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Earthquake lights linked to rift environments, subvertical faults

Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. Credit: Jim Conacher

Rare earthquake lights are more likely to occur on or near rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface, according to a new study published in the Jan./Feb. issue of Seismological Research Letters.From the early days of seismology, the luminous phenomena associated with some earthquakes have intrigued scholars. Earthquake lights (EQL) appear before or during earthquakes, but rarely after.
EQL take a variety of forms, including spheres of light floating through the air. Seconds before the 2009 L’Aquila, Italy earthquake struck, pedestrians saw 10-centimeter high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town’s historical city center. On Nov. 12, 1988, a bright purple-pink globe of light moved through the sky along the St. Lawrence River near the city of Quebec, 11 days before a powerful quake. And in 1906, about 100 km northwest of San Francisco, a couple saw streams of light running along the ground two nights preceding that region’s great earthquake.

Continental rift environments now appear to be the common factor associated with EQL. In a detailed study of 65 documented EQL cases since 1600 A.D., 85 percent appeared spatially on or near rifts, and 97 percent appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults are associated with just 5 percent of Earth’s seismic activity, but 97 percent of documented cases of earthquake lights.

“The numbers are striking and unexpected,” said Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, who, along with colleagues, culled centuries of literature references, limiting the cases in this study to 65 of the best-documented events in the Americas and Europe.

“We don’t know quite yet why more earthquake light events are related to rift environments than other types of faults,” said Thériault, “but unlike other faults that may dip at a 30-35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases.”

Two of the 65 EQL events are associated with subduction zones, but Thériault suggests there may be an unknown subvertical fault present. “We may not know the fault distribution beneath the ground,” said Thériault. “We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure.”

While the 65 earthquakes ranged in magnitude, from M 3.6 to 9.2, 80 percent were greater than M 5.0. The EQL varied in shape and extent, though most commonly appeared as globular luminous masses, either stationary or moving, as atmospheric illuminations or as flame-like luminosities issuing from the ground.

Timing and distance to the epicenter vary widely. Most EQL are seen before and/or during an earthquake, but rarely after, suggesting to the authors that the processes responsible for EQL formation are related to a rapid build-up of stress prior to fault rupture and rapid local stress changes during the propagation of the seismic waves. Stress-activated mobile electronic charge carriers, termed positive holes, flow swiftly along stress gradients. Upon reaching the surface, they ionize air molecules and generate the observed luminosities.

Eyewitness reports and security cameras captured a large number of light flashes during the 2007 Pisco, Peru M 8.0 earthquake. Together with seismic records obtained on a local university campus, the automatic security camera records allow for an exact timing and location of light flashes that illuminated a large portion of the night sky. The light flashes identified as EQL coincided with the passage of the seismic waves.

Thériault likes the account of a local L’Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.

“It’s one of the very few documented accounts of someone acting on the presence of earthquake lights,” said Thériault. “Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake,” said Thériault.

Note : The above story is based on materials provided by Seismological Society of America

Granite research revises heat under Perth’s surface

“The high radiogenic heat generation in the Darling Range appears to be the cause of the hot water within the Perth Basin, as the granites of the Darling Range extend under the Perth Basin, which provides the sedimentary blanket,” Dr Middleton says. Credit: Michael Jefferies

Scientists investigating heat decay from radiogenic granite in the Darling Range have discovered the maximum heat output has exceeded previously known data.

Radiogenic granite, the major rock form of the Darling Range, is known for naturally high elemental concentrations of uranium (U), thorium (Th) and potassium (K).
During radioactive decay the elements release heat, and it is at depths of 3000–4000 metres that temperatures can attain 60 to 110C, making them viable for thermal applications.

Department of Mines and Petroleum research scientist Dr Mike Middleton says the thermal effect can also be observed at the base of a sedimentary rock layer, as is the case for the Perth Basin that lies over the Yilgarn Craton.

The Darling Range is at the boundary of both the Perth Basin and the Yilgarn Craton.

“In addition to establishing the amount of radiogenic heat generation in the Darling Range granites, the study was also about understanding the temperatures that might exist at depth in the Darling Range and adjacent Perth Basin,” he says.

