With global greenhouse gas emissions continuing to increase proposals to limit the effects of climate change through the large-scale manipulation of Earth system are increasingly being discussed. Researchers at the GEOMAR Helmholtz Centre for Ocean Research Kiel have now studied with computer simulations the long-term global consequences of several “climate engineering” methods. They show that all the proposed methods would either be unable to significantly reduce global warming if CO2 emissions remain high, or they could not be stopped without causing dangerous climate disruption.
The study is published in the journal Nature Communications.
Despite international agreements on climate protection and political declarations of intent, global greenhouse gas emissions have not decreased. On the contrary, they continue to increase. With a growing world population and significant industrialization in emerging markets such as India and China the emission trend reversal necessary to limit global warming seems to be unlikely. Therefore, large-scale methods to artificially slow down global warming are increasingly being discussed. They include proposals to fertilize the oceans, so that stimulated plankton can remove carbon dioxide (CO2) from the atmosphere, or to reduce the Sun’s incoming radiation with atmospheric aerosols or mirrors in space, so as to reduce climate warming. All of these approaches can be classified as “climate engineering.” “However, the long-term consequences and side effects of these methods have not been adequately studied,” says Dr. David Keller from the GEOMAR Helmholtz Centre for Ocean Research Kiel. Together with colleagues the expert in earth system modelling has compared several Climate Engineering methods using a computer model.
“The problem with previous research was that in most cases the methods were studied with different models using different assumptions and different sets of earth system components, making it difficult to compare the effects and side effects of different methods,” Dr. Keller says. He adds: “We wanted to simulate different climate engineering methods using the same basic assumptions and Earth system model.” For their study, the researchers chose five well-known climate engineering approaches: The reduction of incoming solar radiation, the afforestation of large desert areas in North Africa and Australia, and three different techniques aimed at increasing ocean carbon uptake. In parallel, the scientists also simulated future changes in Earth system without climate engineering, based on the high-CO2 emission scenario used by the UN IPCC.
Even under ideal conditions assumed in the simulations, the potential benefits of the various climate engineering methods were limited. Only a continuous reduction of solar radiation could prevent Earth from warming significantly. The afforestation of the Sahara and the Australian outback, however even caused some additional global warming: “The forests removed carbon dioxide from the atmosphere, but at the same time Earth’s surface became darker and could store more heat,” Dr. Keller explains of this phenomenon. All of the other techniques showed significant side effects, too. For example, the fertilization of the oceans allowed plankton to remove CO2 from the atmosphere, but also changed the size of ocean oxygen minimum zones.
Another important question for the researchers: What happens if climate engineering is stopped after a few decades for technical or political reasons? “For several methods we saw a rapid change in the simulated climate when climate engineering ended,” says Dr. Keller. For example, if after 50 years the sun’s rays were no longer partially blocked, Earth warmed by several degrees within a few decades. “This change would be much faster than the current rate of climate change, with potentially even more catastrophic consequences,” says Keller.
The study is the basis for further research in the priority program “Climate Engineering: Risks, Challenges, Opportunities?” of the German Research Foundation (DFG), coordinated by co-author Prof. Dr. Andreas Oschlies from GEOMAR. “In addition to natural science studies, we also want to learn more about the potential social, political, legal and ethical aspects of proposed climate engineering methods. For one thing, this study clearly shows that there would always be many losers in addition to possible winners. Some side effects would even affect future generations. A decision for or against climate engineering thus would have to be considered carefully and be fully legitimized, and must thus be based on a much better understanding of possible effects, uncertainties and risks than we have today,” says Professor Oschlies.
Note : The above story is based on materials provided by Helmholtz Centre for Ocean Research Kiel (GEOMAR).
Emerald with Calcite Muzo Mine, Boyaca Dept., Colombia Thumbnail, 2.9 x 1.4 x 1.2 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.
The word “Emerald” is derived (via Old French: Esmeraude and Middle English: Emeraude), from Vulgar Latin: Esmaralda/Esmaraldus, a variant of Latin Smaragdus, which originated in Greek: σμάραγδος (smaragdos; “green gem”).
Properties determining value
Emeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of Connoisseurship: Color, Cut, Clarity and Carat weight. Before the 20th century, jewelers used the term water, as in “a gem of the finest water”, to express the combination of two qualities: color and clarity. Normally, in the grading of colored gemstones, color is by far the most important criterion. However, in the grading of emeralds, clarity is considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure verdant green hue as described below, but also a high degree of transparency to be considered a top gem.
In the 1960s, the American jewelry industry changed the definition of “emerald” to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK and Europe. In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as “Colombian Emerald”.
Emerald localities
Emeralds in antiquity have been mined in Egypt since 1500 BCE, and India, and Austria since at least the 14th century CE.
Colombia is by far the world’s largest producer of emeralds, constituting 50–95% of the world production, with the number depending on the year, source and grade. Emerald production in Colombia has increased drastically in the last decade, increasing by 78% from 2000 to 2010. The three main emerald mining areas in Colombia are Muzo, Coscuez, and Chivor. Rare ‘trapiche’ emeralds are found in Colombia, distinguished by a six-pointed radial pattern made of ray-like spokes of dark carbon impurities.
