Scientists Discover Rare Theropod Dinosaur Wounded in Action in Southern Utah

September 22, 2011

Skeletal elements of Talos and Troodon illustrating select diagnostic characters of Talos sampsoni (UMNH VP 19479). (Credit: Zanno LE, Varricchio DJ, O’Connor PM, Titus AL, Knell MJ (2011) A New Troodontid Theropod, Talos sampsoni gen. et sp. nov., from the Upper Cretaceous Western Interior Basin of North America. PLoS ONE 6(9): e24487. doi:10.1371/journal.pone.0024487)

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Raptor dinosaurs like the iconic Velociraptor from the movie franchise Jurassic Park are renowned for their “fear-factor.” Their terrifying image has been popularized in part because members of this group possess a greatly enlarged talon on their foot — analogous to a butcher’s hook. Yet the function of the highly recurved claw on the foot of raptor dinosaurs has largely remained a mystery to paleontologists. This week a collaboration of scientists unveil a new species of raptor dinosaur discovered in southern Utah that sheds new light on this and several other long-standing questions in paleontology, including how dinosaurs evolved on the “lost continent” of Laramidia (western North America) during the Late Cretaceous — a period known as the zenith of dinosaur diversity.

Their findings will be published in the journal PLoS ONE.

The new dinosaur — dubbed Talos sampsoni — is a member of a rare group of feathered, bird-like theropod dinosaurs whose evolution in North America has been a longstanding source of scientific debate, largely for lack of decent fossil material. Indeed, Talos represents the first definitive troodontid theropod to be named from the Late Cretaceous of North America in over 75 years. “Finding a decent specimen of this type of dinosaur in North America is like a lighting strike… it’s a random event of thrilling proportions,” said Lindsay Zanno, lead author of the study naming the new dinosaur. Zanno is an assistant professor of anatomy at the University of Wisconsin-Parkside and a research associate at the Field Museum of Natural History in Chicago, Illinois. Other members of the research team include Mike Knell (a graduate student at Montana State University) who discovered the new specimen in 2008 in the Kaiparowits Formation of Grand Staircase-Escalante National Monument (GSENM), southern Utah; Bureau of Land Management (BLM) paleontologist Alan Titus, leader of a decade-long paleontology reconnaissance effort in the monument; David Varricchio, Associate Professor of Paleontology, Montana State University; and Patrick O’Connor, Associate Professor of Anatomy, Ohio University Heritage College of Osteopathic Medicine.

Funding for the research was provided in part by the National Science Foundation, the Field Museum of Natural History, the Ohio University Heritage College of Osteopathic Medicine, and the Bureau of Land Management. Zanno’s research was supported by a John Caldwell-Meeker Fellowship and by a Bucksbaum Fellowship for young scientists. The bones of Talos sampsoni will be on exhibit for the first time in the Past Worlds Observatory at the new Utah Museum of Natural History, Salt Lake City, Utah.

The Nature of the Beast Troodontid theropods are a group of feathered dinosaurs closely related to birds. Members of this group are among the smallest non-avian dinosaurs known (as small as 100 grams) and are considered among the most intelligent. The group is known almost exclusively from Asia and prior to the discovery of Talos sampsoni, only two species were recognized in the Late Cretaceous of North America — one of which, the infamous Troodon, was one of the first dinosaurs ever named from North America.

As a result of their distinctive teeth and the possible presence of seeds preserved as gut contents in one species, several scientists have proposed an omnivorous or herbivorous diet for at least some troodontids. Other species possess relatively blade-like teeth indicative of a carnivorous diet. Zanno’s own work on theropod diet suggests that extensive plant eating was confined to more primitive members of the group, with more advanced members of the clade like Troodon and Talos likely consuming at least some prey.

Several troodontid specimens have recently been discovered that not only support a close relationship with birds but also preserve remarkable evidence of bird-like behavior. These include extraordinary specimens such as eggs and embryos within nests that document transitional phases in the evolution of bird-like reproductive physiology and egg-laying behavior, as well as specimens preserved in distinctive avian-like sleeping postures with their heads rotated back and tucked under their “wings.” Other troodontids provide evidence of “four-winged” locomotor capabilities, and perhaps most extraordinary, plumage coloration.

With an estimated body mass of 38 kilograms, the newly discovered Talos sampsoni is neither the smallest nor largest troodontid known. Its skeleton indicates that the new species was much smaller and more slender than its famous cousin Troodon, which is known from sediments of the same age in the northern part of Laramidia (Alberta, Canada and Montana, USA). “Talos was fleet-footed and lightly built,” Zanno says. “This little guy was a scrapper.”

Interestingly, the holotype specimen of Talos also tells us something about theropod behavior, particularly raptor behavior. This is because the second toe — that is, the one with the enlarged talon — of the left foot of the new specimen is deformed, indicating that the animal suffered a fracture or bite during its life.

This Little Talos Takes a Beating

When the team first began studying the Talos specimen, they noticed some unusual features on the second digit of the left foot, but initially assumed they were related to the fact that it belonged to a new species. “When we realized we had evidence of an injury, the excitement was palpable,” Zanno commented. “An injured specimen has a story to tell.” That’s because evidence of injury relates to function. The manner in which an animal is hurt can tell you something about what it was doing during life. An injury to the foot of a raptor dinosaur, for example, provides new evidence about the potential function of that toe and claw. In order to learn about the injury to the animal’s foot, the team scanned the individual bones using a high-resolution Computed Tomography (CT) scanner, similar to those used by physicians to examine bones and other organs inside the human body.

“Although we could see damage on the exterior of the bone, our microCT approach was essential for characterizing the extent of the injury, and importantly, for allowing us to better constrain how long it had been between the time of injury and the time that this particular animal died,” noted Patrick O’Connor, associate professor of anatomy at Ohio University. After additional CT scanning of other parts of the foot, Zanno and her team realized that the injury was restricted to the toe with the enlarged claw, and the rest of the foot was not impacted. More detailed study suggested that the injured toe was either bitten or fractured and then suffered from a localized infection.

“People have speculated that the talon on the foot of raptor dinosaurs was used to capture prey, fight with other members of the same species, or defend the animal against attack. Our interpretation supports the idea that these animals regularly put this toe in harm’s way,” says Zanno.

Perhaps even more interesting is the fact that the injured toe exhibits evidence of bone remodeling thought to have taken place over a period of many weeks to months, suggesting that Talos lived with a serious injury to the foot for quite a long time. “It is clear from the bone remodeling that this animal lived for quite some time after the initial injury and subsequent infection, and that whatever it typically did with the enlarged talon on the left foot, whether that be acquire prey or interact with other members of the species, it must have been capable of doing so fairly well with the one on the right foot,” added O’Connor.

Trackways made by animals closely related to Talos suggest that they held the enlarged talon off the ground when walking. “Our data support the idea that the talon of raptor dinosaurs was not used for purposes as mundane as walking,” Zanno commented. “It was an instrument meant for inflicting damage.”

What’s in a Name?

The name Talos pays homage to a mythological Greek figure of the same name, believed to have protected the island of Crete by throwing stones at invading ships. It is said that the Greek Talos, who was often depicted as a winged bronze figure, could run at lightening speed and circled the ancient island three times a day. The dinosaur Talos belongs to a group of theropods known to have feathery integument (and in some cases “wings”), lived on the small island continent of Laramidia or west North America during the Late Cretaceous, and was also a fast runner. The team chose the name Talos because of these similarities but also because the Greek Talos was said to have died from a wound to the ankle and it was clear that Talos had also suffered a serious wound to the foot. The species name “sampsoni” honors another famous figure — Dr. Scott Sampson of the PBS series Dinosaur Train.

Sampson, a research curator at the Utah Museum of Natural History and research faculty at the University of Utah, helped to spearhead a collaborative research effort known as the Kaiparowits Basin Project, a long-term research project that has been surveying and documenting the Late Cretaceous dinosaur fauna of the Kaiparowits Basin in southern Utah, with a focus on the Kaiparowits and Wahweap formations exposed in Grand Staircase-Escalante National Monument (GSENM). Thus far this effort has resulted in the discovery of up to a dozen new dinosaurs from GSENM that are challenging previous ideas regarding Late Cretaceous dinosaur evolution and diversity within Laramidia and spurring new ideas regarding dinosaur biogeography in the region.

A Tale of Two Continents

Dinosaurs of the Late Cretaceous were living in a greenhouse world. A warm and equitable global climate that was devoid of polar ice caps and above average spreading at mid-oceanic ridges caused massive flooding of low-lying continental areas and created expansive epicontinental seaways. In North America, a shallow seaway running from the Gulf of Mexico through to the Arctic Ocean divided the continent into two landmasses, East America (Appalachia) and West America (Laramidia) for several million years during the Late Cretaceous. It was during this time that the dinosaurs achieved their greatest diversity, and scientists have been working overtime to understand why. Take for example the dinosaurs of Laramidia. The natural assumption is that being large bodied, those dinosaurs that lived on the small island continent would have roamed the whole area.

However, recent fossil discoveries, particularly new dinosaurs from the Kaiparowits Formation, tell us that the true pattern is exactly the opposite. Thus far the dinosaurs from the Kaiparowits Formation in southern Utah are entirely unique, even from those dinosaurs living just a few hundred miles to the north in what is now Montana and Alberta.

Monument Paleontologist Alan Titus observed, “When we began looking in the remote Kaiparowits badlands we expected to see at least a few familiar faces. As it turns out, they are all new to science.

” And while recent discoveries from the Kaiparowits have substantiated this pattern for large-bodied herbivores like duck-bill and horned dinosaurs (for example Utahceratops), the pattern among small-bodied theropods was not clear.

