back to top
27.8 C
New York
Friday, April 4, 2025
Home Blog Page 281

Could Pulses in Earth’s Magnetic Field Forecast Earthquakes?

John L. Wiley/Creative Commons

In the days leading up to some recent moderate-sized earthquakes, instruments nearby have picked up brief low-frequency pulses in Earth’s magnetic field. A few scientists have proposed that such pulses, which seemed to become stronger and more frequent just before the earthquakes occurred, could serve as an early warning sign for impending seismic activity. Now, a team has come up with a model for how these magnetic pulses might be generated, though some critics say they may have a humanmade origin.

Brief fluctuations in Earth’s magnetic field have been detected before many earthquakes in the past 50 years, says Friedemann Freund, a crystallographer at San Jose State University in California. For example, in the weeks before a magnitude-5.4 quake struck about 15 kilometers northeast of San Jose in October 2007, an instrument near the epicenter sensed a number of unusual magnetic pulses, presumably emanating from deep in the Earth. (The largest of them measured 30 nanoteslas, which is about 1/100,000th the typical strength of the planet’s magnetic field measured at Earth’s surface.) Those blips became more frequent as the day of the earthquake approached, Freund says. More recently, prior to several medium- to moderate-sized quakes in Peru, two sensitive magnetometers recorded the same sort of pulses.

One big puzzle, Freund notes, has been how such pulses could be generated. Now, he and his colleagues suggest that these blips stem from microscopic changes in crystals in rocks under seismic stress deep within Earth. In many types of rocks, particularly volcanic rocks that have substantial amounts of water locked inside them, crystals are chock-full of oxygen-oxygen bonds called peroxy bonds. (These bonds formed long ago, after chemical changes split some of the water molecules, freeing the hydrogen atoms to bond together and then diffuse out of the rocks as gas.) When those rocks are squeezed, say, by the sides of a fault zone scraping past one another, some of the peroxy bonds break. Those broken bonds release negatively charged electrons, which remain trapped in place, and create positively charged “holes” in the crystal, Freund explains. In lab experiments, the electrical disturbances associated with those holes diffuse through the surrounding rocks at speeds of about 100 meters per second.

Freund and his team propose that the same process might be happening within Earth’s crust. As stress on large volumes of rock builds in advance of an impending quake, many, many of these electrical holes are created inside them. It’s the mass migration of such holes that creates the large electrical currents responsible for generating the low-frequency magnetic pulses that make their way to detectors on Earth’s surface, they say.

For the Peruvian quakes, most of the pulses sensed by the magnetometers ranged between one-sixth and one-quarter of a second long. But some lasted up to 2 seconds, Freund says—a length that strongly suggests that the pulses weren’t triggered by lightning, either nearby or far away, which some critics of his model have proposed as an alternative explanation. More importantly, he notes, with data from the two sensors in Peru he and his colleagues were able to pinpoint the strongest of those pulses as originating within a few kilometers of the epicenters of subsequent quakes, they report in a paper posted to the arXiv preprint server. For now, Freund admits, the team’s model is preliminary: The paper has been submitted to a journal and is now being reviewed by other scientists.

“This paper only makes sense if the observations [of magnetic pulses] are good,” says John Ebel, a seismologist at Boston College, who wasn’t involved in the research. He points out that two instruments aren’t sufficient to pinpoint the location of an event; to truly “triangulate” an event you need at least three sensors.

But another aspect of the team’s findings is even more worrying, he notes: “I’m concerned that the pulses are not originating deep within the Earth.” It’s possible, he continues, that the blips may have some inexplicable humanmade origin. Decades ago, Ebel notes, his Boston-based magnetometers started picking up a series of odd pulses every morning. Eventually, he and his colleagues identified the sources of those gremlins: It was the engineers cranking up Boston’s trolley cars at a rail yard a few kilometers away from the instruments.

Even if the magnetic pulses originate within Earth along seismic zones under stress, Freund says, the blips don’t always foretell a quake. It’s more likely to be the pattern of pulses—and, in particular, changes in their size and frequency—that Freund and his colleagues say might offer scientists a crystal ball for impending temblors.

Note : The above story is based on materials provided by Sid Perkins ” sciencemag “

How Did the Moon Really Form?

NASA/JPL-Caltech

Planetary scientists have long believed that our moon formed following a collision between Earth and another planet, but studies of Earth and moon rocks suggest otherwise. A new analysis of the composition of moon rocks brought back by Apollo astronauts may help finally resolve the mystery.

Here’s the current thinking about how the moon formed. Early in its history, Earth was struck a glancing blow by a Mars-sized planet. That planet was destroyed by the impact, but much of its debris—and some of Earth’s—formed into a disk around Earth that eventually coalesced into the moon. Much evidence supports this scenario. The moon would have ended up hot, boiling off light elements and water, leaving the arid rocky moon we see today; the moon has a small core, consistent with being made from parts of the colliding planet and outer parts of Earth; the Earth-moon system rotates fast, consistent with a glancing blow.

But one bit of evidence just doesn’t fit: the composition of moon rocks. Researchers have found that rocks from different parts of the solar system (brought to Earth as meteorites) have subtle differences in their composition. Oxygen, for example, comes in different varieties, called isotopes. Oxygen-16 (O-16) is the most common type, followed by oxygen-17 (O-17)—which has one extra neutron in its nucleus—and oxygen-18, with two extra neutrons. Meteorites from different parts of the solar system have different proportions of these isotopes. So a rock from Mars would have a markedly different ratio of O-17 compared with O-16 than, say, a piece of an asteroid or a rock from Earth. These ratios are so reliable that researchers use them to identify where meteorites come from.

Here’s the puzzle: The giant impact hypothesis predicts that the moon should be made of about 70% to 90% material from the impactor, so its isotope ratios should be different from Earth’s. But ever since researchers got hold of Apollo moon rocks for analysis, they have failed to find any significant difference in isotope ratios on Earth and the moon. Studies of the isotopes of oxygen, titanium, calcium, silicon, and tungsten have all drawn a blank.

This discrepancy has troubled planetary scientists so much that in recent years they have put forward a number of alternative scenarios to explain the moon’s origins. One hypothesis suggests that there could have been much greater mixing between Earth and the debris disk as it coalesced after the impact, or if Earth was hit head-on by a similarly sized impactor, their remains could have mixed completely. Another possibility is that a fast-spinning Earth could have been hit by a much smaller impactor, which would have provided little material for the moon. Yet it has been hard to show how you could get from one of those events to the Earth-moon system we have today.

Researchers would prefer to stick with the original, plain vanilla impact scenario because it explains so many things so well. New results, published online today in Science, will give them some hope. Lunar rocks have a measurably higher ratio of O-17 over O-16 compared with those from Earth. The new study began because a team of researchers led by Daniel Herwartz of the University of Cologne in Germany had recently upgraded its mass spectrometer—a form of supersensitive atomic scale—and decided to test the device out on the Earth-moon isotope problem. “Our analysis is now an order of magnitude better than other laboratories,” says team member Andreas Pack of the University of Göttingen in Germany.

They started out analyzing moon rocks that arrived on Earth as meteorites but found that the weathering these rocks experienced on Earth was skewing the results. So they got hold of some rock samples from NASA that had been brought back by Apollo missions 11, 12, and 16. They extracted oxygen from all the samples and then passed it through the spectrometer to find out the proportions of each isotope. Their conclusion was that the lunar samples had an O-17 to O-16 ratio that was 12 parts per million higher than rocks derived from Earth’s mantle. This difference “supports the view that the Moon formed by a giant collision of the proto-Earth with [an impactor],” the team writes. “It is a relief that a [disparity in ratios] has been found, since the total absence of difference between Earth and moon would be hard to explain,” comments planetary scientist David Stevenson of the California Institute of Technology in Pasadena, in an e-mail.