Zambia is the world’s second biggest producer, with its Kafubu River area deposits (Kagem Mines) about 45 km (28 mi) southwest of Kitwe responsible for 20% of the world’s production of gem quality stones in 2004. In the first half of 2011 the Kagem mines produced 3.74 tons of emeralds.
Emeralds are found all over the world in countries such as Afghanistan, Australia, Austria, Brazil, Bulgaria, Cambodia, Canada, China, Egypt, Ethiopia, France, Germany, India, Italy, Kazakhstan, Madagascar, Mozambique, Namibia, Nigeria, Norway, Pakistan, Russia, Somalia, South Africa, Spain, Switzerland, Tanzania, United States, Zambia, and Zimbabwe. In the US, emeralds have been found in Connecticut, Montana, Nevada, North Carolina, and South Carolina. In 1997 emeralds were discovered in the Yukon.
Water-ice clouds, polar ice and other geographic features can be seen in this full-disk image of Mars from 2011. NASA’s Mars Curiosity Rover touched down on the planet on August 6, 2012.
(CNN) — The presence of water on Mars is often talked about in the past tense — as in, billions of years in the past. But researchers have found clues that water could be flowing in the present, at least during warm seasons.
Researchers at Georgia Institute of Technology are looking at dark features on Martian slopes that are finger-shaped. They appear and disappear seasonally.
These flows represent the best suggestion we know of that Mars has water right now, scientists say. The study is published in the journal Geophysical Research Letters.
In 2011, Lujendra Ojha and his colleagues announced the evidence for possible saltwater flows on Mars. They published a study in the journal Science based on data from the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter.
As an undergraduate at the University of Arizona, Tucson, Ojha was the lucky one to spot irregular features in a Martian crater he was studying. He had no idea what they were. Researchers spent months figuring it out, and determined that the finger-like shapes could be briny water.
How an undergrad spotted possible water on Mars
“In HiRISE images, we see them forming, elongating and then fading over time,” Ojha said Monday. “That’s why they’re called seasonal — they form and flow when the temperature is right.”
Since that study, Ojha has enrolled in graduate school at Georgia Institute of Technology, and continued studying the phenomena. He and Georgia Tech assistant professor James Wray looked more deeply at 13 sites with confirmed recurring slope features.
This time they found chemical evidence supporting their earlier findings that water flows may appear and disappear on Mars with the seasons.
In most cases, the possible water features appear to last for the equivalent of about two Earth months, Ojha said.
The researchers used the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument to see if they could find more clues of water. CRISM looks for chemical signatures based on the fact that different substances absorb light at distinct wavelengths.
Wavelengths can reveal a lot about what things are made of, Ojha said.
Mystery rock spotted on Mars
Ojha and colleagues did not find direct evidence of water using the spectrometer method. Instead, they found light absorption features consistent with “something iron in nature” at the flows. The light absorption varied with season, however. The absorption bands are stronger when the features are forming and growing, and weaker when they fade away.
“Something in these areas is actually causing the spectroscopic signature to fluctuate as well,” Ojha said.
Water could explain these variations, Ojha said. Water in the seasonal flow would wash away small-sized grains — dust — and leave bigger grains. When water is not present, the bigger grains would remain, accounting for the changes in light absorption that researchers observed over time.
Grain sizes could vary without water, though. The Martian atmosphere could also be responsible for some variation in the spectrometer data, because one season is dustier than another, but Ojha thinks there is something else going on.
If there is water on Mars, it would be near to the surface and salty. Specifically, the flows may host an iron-containing mineral called ferric sulfate, a substance known to exist on Mars. Ferric sulfate would bring the melting point of ice down to a lower temperature, Ojha said.
More research needs to be done to confirm this idea, obviously, but if there is briny water on Mars, could we drink it?
No life on Earth could survive in water saturated with ferric sulfate, Wray said in an e-mail.
“But if there’s enough water initially to form a dilute solution, maybe it would be OK,” he said. “Personally I wouldn’t want to risk it!”
Note : The above story is based on materials provided by Elizabeth Landau, CNN
Volcanoes spewing Sun-reflecting particles into the atmosphere have partly offset the effects of Man’s carbon emissions over a 15-year period that has become a global-warming battleground, researchers said Sunday.
A so-called hiatus in warming since 1998 has pitched climate sceptics against mainstream scientists.
While temperatures have risen relentlessly—13 of the l4 warmest years on record occurred since the start of the century—they tracked far below the increase in man-made greenhouse gases.
This gap between the expected and actual temperatures has been cited by sceptics as proof that human-induced global warming is either a green scare or bad science.
But a study in the journal Nature Geoscience said volcanic eruptions helped explain the apparent warming slowdown.
Researchers using satellite data found a link between surface temperatures and the impact from nearly 20 volcanic eruptions since 2000.
Sulphuric droplets disgorged by the volcanoes reflected sunlight and slightly cool the lower atmosphere, they said.
The effect of these “aerosols” accounted for as much as 15 percent of the gap between expected and measured temperatures between 1998 and 2012, according to the team’s figures.
“The ‘warming hiatus’ since 1998 has a number of different causes,” study co-author Ben Santer of the Lawrence Livermore National Laboratory in California told AFP by email.
“The cooling caused by early 21st century volcanic eruptions is one of the causes.”
