Gordion.
“When there are large volcanic eruptions, it often scars bristlecone by freezing during the growing season, creating a frost ring,” said second author Matthew Salzer, research scientist at the tree ring laboratory. “Then we compared the dates of the frost rings with what was going on in the Mediterranean trees, which respond to volcanoes by growing wider rings. And it worked. It showed that the wide rings in the Mediterranean chronology occurred in the same years as the frost rings in the bristlecone. We took that to be confirmation that the dating was probably correct.”
The team then thought to use a new piece of technology in the lab called the X-ray fluorescence machine to scan the wood for chemical changes.
“We scanned the entire period across when Thera is known to have happened,” Pearson said, “and we detected a very slight depletion in calcium, right where I saw this lighter ring years ago.”
While it’s a slight fluctuation, it is significant and only occurs at one point in the years around 1560 B.C.
“We put that in the paper and tentatively suggest it’s a possible date for Thera,” Pearson said.
Something changed the chemistry of the environment in which the tree grew; acid deposition from a volcano is one possibility, wildfire is another, but because the date happens to coincide with other tree ring markers for a major eruption, Pearson she says it’s worthy of further exploration.
“I think to do good science you have to investigate everything and keep an open mind until sufficient data comes together,” Pearson said. “This is another little piece of the puzzle.”
Reference:
Charlotte Pearson el al., “Securing timelines in the ancient Mediterranean using multiproxy annual tree-ring data,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1917445117
A seismogram of 2011 Tōhoku earthquake and tsunami recorded at Weston Observatory in Massachusetts, USA. Credit: Image from Wikimedia Commons.
The world’s most powerful earthquakes strike at subduction zones, areas where enormous amounts of stress build up as one tectonic plate dives beneath another. When suddenly released, this stress can cause devastating “megaquakes” like the 2011 Mw 9.0 Tohoku event, which killed nearly 16,000 people and crippled Japan’s Fukushima Dai-ichi Nuclear Power Plant. Now a study published in Geology suggests that sediments atop the downgoing slab can play a key role in determining the magnitude and location of these catastrophic events.
In this newly published study, a team led by Gou Fujie, a senior scientist at the Japan Agency for Marine-Earth Science and Technology, used a trio of geophysical methods to image the subducting sediments in the northeastern Japan arc, where the Tohoku event occurred. The findings suggest that variations caused by volcanic rocks intruded into these sediments can substantially influence the nature of subduction zone earthquakes.
“Our imaging shows that the enormous amount of slip that occurred during the 2011 Tohoku earthquake stopped in an area of thin sediments that are just starting to subduct,” says Fujie. “These results indicate that by disturbing local sediment layers, volcanic activity that occurred prior to subduction can affect the size and the distribution of interplate earthquakes after the layers have been subducted.”
Researchers first began to suspect that variations in subducting sediments could influence megaquakes after the 2011 Tohoku event, when international drilling in the northeastern Japan arc showed that giant amounts of slip during the earthquake occurred in a slippery, clay-rich layer located within the subducting sediments. To better understand the nature of the downgoing slab in this region, Fujie’s team combined several imaging techniques to paint a clearer picture of the subseafloor structure.
The researchers discovered there are what Fujie calls “remarkable regional variations” in the sediments atop the downgoing plate, even where the seafloor topography seems to be flat. There are places, he says, where the sediment layer appears to be extremely thin due to the presence of an ancient lava flow or other volcanic rocks. These volcanic intrusions have heavily disturbed, and in places thermally metamorphosed, the clay layer in which much of the seismic slip occurred.
Because the type of volcanism that caused sediment thinning in the northeastern Japan arc has also been found in many areas, says Fujie, the research suggests such thinning is ubiquitous—and that this type of volcanic activity has also affected other seismic events. “Regional variations in sediments atop descending oceanic plates appear to strongly influence devastating subduction zone earthquakes,” he concludes.
Reference:
Gou Fujie et al. Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes, Geology (2020). DOI: 10.1130/G46757.1
The team’s experiments compared carbon’s compatibility with the silicates that comprise the Earth’s mantle (outer circle) to its compatibility with the iron that comprises the planet’s core (inner circle) while under conditions mimicking the Earth’s interior during its formative period. They found that more carbon would have stayed in the mantle than previously thought. Credit: Rebecca Fischer, Elizabeth Cottrell and Marion Le Voyer, Kanani Lee, and the late Erik Hauri.
Carbon is essential for life as we know it and plays a vital role in many of our planet’s geologic processes — not to mention the impact that carbon released by human activity has on the planet’s atmosphere and oceans. Despite this, the total amount of carbon on Earth remains a mystery, because much of it remains inaccessible in the planet’s depths.
New work published this week in Proceedings of the National Academy of Sciences reveals how carbon behaved during Earth’s violent formative period. The findings can help scientists understand how much carbon likely exists in the planet’s core and the contributions it could make to the chemical and dynamic activity occurring there — including to the convective motion powering the magnetic field that protects Earth from cosmic radiation.