The team acknowledges other possible explanations for the difference, including that Earth was bombarded by material with a lower oxygen isotope ratio at some time after the impact. “Now that a difference has been found, many will work to confirm or deny it and do battle over what it means,” Stevenson says.

The team says the results suggest that the moon is a roughly 50-50 mix of Earth and impactor material. Moreover, the high oxygen isotope ratio suggests that the impactor was principally made of a rare material called enstatite chondrite. The vast majority of meteorites that land on Earth are chondrites, but only about 2% of those are enstatite chondrites. “The possible significance of enstatite chondrites is interesting, but at present we are stuck with speculating about the bodies that went into making Earth, since they are no longer around,” Stevenson says.

Note : The above story is based on materials provided by Daniel Clery ” sciencemag “

Orthoclase

Orthoclase and smoky quartz Gebel quarry – Cuasso al Monte – Ceresio Valley – Varese prov. – Lombardy – Italy Specimen weight:315 gr. Crystal size:mm. 23 Overall size: 112mm x 103 mm x 41 mm © minservice

Chemical Formula: KAlSi3O8
Locality: Common world wide occurrences.
Name Origin: From the Greek orthos – “right” and kalo -” I cleave” in allusion to the mineral’s right angle of good cleavage.

Orthoclase (endmember formula KAlSi3O8) is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for “straight fracture,” because its two cleavage planes are at right angles to each other. Alternate names are potassium feldspar and K-feldspar. The gem known as moonstone  is largely composed of orthoclase.

Formation and Subtypes

Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite.

Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, enriching the remaining orthoclase with potassium. The resulting intergrowth of the two feldspars is called perthite.

The higher-temperature polymorph of orthoclase is sanidine. Sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of orthoclase is microcline. Adularia is found in low temperature hydrothermal deposits, in the Adula Alps of Switzerland. The largest documented single crystal of orthoclase was found in Ural mountains, Russia. It measured ~10×10×0.4 m and weighed ~100 tons.

History

Discovery date : 1823

Optical properties

Optical and misc. Properties : Transparent – Translucide – fluorescent- Gemme, pierre fine
Refractive Index: from 1,51 to 1,52
Axial angle 2V: 35-75°

Physical properties

Hardness : from 6,00 to 6,50
Density: from 2,55 to 2,63
Color: colorless; white; grey; yellow; grey yellow; pink red; reddish; green; greenish; pink
Luster : vitreous; nacreous
Streak : white
Break : irregular; conchoidal; splintery
Cleavage : Yes

Photos:

Orthoclase 4.1×3.8×2.8 cm Bear Lake Diggings Gooderham Ontario, Canada Copyright © David K. Joyce Minerals
Orthoclase Montecatini quarry, Baveno, Piedmont, Italy Specimen weight:181 gr. Crystal size:40 mm Overall size: 78mm x 68 mm x 48 mm © minservice
Orthoclase Montecatini quarry, Baveno, Piedmont, Italy Specimen weight:135 gr. Crystal size:35 mm Overall size: 78mm x 62 mm x 55 mm © minservice

Earth’s breathable atmosphere tied to plate tectonics?

A new study links continents and plate tectonics to the rise of oxygen on Earth. Credit: The International Space Station

The rise of oxygen is one of the biggest puzzle in Earth’s history. Our planet’s atmosphere started out oxygen-free. Then, around 3.5 billion years ago, tiny microbes called cyanobacteria (or blue-green algae) learned out to carry out photosynthesis. They began using energy from sunlight to make their food from carbon dioxide and water, giving off oxygen as waste.
But it took another 3 billion years for oxygen levels to climb from trace amounts to at least 20 percent of the atmosphere, or high enough to support the emergence of complex life. And so far the mechanism behind that rise has remained unclear.

Now a new study by University of Exeter biochemist Benjamin Mills and his colleagues offers a new potential clue.

Using a computer model, they showed that plate tectonics may have indirectly fueled the sharp increase in oxygen between 1.5 billion and half a billion years ago. In particular, a process tied to the way continents remove carbon dioxide from the atmosphere may have increased the supply of phosphorus, a key nutrient for photosynthetic microbes in the ocean. The paper was published this month in the Proceedings of the National Academy of Science.

“This is a novel perspective for the late Proterozoic—a critical time of dramatic climate change, rising oxygen in the ocean and atmosphere, and origins and diversification of complex life,” says Timothy Lyons, a biogeochemist not involved in the study.

From Seafloor to Terrestrial “Weathering’

Continents play a crucial role in the carbon cycle by removing carbon dioxide from the atmosphere. Carbon dioxide mixes with rain water, forming a weak acid (carbonic acid) which slowly wears down or “weathers” rocks on land.

The process releases minerals such as calcium and magnesium from the rocks. These minerals then combine with carbonate and settle at the bottom of the ocean forming layers of calcium carbonate, or limestone.

In other words, the weathering process simply pulls carbon from the atmosphere and turns it into a layer of sediment on the seafloor.

However, continental rocks aren’t the only route by which carbon is removed from the atmosphere. Ocean ridges, the places where fresh crust is made on the seafloor, can undergo a similar “weathering” process. In fact, seafloor weathering was the main route of carbon removal in the early chapter of Earth’s history, before the formation of continents.

According to the new study, the rise of oxygen may have been due to a shift in balance between the two processes—between seafloor and continental weathering.

Potential Culprits

What caused that shift? The model looked at two factors: a brighter sun, and a slowdown in fresh crust production.

Our sun has slowly been getting brighter. It’s now 20 to 30 percent brighter than when our Earth first formed. Because the weathering process depends on temperature, a brighter Sun may have sped up the process on land. What’s more, the amount of fresh ocean floor formed has slowed down over time. And the weathering process generally happens with the newer crust. Taken together, these two factor may have shifted the balance between the seafloor and the terrestrial process.

The Phosphorus Boost

But why does that shift matter? “Rocks on continents contain phosphorus, which is a key limiting nutrient for photosynthetic microbes,” Mills says.

The terrestrial weathering increases the amount of phosphorus in streams and rivers, and ultimately in the ocean. The amount of phosphorus then dictates how much photosynthesis, hence how much oxygen is produced.

“The paper a great step forward,” says Lyons. “The fundamental mechanistic perspective, particularly the co-consideration of seafloor and continental processes, is broadly relevant and clever.”

One drawback, though, Lyons says, is that the model doesn’t account for the shorter-term variations of oxygen’s up and down. “The model, as proposed, isn’t able to explain the details of the transition,” Lyons adds. “But overall it still support the long term increase in oxygen.”

Implications for Astrobiology

The study provides an indirect link between plate tectonic and continents on one hand and the evolution of complex life on the other, an idea worth keeping in mind in the search for life beyond our world.

“This is not the only reason oxygen rose to high levels, but it seems to be an important piece of the puzzle. Whilst the carbon cycle can function without large continents, it seems that their emergence was critical to our own evolution,” Mills says in a news release.

Mills later adds in a phone interview:

“A large number of key limiting nutrients, and not just phosphate, come from the continents. It seems that to develop a biosphere like we have on this planet, you’re going to need significant continental area.”