“We already knew that some of dinosaurs inhabiting southern Utah during the Late Cretaceous were unique,” Zanno said, “but Talos tells us that the singularity of this ecosystem was not just restricted to one or two species. Rather, the whole area was like a lost world in and of itself.”

A Monumental Discovery

Talos sampsoni is the newest member of a growing list of new dinosaur species that have been discovered in Grand Staircase Escalante National Monument (GSENM) in southern Utah. Former President Clinton founded the monument in 1996, in part to protect the world class paleontological resources entombed within its 1.9 million acres of unexplored territory.

GSENM is one of the largest recently designated national monuments managed by the BLM, and one of the last pristine dinosaur graveyards in the US. The area has turned out to be a treasure trove of new dinosaur species, with at least 15 collected in just the past decade. Titus admits, “We had very few large fossils to substantiate the claim of ‘World Class’ paleontology when I started in 2000.

Now, I feel GSENM could easily qualify as a world heritage site on the basis of its dinosaurs alone, dozens of which have been found preserving soft tissue.” He also adds, “BLM support has been critical to the long term viability of the region’s paleontology research and is paying off in countless ways both to the public and scientists.”

Zanno, along with colleague Scott Sampson, named the first dinosaur from the monument — Hagryphus giganteus — in 2005. Hagryphus (widely touted in the press as the “turkey” dinosaur) is also a theropod dinosaur, but one that belongs to a different subgroup known as oviraptorosaurs (or egg thief reptiles). Other GSENM dinosaurs include five new horned dinosaurs including the recently described and bizarrely ornate Kosmoceratops and Utahceratops, three new duck-bill dinosaurs including the “toothy” Gryposaurus monumentensis, two new tyrannosaurs, as well as undescribed ankylosaurs (armored dinosaurs), marine reptiles, giant crocodyliforms, turtles, plants, and a host of other organisms.

The discovery of a new troodontid from the monument is the latest in a long string of incredible fossil discoveries from the area. “I was surprised when I learned that I had found a new dinosaur,” Knell said. “It is a rare discovery and I feel very lucky to be part of the exciting research happening here in the monument.” Knell stumbled across the remains of Talos sampsoni while scouring the badlands of the Kaiparowits Formation for fossil turtles as part of his dissertation research.

Work continues every year in GSENM and new, significant fossil finds are made every field season. Considering there are hundreds of thousands of acres of outcrop that have yet to be surveyed, it is no exaggeration to claim the region will remain an exciting research frontier for decades to come.

Note : The above story is reprinted from materials provided by Public Library of Science,

Carbon cycle reaches Earth’s lower mantle, Science study reports

September 20, 2011

Like an insect in amber, mineral inclusions trapped in diamonds can reveal much about the Earth’s deep interior. The study by Walter et al. in Science reveals mineral inclusions that originated in oceanic crust subducted into the lower mantle. – Image © Science/AAAS

The carbon cycle, upon which most living things depend, reaches much deeper into the Earth than generally supposed-all the way to the lower mantle, researchers report.

The findings, which are based on the chemistry of an unusual set of Brazilian diamonds, will be published online by the journal Science, at the Science Express Web site, on 15 September. Science is published by AAAS, the non-profit, international science society.

“This study shows the extent of Earth’s carbon cycle on the scale of the entire planet, connecting the chemical and biological processes that occur on the surface and in the oceans to the far depths of Earth’s interior,” said Nick Wigginton, associate editor at Science.

“Results of this kind offer a broader perspective of planet Earth as an integrated, dynamic system,” he said.

The carbon cycle generally refers to the movement of carbon through the atmosphere, oceans, and the crust. Previous observations suggested that the carbon cycle may even extend to the upper mantle, which extends roughly 400 kilometers into the Earth. In this region, plates of ocean crust-bearing a carbon-rich sediment layer-sink beneath other tectonic plates and mix with the molten rock of the mantle.

Seismological and geochemical studies have suggested that oceanic crust can sink all the way to the lower mantle, more than 660 kilometers down. But actual rock samples with this history have been hard to come by.

Michael Walter of the University of Bristol and colleagues in Brazil and the United States analyzed a set of “superdeep” diamonds from the Juina kimberlite field in Brazil. Most diamonds excavated at Earth’s surface originated at depths of less than 200 kilometers. Some parts of the world, however, have produced rare, superdeep diamonds, containing tiny inclusions of other material whose chemistry indicates that the diamonds formed at far greater depths.

The Juina-5 diamonds studied by Walter and colleagues contain inclusions whose bulk compositions span the range of minerals expected to form when basalt melts and crystallizes under the extreme high pressures and temperatures of the lower mantle.

Thus, these inclusions probably originated when diamond-forming fluids incorporated basaltic components from oceanic lithosphere that had descended into the lower mantle, the researchers have concluded.

If this hypothesis is correct, then the carbon from which the diamonds formed may have been deposited originally within ocean crust at the seafloor. A relative abundance of light carbon isotopes in the Juina-5 diamonds supports this idea, since this lighter form of carbon is found at the surface but not generally in the mantle, the authors say.

The diamond inclusions also include separate phases that appear to have “unmixed” from the homogenous pool of material. This unmixing likely happened as the diamonds traveled upward hundreds of kilometers into the upper mantle, the researchers say.

After the diamonds formed in the lower mantle, they may have been launched back near the surface by a rising mantle plume, Walter and colleagues propose.

Note: This story has been adapted from a news release issued by the American Association for the Advancement of Science

Diamonds Show Depth Extent of Earth’s Carbon Cycle

September 19, 2011

Scientists have speculated for some time that Earth’s carbon cycle extends deep into the planet’s interior, but until now there has been no direct evidence. The mantle-Earth’s thickest layer -is largely inaccessible. A team of researchers analyzed diamonds that originated from the lower mantle at depths of 435 miles (700 kilometers) or more, and erupted to the surface in volcanic rocks called kimberlites. The diamonds contain what are impurities to the gemologist, but are known as mineral inclusions to the geologist. Analysis shows compositions consistent with the mineralogy of oceanic crust. This finding is the first direct evidence that slabs of oceanic crust sank or subducted into the lower mantle and that material, including carbon, is cycled between Earth’s surface and depths of hundreds of miles.

The research is published online in Science Express.

The mantle extends from as little as 5 to 1,800 miles (10-2,900 kilometers) beneath Earth’s surface. Most diamonds are free from inclusions and come from depths less than 120 miles (200 km). But in a few localities researchers have found super-deep diamonds from the depths of the convecting upper and lower mantle, as well as the transition zone in between. Whereas inclusions in diamonds from the depths of the upper mantle and transition zone have been consistent with a surface-rock origin, none from the lower mantle have borne this signature until now.

The team, which included Carnegie scientists, was led by former Carnegie postdoctoral fellow Michael Walter, now a professor at the University of Bristol, UK. The scientists analyzed minute (one to two hundredths of a millimeter) mineral grains from six diamonds from the Juina region in Brazil. The analysis showed that diamond inclusions initially crystallized as a single mineral that could form only at depths greater than 435 miles (700 km). But the inclusions recrystallized into multiple minerals as they were carried up to the surface — first probably from a mantle upwelling known as a plume, then as they erupted to the surface in kimberlites

The diamonds were analyzed for carbon at Carnegie. Four of the diamonds contained low amounts of carbon-13, a signature not found in the lower mantle and consistent with an ocean-crust origin at Earth’s surface. “The carbon identified in other super-deep, lower mantle diamonds is chiefly mantle-like in composition,” remarked co-author Steven Shirey at Carnegie. “We looked at the variations in the isotopes of the carbon atoms in the diamonds. Carbon originating in a rock called basalt, which forms from lava at the surface, is often different from that which originates in the mantle, in containing relatively less carbon-13. These super-deep diamonds contained much less carbon-13, which is most consistent with an origin in the organic component found in altered oceanic crust.”

“I find it astonishing that we can use the tiniest of mineral grains to show some of the motions of the Earth’s mantle at the largest scales,” concluded Shirey.

The researchers on the paper are M.J. Walter, S. Kohn, G. Bulanova, and C. Smith of University of Bristol, UK; D. Araujo of Universidade de Brasilia-DF Brazil; A. Steele of Carnegie’s Geophysical Laboratory, and S. Shirey, E. Gaillou, and J. Wang of Carnegie’s Department of Terrestrial Magnetism. Funding was provided by the NSF in the US, the National Environmental Research Council (NERC) in the UK, and the Carnegie Institution for Science.

Note: This story has been adapted from a news release issued by the Carnegie Institution

The Cause of Earth’s Largest Environmental Catastrophe

September 18, 2011

The eruption of giant masses of magma in Siberia 250 million years ago led to the Permo-Triassic mass extinction when more than 90 % of all species became extinct. Scientists* report on a new idea with respect to the origin of the Siberian eruptions and their relation to the mass extinction in the recent issue of Nature.

Large Igneous Provinces (LIPs) are huge accumulations of volcanic rock at Earth’s surface. Within short geological time spans of often less than one million years their eruptions cover areas of several hundred thousand square kilometres with up to 4 kilometers thick lava flows. The Siberian Traps are considered the largest continental LIP.

A widely accepted idea is that LIPs originate through melting within thermal mantle plumes, a term applied to giant mushroom-shaped volumes of plastic mantle material that rise from the base of the mantle to the lithosphere, Earth’s rigid outer shell. The high buoyancy of purely thermal mantle plumes, however, should cause kilometer-scale uplift of the lithosphere above the plume head, but such uplift is not always present. Moreover, estimates of magmatic degassing from many LIPs are considered insufficient to trigger climatic crises. The team of scientists presents a numerical model and new geochemical data with which unresolved questions can now be answered.