Earth’s core is comprised mostly of iron and nickel, but its density indicates the presence of other lighter elements, such as carbon, silicon, oxygen, sulfur, or hydrogen. It’s been long suspected that there’s a tremendous reservoir of carbon hiding down there. But to attempt to quantify it, the research team used laboratory mimicry to understand how it got into the core in the first place.
The group was comprised of Harvard University’s Rebecca Fischer, the Smithsonian Institution’s Elizabeth Cottrell and Marion Le Voyer, both former Carnegie postdoctoral fellows, Yale University’s Kanani Lee, and Carnegie’s late Erik Hauri, the memory of whom the authors acknowledge.
“To understand present day Earth’s carbon content, we went back to our planet’s babyhood, when it accreted from material surrounding the young Sun and eventually separated into chemically distinct layers — core, mantle, and crust,” said Fischer. “We set out to determine how much carbon entered the core during these processes.”
This was accomplished by lab experiments that compared carbon’s compatibility with the silicates that comprise the mantle to its compatibility with the iron that comprises the core while under the extreme pressures and temperatures found deep inside the Earth during its formative period.
“We found that more carbon would have stayed in the mantle than we previously suspected,” explained Cottrell. “This means the core must contain significant amounts of other lighter elements, such as silicon or oxygen, both of which become more attracted to iron at high temperatures.”
Despite this surprising discovery, the majority of Earth’s total carbon inventory does likely exist down in the core. But it still makes up only a negligible component of the core’s overall composition.
“Overall, this important work improves our understanding of how Earth’s carbon was accumulated during the planetary formation process and sequestered into the mantle and core as they chemically differentiated,” concluded Richard Carlson, Director of Carnegie’s Earth and Planets Laboratory, where Hauri worked. “I only wish Erik was still with us to see the results published this week.”
This work was supported by a National Science Foundation postdoctoral fellowship.
Reference:
Rebecca A. Fischer, Elizabeth Cottrell, Erik Hauri, Kanani K. M. Lee, Marion Le Voyer. The carbon content of Earth and its core. Proceedings of the National Academy of Sciences, 2020; 201919930 DOI: 10.1073/pnas.1919930117
Formation pressure governs the generation, expulsion, migration, accumulation and preservation of petroleum. Fluid-rock interactions during diagenesis and mineralization are also affected by the formation pressure. Thus, investigating the formation paleo-pressure in sedimentary basins is an important aspect of research into the mechanisms and processes related to hydrocarbon accumulation, and it plays an increasingly important role in hydrocarbon exploration and prospective prediction.
Formation pressure occurs during the long-term evolution of basins, and is regulated by tectonism, deposition, diagenesis, fluid flow, geothermal field, and magmatic activity. Oil and gas exploration is increasingly directed at deep, ultra-deep and ancient strata which, however, have generally experienced multiple stages of tectonic movements. Reconstruction of formation paleo-pressure in these strata is not easy.
Various methods have been established for paleo-pressure reconstruction in sedimentary basins, including approaches based on basin modelling, fluid inclusion analysis, differential stress of rocks, transformation of clay minerals, acoustic transit time of mudstones, and seismic wave velocity. Each of these methods has advantages and limitations, but most can only determine the formation pressure in a certain geological period, rather than the whole pressure evolution process. Furthermore, some of these methods were established based on simple porosity evolution models, which are not applicable to reservoirs with complex fluid flows, intense tectonic activities, and abnormal porosity evolution paths.
Origins of abnormal pressures typically change during geological history. In this study, a new method is proposed for reconstructing the paleo-pressures in strata by integrating various paleo-pressure calculation methods according to the identification of the formation mechanism and the main factors responsible for controlling abnormal pressures. According to the geological background, quantitative analyses of the factors that might control overpressure were first conducted to clarify the contributions of each mechanism during different geological periods. Pressure evolution was reconstructed by fluid-compaction modelling with constraints imposed by paleo-pressures obtained from fluid inclusions or differential stress methods. Determining the mechanisms responsible for overpressures during geological history is the basic prerequisite for paleo-pressure research. Thus, quantitative studies were conducted of the contributions of disequilibrium compaction, gas charging, oil cracking, temperature reduction, and tectonic uplift and subsidence to overpressures.
Three case studies of paleo-pressure reconstruction were performed for the Sinian strata in the Sichuan Basin, Ordovician strata in the north uplift in the Tarim Basin and the Permian strata in the Sulige Gas Field in the Ordos Basin, where these three study sites are normally pressured, weakly over-pressured and abnormally low pressured at present, respectively.
The Sinian formation in the central Sichuan Basin is mainly normally pressured at present. Under the constraint of the trapping pressures due to fluid inclusions in three periods, which were calculated using PVTsim software, the evolution of pressure in the Dengying Formation was obtained by basin modelling with a fluid-compaction coupling model. Pressure in the Sinian Dengying Formation is due to a combination of hydrocarbon accumulation, oil cracking to form gas, and temperature reductions caused by tectonic uplift, where these different factors played dominant roles during diverse periods.