In fact, the recycling of continents via plate tectonics has become of major interest for many astrobiologists. Several have argued that, along with water, plate tectonics could be an essential requirement for life.

“What I like in particular is the rigorous links between tectonic drivers and oxygen (and life by association), which must be a considered in any view of extrasolar planets and their ability to sustain life through nutrient balances—with oxygenation as a possible consequence,” Lyons adds. “Plate tectonics and relationships to nutrient cycling, phosphorus in particular, should be an essential part in any exploration for life—on the early Earth and farther from home.”

More information:
Benjamin Mills, Timothy M. Lenton, and Andrew J. Watson. “Proterozoic oxygen rise linked to shifting balance between seafloor and terrestrial weathering.” PNAS 2014 ; published ahead of print June 9, 2014, DOI: 10.1073/pnas.1321679111

Note : The above story is based on materials provided by courtesy of NASA’s Astrobiology Magazine. Explore the Earth and beyond at Astrobio.net

Swarm reveals Earth’s changing magnetism

Changes in Earth’s magnetic field from January to June 2014 as measured by the Swarm constellation of satellites. These changes are based on the magnetic signals that stem from Earth’s core. Shades of red represent areas of strengthening, while blues show areas of weakening over the 6-month period. Credit: ESA/DTU Space

The first set of high-resolution results from ESA’s three-satellite Swarm constellation reveals the most recent changes in the magnetic field that protects our planet.
Launched in November 2013, Swarm is providing unprecedented insights into the complex workings of Earth’s magnetic field, which safeguards us from the bombarding cosmic radiation and charged particles.

Measurements made over the past six months confirm the general trend of the field’s weakening, with the most dramatic declines over the Western Hemisphere.

But in other areas, such as the southern Indian Ocean, the magnetic field has strengthened since January.

The latest measurements also confirm the movement of magnetic North towards Siberia.

These changes are based on the magnetic signals stemming from Earth’s core. Over the coming months, scientists will analyse the data to unravel the magnetic contributions from other sources, namely the mantle, crust, oceans, ionosphere and magnetosphere.

This will provide new insight into many natural processes, from those occurring deep inside our planet to space weather triggered by solar activity. In turn, this information will yield a better understanding of why the magnetic field is weakening.

“These initial results demonstrate the excellent performance of Swarm,” said Rune Floberghagen, ESA’s Swarm Mission Manager.

“With unprecedented resolution, the data also exhibit Swarm’s capability to map fine-scale features of the magnetic field.”

The first results were presented June 19, 2014 at the ‘Third Swarm Science Meeting’ in Copenhagen, Denmark.

Sofie Carsten Nielsen, Danish Minister of Higher Education and Science, highlighted the Danish contribution to the mission. Swarm continues the legacy of the Danish Ørsted satellite, which is still operational, as well as the German Champ mission. Swarm’s core instrument — the Vector Field Magnetometer — was provided by the Technical University of Denmark.

Denmark’s National Space Institute, DTU Space, has a leading role — together with 10 European and Canadian research institutes — in the Swarm Satellite Constellation Application and Research Facility, which produces advanced models based on Swarm data describing each of the various sources of the measured field.

“I’m extremely happy to see that Swarm has materialised,” said Kristian Pedersen, Director of DTU Space.

Note : The above story is based on materials provided by European Space Agency.

Opal

OPAL Welo, Afar Province, Ethiopia Thumbnail, 1.2 x 1.1 x 0.4 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”

Chemical Formula: SiO2·nH2O
Locality: World wide occurrences.
Name Origin: From the Old Indian upala – “precious stone.”

What is Opal?

“What is Opal?” Opal is a hydrated amorphous form of silica; its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Because of its amorphous character it is classed as a mineraloid, unlike the other crystalline forms of silica which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl and basalt. Opal is the national gemstone of Australia, which produces 97% of the world’s supply. This includes the production of the state of South Australia, which accounts for approximately 80% of the world’s supply.

The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent.

Common opal, called “potch” by miners, does not show the display of color exhibited in precious opal.

Related:
Types of Opal
Why is Australian Opal Unique?
How Do Opalised Fossils Form?

Optical properties

Optical and misc. Properties:  Transparent  –   Opaque  –   Translucide
Refractive Index: from 1,43 to 1,45

Physical Properties

Cleavage: None
Color:     White, Yellow, Red, Brown, Blue.
Density: 1.9 – 2.3, Average = 2.09
Diaphaneity: Transparent to translucent to opaque
Fracture: Conchoidal – Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Luminescence: Fluorescent, Short UV=greenish yellow, Long UV=white.
Luster: Vitreous – Dull
Streak: white

Photos :

OPAL Welo, Afar Province, Ethiopia Thumbnail, 3.1 x 2.3 x 0.8 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
OPAL Welo, Afar Province, Ethiopia Thumbnail, 1.3 x 0.9 x 0.6 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
OPAL Welo, Afar Province, Ethiopia Thumbnail, 1.9 x 1.2 x 0.5 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
OPAL Welo, Afar Province, Ethiopia Thumbnail, 1.3 x 1.1 x 0.8 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Name: Opal Locality: Mexico Weight: 2.46 carats Size: 9.50 x 6.05 mm © minclassics.

Researchers find link between amount of silica in subduction zones and frequency of ‘slow’ earthquakes

Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Credit: Wikipedia.

A pair of researchers, Pascal Audet and Roland Burgmann of the Universities of Ottawa and California, respectively, has found a connection between the amount of silica rich quartz above subduction zones and the frequency rate of “slow” earthquakes. In their paper published in the journal Nature, the two describe how they measured quartz amounts in the Cascadia subduction zone using seismic waves, and how it relates to slow earthquakes.

Scientists have only known about slow earthquakes for a few years—since they can’t be felt, there was no real indication that they were occurring. They happen when silica rich sediment is pushed from below when one plate pushes beneath another. The fluid is trapped causing pressure to build—eventually that pressure is released by slow sliding (due to lubrication provided by the silica), rather than the jolt associated with surface quakes. After the sliding stops, the pressure begins to build up again and the whole process is repeated. Such quakes can occur over days or even weeks, releasing energy equivalent to large surface quakes. Scientists now know that such quakes occur off the coast of Japan, New Zealand, the United States and Canada, but, they all have a different frequency rate. They happen every two years in New Zealand, every six months in Japan and every 14 months beneath Canada’s Vancouver Island. The difference in rates, the researchers have found, is due to the amount of silica in the fluid—there more there is, the faster faults knit together after the sliding has stopped.

The pair of researchers note that much more study needs to be done before it can be determined if slow earthquakes can be used to help predict surface quakes. In their experiments, they found the crust to be 5 to 15 percent quartz above the plates in the Cascadia subduction zone, an area that experienced a magnitude 9 quake in 1700. Scientists believe a major quake will likely occur again there sometime over the next 200 years. If slow earthquakes are found to portend larger ones, perhaps enough warning time can be given to save lives in the heavily populated area.