They suggest that the Siberian mantle plume contained a large fraction of about 15 percent of recycled oceanic crust; i.e. the crust that had long before been subducted into the deep mantle and then, through the hot mantle plume, brought back to Earth’s lithosphere. This recycled oceanic crust was present in the plume as eclogite, a very dense rock which made the hot mantle plume less buoyant. For this reason the impingement of the plume caused negligible uplift of the lithosphere. The recycled crustal material melts at much lower temperatures than the normal mantle material peridotite, and therefore the plume generated exceptionally large amounts of magmas and was able to destroy the thick Siberian lithosphere thermally, chemically and mechanically during a very short period of only a few hundred thousand years. During this process, the recycled crust, being exceptionally rich in volatiles such as CO₂

and halogens, degassed and liberated gases that passed through Earth crust into the atmosphere to trigger the mass extinction.

The model predicts that the mass extinction should have occurred before the main magmatic eruptions. Though based on sparse available data, this prediction seems to be valid for many LIPs.

*The international team of scientists included geodynamic modelers from the GFZ German Research Centre for Geosciences together with geochemists from the J. Fourier University of Grenoble, the Max Plank Institute in Mainz, and Vernadsky-, Schmidt- and Sobolev-Institutes of the Russian Academy of Sciences.

Note : The above story is reprinted from materials provided by Helmholtz Association of German Research Centres.

Tree Resin Captures Evolution of Feathers On Dinosaurs and Birds

September 17, 2011

Numerous individual filaments in Late Cretaceous Canadian amber (specimen UALVP 52821). These filaments are morphologically similar to the protofeathers that have been found as compression fossils associated with some dinosaur skeletons. Pigment distributions within these filaments range from translucent (unpigmented) to near-black (heavily pigmented). (Credit: Image courtesy of University of Alberta)

Secrets from the age of the dinosaurs are usually revealed by fossilized bones, but a University of Alberta research team has turned up a treasure trove of Cretaceous feathers trapped in tree resin. The resin turned to resilient amber, preserving some 80 million-year-old protofeathers, possibly from non-avian dinosaurs, as well as plumage that is very similar to modern birds, including those that can swim under water.

U of A paleontology graduate student Ryan McKellar discovered a wide range of feathers among the vast amber collections at the Royal Tyrrell Museum in southern Alberta. This material stems from Canada’s most famous amber deposit, near Grassy Lake in southwestern Alberta.

The discovery of the 11 feather specimens is described as the richest amber feather find from the late Cretaceous period. The amber preserves microscopic detail of the feathers and even their pigment or colour. McKellar describes the colours as typically ranging from brown to black.

No dinosaur or avian fossils were found in direct association with the amber feather specimens, but McKellar says comparison between the amber and fossilized feathers found in rock strongly suggest that some of the Grassy Lake specimens are from dinosaurs. The non-avian dinosaur evidence points to small theropods as the source of the feathers

Some of the feather specimens with modern features are very similar to those of modern birds like the Grebe, which are able to swim underwater. The feathers can take on water giving the bird the ballast required to dive more effectively..

McKellar says the Grassy Lake find demonstrates that numerous evolutionary stages of feathers were present in the late Cretaceous period and that plumage served a range of functions in both dinosaurs and birds.

The U of A team’s research was published September 15, in the journal Science.

Note : The above story is reprinted from materials provided by University of Alberta,

Shell partners with UT Austin to pursue new solutions to unlock gas resources

September 17, 2011

Shell and the University of Texas at Austin (UT) today signed a five-year agreement to invest $7.5 million to address short- and long-term challenges facing the growing worldwide unconventional oil and gas industry.

“This agreement marks an important milestone in Shell’s commitment to continually research and develop innovative technology that will help to meet global demands by bringing more energy resources to market,” said Marvin Odum, president, Shell Oil Company. “We chose to collaborate with UT because it brings together an extraordinary amount of talent from both organizations that will push the technological envelope in the field of developing even the most challenging hydrocarbons safely and responsibly.”

Shale gas is abundant, widely used, and a growing source of energy in the United States. According to the U.S. Energy Information Administration, shale gas, tight gas, and coalbed methane accounted for 50 percent of U.S. production in 2009 and are expected to account for 75 percent of production by 2035.

The new Shell-UT Program on Unconventional Resources will be managed by the university’s Bureau of Economic Geology with participation across the campus, including geoscience, engineering, economics, business, environmental and regulatory affairs. In addition to top-ranking geology and petroleum engineering programs, the university has dedicated centers working in energy law, economics, finance and energy and environmental policy.

“The pursuit of unconventional energy resources is a complex, integrated problem that requires uniting the scientific and engineering efforts below ground with above-ground efforts in water, regulation, and public awareness,” said William Powers, president of The University of Texas at Austin. “As a major research university and leader in energy, we’ve got the integrated expertise to help solve it.”

Scott Tinker, director of the Bureau of Economic Geology and an expert on global energy, notes that unconventional resources such as shale gas could extend natural gas production in the U.S. and globally from 50 to 100 years beyond recent estimates.

“Increased production of shale gas and other unconventional hydrocarbons could significantly enhance U.S. energy security,” said Tinker, “since these are largely available, affordable, and reliable domestic energy sources that contribute directly to the U.S. and global economy.”

The agreement will also support students at The University of Texas at Austin, significantly enhancing the employability of students working on Shell-UT projects in the Jackson School of Geosciences, Department of Petroleum & Geosystems Engineering, and other departments at the university.

Note: This story has been adapted from a news release issued by the University of Texas at Austin

Where Does All Earth’s Gold Come From?

September 17, 2011

Gold. (Credit: © Martin Kreutz / Fotolia)

Ultra high precision analyses of some of the oldest rock samples on Earth by researchers at the University of Bristol provides clear evidence that the planet’s accessible reserves of precious metals are the result of a bombardment of meteorites more than 200 million years

The research is published in Nature.

During the formation of Earth, molten iron sank to its centre to make the core. This took with it the vast majority of the planet’s precious metals — such as gold and platinum. In fact, there are enough precious metals in the core to cover the entire surface of Earth with a four-metre thick layer.

The removal of gold to the core should leave the outer portion of Earth bereft of bling. However, precious metals are tens to thousands of times more abundant in Earth’s silicate mantle than anticipated. It has previously been argued that this serendipitous over-abundance results from a cataclysmic meteorite shower that hit Earth after the core formed. The full load of meteorite gold was thus added to the mantle alone and not lost to the deep interior.

To test this theory, Dr Matthias Willbold and Professor Tim Elliott of the Bristol Isotope Group in the School of Earth Sciences analysed rocks from Greenland that are nearly four billion years old, collected by Professor Stephen Moorbath of the University of Oxford. These ancient rocks provide a unique window into the composition of our planet shortly after the formation of the core but before the proposed meteorite bombardment.

The researchers determined the tungsten isotopic composition of these rocks. Tungsten (W) is a very rare element (one gram of rock contains only about one ten-millionth of a gram of tungsten) and, like gold and other precious elements, it should have entered the core when it formed. Like most elements, tungsten is composed of several isotopes, atoms with the same chemical characteristics but slightly different masses. Isotopes provide robust fingerprints of the origin of material and the addition of meteorites to Earth would leave a diagnostic mark on its W isotope composition.

Dr Willbold observed a 15 parts per million decrease in the relative abundance of the isotope 182W between the Greenland and modern day rocks. This small but significant change is in excellent agreement with that required to explain the excess of accessible gold on Earth as the fortunate by-product of meteorite bombardment.

Dr Willbold said: “Extracting tungsten from the rock samples and analysing its isotopic composition to the precision required was extremely demanding given the small amount of tungsten available in rocks. In fact, we are the first laboratory world-wide that has successfully made such high-quality measurements.”

The impacting meteorites were stirred into Earth’s mantle by gigantic convection processes. A tantalising target for future work is to study how long this process took. Subsequently, geological processes formed the continents and concentrated the precious metals (and tungsten) in ore deposits which are mined today.

Dr Willbold continued: “Our work shows that most of the precious metals on which our economies and many key industrial processes are based have been added to our planet by lucky coincidence when the Earth was hit by about 20 billion billion tonnes of asteroidal material.”

This research was funded by the Natural Environment Research Council (NERC), the Science and Technology Facilities Council (STFC) and the Deutsche Forschungsgemeinschaft (DFG).

Reference:
Matthias Willbold, Tim Elliott, Stephen Moorbath. The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment. Nature, 2011; 477 (7363): 195 DOI: 10.1038/nature10399

Note : The above story is reprinted from materials provided by University of Bristol.

Discovery of a 160-Million-Year-Old Fossil Represents a New Milestone in Early Mammal Evolution

September 17, 2011

New Jurassic eutherian mammal Juramaia sinensis: The original fossil (type specimen) is preserved on a shale slab from the Jurassic Tiaojishan Formation. The fossil belongs to the Beijing Museum of Natural History (BMNH PM1143) and is being jointly studied by Chinese and American scientists. Etymology: “Jura” represents the Jurassic Period of the geological time scale; “-maia” means “mother;” sinensis means “from China.” The full name means “Jurassic mother from China.” (Credit: Zhe-Xi Luo/Carnegie Museum of Natural History)

A remarkably well-preserved fossil discovered in northeast China provides new information about the earliest ancestors of most of today’s mammal species — the placental mammals. According to a paper published August 25 in the journal Nature, this fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought, filling an important gap in the fossil record and helping to calibrate modern, DNA-based methods of dating the evolution.

The paper by a team of scientists led by Carnegie Museum of Natural History paleontologist Zhe-Xi Luo describes Juramaia sinensis, a small shrew-like mammal that lived in China 160 million years ago during the Jurassic period. Juramaia is the earliest known fossil of eutherians — the group that evolved to include all placental mammals, which provide nourishment to unborn young via a placenta. As the earliest known fossil ancestral to placental mammals, Juramaia provides fossil evidence of the date when eutherian mammals diverged from other mammals: metatherians (whose descendants include marsupials such as kangaroos) and monotremes (such as the platypus). As Luo explains, “Juramaia, from 160 million years ago, is either a great-grand-aunt, or a ‘great-grandmother’ of all placental mammals that are thriving today.”