Other explanations for the “hiatus” have been a bigger-than-expected takeup of atmospheric heat by the ocean, or a decline in solar activity.
Blockbuster eruptions, notably that of Mount Pinatubo in the Philippines in 1991, were known to have discernible cooling effects on Earth’s surface.
But volcanoes have not featured in the “hiatus” debate mainly because there had been no major eruptions since the mooted pause began in 1998, only smaller ones whose impact is harder to measure.
– Better models needed –
This is a gap, as it left computer models of climate change incomplete, the new study suggested.
“Better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these… in climate model simulations,” it said.
Global warming sceptics have pointed to the “hiatus” as proof of flaws in models used to predict warming and thus play a key role in driving policies to tackle climate change.
They contend that these models exaggerate the heat-trapping effect from carbon dioxide (CO2) emitted by fossil fuel burning.
Santer said the new findings “do not support” such an argument.
“We’ve been lucky that a natural cooling influence (an uptick in 21st century volcanic activity) has partly counteracted human-caused warming,” he said.
“We do not know how volcanic activity will evolve over the coming decades, and thus we do not know how long our luck will continue.”
Experts generally agree that Earth is on track for greatly exceeding the maximum two degrees Celsius (3.6 degrees Fahrenheit) of warming targeted in UN climate negotiations.
Last year the level of carbon dioxide (CO2) in the atmosphere crossed a threshold of 400 parts per million (ppm)—a level never experienced by humans.
CO2 concentrations are rising at two or three ppm per year, driven especially by the burning of coal in emerging economies.
Commenting on the study, Piers Forster, a professor of climate change at the University of Leeds, said it confirmed that volcanoes contributed to the slowdown, but could not be the only cause.
“Volcanoes give us only a temporary respite from the relentless warming pressure of continued increases in CO2,” he added.
Chemical Formula: Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH) Locality: Island of Elba, Italy. Name Origin: Named for the locality.
Elbaite, a sodium, lithium, aluminium boro-silicate, is a mineral species belonging to the six member ring cyclosilicate tourmaline group, with the following general composituion: Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Elbaite forms three series, with dravite, with fluor-liddicoatite, and with schorl. Due to these series, specimens with the ideal end-member formula are not found occurring naturally.
As a gemstone, elbaite is a desirable member of the tourmaline group because of the variety and depth of its colours and quality of the crystals. Originally discovered on the island of Elba, Italy in 1913, it has since been found in many parts of the world. In 1994, a major locality was discovered in Canada, at O’Grady Lakes in the Yukon.
Elbaite forms in igneous and metamorphic rocks and veins in association with lepidolite, microcline, and spodumene in granite pegmatites; with andalusite and biotite in schist; and with molybdenite and cassiterite in massive hydrothermal replacement deposits.
Cleavage: {1011} Indistinct Color: Blue, Colorless, Green, Yellow, White. Density: 2.9 – 3.2, Average = 3.05 Diaphaneity: Transparent to translucent to opaque Fracture: Sub Conchoidal – Fractures developed in brittle materials characterized by semi-curving surfaces. Hardness: 7.5 – Garnet Luminescence: Fluorescent, Short UV=weak blue white to blue. Luster: Vitreous (Glassy) Streak: white
The Terreneuvian is the lowermost and oldest Series of the Cambrian geological System.Its base is defined by the first appearance datum of the trace fossil Treptichnus pedum around 541.0 ± 1.0 million years ago. Its top is defined as the first appearance of trilobites in the stratigraphic record around ~521 million years ago. This series was formally ratified by the International Commission on Stratigraphy in 2012.
The Fortunian Stage and presently unnamed Cambrian Stage 2 are the Stages within this Series. The Terreneuvian corresponds to the pre-trilobitic Cambrian.
The name Terreneuvian is derived from Terre Nueve, a French name for the island of Newfoundland, Canada, where many rocks of this age are found, including the type section.
Type locality
The type locality (GSSP) of the Terreneuvian is in Fortune Head, at the northern edge of the Burin Peninsula, Newfoundland, Canada (47.0762°N 55.8310°W). The outcrops show a carbonate-siliciclastic succession which is mapped as the Chapel Island Formation. The formation is divided into the following members that are composed of peritidal sandstones and shales (Member 1), muddy deltaic and shelf sandstones and mudstones (Member 2A), laminated siltstones (Member 2B and 3) and mudstones and limestones of the inner shelf (Member 4). The Precambrian-Cambrian boundary lies 2.4 m above the base of the second member, which is the lowest occurrence of Treptichnus pedum. The traces can be seen on the lower surface of the sandstone layers. The first calcareous shelled skeletal fossils (Ladatheca cylindrica) are 400 m above the boundary. The first trilobites appear 1400 m above the boundary, which corresponds to the beginning of the Branchian Series.
Note : The above story is based on materials provided by Wikipedia
Chemical Formula: Na2ZrSi6O15 · 3H2O Locality: Narsarsuk in the Julianehaab district, southern Greenland. Name Origin: From the Greek “ELPIS” = hope, in allusion to the hope of finding another mineral in the layer
Elpidite is in the long list of unusual mineral that come from agpaitic pegmatite rocks. Agpaitic pegmatite intrusions are unusual igneous rocks that are high in alkaline metals (such as sodium) and poor in silica. These intrusions also contain a large number of unusual elements such as zirconium. Elpidite was first discovered at Narsarsuk, Greenland, from where the first specimens were described in 1932.