More information:
Possible control of subduction zone slow-earthquake periodicity by silica enrichment, Nature 510, 389–392 (19 June 2014) DOI: 10.1038/nature13391

Abstract

Seismic and geodetic observations in subduction zone forearcs indicate that slow earthquakes, including episodic tremor and slip, recur at intervals of less than six months to more than two years. In Cascadia, slow slip is segmented along strike and tremor data show a gradation from large, infrequent slip episodes to small, frequent slip events with increasing depth of the plate interface. Observations and models of slow slip and tremor require the presence of near-lithostatic pore-fluid pressures in slow-earthquake source regions; however, direct evidence of factors controlling the variability in recurrence times is elusive. Here we compile seismic data from subduction zone forearcs exhibiting recurring slow earthquakes and show that the average ratio of compressional (P)-wave velocity to shear (S)-wave velocity (vP/vS) of the overlying forearc crust ranges between 1.6 and 2.0 and is linearly related to the average recurrence time of slow earthquakes. In northern Cascadia, forearc vP/vS values decrease with increasing depth of the plate interface and with decreasing tremor-episode recurrence intervals. Low vP/vS values require a large addition of quartz in a mostly mafic forearc environment. We propose that silica enrichment varying from 5 per cent to 15 per cent by volume from slab-derived fluids and upward mineralization in quartz veins can explain the range of observed vP/vS values as well as the downdip decrease in vP/vS. The solubility of silica depends on temperature, and deposition prevails near the base of the forearc crust. We further propose that the strong temperature dependence of healing and permeability reduction in silica-rich fault gouge via dissolution–precipitation creep can explain the reduction in tremor recurrence time with progressive silica enrichment. Lower gouge permeability at higher temperatures leads to faster fluid overpressure development and low effective fault-normal stress, and therefore shorter recurrence times. Our results also agree with numerical models of slip stabilization under fault zone dilatancy strengthening15 caused by decreasing fluid pressure as pore space increases. This implies that temperature-dependent silica deposition, permeability reduction and fluid overpressure development control dilatancy and slow-earthquake behaviour.

Note : The above story is based on materials provided by  © 2014 Phys.org

T. rex’s killer smile revealed

Miriam Reichel’s research shows that the T. rex’s front teeth gripped and pulled, while the teeth along the side of the jaw punctured and tore flesh. Credit: Image courtesy of University of Alberta

One of the most prominent features of life-size models of Tyrannosaurus rex is its fearsome array of flesh-ripping, bone-crushing teeth.

Until recently, most researchers who studied the carnivore’s smile only noted the varying sizes of its teeth. But University of Alberta paleontologist Miriam Reichel discovered that beyond the obvious size difference in each tooth family in T. rex’s gaping jaw, there is considerable variation in the serrated edges of the teeth.

“The varying edges, or keels, not only enabled T. rex’s very strong teeth to cut through flesh and bone,” says Reichel, “the placement and angle of the teeth also directed food into its mouth.”

Reichel analyzed the teeth of the entire tyrannosaurid family of meat-eating dinosaurs and found T. rex had the greatest variation in tooth morphology or structure. The dental specialization was a great benefit for a dinosaur whose preoccupation was ripping other dinosaurs apart.

Reichel’s research shows that the T. rex’s front teeth gripped and pulled, while the teeth along the side of the jaw punctured and tore flesh. The teeth at the back of the mouth did double duty: not only could they slice and dice chunks of prey, they forced food to the back of the throat.

Reichel says her findings add strength to the classification of tyrannosaurids as heterodont animals, which are animals with teeth adapted for different functions depending on their position in the mouth.

One surprising aspect of T. rex teeth, common to all tyrannosaurid’s, is that they weren’t sharp and dagger-like. “They were fairly dull and wide, almost like bananas,” said Reichel. “If the teeth were flat, knife-like and sharp, they could have snapped if the prey struggled violently when T. rex’s jaws first clamped down.”

Reichel’s research was published in The Canadian Journal of Earth Science.

Journal Reference:

Miriam Reichel, Hans-Dieter Sues. The variation of angles between anterior and posterior carinae of tyrannosaurid teeth. Canadian Journal of Earth Sciences, 2012; 49 (3): 477 DOI: 10.1139/e11-068

Note : The above story is based on materials provided by University of Alberta.

Olivenite

Locality: Clara Mine, Rankach valley, Oberwolfach, Wolfach, Black Forest, Baden-Württemberg, Germany Photo Copyright © Chinellato Matteo

Chemical Formula: Cu2(AsO4)(OH)
Locality: Carharrack mine, Gwennap, Cornwall, England, GB
Name Origin: From the German olivernerz, literally “olive” ore, in allusion to its typical color.

Olivenite is a copper arsenate mineral, formula Cu2(AsO4)(OH). It crystallizes in the monoclinic system (pseudo-orthorhombic), and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces. More commonly, it occurs as globular aggregates of acicular crystals, these fibrous forms often having a velvety lustre; sometimes it is lamellar in structure, or soft and earthy.

A characteristic feature, and one to which the name alludes (German, Olivenerz, of A. G. Werner, 1789), is the olive-green color, which varies in shade from blackish-green in the crystals to almost white in the finely fibrous variety known as woodcopper. The hardness is 3, and the specific gravity is 4.3. The mineral was formerly found in some abundance, associated with limonite and quartz, in the upper workings in the copper mines of the St Day district in Cornwall; also near Redruth, and in the Tintic Mining District in Utah. It is a mineral of secondary origin, a result of the oxidation of copper ores and arsenopyrite.

The arsenic of olivenite is sometimes partly replaced by a small amount of phosphorus, and in the species libethenite we have the corresponding copper phosphate Cu2PO4OH. This is found as small dark green crystals resembling olivenite at Libethen in the Slovak Republic, and in small amount also in Cornwall. Other members of this isomorphous group of minerals are adamite, Zn2(AsO4)(OH), and eveite, Mn2(AsO4)(OH).

History

Discovery date : 1820
Town of Origin: CORNOUAILLES
Country of Origin: ANGLETERRE

Physical Properties

Hardness: 3,00
Density: from 4,37 to 4,38
Color : olive-green; greenish brown; yellow; grayish green; yellowish white; blackish green; brown; grayish white
Luster: vitreous;silky; greasy
Streak : green yellow; white
Break: irregular; conchoidal
Cleavage: {110} Indistinct, {010} Indistinct, {110} Indistinct

Photos:

OLIVENITE Wheal Phoenix, Linkinhorne, Liskeard, Cornwall, England, Europe Size: 6.5 x 6 x 3 cm (Small Cabinet) Owner: Crystal Classics
Olivenite Inubia mine, Bahia, Brazil Specimen weight:76 gr. Crystal size:3 mm Overall size: 72mm x 60 mm x 30 mm minservice
Olivenite Mine du Cap Garonne, Pradet, Var, Provence-Alpes-Côte d’Azur, France Specimen weight:18 gr. Crystal size:0,15 cm Overall size:4 x 3,7 x 1,3 cm minservice
OLIVENITE on CORNWALLITE Wheal Phoenix, Linkinhorne, Liskeard, Cornwall, England, Europe Size: 5 x 3 x 2.5 cm (Small Cabinet) Owner: Crystal Classics

Scientists ready to study magma formation beneath Mount St. Helens

Mount St. Helens as it appeared two years after its catastrophic eruption on May 18, 1980. Credit: U.S. Geological Survey

University and government scientists are embarking on a collaborative research expedition to improve volcanic eruption forecasting by learning more about how a deep-underground feeder system creates and supplies magma to Mount St. Helens.

They hope the research will produce science that will lead to better understanding of eruptions, which in turn could lead to greater public safety.

The Imaging Magma Under St. Helens project involves three distinct components: active-source seismic monitoring, passive-source seismic monitoring and magnetotelluric monitoring, using fluctuations in Earth’s electromagnetic field to produce images of structures beneath the surface.

Researchers are beginning passive-source and magnetotelluric monitoring, while active-source monitoring – measuring seismic waves generated by underground detonations – will be conducted later.