The “Jurassic mother from China”

The fossil of Juramaia sinensis was discovered in the Liaoning Province in northeast China and examined in Beijing by Zhe-Xi Luo and his collaborators: Chong-Xi Yuan and Qiang Ji from the Chinese Academy of Geological Sciences, and Qing-Jin Meng from the Beijing Museum of Natural History, where the fossil is stored. The name Juramaia sinensis means “Jurassic mother from China.” The fossil has an incomplete skull, part of the skeleton, and, remarkably, impressions of residual soft tissues such as hair. Most importantly, Juramaia‘s complete teeth and forepaw bones enable paleontologists to pin-point that it is closer to living placentals on the mammalian family tree than to the pouched marsupials, such as kangaroos.

Resetting the evolutionary clock

“Understanding the beginning point of placentals is a crucial issue in the study of all mammalian evolution,” says Luo. The date of an evolutionary divergence — when an ancestor species splits into two descendant lineages — is among the most important pieces of information an evolutionary scientist can have. Modern molecular studies, such as DNA-based methods, can calculate the timing of evolution by a “molecular clock.” But the molecular clock needs to be cross-checked and tested by the fossil record. Prior to the discovery of Juramaia, the divergence point of eutherians from metatherians posed a quandary for evolutionary historians: DNA evidence suggested that eutherians should have shown up earlier in the fossil record — around 160 million years ago. Yet, the oldest known eutherian, was Eomaia*, dated to 125 million years ago. The discovery of Juramaia gives much earlier fossil evidence to corroborate the DNA findings, filling an important gap in the fossil record of early mammal evolution and helping to establish a new milestone of evolutionary history.

Juramaia also reveals adaptive features that may have helped the eutherian newcomers to survive in a tough Jurassic environment. Juramaia‘s forelimbs are adapted for climbing; since the majority of the Jurassic mammals lived exclusively on the ground, the ability to escape to the trees and explore the canopy might have allowed eutherian mammals to exploit an untapped niche.

Luo supports this perspective: “The divergence of eutherian mammals from marsupials eventually led to placental birth and reproduction that are so crucial for the evolutionary success of placentals. But it is their early adaptation to exploit niches on the tree that paved their way toward this success.”

*Eomaia was originally described in 2002 by a team of scientists led by Zhe-Xi Luo and Carnegie mammalogist John Wible.

Note : The above story is reprinted from materials provided by Carnegie Museum of Natural History, via EurekAlert!, a service of AAAS.

Oldest Fossils On Earth Discovered

September 17, 2011

Fossilized cells from 3.4 billion years ago. (Credit: David Wacey)

Earth’s oldest fossils have been found in Australia by a team from the University of Western Australia and Oxford University. The microscopic fossils show convincing evidence for cells and bacteria living in an oxygen-free world over 3.4 billion years ago.

The team, led by Dr David Wacey of the University of Western Australia and including Professor Martin Brasier of Oxford University, report the finding in the journal Nature Geoscience.

‘At last we have good solid evidence for life over 3.4 billion years ago. It confirms there were bacteria at this time, living without oxygen,’ says Professor Brasier of the Department of Earth Sciences at Oxford.

Earth was still a hot, violent place at this time, with volcanic activity dominating the early Earth. The sky was cloudy and grey, keeping the heat in despite the sun being weaker than today. The water temperature of the oceans was much higher at 40-50 degrees — the temperature of a hot bath — and circulating currents were very strong. Any land masses were small, or about the size of Caribbean islands, and the tidal range was huge.

Significantly, there was very little oxygen present as there were no plants or algae yet to photosynthesise and produce oxygen. The new evidence points to early life being sulfur-based, living off and metabolizing compounds containing sulfur rather than oxygen for energy and growth.

‘Such bacteria are still common today. sulfur bacteria are found in smelly ditches, soil, hot springs, hydrothermal vents — anywhere where there’s little free oxygen and they can live off organic matter,’ explains Professor Brasier.

The microfossils were found in a remote part of Western Australia called Strelley Pool. They are very well preserved between the quartz sand grains of the oldest beach or shoreline known on Earth, in some of the oldest sedimentary rocks that can be found anywhere.

‘We can be very sure about the age as the rocks were formed between two volcanic successions that narrow the possible age down to a few tens of millions of years,’ says Professor Brasier. ‘That’s very accurate indeed when the rocks are 3.4 billion years old.’

The microfossils satisfy three crucial tests that the forms seen in the rocks are biological and have not occurred through some mineralization process.

The fossils are very clearly preserved showing precise cell-like structures all of a similar size. They look like well known but much newer microfossils from 2 billion years ago, and are not odd or strained in shape.

The fossils suggest biological-like behavior. The cells are clustered in groups, are only present in appropriate habitats and are found attached to sand grains.

And crucially, they show biological metabolisms. The chemical make-up of the tiny fossilized structures is right, and crystals of pyrite (fool’s gold) associated with the microfossils are very likely to be by-products of the sulfur metabolism of these ancient cells and bacteria.

Early fossils of life on Earth has been a controversial area. In the past decade, the barriers that need to be overcome before claiming such evidence have been raised significantly, aided by new techniques for mapping the chemistry of rocks at fine scales.

In 2002, the same Oxford group suggested well-known microfossils from the Apex chert in Australia were not the preserved forms of ancient bacteria after all. They argued that the context, shape and mineralogy of the forms were all wrong for them to be of biological origin.

They believe the current fossils, found just 20 miles away, satisfy all criteria for judging such finds.

The researchers are now using the techniques and approaches they used in this study to re-examine other fossil finds that have been proposed to contain evidence for life on Earth at these extremely early times.

‘We’re now making detailed comparisons with all other early microfossils, and we’re very optimistic for future finds,’ says Professor Brasier.

The work also has implications for looking for life on other planets, giving an indication of what evidence for such life might look like.

Should there be life elsewhere in our solar system — on Mars or on the moons of Titan or Europa — it is likely to be similar sorts of bacteria and cells living in similar environments. So any fossils in rocks from these planets and moons ought to look like these Australian microfossils and pass the same evidence tests.

‘Could these sorts of things exist on Mars? It’s just about conceivable,’ says Professor Brasier. ‘But it would need these approaches — mapping the chemistry of any microfossils in fine detail and convincing three-dimensional images — to support any evidence for life on Mars.’

Note : The above story is reprinted from materials provided by University of Oxford.

New data shows El Mayor-Cucapah earthquake was simple on surface, complicated at depth

September 17, 2011

A 3-D view of the surface rupture of the April 4, 2010

El Mayor-Cucapah Earthquake (red line) reveals a new fault line connecting the Gulf of California with the Elsinore fault, which is likely to become the main fault at the boundary between the Pacific and the North America plates. – Caltech’s Tectonics Observatory

Like scars that remain on the skin long after a wound has healed, earthquake fault lines can be traced on Earth’s surface long after their initial rupture. Typically, this line of intersection between the area where the fault slips and the ground is more complicated at the surface than at depth. But a new study of the April 4, 2010, El Mayor-Cucapah earthquake in Mexico reveals a reversal of this trend. While the fault involved in the event appeared to be superficially straight, the fault zone is warped and complicated at depth.

The study-led by researchers at the California Institute of Technology (Caltech) and documenting findings from the magnitude 7.2 event, which was centered in the Baja California state of Mexico-is available online in the journal Nature Geoscience.

The El Mayor-Cucapah earthquake happened along a system of faults that run from Southern California into Mexico, cutting through the Cucapah mountain range and across the Colorado River delta. This system of faults forms a portion of the plate boundary between the Pacific Plate and the North American Plate. Two main segments of the fault tilt downward steeply from the surface at opposing angles: the northwestern half angles downward beneath the Mexicali Valley, whereas the southeastern half angles away from the valley.

In a standard model, transform plate boundary structures-where two plates slide past one another-tend to be vertically oriented, which allows for lateral side-by-side shear fault motion. In the case of this quake, however, lead author Shengji Wei, a postdoctoral scholar in geophysics, and colleagues showed that the 120-kilometer-long rupture involved angled, non-vertical faults and that the event was initiated on a connecting extension fault between the two segments.

“Although the surface trace is nearly linear, we found that the event, which started with a smaller quake, happened mainly on two faults with opposite dipping directions,” says Wei.

In fact, the seismic rupture traveled through a relatively complicated set of preexisting faults that are dipping in various directions. “It was really surprising to see a straight fault trace that cuts through the Colorado delta and the rugged topography of the Sierra Cucapah as a result of this event,” says Jean-Philippe Avouac, director of Caltech’s Tectonics Observatory and principal investigator on the study.

The team used interferometric synthetic aperture radar (InSAR) and optical images gathered from satellites, global positioning system (GPS) data, and seismological data to study the rupture process. By combining the GPS data and remote sensing techniques-which provide measurements of surface displacement-and seismological techniques to study the ground vibrations generated by the temblor, the researchers were able to produce an extremely well-resolved model of the earthquake.

The model describes the geometry of the faults that broke during the quake and the time evolution of the rupture. It shows that once the earthquake began with an extensional deep break that pulled the two segments apart, it spread bilaterally to the northwest and the southeast. As the rupture spread northwestward, it continued to break erratically through the faults below the Cucapah mountain range. Simultaneously, the rupture spread towards the southeast, breaking a fault that had been covered over by a blanket of sediments that forms the Colorado River delta.

“High-resolution satellite radar images allowed us to locate a previously unmapped fault-the Indiviso Fault-beneath the Colorado River Delta that had been buried by river sediments since its last earthquake,” says NASA’s Jet Propulsion Laboratory (JPL) geophysicist Eric Fielding, who was a coauthor of the study. “This fault moved up to 16 feet, or 5 meters, in the April 4, 2010, earthquake.”