Color: Brown, Colorless, Yellow brown, White, Light red. Density: 2.54 Diaphaneity: Transparent to translucent Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals. Habit: Fibrous – Crystals made up of fibers. Hardness: 7 – Quartz Luminescence: Fluorescent, Short UV=yellow-green, Long UV=yellow-green. Luster: Vitreous (Glassy) Streak: white
This is a timeline of the history of our planet places the formation of the Jack Hills zircon and a “cool early Earth” at 4.4 billion years. Credit: Andree Valley
With the help of a tiny fragment of zircon extracted from a remote rock outcrop in Australia, the picture of how our planet became habitable to life about 4.4 billion years ago is coming into sharper focus.
Writing today (Feb. 23, 2014) in the journal Nature Geoscience, an international team of researchers led by University of Wisconsin-Madison geoscience Professor John Valley reveals data that confirm the Earth’s crust first formed at least 4.4 billion years ago, just 160 million years after the formation of our solar system. The work shows, Valley says, that the time when our planet was a fiery ball covered in a magma ocean came earlier.
“This confirms our view of how the Earth cooled and became habitable,” says Valley, a geochemist whose studies of zircons, the oldest known terrestrial materials, have helped portray how the Earth’s crust formed during the first geologic eon of the planet. “This may also help us understand how other habitable planets would form.”
The new study confirms that zircon crystals from Western Australia’s Jack Hills region crystallized 4.4 billion years ago, building on earlier studies that used lead isotopes to date the Australian zircons and identify them as the oldest bits of the Earth’s crust. The microscopic zircon crystal used by Valley and his group in the current study is now confirmed to be the oldest known material of any kind formed on Earth.
The study, according to Valley, strengthens the theory of a “cool early Earth,” where temperatures were low enough for liquid water, oceans and a hydrosphere not long after the planet’s crust congealed from a sea of molten rock. “The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago,” and possibly life not long after, says Valley.
The study was conducted using a new technique called atom-probe tomography that, in conjunction with secondary ion mass spectrometry, permitted the scientists to accurately establish the age and thermal history of the zircon by determining the mass of individual atoms of lead in the sample. Instead of being randomly distributed in the sample, as predicted, lead atoms in the zircon were clumped together, like “raisins in a pudding,” notes Valley.
The clusters of lead atoms formed 1 billion years after crystallization of the zircon, by which time the radioactive decay of uranium had formed the lead atoms that then diffused into clusters during reheating. “The zircon formed 4.4 billion years ago, and at 3.4 billion years, all the lead that existed at that time was concentrated in these hotspots,” Valley says. “This allows us to read a new page of the thermal history recorded by these tiny zircon time capsules.”
The formation, isotope ratio and size of the clumps — less than 50 atoms in diameter — become, in effect, a clock, says Valley, and verify that existing geochronology methods provide reliable and accurate estimates of the sample’s age. In addition, Valley and his group measured oxygen isotope ratios, which give evidence of early homogenization and later cooling of the Earth.
“The Earth was assembled from a lot of heterogeneous material from the solar system,” Valley explains, noting that the early Earth experienced intense bombardment by meteors, including a collision with a Mars-sized object about 4.5 billion years ago “that formed our moon, and melted and homogenized the Earth. Our samples formed after the magma oceans cooled and prove that these events were very early.”
Note : The above story is based on materials provided by University of Wisconsin-Madison. The original article was written by Terry Devitt.
This photo shows one-billion-year-old weathering profiles from Michigan. Ancient soils like these provide evidence for low atmospheric oxygen levels through much of Earth’s history. Credit: Noah Planavsky.
A team of biogeochemists at the University of California, Riverside, give us a nontraditional way of thinking about the earliest accumulation of oxygen in the atmosphere, arguably the most important biological event in Earth history.
A general consensus asserts that appreciable oxygen first accumulated in Earth’s atmosphere around 2.3 billion years ago during the so-called Great Oxidation Event (GOE). However, a new picture is emerging: Oxygen production by photosynthetic cyanobacteria may have initiated as early as 3 billion years ago, with oxygen concentrations in the atmosphere potentially rising and falling episodically over many hundreds of millions of years, reflecting the balance between its varying photosynthetic production and its consumption through reaction with reduced compounds such as hydrogen gas.
“There is a growing body of data that points to oxygen production and accumulation in the ocean and atmosphere long before the GOE,” said Timothy W. Lyons, a professor of biogeochemistry in the Department of Earth Sciences and the lead author of the comprehensive synthesis of more than a decade’s worth of study within and outside his research group.
Lyons and his coauthors, Christopher T. Reinhard and Noah J. Planavsky, both former UCR graduate students, note that once oxygen finally established a strong foothold in the atmosphere starting about 2.3 billion years ago it likely rose to high concentrations, potentially even levels like those seen today. Then, for reasons not well understood, the bottom fell out, oxygen plummeted to a tiny fraction of today’s level, and the ocean remained mostly oxygen free for more than a billion years.
The paper appears in Nature on Feb. 19.