Passive-source monitoring involves burying seismometers at 70 different sites throughout a 60-by-60-mile area centered on Mount St. Helens in southwestern Washington. The seismometers will record data from a variety of seismic events.

“We will record local earthquakes, as well as distant earthquakes. Patterns in the earthquake signatures will reveal in greater detail the geological structures beneath St. Helens,” said John Vidale, director of the University of Washington-based Pacific Northwest Seismic Network.

Magnetotelluric monitoring will be done at 150 sites spread over an area running 125 miles north to south and 110 miles east to west, which includes both Mount Rainier and Mount Adams. Most of the sites will only be used for a day, with instruments recording electric and magnetic field signals that will produce images of subsurface structures.

Besides the UW, collaborating institutions are Oregon State University, Lamont-Doherty Earth Observatory at Columbia University, Rice University, Columbia University, the U.S. Geological Survey and ETH-Zurich in Switzerland. The work is being funded by the National Science Foundation.

Mount St. Helens has been the most active volcano in the Cascade Range during the last 2,000 years and has erupted twice in the last 35 years. It also is more accessible than most volcanoes for people and equipment, making it a prime target for scientists trying to better understand how volcanoes get their supply of magma.

The magma that eventually comes to the surface probably originates 60 to 70 miles deep beneath St. Helens, at the interface between the Juan de Fuca and North American tectonic plates. The plates first come into contact off the Pacific Northwest coast, where the Juan de Fuca plate subducts beneath the North American plate and reaches great depth under the Cascades. As the magma works its way upward, it likely accumulates as a mass several miles beneath the surface.

As the molten rock works its way toward the surface, it is possible that it gathers in a large chamber a few miles beneath the surface. The path from great depth to this chamber is almost completely unknown and is a main subject of the study.

The project is expected to conclude in the summer of 2016.

Note : The above story is based on materials provided by University of Washington

Unexpected findings: Small asteroids can be flying rock clusters or even clouds of dust surrouding solid rocks

An artist’s conception of two possible views of asteroid 2011 MD. Credit: Image courtesy NASA Jet Propulsion Laboratory

What seemed to be rock-solid assumptions about the nature of small asteroids may end in collections of rubble or even a cloud of dust, but in such findings lies the lure of the unexpected.

Northern Arizona University researchers David Trilling and Michael Mommert, while playing a well-defined role in the NASA Asteroid Initiative, are beginning to wonder if they have found a separate path of investigation.
The two researchers presented their findings about asteroid 2011 MD on Thursday during a NASA event updating progress on the path to capturing a small asteroid and relocating it for a closer look by astronauts in the 2020s.

The job of Trilling and Mommert was to use the infrared capabilities of the Spitzer Space Telescope to determine the size of 2011 MD, which needs to be within a narrow range for the mission to succeed. Trilling, an associate professor, explained that using infrared light is the most accurate way to determine an asteroid’s size because visible light through a traditional telescope fails to distinguish a small, highly reflective asteroid from a large one with little reflectivity.

At around 6 meters in diameter, 2011 MD is just right. But that’s not the whole story.

“People have assumed that small asteroids are debris from collisions of larger asteroids, so those really small guys would be just single slabs of rock flying in space,” said Mommert, a post-doctoral researcher. “But we found that this one is 65 percent empty.”

The findings, which suggest a flying cluster of rocks or a cloud of dust with a solid rock at its nucleus, are similar to observations the NAU researchers published earlier this year of yet another asteroid, 2009 BD.

Trilling said long-held assumptions are yielding to something “weirder and more exotic. The first time you see it, you think, ‘Well, that’s just an anomaly.’ But two out of two, and you start to think that maybe the small ones really don’t look like everyone thought.”

The latest findings appear online today in Astrophysical Journal Letters, coinciding with the NASA presentation. And while NASA seeks to use the asteroid mission to test the technologies and capabilities needed to send astronauts to Mars, Trilling and Mommert are setting their sights elsewhere.

“Now we can go back and propose some more observation time just for the science investigation,” Trilling said. “Now we want to learn something more about the universe.” Mommert said this is a prime opportunity to add data to a field — the study of small asteroids — that is sparsely populated.

“It’s a field that hasn’t been studied a lot because it’s really difficult to observe them and derive their physical properties,” he said. “The density of 99.9 percent of all asteroids is unknown.” He and Trilling have now added two to a single-digit list.

As far as 2011 MD is concerned, NASA will have to be satisfied with the information compiled by the full team, which includes NAU, the University of Hawaii and a number of other NASA and affiliated labs. The asteroid is about to disappear behind the sun, at least from Earth’s perspective, for the next seven years, and will not be observable again before the spacecraft to retrieve it would have to be launched.

Note : The above story is based on materials provided by Northern Arizona University.

Oligoclase

Oligoclase Locality: Pili Mine, Sonora, Mexico Size: miniature, 4.5 x 3.4 x 3 cm © Rob Lavinsky / iRocks

Chemical Formula: (Na,Ca)[Al(Si,Al)Si2O8]
Locality: Twedestrand, Norway.
Name Origin: From the Greek, oligos and kasein, “little cleavage.”
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). The albite:anorthite molar ratio ranges from 90:10 to 70:30.

Oligoclase is a high sodium feldspar crystallizing in the triclinic system. The Mohs hardness is 6 to 6.5 and the specific gravity is 2.64 to 2.66. The refractive indices are: nα=1.533–1.543, nβ=1.537–1.548, and nγ=1.542–1.552. In color it is usually white, with shades of grey, green, or red.

Name and discovery

The name oligoclase was given by August Breithaupt in 1826 from the Greek oligos, little, and clasein, to break, because the mineral was thought to have a less perfect cleavage than albite. It had previously been recognized as a distinct species by J. J. Berzelius in 1824, and was named by him soda-spodumene (Natron-spodumen), because of its resemblance in appearance to spodumene.

History

Discovery date : 1826
Town of Origin: DANVIKS-ZOLL, STOCKHOLM
Country of Origin: SUEDE

Physical Properties

Cleavage: {001} Perfect, {010} Good
Color:     Brown, Colorless, Greenish, Gray, Yellowish.
Density: 2.64 – 2.66, Average = 2.65
Diaphaneity: Transparent to Translucent
Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern.
Hardness: 7 – Quartz
Luminescence: Fluorescent, Long UV=yellow.
Luster: Vitreous (Glassy)
Streak: white

Photos:

Oligoclase Tanzania Thumbnail, 11.9 mm x 8.0 mm ; 2.20 cts © irocks
Oligoclase (Feldspar) Locality: Tanzania Weight: 2.14 carats Size: 8.08 x 6.57 mm © minclassics
ligoclase, Sphalerite, Pyrite Locality: San Luis Potosi, Mexico Overall Size: 7x5x4 cm Crystals: 1-16 mm © JohnBetts-FineMinerals

New horned dinosaur reveals unique wing-shaped headgear

Mercuriceratops gemini (center) compared to horned dinosaurs Centrosaurus (left) and Chasmosaurus (right), also from the Dinosaur Park Formation of Alberta, Canada. Credit: Courtesy Danielle Dufault

Scientists have named a new species of horned dinosaur (ceratopsian) based on fossils collected from Montana in the United States and Alberta, Canada. Mercuriceratops (mer-cure-E-sare-ah-tops) gemini was approximately 6 meters (20 feet) long and weighed more than 2 tons. It lived about 77 million years ago during the Late Cretaceous Period. Research describing the new species is published online in the journal Naturwissenschaften.
Mercuriceratops (Mercuri + ceratops) means “Mercury horned-face,” referring to the wing-like ornamentation on its head that resembles the wings on the helmet of the Roman god, Mercury. The name “gemini” refers to the almost identical twin specimens found in north central Montana and the UNESCO World Heritage Site, Dinosaur Provincial Park, in Alberta, Canada. Mercuriceratops had a parrot-like beak and probably had two long brow horns above its eyes. It was a plant-eating dinosaur.