Wei says that since the new analysis indicates the responsible fault is more segmented deep down than its straight surface trace suggests, the evolution and extent of this earthquake’s rupture could not have been accurately anticipated from the surface geology alone. Anticipating the characteristics of an earthquake that would likely happen on a young fault system (like the event in the study) is a challenge, since the geologic structures involved in the new fault system are not clear enough.

According to Avouac, the data can also be used to illustrate the process by which the plate boundary-which separates the Pacific Plate from North America- evolves and starts connecting the Gulf of California to the Elsinore fault in Southern California.

“We may have to wait for a couple of million years to clearly see the active fault zone in the topography, as we can now see further north in Central California, for example,” Avouac says. “Earthquakes with magnitude 7.5 and lower are probably typical of this kind of younger fault zone, while fault zones with a longer geological history and simpler fault geometries are more prone to produce larger ruptures.”

This is important information, since damage estimates from the earthquake, which mostly affected agribusinesses, topped $440 million in the Mexicali Valley of Baja California and $90 million in the Imperial Valley of California.

Note: This story has been adapted from a news release issued by the California Institute of Technology

Tohoku tsunami created icebergs in Antarctica

September 17, 2011

Before (left) and after (right) photos of the Sulzberger Ice Shelf illustrate the calving event associated with the Japan earthquake and resulting tsunami that occurred on March 11, 2011. The icebergs have just begun to separate in the left image. – European Space Agency/Envisat

A NASA scientist and her colleagues were able to observe for the first time the power of an earthquake and tsunami to break off large icebergs a hemisphere away.

Kelly Brunt, a cryosphere specialist at Goddard Space Flight Center, Greenbelt, Md., and colleagues were able to link the calving of icebergs from the Sulzberger Ice Shelf in Antarctica following the Tohoku Tsunami, which originated with an earthquake off the coast of Japan in March 2011. The finding, detailed in a paper published online today in the Journal of Glaciology, marks the first direct observation of such a connection between tsunamis and icebergs.

The birth of an iceberg can come about in any number of ways. Often, scientists will see the towering, frozen monoliths break into the polar seas and work backwards to figure out the cause.

So when the Tohoku Tsunami was triggered in the Pacific Ocean on March 11 this spring, Brunt and colleagues immediately looked south. All the way south. Using multiple satellite images, Brunt, Emile Okal at Northwestern University and Douglas MacAyeal at University of Chicago were able to observe new icebergs floating off to sea shortly after the sea swell of the tsunami reached Antarctica.

To put the dynamics of this event in perspective: An earthquake off the coast of Japan caused massive waves to explode out from its epicenter. Swells of water swarmed toward an ice shelf in Antarctica, 8,000 miles (13,600 km) away, and about 18 hours after the earthquake occurred, those waves broke off several chunks of ice that together equaled about two times the surface area of Manhattan. .According to historical records, this particular piece of ice hadn’t budged in at least 46 years before the tsunami came along.

And as all that was happening, scientists were able to watch the Antarctic ice shelves in as close to real-time as satellite imagery allows, and catch a glimpse of a new iceberg floating off into the Ross Sea.

“In the past we’ve had calving events where we’ve looked for the source. It’s a reverse scenario – we see a calving and we go looking for a source,” Brunt said. “We knew right away this was one of the biggest events in recent history – we knew there would be enough swell. And this time we had a source.”

Scientists first speculated in the 1970s that repeated flexing of an ice shelf – a floating extension of a glacier or ice sheet that sits on land – by waves could cause icebergs to break off. Scientific papers in more recent years have used models and tide gauge measurements in an attempt to quantify the impact of sea swell on ice shelf fronts.

The swell was likely only about a foot high (30 cm) when it reached the Sulzberger shelf. But the consistency of the waves created enough stress to cause the calving. This particular stretch of floating ice shelf is about 260 feet (80 meters) thick, from its exposed surface to its submerged base.

When the earthquake happened, Okal immediately honed in on the vulnerable faces of the Antarctic continent. Using knowledge of iceberg calving and what a NOAA model showed of the tsunami’s projected path across the unobstructed Pacific and Southern oceans, Okal, Brunt and MacAyeal began looking at what is called the Sulzberger Ice Shelf. The Sulzberger shelf faces Sulzberger Bay and New Zealand.

Through a fortuitous break in heavy cloud cover, Brunt spotted what appeared to be a new iceberg in MODerate Imaging Spectroradiometer (MODIS) data.

“I didn’t have strong expectations either way whether we’d be able to see something,” Brunt said. “The fastest imagery I could get to was from MODIS Rapid Response, but it was pretty cloudy. So I was more pessimistic that it would be too cloudy and we couldn’t see anything. Then, there was literally one image where the clouds cleared, and you could see a calving event.”

A closer look with synthetic aperture radar data from the European Space Agency satellite, Envisat, which can penetrate clouds, found images of two moderate-sized icebergs – with more, smaller bergs in their wake. The largest iceberg was about four by six miles in surface area – itself about equal to the surface area of one Manhattan. All of the ice surface together about equaled two Manhattans. After looking at historical satellite imagery, the group determined the small outcropping of ice had been there since at least 1965, when it was captured by USGS aerial photography.

The proof that seismic activity can cause Antarctic iceberg calving might shed some light on our knowledge of past events, Okal said.

“In September 1868, Chilean naval officers reported an unseasonal presence of large icebergs in the southernmost Pacific Ocean, and it was later speculated that they may have calved during the great Arica earthquake and tsunami a month earlier,” Okal said. “We know now that this is a most probable scenario.”

MacAyeal said the event is more proof of the interconnectedness of Earth systems.

“This is an example not only of the way in which events are connected across great ranges of oceanic distance, but also how events in one kind of Earth system, i.e., the plate tectonic system, can connect with another kind of seemingly unrelated event: the calving of icebergs from Antarctica’s ice sheet,” MacAyeal said.

In what could be one of the more lasting observations from this whole event, the bay in front of the Sulzberger shelf was largely lacking sea ice at the time of the tsunami. Sea ice is thought to help dampen swells that might cause this kind of calving. At the time of the Sumatra tsunami in 2004, the potentially vulnerable Antarctic fronts were buffered by a lot of sea ice, Brunt said, and scientists observed no calving events that they could tie to that tsunami.

“There are theories that sea ice can protect from calving. There was no sea ice in this case,” Brunt said. “It’s a big chunk of ice that calved because of an earthquake 13,000 kilometers away. I think it’s pretty cool.”

Note: This story has been adapted from a news release issued by the NASA/Goddard Space Flight Center

Sea level rise less from Greenland, more from Antarctica, than expected during last interglacial

September 17, 2011

Anders Carlson, a UW–Madison geologist, surveys an outlet glacier in southwest Greenland. Carlson and colleagues from UW–Madison and Oregon State University have shown that melting ice from Greenland may have raised ocean levels less than expected during the most-recent prolonged warm spell on Earth. The surprising patterns of ice melt found by new research suggest that Greenland’s ice sheet may be more stable — and Antarctica’s less stable — than previously thought. Credit: Photo courtesy Robert Hatfield, Oregon State University — Anders Carlson, a UW–Madison geologist, surveys an outlet glacier in southwest Greenland. Carlson and colleagues from UW–Madison and Oregon State University have shown that melting ice from Greenland may have raised ocean levels less than expected during the most-recent prolonged warm spell on Earth. The surprising patterns of ice melt found by new research suggest that Greenland’s ice sheet may be more stable — and Antarctica’s less stable — than previously thought.
Credit: Photo courtesy Robert Hatfield, Oregon State University

During the last prolonged warm spell on Earth, the oceans were at least four meters – and possibly as much as 6.5 meters, or about 20 feet – higher than they are now.

Where did all that extra water come from? Mainly from melting ice sheets on Greenland and Antarctica, and many scientists, including University of Wisconsin-Madison geoscience assistant professor Anders Carlson, have expected that Greenland was the main culprit.

But Carlson’s new results, published July 29 in Science, are challenging that assertion, revealing surprising patterns of melting during the last interglacial period that suggest that Greenland’s ice may be more stable – and Antarctica’s less stable – than many thought.
“The Greenland Ice Sheet is melting faster and faster,” says Carlson, who is also a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies. But despite clear observations of that fact, estimates of just how much the ice will melt and contribute to sea level rise by the end of this century are highly varied, ranging from a few centimeters to meters. “There’s a clear need to understand how it has behaved in the past, and how it has responded to warmer-than-present summers in the past.”

The ice-estimation business is rife with unknown variables and has few known physical constraints, Carlson explains, making ice sheet behavior – where they melt, how much, how quickly – the largest source of uncertainty in predicting sea level rises due to climate change.
His research team sought a way to constrain where ice remained on Greenland during the last interglacial period, around 125,000 years ago, to better define past ice sheet behavior and improve future projections.

The researchers analyzed silt from an ocean-floor core taken from a region off the southern tip of Greenland that receives sediments carried by meltwater streams off the ice sheet. They used different patterns of radiogenic isotopes to identify sources of the sediment, tracing the silt back to one of three “terranes” or regions, each with a distinct geochemical signature. The patterns of sedimentation show which terranes were still glaciated at that time.

“If the land deglaciates, you lose that sediment,” Carlson explains. But to their surprise, they found that all the terranes were still supplying sediment throughout the last interglacial period and thus still had some ice cover.

“The ice definitely retreated to smaller than present extent and definitely raised sea level to higher than present” and continued to melt throughout the warm period, he adds, but the sediment analysis indicates that “the ice sheet seems to be more stable than some of the greater retreat values that people have presented.”