“This period of extended low oxygen spanning from roughly 2 to less than 1 billion years ago was a time of remarkable chemical stability in the ocean and atmosphere,” Lyons said.
His research team envisions a series of interacting processes, or feedbacks, that maintained oxygen at very low levels principally by modulating the availability of life-sustaining nutrients in the ocean and thus oxygen-producing photosynthetic activity.
“We suggest that oxygen was much lower than previously thought during this important middle chapter in Earth history, which likely explains the low abundances and diversity of eukaryotic organisms and the absence of animals,” Lyons said.
The late Proterozoic—the time period beginning less than a billion years ago following this remarkable chapter of sustained low levels of oxygen—was strikingly different, marked by extreme climatic events manifest in global-scale glaciation, indications of at least intervals of modern-like oxygen abundances, and the emergence and diversification of the earliest animals. Lyons notes that the factors controlling the rise of animals are under close scrutiny, including challenges to the long-held view that a major rise in atmospheric oxygen concentrations triggered the event.
“Despite the new ideas about animal origins, we suspect that oxygen played a major if not dominant role in the timing of that rise and, in particular, in the subsequent emergence of complex ecologies for animal life on and within the sediment, predator-prey relationships, and large bodies” said Lyons. “But, again, feedbacks always rule the day. Environmental change drives evolution, and steps in the progression of life change the environment.”
No single factor is likely to be the whole story, and there is much more to be written in the tale. Lyons and coauthors, along with research groups from around world over, are focusing current efforts on the timing and drivers of oxygenation in the late Proterozoic, favoring a combination of global-scale mountain building, evolutionary controls on the way carbon is cycled in the biosphere, and concomitant climate events.
“We are faced with a lot of chicken-and-egg questions when it comes to unraveling the timing and sequence of oxygenation of the ocean and atmosphere,” Lyons said. “But now, armed with new and better data, more sophisticated numerical simulations, and highly integrated investigations in the lab and the field, Earth’s oxygenation history seems much longer and more dynamic than envisioned before, and we are getting closer to understanding the mechanisms behind such change.”
Note : The above story is based on materials provided by University of California – Riverside
Chemical Formula: NaCa2Mg5(Si7Al)O22(OH)2 Locality: Edenville, Orange County, New York, USA. Name Origin: Named for the locality.
Edenite is a double chain silicate mineral of the amphibole group with the general chemical composition NaCa2Mg5(Si7Al)O22(OH)2. Edenite is named for the locality of Edenville, Orange County, New York, where it was first described.
The Selenga River is a major river in Mongolia and Buryatia, Russia. Its source rivers are the Ider River and the Delgermörön river. It flows into Lake Baikal and has a length of 616 miles (992 km) (1024 km according to other sources). The Selenga River is the headwaters of the Yenisei-Angara River system. It carries 935 m³/s of water into Lake Baikal which comprises almost half of riverine inflow and forms a wide delta when it reaches the lake (680 km²).
The name derives from Evenki sele ‘iron’ + -nga (suffix). Selenge Province in northern Mongolia is derived from the name of this river. The Mongolian verb “sele-” means swim.
Note : The above story is based on materials provided by Wikipedia
Chemical Formula: Ag3Sb Locality: Wolfach, Baden, Germany. Name Origin: From the Greek, meaning “bad alloy.”
The silver antimonide mineral dyscrasite has the chemical formula Ag3Sb. It is an opaque, silver white, metallic mineral which crystallizes in the orthorhombic crystal system. It forms pyramidal crystals up to 5 cm and can also form cylindrical and prismatic crystals.
Dyscrasite is a metal ore and is opaque. In reflected light, however, it demonstrates weak anisotropism. Dyscrasite’s color under plane polarized light is most likely dark grey/black. When spun on a rotatable stage of a microscope (under plane polarized light), dyscrasite’s color should slightly change shades. This property is called pleochroism. Dyscrasite exhibits very weak reflected light pleochroism.
Dyscrasite belongs to the orthorhombic crystal class, meaning all three of its axes (a, b, and c) are unequal in length and are 90° to each other.
Physical Properties
Cleavage: {001} Distinct, {011} Distinct, {110} Imperfect Color: Gray, Yellow, Black, Silver white. Density: 9.4 – 10, Average = 9.69 Diaphaneity: Opaque Fracture: Sectile – Curved shavings or scrapings produced by a knife blade, (e.g. graphite). Hardness: 3.5-4 – Copper Penny-Fluorite Luminescence: Non-fluorescent. Luster: Metallic Magnetism: Nonmagnetic Streak: silver white
Volcanoes are among the most dangerous and least predictable natural forces on our planet. New findings may contribute to better volcano surveillance and eruption prognoses.
To understand the processes at work inside volcanoes, geologists survey cracks filled with magma, so-called dykes. These dykes are the main transport channels for magma through the Earth’s crust, and they control the growth of the magma chambers and the size of eruptions.
Understanding how dykes form and grow is crucial to volcano research. A new study published in Nature Communications, led by researchers at Uppsala University, shows that the strength of the rock surrounding a magma chamber determines the size of its dykes.
During several months’ field work in Iceland and on the Canary Islands, researchers measured the thickness of thousands of dykes. The results were analysed statistically, giving some surprising results.