“Mercuriceratops took a unique evolutionary path that shaped the large frill on the back of its skull into protruding wings like the decorative fins on classic 1950s cars. It definitively would have stood out from the herd during the Late Cretaceous,” said lead author Dr. Michael Ryan, curator of vertebrate paleontology at The Cleveland Museum of Natural History. “Horned dinosaurs in North America used their elaborate skull ornamentation to identify each other and to attract mates — not just for protection from predators. The wing-like protrusions on the sides of its frill may have offered male Mercuriceratops a competitive advantage in attracting mates.”

“The butterfly-shaped frill, or neck shield, of Mercuriceratops is unlike anything we have seen before,” said co-author Dr. David Evans, curator of vertebrate palaeontology at the Royal Ontario Museum. “Mercuriceratops shows that evolution gave rise to much greater variation in horned dinosaur headgear than we had previously suspected.”

The new dinosaur is described from skull fragments from two individuals collected from the Judith River Formation of Montana and the Dinosaur Park Formation of Alberta. The Montana specimen was originally collected on private land and acquired by the Royal Ontario Museum. The Alberta specimen was collected by Susan Owen-Kagen, a preparator in Dr. Philip Currie’s lab at the University of Alberta. “Susan showed me her specimen during one of my trips to Alberta,” said Ryan. “I instantly recognized it as being from the same type of dinosaur that the Royal Ontario Museum had from Montana.”

The Alberta specimen confirmed that the fossil from Montana was not a pathological specimen, nor had it somehow been distorted during the process of fossilization,” said Dr. Philip Currie, professor and Canada research chair in dinosaur paleobiology at the University of Alberta. “The two fossils — squamosal bones from the side of the frill — have all the features you would expect, just presented in a unique shape.”

“This discovery of a previously unknown species in relatively well-studied rocks underscores that we still have many more new species of dinosaurs to left to find,” said co-author Dr. Mark Loewen, research associate at the Natural History Museum of Utah.

This dinosaur is just the latest in a series of new finds being made by Ryan and Evans as part of their Southern Alberta Dinosaur Project, which is designed to fill in gaps in our knowledge of Late Cretaceous dinosaurs and study their evolution. This project focuses on the paleontology of some of oldest dinosaur-bearing rocks in Alberta and the neighbouring rocks of northern Montana that are of the same age.

Journal Reference:

Michael J. Ryan, David C. Evans, Philip J. Currie, Mark A. Loewen. A new chasmosaurine from northern Laramidia expands frill disparity in ceratopsid dinosaurs. Naturwissenschaften, 2014; 101 (6): 505 DOI: 10.1007/s00114-014-1183-1

Note : The above story is based on materials provided by Cleveland Museum of Natural History.

Hunting for heat deep in the Earth

Geothermal energy is harvested by pumping cold water down an injection well, and bringing hot water up again via a production well. Left: In areas that produce geothermal energy today, the water flows through natural fractures in the bedrock between the wells, heating up in the process. Right: In future drilling in hard rock that lacks natural cracks, as in Norway, drilling a series of radiating bore-holes between the wells is a possibility. An alternative method is to create such cracks by subjecting the bedrock to extremely high hydraulic pressure (so-called “fracking”). Click Here for large photo Credit: SINTEF/Knut Gangåssæter.

Capturing green energy from deep in the Earth will bring competitive electricity and district heating – with help from Norway.

Ever since Jules Verne’s 1864 novel ” A Journey to the Centre of the Earth”, people have dreamt of capturing the heat of planet Earth. It exists in huge amounts, is completely renewable and emits no CO2.

“What we have done so far is no more than to scratch the surface of the Earth. The heat that many people extract from their gardens and then upgrade in heat pumps is not geothermal, but rather solar energy,” says SINTEF research scientist Alexandre Kane.

Backed by a troop of industrial and technology companies, Kane is manager of the Nextdrill research project, whose members are going ahead at full speed to develop drilling tools that will make it profitable to exploit true geothermal heat.

Stringent cost requirements

The immediate aim is to drill wells to depths of five to six kilometres, where we encounter temperatures that are high enough to allow the heat to be used for district heating and electricity generation.

“For this to be commercially viable we will need to drill much more cheaply than the petroleum industry does, and without needing permanent subsidies. At the same time, we need to penetrate bedrock that is much harder than we find on the continental shelf in the North Sea. It may sound as though it will be impossible to do both of these things at once, but we have a great belief in the possibility, as long as research continues along the same lines after this preliminary project has come to an end,” says Kane.

High speed; long working life

As in all drilling operations, the taximeter rises rapidly. If geothermal heat is to be competitive as a source of energy, the time put into drilling must be kept to a minimum. Drilling operators who want to capture this heat therefore need to be able to drill at high speed. Nor can they afford the loss of time involved if the drill-bit is always having to be brought to the surface and replaced.

The Nextdrill project is a response to this challenge. Three of its members – SINTEF, the Swedish company Sandvik and Germany’s H.C. Starck – are collaborating on the development of materials for a drill-bit with a long working life.

Another participant is the Norwegian technology company Resonator, which is in the process of developing an electric percussion rotary drill, a tool that crushes rock by dealing it hammer-like blows as the drill-bit turns. Electrical operation offers the possibility of remote control and more energy-efficient drilling systems than technology based on today’s pneumatic or hydraulic systems.

First test in August

In the course of this year the Nextdrill project will carry out its first small-scale drilling trials near Ås in Akershus County. In August and again in November, a specially designed version of Resonator’s percussion rotary drill will tackle hard rock. It will be fitted in turn with commercially available drill-bits and bits made of the highly wear-resistant materials that are being developed by the project.

These trials have two main purposes. They will provide new knowledge about how wear occurs on drill-bits when rock is crushed using an electric percussion rotary drill. The tests will also show how the number of impacts per unit time affects the speed of drilling.

“Although we will not be drilling very deep during these tests we do expect to gather important data for the next stages of our efforts to develop highly durable materials,” says Kane.

Geothermal energy

The heat that SINTEF’s French project manager wants to capture is known as geothermal energy, and is derived from two sources that lie far beneath our feet. About one third of it is heat that has been stored in the Earth’s molten core since our planet was formed. The other two-thirds have their origin in the decay of radioactive isotopes in the Earth’s crust. This process releases heat, which means that the temperature rises, metre by metre, the further we drill into the interior of the planet.

Two types of well need to be drilled to exploit this heat; one to pump cold water down, and the other to bring hot water up again (see illustration). The drill-bit that does this job must be able to crush hard rock types such as granite. The main aim of the Nextdrill project is to identify a combination of hard-wearing, durable materials and technical solutions that can do this (see fact-sheet).

Laboratory trials and computer models

The drill-bit needs to be able to withstand a high level of friction, in addition to enormous amounts of mechanical abuse resulting from the high-frequency hammer impacts.