The team used their results to evaluate several existing models of Greenland ice sheet melting during the last interglacial period. The models consistent with the new findings indicate that melting Greenland ice was responsible for a sea level rise of 1.6 to 2.2 meters – at most, roughly half of the minimum four-meter total increase.

Even after accounting for other Arctic ice and the thermal expansion of warmer water, most of the difference must have come from a melting Antarctic ice sheet, Carlson says.
“The implication of our results is that West Antarctica likely was much smaller than it is today,” and responsible for much more of the sea level rise than many scientists have thought, he says. “If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary.”

Ultimately, Carlson says he hopes this line of research will improve the representation of ice sheet responses to a warming planet in future Intergovernmental Panel on Climate Change (IPCC) reports. Temperatures during the last interglacial period were similar to those expected by the end of this century, and present-day temps have already reached a point that Greenland’s glaciers are melting.

Note: This story has been adapted from a news release issued by the University of Wisconsin-Madison

Diamond impurities bonanza for geologists studying Earth’s history

September 17, 2011

This is an optical photomicrograph of a sulfide-inclusion-bearing rough diamond from Botswana. – Steven Shirey

Jewelers abhor diamond impurities, but they are a bonanza for scientists.

Safely encased in super-hard diamond, impurities are unaltered, ancient minerals that tell the story of Earth’s distant past.

Researchers analyzed data from more than 4,000 of these mineral inclusions to find that continents started the cycle of breaking apart, drifting, and colliding about three billion years ago.

The research results, published in this week’s issue of the journal Science, pinpoint when this so-called Wilson cycle began.

Lead author Steven Shirey of the Carnegie Institution’s Department of Terrestrial Magnetism says that the Wilson cycle is responsible for the growth of the Earth’s continental crust, the continental structures we see today, the opening and closing of ocean basins through time, mountain building, and the distribution of ores and other materials in the crust.

“But when it all began has remained elusive until now,” Shirey says.

“We used the impurities, or inclusions, contained in diamonds, because they are perfect time capsules from great depth beneath the continents.

“They provide age and chemical information for a span of more than 3.5 billion years that includes the evolution of the atmosphere, the growth of the continental crust, and the beginning of plate tectonics.”

Co-author Stephen Richardson of the University of Cape Town says that it’s “astonishing that we can use the smallest mineral grains that can be analyzed to reveal the origin of some of Earth’s largest geological features.”

“The tiny inclusions found inside diamonds studied by this team have recorded the chemistry and evolution of the Earth over 3.5 billion years,” says Jennifer Wade, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “They help pinpoint when the cycle of plate tectonics first began on Earth.”

The largest diamonds come from cratons, the most ancient formations within continental interiors that have deep mantle roots or keels around which younger continental material gathered.

Cratons contain the oldest rocks on the planet, and their keels extend into the mantle more than 125 miles where pressures are sufficiently high, but temperatures sufficiently low, for diamonds to form and be stored for billions of years.

Over time, diamonds have arrived at the surface as accidental passengers during volcanic eruptions of deep magma that solidified into rocks called kimberlites.

The inclusions in diamonds come in two major varieties: peridotitic and eclogitic.

Peridotite is the most abundant rock type in the upper mantle, whereas eclogite is generally thought to be the remnant of oceanic crust recycled into the mantle by the subduction or sinking of tectonic plates.

Shirey and Richardson reviewed the data from more than 4,000 inclusions of silicate–the Earth’s most abundant material–and more than 100 inclusions of sulfide from five ancient continents.

The most crucial aspects, they say, looked at when the inclusions were encapsulated and the associated compositional trends.

Compositions vary and depend on the geochemical processing that precursor components underwent before they were encapsulated.

Two systems used to date inclusions were compared. Both rely on natural isotopes that decay at exceedingly slow but predictable rates–about one disintegration every ten years on the scale of an inclusion–making them excellent atomic clocks for determining absolute ages.

The researchers found that before 3.2 billion years ago, only diamonds with peridotitic compositions formed, whereas after three billion years ago, eclogitic diamonds dominated.

“The simplest explanation,” says Shirey, “is that this change came from the initial subduction of one tectonic plate under the deep mantle keel of another as continents began to collide on a scale similar to that of the supercontinent cycle today.

“The sequence of underthrusting and collision led to the capture of eclogite in the subcontinental mantle keel along with the fluids that are needed to make diamond.”

Concludes Richardson, “This transition marks the onset of the Wilson cycle of plate tectonics.”

Note: This story has been adapted from a news release issued by the National Science Foundation

Deep below the Deepwater Horizon oil spill

September 17, 2011

This is a graphic explanation of escaped petroleum dispersion 1,000 meters below the sea. – EPFL

For the first time, scientists gathered oil and gas directly as it escaped from a deep ocean wellhead – that of the damaged Deepwater Horizon oil rig. What they found allows a better understanding of how pollution is partitioned and transported in the depths of the Gulf of Mexico and permits superior estimation of the environmental impact of escaping oil, allowing for a more precise evaluation of previously estimated repercussions on seafloor life in the future.

The explosion of the Deepwater Horizon rig in April 2010 was both a human and an environmental catastrophe. Getting the spill under control was an enormous challenge. The main problem was the depth of the well, nearly 1,500 meters below the sea surface. It was a configuration that had never been tried before, and the pollution it unleashed after methane gas shot to the surface and ignited in a fiery explosion is also unequalled. Much research has been done since the spill on the effects on marine life at the ocean’s surface and in coastal regions. Now, École Polytechnique Fédérale de Lausanne (EPFL) professor Samuel Arey and the Woods Hole Oceanographic Institute reveal in the advance online edition of Proceedings of the National Academy of Sciences how escaped crude oil and gas behave in the deep water environment.

Into the deep

In June 2010, with the help of a remotely operated vehicle (ROV), Woods Hole scientists reached the base of the rig and gathered samples directly from the wellhead using a robotic arm. The oceanographers also made more than 200 other measurements at various water depths over a 30-kilometer area. These samples were then analyzed with the help of the US National Oceanic and Atmospheric Administration and the dissolution of hydrocarbons was modeled at EPFL. This model showed how the properties of hydrocarbons are important in understanding the wellhead structure and pollution diffusion-how pollution spreads out-in the depths.

From the ROV to the lab

Lab analysis led the scientists to describe for the first time the physical basis for the deep sea trajectories of light-weight, water-soluble hydrocarbons such as methane, benzene, and naphthalene released from the base of the rig. The researchers observed, for example, that at a little more than 1,000 meters below the surface, a large plume spread out from the original gusher, moving horizontally in a southwest direction with prevailing currents. Unlike a surface spill, from which these volatile compounds evaporate into the atmosphere, in the deep water under pressure, light hydrocarbon components predominantly dissolve or form hydrates, compounds containing water molecules. And depending on its properties, the resulting complex mixture can rise, sink, or even remain suspended in the water, and possibly go on to cause damage to seafloor life far from the original spill.

By comparing the oil and gas escaping from the well with the mixture at the surface, EPFL’s Samuel Arey, head of Environmental Chemistry Modeling Laboratory, and colleagues were able to show that the composition of the deep sea plumes could be explained by significant dissolution of light hydrocarbons at 1 kilometer depth. In other words, an important part of the oil spreads out in underwater plumes, so we need a more precise evaluation of previously estimated repercussions on seafloor life in the future. Arey’s methodology offers a better estimation of how pollution travels and the potential deep sea consequences of spills.

“Modeling the environmental fate of hydrocarbons in deep water ecosystems required a new approach, with a global view, in order to correctly understand the impact of the pollution,” explains Arey. This research will have a significant impact on assessments of the environmental impact of deep water oil spills.

Note: This story has been adapted from a news release issued by the Ecole Polytechnique Fédérale de Lausanne

Heavy metal meets hard rock: Battling through the ocean crust’s hardest rocks

September 17, 2011

A granoblastic basalt viewed under the microscope (picture is 2.3 mm across). Magnification shows a rock formed of small rounded mineral grains annealed together (plagioclase: white, pyroxene: light green and light brown, and magnetite or ilmenite: black). They may look inoffensive, but these rocks are the hardest material ever drilled in more than four decades of scientific ocean drilling. The rocks are very abrasive and aggressive to the drilling and coring tools, and difficult to penetrate. However, the samples recovered provide a treasure trove of information, recording the rocks’ initial crystallization as a basaltic dike then their reheating at the top of the mid-ocean ridge magma chamber. These rocks represent the heat exchanger where thermal energy from the cooling and solidifying melt in the magma chamber below is exchanged with seawater infiltrating from the oceans, leading to the ‘black smoker-type’ hot (>350°C) water vents on the seafloor. – IODP/USIO

Integrated Ocean Drilling Program (IODP) Expedition 335 Superfast Spreading Rate Crust 4 recently completed operations in Ocean Drilling Program (ODP) Hole 1256D, a deep scientific borehole that extends more than 1500 meters below the seafloor into the Pacific Ocean’s igneous crust – rocks that formed through the cooling and crystallization of magma, and form the basement of the ocean floor.

An international team of scientists led by co-chief scientists Damon Teagle (National Oceanographic Center Southampton, University of Southampton in the UK) and Benoît Ildefonse (CNRS, Université Montpellier 2 in France) returned to ODP Hole 1256D aboard the scientific research vessel, JOIDES Resolution, to sample a complete section of intact oceanic crust down into gabbros.

This expedition was the fourth in a series and builds on the efforts of three expeditions in 2002 and 2005.

Gabbros are coarse-grained intrusive rocks formed by the slow cooling of basaltic magmas. They make up the lower two-thirds of the ocean crust. The intrusion of gabbros at the mid-ocean ridges is the largest igneous process active on our planet with more than 12 cubic kilometers of new magma from the mantle intruded into the crust each year. The minerals, chemistry, and textures of gabbroic rocks preserve records of the processes that occur deep within the Earth’s mid-ocean ridges, where new ocean crust is formed.