“We were surprised that all our datasets showed the same statistical distribution. Neither the type of volcano, nor the type of dyke seemed to make any real difference. The Weibull distribution was always the best fit”, says lead author Michael Krumbholz, researcher at the Department of Earth Sciences at Uppsala University.
The Weibull distribution is well-known in materials science and is named after Waloddi Weibull who was active at Uppsala University. The Weibull distribution is known as the “weakest link theory” and predicts mathematically that a material will break first at its weakest point.
“The Weibull distribution’s surprisingly good conformity with our measurements showed us the way”, says Michael Krumbholz. “This means that the strength of the rock surrounding the magma chamber decides when and how new dykes form. The magma breaks the rock apart where it is the weakest.”
The research group now hope to apply their findings in volcano surveillance and prediction of eruptions.
Note : The above story is based on materials provided by Uppsala University
Chemical Formula: (Al,Fe3+)7(SiO4)3(BO3)O3 Locality: San Diego Co., California. Name Origin: Named after the French paleontologist, M. E. Dumortier (1803-1873).
Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, (Al,Fe3+)7(SiO4)3(BO3)O3. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.
Dumortierite was first described in 1881 for an occurrence in Chaponost, in the Rhône-Alps of France and named for the French paleontologist Eugène Dumortier (1803–1873). It typically occurs in high temperature aluminium rich regional metamorphic rocks, those resulting from contact metamorphism and also in boron rich pegmatites. The most extensive investigation on dumortierite was done on samples from the high grade metamorphic Gfohl unit in Austria by Fuchs et al. (2005).
It is used in the manufacture of high grade porcelain. It is sometimes mistaken for sodalite and has been used as imitation lapis lazuli.
Sources of Dumortierite include Austria, Brazil, Canada, France, Italy, Madagascar, Namibia, Nevada, Norway, Poland, Russia and Sri Lanka.
Slooh will cover NEA 2000 EM26, a “Potentially Hazardous Asteroid”, as it makes its closest-approach on Monday, February 17th starting at 6PM PST / 9PM EST / 02:00UTC (2/18) International times: http://tinyurl.com/NEA2000EM26-LIVE . The live image stream will be accompanied by discussions led by Slooh host and astronomer Bob Berman with special guests including experts and eyewitnesses from Russia, who experienced the unexpected asteroid impact that day.
Chemical Formula: PbCu(AsO4)(OH) Locality: Tsumeb, Namibia. Name Origin: Named in 1920 for G. Duft, general manager of the mine at Tsumeb, Namibia.
Duftite is a relatively common arsenate mineral with the formula PbCu(AsO4)(OH), related to conichalcite. It is green and often forms botryoidal aggregates. It is a member of the Adelite-Descloizite Group, Conichalcite-Duftite Series. Duftite and conichalcite specimens from Tsumeb are commonly zoned in colour and composition. Microprobe analyses and X-ray powder-diffraction studies indicate extensive substitution of Zn for Cu, and Ca for Pb in the duftite structure.
This indicates a solid solution among conichalcite, CaCu(AsO4 )(OH), austinite, CaZn(AsO4)(OH) and duftite PbCu(AsO4)(OH), all of them belonging to the adelite group of arsenates. It was named after Mining Councilor G Duft, Director of the Otavi Mine and Railroad Company, Tsumeb, Namibia. The type locality is the Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia.
Cliffs at Zumaia (Basque Country). Credit: Image courtesy of University of the Basque Country
Research at the Faculty of Science and Technology of the University of the Basque Country (UPV/EHU), entitled ‘Detailed Correlation and Orbital Control of succession during the Upper Maastrichtian in the Basque-Cantabrian Basin’ and focusing on the last 3 million years of the Cretaceous period, managed to detail exactly the chronology of the climatic, magnetic and biological events prior to the great extinction of 66 million years ago (Ma.), which includes the disappearance of almost all dinosaurs (except birds).
The traditional method for establishing absolute chronological and geological events has been using radiometric dating methods, based on the decomposition of radioactive isotopes. This method, however, is only applicable with the intervals such isotopes have, so the ages of certain zones can only be estimated through interpolation.
As the title of the research suggests, the method applied by this research team was based on a different principle, concretely on what is known as orbital control, which analyses gravitational interactions between the Earth, the Moon, the Sun and the planets of the Solar System (principally Jupiter). These interactions produce periodic variations of the terrestrial orbit, known as Milankovitch cycles, in honour of the Serbian astrophysicist who discovered them. It is thus known that the terrestrial orbit varies with intervals of one hundred thousand and four hundred thousand years; the inclination or obliquity of Earth’s axis every forty thousand years; and the orientation of this axis in relation to the sun approximately every twenty thousand years.
“It has been shown that such orbital variations influence, to a greater or lesser degree, the Earth’s climate, due mainly to differences in solar radiation received by the planet. The variations of the terrestrial orbit, for example, also controlled the duration of the glacial periods during the Quaternary (from 2.6 Ma until today),” explained Victoriano Pujalte, Professor of Geology of the Faculty of Science and Technology at the UPV/EHU and co-author of the research.