“Laboratory trials and virtual experiments performed by computer models have taught us a great deal about drilling through granite, and have enabled us to develop models that we use to find the optimal form and composition of the drill-bit. The drilling trials at Ås will give us measurements that will let us further improve the computer model,” says Kane.

Note : The above story is based on materials provided by SINTEF

Okenite

Okenite Locality: Bombay Quarry, Mumbai District (Bombay District), Maharashtra, India Dimensions: 17.5 cm x 12.5 cm x 10.5 cm Photo Copyright © Rob Lavinsky & irocks.

Chemical Formula: CaSi2O5·2H2O
Locality: Disko Island, Greenland. Poona, near Bombay, India.
Name Origin: Named for Lorenz Oken (1779-1851), German natural historian, Munich Germany.

Okenite (CaSi2O5·2H2O) is a silicate mineral that is usually associated with zeolites. It most commonly is found as small white “cotton ball” formations within basalt geodes. These formations are clusters of straight, radiating, fibrous crystals that are both bendable and fragile.

Discovery and occurrence

It was first described in 1828 for an occurrence at Disko Island, Greenland and named for German naturalist Lorenz Oken (1779–1851).

Minerals associated with okenite include apophyllite, gyrolite, prehnite, chalcedony, goosecreekite and many of the other zeolites. Okenite is found in India, mainly within the state of Maharashtra. Other localities include Bulla Island, Azerbaijan; Aranga, New Zealand; Chile; Ireland and Bordo Island in the Faroe Islands.

History

Discovery date: 1828
Town of Origin : ILE DISKO
Country of Origin: GROENLAND

Physical Properties

Cleavage: {001} Good
Color:     White, Yellowish white, Bluish white.
Density: 2.3 – 2.33, Average = 2.31
Diaphaneity:Transparent to Translucent
Fracture: Conchoidal – Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Hardness: 5 – Apatite
Luminescence: Non-Fluorescent.
Luster: Pearly
Streak: white

Photos:

Okenite Locality: Pune District, Maharashtra, India Overall Size:    8x5x5 cm Crystals: 2-3 cm balls © JohnBetts-FineMinerals
Gyrolite, Okenite, Quartz Locality: Poona, near Bombay, India Size: large cabinet Rob Lavinsky / iRocks.

Few, if any, big impact craters remain to be discovered on Earth, new model finds

Clouds over Australia are shown. Credit: NASA

It is likely that most of the large impact craters on Earth have already been discovered and that others have been erased, according to a new calculation by a pair of Purdue University graduate students.
“Over the past 3.5 billion years it is thought that more than 80 asteroids similar in size to, or larger than, the one which killed the dinosaurs have struck the Earth, leaving behind craters which are over 100 kilometers across, but our model suggests only about eight of these massive craters could still exist today,” said Timothy Bowling, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences. “Geologists have already found six or seven such craters, so odds are not in the favor of those hoping to find the next big crater.”

The movement of the Earth’s tectonic plates and other geologic processes erase craters over time, he said.

“Impact craters dominate the surface of other planets and bodies in our solar system, like the famously pockmarked moon and Mercury, but the Earth looks different,” Bowling said. “The Earth’s crust is very dynamic and active, and over time it pushes and pulls these craters deep below the surface, until eventually they are sunk into the Earth’s mantle and disappear.”

Although it is known that natural processes erase craters fairly quickly from the Earth’s surface, this model was the first to quantify how many craters have likely been erased, he said.

Brandon Johnson, a postdoctoral researcher at the Massachusetts Institute of Technology who at the time was a graduate student at Purdue, led the study, which is to be published in the journal Geology. Both Bowling and Johnson worked under Jay Melosh, a Purdue distinguished professor of earth, atmospheric and planetary sciences and physics. A NASA planetary geology and geophysics grant funded this research.

Bowling and Johnson used the age of the Earth’s terrestrial and oceanic crusts and three different scenarios of Earth’s bombardment history to determine the maximum probability that a crater made a given number of years ago would still exist today. They then estimated the percentage of craters that could persist and be observed today for each of the bombardment scenarios.

The model’s ability to estimate the percentage of large craters that would survive to present day could be useful in supporting or refuting different theories of the ratio of large to small impacts, called the size frequency distribution, Bowling said.

“The number of smaller impacts that would have likely occurred for every large impact we find is a looming question in the field,” he said. “Existing theories are mostly based on studies of craters on the surfaces of other bodies, like the moon. No one had attempted this before using the Earth’s crater record because it couldn’t be done without having an idea of how many craters have been erased. This model could be used to help confirm or refute proposed theories.”

While the model could be applied to studies of the size frequency distribution, it cannot be used to distinguish between different models of the rate at which large objects hit Earth, he said. These models vary from those that expect constant bombardment to those that predict that earlier time periods were responsible for a greater number of impacts.

An ability to accurately determine the date of impact is needed to distinguish between different proposed bombardment scenarios, Bowling said.

Instead of hunting for craters, scientists should search for layers of debris ejected on impact to better understand the Earth’s bombardment history, Bowling said.

When asteroids larger than about 10 kilometers, or six miles, in diameter crash into the Earth a plume of vaporized rock rises into space. Small droplets of this plume condense, solidify and fall back to the surface. A thin layer of these particles, called spherules, then blankets the Earth. This layer of spherules persists in the geologic record and can be used to determine the date of impact. The thickness of the spherule layer and the size of the individual spherules within it also provide information about the asteroid and its size. These spherule layers persist long after the craters have been erased, he said.

More information:
Paper: Where have all the craters gone? Earth’s bombardment history and the expected terrestrial cratering record, Geology, 2014.

Note : The above story is based on materials provided by Purdue University

Our planet’s most abundant mineral now has a name

A sample of the 4.5 billion-year-old Tenham meteorite that contains submicrometer-sized crystals of bridgmanite. Credit: Chi Ma / Caltech

Deep below the earth’s surface lies a thick, rocky layer called the mantle, which makes up the majority of our planet’s volume. For decades, scientists have known that most of the lower mantle is a silicate mineral with a perovskite structure that is stable under the high-pressure and high-temperature conditions found in this region. Although synthetic examples of this composition have been well studied, no naturally occurring samples had ever been found in a rock on the earth’s surface. Thanks to the work of two scientists, naturally occurring silicate perovskite has been found in a meteorite, making it eligible for a formal mineral name.
The mineral, dubbed bridgmanite, is named in honor of Percy Bridgman, a physicist who won the 1946 Nobel Prize in Physics for his fundamental contributions to high-pressure physics.

“The most abundant mineral of the earth now has an official name,” says Chi Ma, a mineralogist and director of the Geological and Planetary Sciences division’s Analytical Facility at Caltech.

“This finding fills a vexing gap in the taxonomy of minerals,” adds Oliver Tschauner, an associate research professor at the University of Nevada-Las Vegas who identified the mineral together with Ma.

High-pressure and temperature experiments, as well as seismic data, strongly suggest that (Mg,Fe)SiO3-perovskite—now simply called bridgmanite—is the dominant material in the lower mantle. But since it is impossible to get to the earth’s lower mantle, located some 400 miles deep within the planet and rocks brought to the earth’s surface from the lower mantle are exceedingly rare, naturally occurring examples of this material had never been fully described.

That is until Ma and Tschauner began poking around a sample from the Tenham meteorite, a space rock that fell in Australia in 1879.

Because the 4.5 billion-year-old meteorite had survived high-energy collisions with asteroids in space, parts of it were believed to have experienced the high-pressure conditions we see in the earth’s mantle. That, scientists thought, made it a good candidate for containing bridgmanite.