“The formation of new crust is the first step in Earth’s plate tectonic cycle,” explained Teagle. “This is the principal mechanism by which heat and material rise from within the Earth to the surface of the planet. And it’s the motion and interactions of Earth’s tectonic plates that drive the formation of mountains and volcanoes, the initiation of earthquakes, and the exchange of elements (such as carbon) between the Earth’s interior, oceans, and atmosphere.”

“Understanding the mechanisms that construct new tectonic plates has been a major, long-standing goal of scientific ocean drilling,” added Ildefonse, “but progress has been inhibited by a dearth of appropriate samples because deep drilling (at depths greater than 1000 meters into the crust) in the rugged lavas and intrusive rocks of the ocean crust continues to

pose significant technical challenges.”

ODP Hole 1256D lies in the eastern equatorial Pacific Ocean about 900 kilometers to the west of Costa Rica and 1150 kilometers east of the present day East Pacific Rise. This hole is in 15 million year old crust that formed during an episode of “superfast” spreading at the ancient East Pacific Rise, when the newly formed plates were moving apart by more than 200 millimeters per year (mm/yr).

“Although a spreading rate of 200 mm/yr is significantly faster than the fastest spreading rates on our planet today, superfast-spread crust was an attractive target,” stated Teagle, “because seismic experiments at active mid-ocean ridges indicated that gabbroic rocks should occur at much shallower depths than in crust formed at slower spreading rates. In 2005, we recovered gabbroic rocks at their predicted depth of approximately 1400 meters below the seafloor, vindicating the overall ‘Superfast’ strategy.”Previous expeditions to Hole 1256D successfully drilled through the erupted lavas and thin (approximately one-meter-wide) intrusive “dikes” of the upper crust, reaching into the gabbroic rocks of the lower crust. The drilling efforts of Expedition 335 were focused just below the 1500-meter mark in the critical transition zone from dikes to gabbros, where magma at 1200°C exchanges heat with super-heated seawater circulating within cracks in the upper crust. This heat exchange occurs across a narrow thermal boundary that is perhaps only a few tens of meters thick.

In this zone, the intrusion of magma causes profound textural changes to the surrounding rocks, a process known as contact metamorphism. In the mid-ocean ridge environment this results in the formation of very fine-grained granular rocks, called granoblastic basalts, whose constituent minerals recrystallize at a microscopic scale and become welded together by magmatic heat. The resulting metamorphic rock is as hard as any formation encountered by ocean drilling and sometimes even tougher than the most resilient of hard formation

drilling and coring bits.

Expedition 335 reentered Hole 1256D more than five years after the last expedition to this site. The expedition encountered and overcame a series of significant engineering challenges, each of which was unique, although difficulties were not unexpected when drilling in a deep, uncased, marine borehole into igneous rocks.

The patient, persistent efforts of the drilling crew successfully cleared a major obstruction at a depth of 920 that had initially prevented reentry into the hole to its full depth of 1507 meters. Then at the bottom of the hole the very hard granular rocks that had proved challenging during the previous Superfast expedition were once more encountered. Although there may only be a few tens of meters of these particularly tenacious granoblastic basalts, their extreme toughness once more proved challenging to sample- resulting in the grinding down of one of the hardest formation coring bits into a smooth stump.

A progressive, logical course of action was then undertaken to clear the bottom of the hole of metal debris from the failed coring bit and drilling cuttings. This effort required the innovative use of hole-clearing equipment such as large magnets, and involved over 240 kilometers of drilling pipe deployments (trips) down into the hole and back onto the ship. (The total amount of pipe “tripped” was roughly equivalent to the distance from Paris to the English coast, or from New York City to Philadelphia, or Tokyo to Niigata). These efforts returned hundreds of kilograms of rocks and drill cuttings, including large blocks (up to 5 kilograms) of the culprit granoblastic basalts that hitherto had only been very poorly recovered through coring. A limited number of gabbro boulders were also recovered, indicating that scientists are tantalizingly close to breaking through into the gabbroic layer.

Expedition 335 operations also succeeded in clearing Hole 1256D of drill cuttings, much of

which appear to have been circulating in the hole since earlier expeditions

“We recovered a remarkable sample suite of granoblastic basalts along with minor gabbros, providing a detailed picture of a rarely sampled, yet critical interval of the oceanic crust,” Ildefonse observed. “Most importantly,” he added, “the hole has been stabilized and cleared to its full depth, and is ready for deepening in the near future.”

Note: This story has been adapted from a news release issued by the Integrated Ocean Drilling Program Management International

Researchers discover new force driving Earth’s tectonic plates

September 17, 2011

A view of the bends of the fracture zones on the Southwest Indian Ridge caused by the slowdown of Africa in response to the Reunion plume head. The image shows the gravity field. – Scripps Institution of Oceanography,UC San Diego

Bringing fresh insight into long-standing debates about how powerful geological forces shape the planet, from earthquake ruptures to mountain formations, scientists at Scripps Institution of Oceanography at UC San Diego have identified a new mechanism driving Earth’s massive tectonic plates.

Scientists who study tectonic motions have known for decades that the ongoing “pull” and “push” movements of the plates are responsible for sculpting continental features around the planet. Volcanoes, for example, are generally located at areas where plates are moving apart or coming together. Scripps scientists Steve Cande and Dave Stegman have now discovered a new force that drives plate tectonics: Plumes of hot magma pushing up from Earth’s deep interior. Their research is published in the July 7 issue of the journal Nature.

Using analytical methods to track plate motions through Earth’s history, Cande and Stegman’s research provides evidence that such mantle plume “hot spots,” which can last for tens of millions of years and are active today at locations such as Hawaii, Iceland and the Galapagos, may work as an additional tectonic driver, along with push-pull forces.

Their new results describe a clear connection between the arrival of a powerful mantle plume head around 70 million years ago and the rapid motion of the Indian plate that was pushed as a consequence of overlying the plume’s location. The arrival of the plume also created immense formations of volcanic rock now called the “Deccan flood basalts” in western India, which erupted just prior to the mass extinction of dinosaurs. The Indian continent has since drifted north and collided with Asia, but the original location of the plume’s arrival has remained volcanically active to this day, most recently having formed Réunion island near Madagascar.

The team also recognized that this “plume-push” force acted on other tectonic plates, and pushed on Africa as well but in the opposite direction.

“Prior to the plume’s arrival, the African plate was slowly drifting but then stops altogether, at the same time the Indian speeds up,” explains Stegman, an assistant professor of geophysics in Scripps’ Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics. “It became clear the motion of the Indian and African plates were synchronized and the Réunion hotspot was the common link.”

After the force of the plume had waned, the African plate’s motion gradually returned to its previous speed while India slowed down.

“There is a dramatic slow down in the northwards motion of the Indian plate around 50 million years ago that has long been attributed to the initial collision of India with the Eurasian plate,” said Cande, a professor of marine geophysics in the Geosciences Research Division at Scripps.

“An implication of our study is that the slow down might just reflect the waning of the mantle plume-the actual collision might have occurred a little later.”

Note: This story has been adapted from a news release issued by the University of California – San Diego

Ocean currents speed melting of Antarctic ice

September 17, 2011

Upwelling seawater along parts of Pine Island Glacier Ice Shelf has carved out caves in the ice and drawn wildlife like this whale. – Maria Stenzel, all rights reserved.

Stronger ocean currents beneath West Antarctica’s Pine Island Glacier Ice Shelf are eroding the ice from below, speeding the melting of the glacier as a whole, according to a new study in Nature Geoscience. A growing cavity beneath the ice shelf has allowed more warm water to melt the ice, the researchers say-a process that feeds back into the ongoing rise in global sea levels. The glacier is currently sliding into the sea at a clip of four kilometers (2.5 miles) a year, while its ice shelf is melting at about 80 cubic kilometers a year – 50 percent faster than it was in the early 1990s – the paper estimates.

“More warm water from the deep ocean is entering the cavity beneath the ice shelf, and it is warmest where the ice is thickest,” said study’s lead author, Stan Jacobs, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory.

In 2009, Jacobs and an international team of scientists sailed to the Amundsen Sea aboard the icebreaking ship Nathaniel B. Palmer to study the region’s thinning ice shelves-floating tongues of ice where landbound glaciers meet the sea. One goal was to study oceanic changes near the Pine Island Glacier Ice Shelf, which they had visited in an earlier expedition, in 1994. The researchers found that in 15 years, melting beneath the ice shelf had risen by about 50 percent. Although regional ocean temperatures had also warmed slightly, by 0.2 degrees C or so, that was not enough to account for the jump.

The local geology offered one explanation. On the same cruise, a group led by Adrian Jenkins, a researcher at British Antarctic Survey and study co-author, sent a robot submarine beneath the ice shelf, revealing an underwater ridge. The researchers surmised that the ridge had once slowed the glacier like a giant retaining wall. When the receding glacier detached from the ridge, sometime before the 1970s, the warm deep water gained access to deeper parts of the glacier. Over time, the inner cavity grew, more warm deep water flowed in, more melt water flowed out, and the ice thinned. With less friction between the ice shelf and seafloor, the landbound glacier behind it accelerated its slide into the sea. Other glaciers in the Amundsen region have also thinned or widened, including Thwaites Glacier and the much larger Getz Ice Shelf.

One day, near the southern edge of Pine Island Glacier Ice Shelf, the researchers directly observed the strength of the melting process as they watched frigid, seawater appear to boil on the surface like a kettle on the stove. To Jacobs, it suggested that deep water, buoyed by added fresh glacial melt, was rising to the surface in a process called upwelling. Jacobs had never witnessed upwelling first hand, but colleagues had described something similar in the fjords of Greenland, where summer runoff and melting glacier fronts can also drive buoyant plumes to the sea surface.