Sopelana, Zumaia and Hendaia
The research focused on locating the effects that these astronomical cycles have had on the layers analysed, a Flysch-type succession (rock sequences of a sedimentary origin made up of alternating layers of hard calcareous rock with other, softer loams) accumulated on a deep-lying sea basin — the Basque Basin — between 69 and 66 Ma, and which today is exposed to the naked eye in cliffs at Sopelana (Bizkaia province), Zumaia (province of Gipuzkoa) and Hendaia (Lapurdi). Using the “Fourier analysis” (a mathematical tool to analyse periodic functions), it has been possible to identify cycles of 400,000, 100,000 and 20,000 years, represented “by successive alternations of a loamy layer and another calcareous one,” known as “pairs,” of which 125 have been identified and enumerated. This has enabled narrowing the layers of the emerging successions to stages of twenty thousand years. “On a human scale twenty thousand years may seem a long time. On a geological scale, however, it represents spectacular precision,” explained Mr. Pujalte.
Geology is a “historical science” and, as such, any advance enabling greater precision in the chronology of events represents significant progress. “This is what the purpose of our work has been: to establish the chronology, approximately, of the past three million years of this Cretaceous period, and which in future research will enable establishing the geological and oceanographic phenomena of such an interval with precision,” pointed out the Professor of Geology at the UPV/EHU Faculty of Science and Technology.
Note : The above story is based on materials provided by University of the Basque Country.
Mount Hood, in the Oregon Cascades, doesn’t have a highly explosive history. Credit: Photo courtesy Alison M Koleszar
A new study suggests that the magma sitting 4-5 kilometers beneath the surface of Oregon’s Mount Hood has been stored in near-solid conditions for thousands of years, but that the time it takes to liquefy and potentially erupt is surprisingly short — perhaps as little as a couple of months.
The key, scientists say, is to elevate the temperature of the rock to more than 750 degrees Celsius, which can happen when hot magma from deep within the Earth’s crust rises to the surface. It is the mixing of the two types of magma that triggered Mount Hood’s last two eruptions — about 220 and 1,500 years ago, said Adam Kent, an Oregon State University geologist and co-author of the study.
Results of the research, which was funded by the National Science Foundation, were published this week in the journal Nature.
“If the temperature of the rock is too cold, the magma is like peanut butter in a refrigerator,” Kent said. “It just isn’t very mobile. For Mount Hood, the threshold seems to be about 750 degrees (C) — if it warms up just 50 to 75 degrees above that, it greatly increases the viscosity of the magma and makes it easier to mobilize.”
Thus the scientists are interested in the temperature at which magma resides in the crust, they say, since it is likely to have important influence over the timing and types of eruptions that could occur. The hotter magma from down deep warms the cooler magma stored at 4-5 kilometers, making it possible for both magmas to mix and to be transported to the surface to eventually produce an eruption.
The good news, Kent said, is that Mount Hood’s eruptions are not particularly violent. Instead of exploding, the magma tends to ooze out the top of the peak. A previous study by Kent and OSU postdoctoral researcher Alison Koleszar found that the mixing of the two magma sources — which have different compositions — is both a trigger to an eruption and a constraining factor on how violent it can be.
“What happens when they mix is what happens when you squeeze a tube of toothpaste in the middle,” said Kent, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “A big glob kind of plops out the top, but in the case of Mount Hood — it doesn’t blow the mountain to pieces.”
The collaborative study between Oregon State and the University of California, Davis is important because little was known about the physical conditions of magma storage and what it takes to mobilize the magma. Kent and UC-Davis colleague Kari Cooper, also a co-author on the Nature article, set out to find if they could determine how long Mount Hood’s magma chamber has been there, and in what condition.
When Mount Hood’s magma first rose up through the crust into its present-day chamber, it cooled and formed crystals. The researchers were able to document the age of the crystals by the rate of decay of naturally occurring radioactive elements. However, the growth of the crystals is also dictated by temperature — if the rock is too cold, they don’t grow as fast.
Thus the combination of the crystals’ age and apparent growth rate provides a geologic fingerprint for determining the approximate threshold for making the near-solid rock viscous enough to cause an eruption. The diffusion rate of the element strontium, which is also sensitive to temperature, helped validate the findings.
“What we found was that the magma has been stored beneath Mount Hood for at least 20,000 years — and probably more like 100,000 years,” Kent said. “And during the time it’s been there, it’s been in cold storage — like the peanut butter in the fridge — a minimum of 88 percent of the time, and likely more than 99 percent of the time.”
In other words — even though hot magma from below can quickly mobilize the magma chamber at 4-5 kilometers below the surface, most of the time magma is held under conditions that make it difficult for it to erupt.
“What is encouraging from another standpoint is that modern technology should be able to detect when magma is beginning to liquefy, or mobilize,” Kent said, “and that may give us warning of a potential eruption. Monitoring gases, utilizing seismic waves and studying ground deformation through GPS are a few of the techniques that could tell us that things are warming.”
The researchers hope to apply these techniques to other, larger volcanoes to see if they can determine their potential for shifting from cold storage to potential eruption, a development that might bring scientists a step closer to being able to forecast volcanic activity.
Note : The above story is based on materials provided by Oregon State University.
Chemical Formula: Pb2As2S5 Locality: Binnental, Valais, Switzerland. Name Origin: For Ours Pierre Armand Petit Dufrenoy (1792-1857), French mineralogist, National School of Mines, Paris, France.