Tschauner used synchrotron X-ray diffraction mapping to find indications of the mineral in the meteorite. Ma then examined the mineral and its surroundings with a high-resolution scanning electron microscope and determined the composition of the tiny bridgmanite crystals using an electron microprobe. Next, Tschauner analyzed the crystal structure by synchrotron diffraction. After five years and multiple experiments, the two were finally able to gather enough data to reveal bridgmanite’s chemical composition and crystal structure.

“It is a really cool discovery,” says Ma. “Our finding of natural bridgmanite not only provides new information on shock conditions and impact processes on small bodies in the solar system, but the tiny bridgmanite found in a meteorite could also help investigations of phase transformation mechanisms in the deep Earth. ”

The mineral and the mineral name were approved on June 2 by the International Mineralogical Association’s Commission on New Minerals, Nomenclature and Classification.

Note : The above story is based on materials provided by California Institute of Technology

Nickel

Nickel electrolytic and 1cm3 cube © pse-mendelejew ” Alchemist-hp “

Chemical Formula: Ni
Locality: Bogota, Canala, New Caledonia.
Name Origin: From the German Nickel – “demom”, from a contraction of kupfernickel, or “Devil’s Copper”, as the mineral was believed to contain copper but yielded none when smelted.

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel shows a significant chemical activity that can be observed when nickel is powdered to maximize the exposed surface area on which reactions can occur, but larger pieces of the metal are slow to react with air at ambient conditions due to the formation of a protective oxide surface. Even then, nickel is reactive enough with oxygen that native nickel is rarely found on Earth’s surface, being mostly confined to the interiors of larger nickel–iron meteorites that were protected from oxidation during their time in space. On Earth, such native nickel is always found in combination with iron, a reflection of those elements’ origin as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth’s inner core.

The use of nickel (as a natural meteoric nickel–iron alloy) has been traced as far back as 3500 BC. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook its ore for a copper mineral. The element’s name comes from a mischievous sprite of German miner mythology, Nickel (similar to Old Nick), that personified the fact that copper-nickel ores resisted refinement into copper. An economically important source of nickel is the iron ore limonite, which often contains 1-2% nickel. Nickel’s other important ore minerals include garnierite, and pentlandite. Major production sites include the Sudbury region in Canada (which is thought to be of meteoric origin), New Caledonia in the Pacific, and Norilsk in Russia.

History

Discovery date : 1967
Town of Origin : BOGOTA, CANALA
Country of Origin: NOUVELLE CALEDONIE

Optical Properties

Optical and misc. Properties : Opaque

Physical Properties

Color: Gray white, Silvery white.
Density: 7.8 – 8.2, Average = 8
Diaphaneity: Opaque
Fracture: Hackly – Jagged, torn surfaces, (e.g. fractured metals).
Hardness: 4-5 – Fluorite-Apatite
Luster: Metallic
Streak: grayish white

Photos :

Nickel chunk © Samsara
Nickel-Copper-Platinum Ore Locality: Norilsk Mine, Talnakh Intrusive Complex, Krasnoyarsk Krai, Russia Overall Size: 9x9x5.5 cm © JohnBetts-FineMinerals

Virtual Geoscience Workbench

Project Information

About this project:

This is the VIRTUAL GEOSCIENCE WORKBENCH project (“vgw”)

This project was registered on SourceForge.net on Aug 21, 2008, and is described by the project team as follows:

The Virtual Geoscience Workbench for discontinuous systems is a computer software environment for modelling. We have made the combined Finite-Discrete Element Method (FEMDEM) the core of our solids technology.

Screenshots :

Download :

Source code for this project may be available as downloads or through one of the SCM repositories used by the project, as accessible from the project develop page.

Copyright © 2014 Dice. All Rights Reserved.
SourceForge is a Dice Holdings, Inc. service.

Niger River

A map of the River Niger, with national boundaries included

Table of Contents

The Niger River is the principal river of western Africa, extending about 4,180 km (2,600 mi). Its drainage basin is 2,117,700 km2 (817,600 sq mi) in area. Its source is in the Guinea Highlands in southeastern Guinea. It runs in a crescent through Mali, Niger, on the border with Benin and then through Nigeria, discharging through a massive delta, known as the Niger Delta or the Oil Rivers, into the Gulf of Guinea in the Atlantic Ocean. The Niger is the third-longest river in Africa, exceeded only by the Nile and the Congo River (also known as the Zaïre River). Its main tributary is the Benue River.

Etymology

The Niger is called Jeliba or Joliba “great river” in Manding; Orimiri or Orimili “great water” in Igbo; Egerew n-Igerewen “river of rivers” in Tuareg; Isa Ber “big river” in Songhay; Kwara in Hausa; and Oya in Yoruba. The origin of the name Niger, which originally applied only to the middle reaches of the river, is uncertain. The likeliest possibility is an alteration, by influence of Latin niger “black”, of the Tuareg name egerew n-igerewen, which is used along the middle reaches of the river around Timbuktu. As Timbuktu was the southern end of the principal Trans-Saharan trade route to the western Mediterranean, it was the source of most European knowledge of the region.

Medieval European maps applied the name Niger to the middle reaches of the river, in modern Mali, but Quorra (Kworra) to the lower reaches in modern Nigeria, as these were not recognized as being the same river. When European colonial powers began to send ships along the West coast of Africa in the 16th and 17th centuries, the Senegal River was often postulated to be seaward end of the Niger. The Niger Delta, pouring into the Atlantic through mangrove swamps and thousands of distributaries along more than a hundred miles, was thought to be no more than coastal wetlands. It was only with the 18th century visits of Mungo Park, who travelled down the Niger River and visited the great Sahelian empires of his day, that Europeans correctly identified the course of the Niger, and extending the name to its entire course.

The modern nations of Nigeria and Niger take their names from the river, marking contesting national claims by colonial powers of the “Upper”, “Lower” and “Middle” Niger river basin during the Scramble for Africa at the end of the 19th century.

Geography

The Niger River is a relatively “clear” river, carrying only a tenth as much sediment as the Nile because the Niger’s headwaters lie in ancient rocks that provide little silt. Like the Nile, the Niger floods yearly; this begins in September, peaks in November, and finishes by May.

An unusual feature of the river is the Inner Niger Delta, which forms where its gradient suddenly decreases. The result is a region of braided streams, marshes, and lakes the size of Belgium; the seasonal floods make the Delta extremely productive for both fishing and agriculture.

The river ‘loses’ nearly two-thirds of its potential flow in the Inner Delta between Ségou and Timbuktu to seepage and evaporation. All the water from the Bani River, which flows into the Delta at Mopti, does not compensate for the ‘losses’. The average ‘loss’ is estimated at 31 km3/year, but varies considerably between years. The river is then joined by various tributaries, but also loses more water to evaporation. The quantity of water entering Nigeria measured in Yola was estimated at 25 km3/year before the 1980s and at 13.5 km3/year during the 1980s. The most important tributary of the Niger in Nigeria is the Benue River which merges with the river at Lokoja in Nigeria. The total volume of tributaries in Nigeria is six times higher than the inflow into Nigeria, with a flow near the mouth of the river standing at 177.0 km3/year before the 1980s and 147.3 km3/year during the 1980s.

The above story is based on materials provided by Wikipedia

1...280281282...336Page 281 of 336

Related Articles

All
Facebook Instagram Linkedin TikTok Twitter Youtube
© 2011-2025. All Rights Reserved.