In recent decades, researchers have found evidence that Antarctica is getting windier, and this may also help explain the changes in ocean circulation. Stronger circumpolar winds would tend to push sea ice and surface water north, says Jacobs. That in turn, would allow more warm water from the deep ocean to upwell onto the Amundsen Sea’s continental shelf and into its ice shelf cavities.

Pine Island Glacier, among other ice streams in Antarctica, is being closely watched for its potential to redraw coastlines worldwide. Global sea levels are currently rising at about 3 millimeters (.12 inches) a year. By one estimate, the total collapse of Pine Island Glacier and its tributaries could raise sea level by 24 centimeters (9 inches).

The paper adds important and timely insights about oceanic changes in the region, says Eric Rignot, a professor at University of California at Irvine and a senior research scientist at NASA’s Jet Propulsion Laboratory. “The main reason the glaciers are thinning in this region, we think, is the presence of warm waters,” he said. “Warm waters did not get there because the ocean warmed up, but because of subtle changes in ocean circulation. Ocean circulation is key. This study reinforces this concept.”

Note: This story has been adapted from a news release issued by the The Earth Institute at Columbia University

Stiff sediments made 2004 Sumatra earthquake deadliest in history

September 17, 2011

At a typical subduction zone, the fault ruptures primarily along the boundary between the two tectonic plates and dissipates in weak sediments (a), or ruptures along ‘splay faults’ (b); in either case, stopping far short of the trench. In the area of the 2004 Sumatra earthquake, sediments are thicker and stronger, extending the rupture closer to the trench for a larger earthquake and, due to deeper water, a much larger tsunami. – UT Austin

An international team of geoscientists has discovered an unusual geological formation that helps explain how an undersea earthquake off the coast of Sumatra in December 2004 spawned the deadliest tsunami in recorded history.

Instead of the usual weak, loose sediments typically found above the type of geologic fault that caused the earthquake, the team found a thick plateau of hard, compacted sediments. Once the fault snapped, the rupture was able to spread from tens of kilometers below the seafloor to just a few kilometers below the seafloor, much farther than weak sediments would have permitted. The extra distance allowed it to move a larger column of seawater above it, unleashing much larger tsunami waves.

“The results suggest we should be concerned about locations with large thicknesses of sediments in the trench, especially those which have built marginal plateaus,” said Sean Gulick, research scientist at The University of Texas at Austin’s Institute for Geophysics. “These may promote more seaward rupture during great earthquakes and a more significant tsunami.”

The team’s results appear this week in an article lead-authored by Gulick in an advance online publication of the journal Nature Geoscience.

The team from The University of Texas at Austin, The University of Southampton in the United Kingdom, The Agency for the Assessment and Application of Technology in Indonesia and The Indonesia Institute for Sciences used seismic instruments, which emit sound waves, to visualize subsurface structures.

Early in the morning of Dec. 26, 2004 a powerful undersea earthquake started off the west coast of Sumatra, Indonesia. The resulting tsunami caused devastation along the coastlines bordering the Indian Ocean with tsunami waves up to 30 meters (100 feet) high inundating coastal communities. With very little warning of impending disaster, more than 230,000 people died and millions became homeless.

The earthquake struck along a fault where the Indo-Australian plate is being pushed beneath the Sunda plate to the east. This is known as a subduction zone and in this case the plates meet at the Sunda Trench, around 300km west of Sumatra. The Indo-Australian plate normally moves slowly under the Sunda plate, but when the rupture occurred, it violently surged forward.

The Sunda Trench is full of ancient sediment, some of which has washed out of the Ganges over millions of years forming a massive accumulation of sedimentary rock called the Nicobar Fan. As the Indo-Australian plate is subducted, these sediments are scraped off to form what’s called an accretionary prism. Usually an accretionary prism slopes consistently away from the trench, but here the seabed shallows steeply before flattening out, forming a plateau.

Subduction earthquakes are thought to start tens of kilometers beneath the Earth’s surface. Displacement or “slip” on the fault, as geologists call it, propagates upwards and generally dissipates as it reaches weaker rocks closer to the surface. If it were an ordinary seismic zone, the sediment in the Sunda Trench should have slowed the upward and westward journey of the 2004 earthquake, generating a tsunami in the shallower water on the landward (east) side of the trench.

But in fact the fault slip seems to have reached close to the trench, lifting large sections of the seabed in deeper water and producing a much larger tsunami.

This latest report extends work published last year in the journal Science that found a number of unusual features at the rupture zone of the 2004 earthquake such as the seabed topography, how the sediments are deformed and the locations of small earthquakes (aftershocks) following the main earthquake. The researchers also reported then that the fault zone was a much lower density zone than surrounding sediments, perhaps reducing friction and allowing a larger slip.

Note: This story has been adapted from a news release issued by the University of Texas at Austin

Earth from space: A gush of volcanic gas

September 17, 2011

This image shows the huge plume of sulphur dioxide that spewed from Chile’s Puyehue-Cordón Caulle Volcanic Complex, which lies in the Andes about 600 km south of Santiago.

After lying dormant for more than 50 years, a series of rumbling earthquakes signalled the beginnings of this major volcanic eruption. On 4 June, a fissure opened, sending a towering plume of volcanic ash and gas over 10 km high. Several thousand people were evacuated as a thick layer of ash and pumice fell and blanketed a wide area. Airports in Chile and Argentina were closed as a result.

The image was generated on 6 June using data from the Infrared Atmospheric Sounding Interferometer on Eumetsat’s MetOp-A satellite. As the eruption continued, the image shows how strong winds initially swept the broad plume of sulphur dioxide northwards and then eastwards across Argentina and out over the southern Atlantic Ocean.

Strong westerly winds are common in this region because it lies within the belt of the ‘Roaring Forties’. Since there is little land south of 40º, higher wind speeds can develop than at the same latitudes in the Northern Hemisphere.

Interestingly, over the South Atlantic, the plume take a sharp turn to the north as a pressure system causes the wind to change direction.

The Puyehue-Cordón Caulle complex is a chain of volcanoes that includes the Puyehue volcano, the Cordilera Nevada caldera and the Cordón Caulle rift zone. This event appears to have stemmed from the rift zone and is the most serious since the eruption of 1960, also from the same vent.

Chile has more than 3000 volcanoes, of which around 80 are currently active.

The image represents sulphur dioxide concentrations within the full vertical column of atmosphere. It was generated using data from the interferometer, which was developed by the French space agency CNES for MetOp-A.

Note: This story has been adapted from a news release issued by the European Space Agency

Going with the flow: Researchers find compaction bands in sandstone are permeable

September 17, 2011

Compaction bands at multiple scales ranging from the field scale to the specimen scale to the meso and grain scale. At the field scale, picture shows the presence of narrow tabular structures within the host rock in the Valley of Fire. At the grain scale, images show clear differences in porosity (dark spots) density. This research aims at quantifying the impact of grain scale features in macroscopic physical properties that control behavior all the way to the field scale. – José Andrade/Caltech

When geologists survey an area of land for the potential that gas or petroleum deposits could exist there, they must take into account the composition of rocks that lie below the surface. Take, for instance, sandstone-a sedimentary rock composed mostly of weakly cemented quartz grains. Previous research had suggested that compaction bands-highly compressed, narrow, flat layers within the sandstone-are much less permeable than the host rock and might act as barriers to the flow of oil or gas.

Now, researchers led by José Andrade, associate professor of civil and mechanical engineering at the California Institute of Technology (Caltech), have analyzed X-ray images of Aztec sandstone and revealed that compaction bands are actually more permeable than earlier models indicated. While they do appear to be less permeable than the surrounding host rock, they do not appear to block the flow of fluids. Their findings were reported in the May 17 issue of Geophysical Research Letters.

The study includes the first observations and calculations that show fluids have the ability to flow in sandstone that has compaction bands. Prior to this study, there had been inferences of how permeable these formations were, but those inferences were made from 2D images. This paper provides the first permeability calculations based on actual rock samples taken directly from the field in the Valley of Fire, Nevada. From the data they collected, the researchers concluded that these formations are not as impermeable as previously believed, and that therefore their ability to trap fluids-like oil, gas, and CO2-should be measured based on 3D images taken from the field.

“These results are very important for the development of new technologies such as CO2 sequestration-removing CO2 from the atmosphere and depositing it in an underground reservoir-and hydraulic fracturing of rocks for natural gas extraction,” says Andrade. “The quantitative connection between the microstructure of the rock and the rock’s macroscopic properties, such as hydraulic conductivity, is crucial, as physical processes are controlled by pore-scale features in porous materials. This work is at the forefront of making this quantitative connection.”

The research team connected the rocks’ 3D micromechanical features-such as grain size distribution, which was obtained using microcomputed tomography images of the rocks to build a 3D model-with quantitative macroscopic flow properties in rocks from the field, which they measured on many different scales. Those measurements were the first ever to look at the three-dimensional ability of compaction bands to transmit fluid. The researchers say the combination of these advanced imaging technologies and multiscale computational models will lead to unprecedentedly accurate measurements of crucial physical properties, such as permeability, in rocks and similar materials.

Andrade says the team wants to expand these findings and techniques. “An immediate idea involves the coupling of solid deformation and chemistry,” he says. “Accounting for the effect of pressures and their potential to exacerbate chemical reactions between fluids and the solid matrix in porous materials, such as compaction bands, remains a fundamental problem with multiple applications ranging from hydraulic fracturing for geothermal energy and natural gas extraction, to applications in biological tissue for modeling important processes such as osteoporosis. For instance, chemical reactions take place as part of the process utilized in fracturing rocks to enhance the extraction of natural gas.”

Note: This story has been adapted from a news release issued by the California Institute of Technology

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