The Cambrian is the first geological period of the Paleozoic Era, lasting from 541.0 ± 1.0 to 485.4 ± 1.9 million years ago (mya) and is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain’s Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätten. These are sites of exceptional preservation, where ‘soft’ parts of organisms are preserved as well as their more resistant shells. This means that our understanding of the Cambrian biology surpasses that of some later periods.
The Cambrian Period marked a profound change in life on Earth; prior to the Cambrian, living organisms on the whole were small, unicellular and simple. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of many modern phyla, representing the evolutionary stems of modern groups of species, such as the molluscs and arthropods. While diverse life forms prospered in the oceans, the land was comparatively barren – with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.
Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that this time period was internationally ratified. The base of the Cambrian is defined on a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Nevertheless, the usage of Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, for the stratigraphic detection of this boundary is always risky because of occurrence of very similar trace fossils belonging to the Treptichnids group well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
Subdivisions
The Cambrian period follows the Ediacaran and is followed by the Ordovician period. The Cambrian is divided into four epochs or series and ten ages or stages. Currently only two series and five stages are named and have a GSSP.
Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, 541 ± 0.3 to 509 ± 1.7 mya), Middle Cambrian (St Davids or Albertan, 509 ± 0.3 to 497 ± 1.7 mya) and Furongian (497 ± 0.3 to 485.4 ± 1.7 mya; also known as Late Cambrian, Merioneth or Croixan). Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
Trilobite zones allow biostratigraphic correlation in the Cambrian.
Cambrian dating
The time range for the Cambrian has classically been thought to have been from about 542 mya to about 488 mya. The lower boundary of the Cambrian was traditionally set at the earliest appearance of trilobites and also unusual forms known as archeocyathids (literally “ancient cup”) that are thought to be the earliest sponges and also the first non-microbial reef builders.
The end of the period was eventually set at a fairly definite faunal change now identified as an extinction event. Fossil discoveries and radiometric dating in the last quarter of the 20th century have called these dates into question. Date inconsistencies as large as 20 million years are common between authors. Framing dates of ca. 545 to 490 mya were proposed by the International Subcommission on Global Stratigraphy as recently as 2002.
A radiometric date from New Brunswick puts the end of the Lower Cambrian around 511 mya. This leaves 21 mya for the other two series/epochs of the Cambrian.
A more precise date of 542 ± 0.3 mya for the extinction event at the beginning of the Cambrian has recently been submitted. The rationale for this precise dating is interesting in itself as an example of paleological deductive reasoning. Exactly at the Cambrian boundary there is a marked fall in the abundance of carbon-13, a “reverse spike” that paleontologists call an excursion. It is so widespread that it is the best indicator of the position of the Precambrian-Cambrian boundary in stratigraphic sequences of roughly this age. One of the places that this well-established carbon-13 excursion occurs is in Oman. Amthor (2003) describes evidence from Oman that indicates the carbon-isotope excursion relates to a mass extinction: the disappearance of distinctive fossils from the Precambrian coincides exactly with the carbon-13 anomaly. Fortunately, in the Oman sequence, so too does a volcanic ash horizon from which zircons provide a very precise age of 542 ± 0.3 mya (calculated on the decay rate of uranium to lead). This new and precise date tallies with the less precise dates for the carbon-13 anomaly, derived from sequences in Siberia and Namibia.
PaleogeographyPlate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the period, with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses. Most continental land was clustered in the Southern Hemisphere at this time, but was gradually drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian.
With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for thriving life. The sea levels fluctuated somewhat, suggesting there were ‘ice ages’, associated with pulses of expansion and contraction of a south polar ice cap.
ClimateThe Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. There were likely polar ice caps and a series of glaciations, as the planet was still recovering from an earlier Snowball Earth. It became warmer towards the end of the period; the glaciers receded and eventually disappeared, and sea levels rose dramatically. This trend would continue into the Ordovician period.FloraAlthough there were a variety of macroscopic marine plants (e.g. Margaretia and Dalyia), no true land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches., and further inland were a variety of lichens, fungi and microbes forming microbial earth ecosystems, comparable with modern soil crust of desert regions, contributing to soil formation.FaunaMost animal life during the Cambrian was aquatic, with trilobites as the dominant life form. The period marked a steep change in the diversity and composition of Earth’s biosphere. The incumbent Ediacaran biota suffered a mass extinction at the base of the period, which corresponds to an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the period, burrowing animals had destroyed the mats through bioturbation, and gradually turned the seabeds into what they are today. As a consequence, many of those organisms that were dependent on the mats went extinct, while the other species adapted to the changed environment that now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla except the Bryozoa, which appear in the Lower Ordovician. However, many of these phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.
While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when it was exposed to a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the amount of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also the speciation rate in many groups was reduced to between a fifth and a third of previous levels. The later half of Cambrian was surprisingly barren; the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids went extinct. This declining trend did not change before Ordovician.
Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites. Fossils of the maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusk.
In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor; and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry.
Many modes of preservation are unique to the Cambrian, resulting in an abundance of Lagerstätten.
Note : The above story is based on materials provided by Wikipedia
Archeocyathids from the Poleta formation in the Death Valley area