The Sulige Gas Field in the Ordos Basin is a typical gas field with an abnormally low pressure. A great temperature reduction from 165°C to 105°C occurred in the last 100 Ma. Regardless of gas dissipation, pressure would be decreased by 17.7-22% when temperature declined by 50-60°C. On the other hand, gases were dissipated 17-24 vol%, resulting in 23-32% decreases in the formation pressure. Based on fluid inclusion analysis and numerical modelling, weak overpressures occurred twice throughout the geological history, where the first overpressure was generated at 195 Ma, which was suspended by the uplift at 160 Ma before, overpressure was generated again after 140 Ma, where it was maximized in 98 Ma at a greatest depth of 4425.6 m and with a pressure coefficient value of 1.1. Subsequently, both the formation pressure and pressure coefficient decreased gradually due to uplift and denudation, and changed to an abnormally low pressure with a coefficient of 0.85 at present.
The fluid pressure during the critical period of tectonic compression can be quantitatively calculated using the differential stress method with calcite twins as a paleo-barometer. The paleo- pressure in the Ordovician Yinshan carbonate strata in the Shunnan Area of the Tarim Basin was reconstructed as a case study. The Shunnan Area was in a tectonic compression environment from the middle and late Caledonian to the Hercynian period, and the orientation of the principal stress changed from SW-NE to SE-NW. The paleo-stress ranged from 66.15 to 89.17 MPa, with an average of 82.06 MPa in the Caledonian, and ranged from 56.97 to 79.29 MPa, with an average value of 66.80 MPa in the Hercynian. The excess fluid pressure in the carbonate strata during tectonic compression deformation was calculated by the difference between realistic effective vertical stress and theoretical vertical stress. Combined with modelling results, a weak overpressure was developed in the Ordovician strata during the middle to late Caledonian period by the strong compression related to the Paleo-Kunlun Ocean subduction. The formation pressure gradually deceased to normal pressure because of strata uplift and stress field conversion. Another two phases of overpressure were formed at the end of the Permian and Neogene periods, originated from southeast-trending compression and gas filling, respectively.
Pressure analysis is the basis of fluid dynamic system analysis, which is significant for hydrocarbon migration and reservoir diagenesis. The development of effective paleo-pressure recovery methods for carbonate strata may be essential for addressing various problems in deep and ultra-deep layer pressure research.
Reference:
Nansheng Qiu et al, Quantitative reconstruction of formation paleo-pressure in sedimentary basins and case studies, Science China Earth Sciences (2020). DOI: 10.1007/s11430-019-9556-8
Photomicrographs showing anorthosites with ‘correct’ and ‘wrong’ proportions of chromite from the Bushveld Complex, South Africa. Credit: Wits University
Researchers at Wits University in Johannesburg, South Africa, have found the answer to an enigma that has had geologists scratching their heads for years.
The question is that of how certain magmatic rocks that are formed through crystallisation in magmatic chambers in the Earth’s crust, defy the norm, and contain minerals in random proportions.
Normally, magmatic rocks consist of some fixed proportions of various minerals. Geologists know, for instance, that a certain rock will have 90% of one mineral and 10% of another mineral.
However, there are some magmatic rocks that defy this norm and do not adhere to this general rule of thumb. These rocks, called non-cotectic rocks, contain minerals in completely random proportions.
One example is chromite-bearing anorthosite from the famous Bushveld Complex in South Africa. These rocks contain up to 15% to 20% of chromite, instead of only 1%, as would normally be expected.
“Traditionally, these rocks with a ‘wrong’ composition were attributed to either mechanical sorting of minerals that crystallised from a single magma or mechanical mixing of minerals formed from two or more different magmas,” says Professor Rais Latypov from the Wits School of Geosciences.
Seeing serious problems with both these approaches, Latypov and his colleague Dr. Sofya Chistyakova, also from the Wits School of Geosciences, found that there is actually a simple explanation to this question—and it has nothing to do with the mechanical sorting or mixing of minerals to produce these rocks.
Their research, published in the journal Geology, shows that an excess amount of some minerals contained in these rocks may originate in the feeder conduits along which the magmas are travelling from the deep-seated staging chambers towards Earth’s surface.
“While travelling up through the feeder channels, the magma gets into contact with cold sidewalls and starts crystallising, thereby producing more of the mineral(s) than what should be expected,” says Chistyakova.
The general principle of this approach can be extended to any magmatic rocks with ‘wrong’ proportions of minerals in both plutonic and volcanic environments of the Earth.
“It is possible that a clue to some other petrological problems of magmatic complexes should be searched for in the feeder conduits rather than in magma chambers themselves. This appealing approach holds great promise for igneous petrologists working with basaltic magma complexes,” says Latypov.
Reference:
R.M. Latypov et al, Origin of non-cotectic cumulates: A novel approach, Geology (2020). DOI: 10.1130/G47082.1