Measuring exposed granite at 13 sites across the Darling Range using a Geiger Muller counter and RS 125 Spectrometer Dr Middleton and his team were able to model the data as an estimation of heat production.

Results indicate providing a uniform thickness in the granite profile (of 6km), heat generation can be within the vicinity of 50C at 1000m, 75C at 2000m, 100C at 3000m and 120C at 4000m.

Despite these geothermally considered lower temperatures Dr Middleton says this, “has a significant role to play in Perth’s energy mix, albeit with low-temperature applications”.

“The high radiogenic heat generation in the Darling Range appears to be the cause of the hot water within the Perth Basin, as the granites of the Darling Range extend under the Perth Basin, which provides the sedimentary blanket.”

“Indeed, hot water springs were noted in Dalkeith, near the Swan River, back in the early 1900s.”

Metropolitan Perth is ideally situated to take advantage of the low temperature geothermal energy, especially by the use of organic Rankine-cycle turbines or absorption chillers that operate at 70–120C.

“A current study is being carried out in the Vasse region, where hot pools and natural hot springs may be developed to support the tourist industry, especially in the colder months of the year,” he says.

Geothermal potential may also occur in Albany and Esperance.

Dr Middleton says studies are continuing in the regions south of Perth.

Note : The above story is based on materials provided by Science Network WA

Atlas Mountains in Morocco are buoyed up by superhot rock, study finds

This is a profile depicting the height and depth of the Atlas Mountains. The blue bars indicate the boundary between the crust and the superhot rock below, about 15 km shallower than predicted by previous models. Credit: Meghan Miller and Thorsten Becker

The Atlas Mountains defy the standard model for mountain structure in which high topography must have deep roots for support, according to a new study from Earth scientists at USC.

In a new model, the researchers show that the mountains are floating on a layer of hot molten rock that flows beneath the region’s lithosphere, perhaps all the way from the volcanic Canary Islands, just offshore northwestern Africa.

“Our findings confirm that mountain structures and their formation are far more complex than previously believed,” said lead author Meghan Miller, assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences.

The study, coauthored by Thorsten Becker, professor of Earth sciences at USC Dornsife, was published by Geology on Jan. 1, 2014 and highlighted by Nature Geoscience.

A well-established model for the Earth’s lithosphere suggests that the height of the Earth’s crust must be supported by a commensurate depth, much like how a tall iceberg doesn’t simply float on the surface of the water but instead rests on a large submerged mass of ice. This property is known as “istostacy.”

“The Atlas Mountains are at present out of balance, likely due to a confluence of existing lithospheric strength anomalies and deep mantle dynamics,” Becker said.

Miller and Becker used seismometers to measure the thickness of the lithosphere – that is, the Earth’s rigid outermost layer – beneath the Altas Mountains in Morocco. By analyzing 67 distant seismic events with 15 seismometers, the team was able to use the Earth’s vibrations to “see” into the deep subsurface.

They found that the crust beneath the Atlas Mountains, which rise to an elevation of more than 4,000 meters, reaches a depth of only about 35 km – about 15 km shy of what the traditional model predicts.

“This study shows that deformation can be observed through the entire lithosphere and contributes to mountain building even far away from plate boundaries” Miller said.

Miller’s lab is currently conducting further research into the timing and effects of the mountain building on other geological processes.

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

Cronstedtite

Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain Copyright © Fontana Gianluca

Chemical Formula: Fe22+Fe3+((Si,Fe3+)2O5)(OH)4
Locality: Pribram and Kuttenberg, Bohemia of Czechoslovakia.
Name Origin: Named for Axel Fredrik Cronstedt (1722-1765), Swedish mineralogist and chemist.

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. It has a formula of Fe22+Fe3+((Si,Fe3+)2O5)(OH)4.

It was discovered in 1821 and named in honor of Swedish mineralogist Axel Fredrik Cronstedt (1722–1765). It has been found in Bohemia in the Czech Republic and in Cornwall, England.

Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.

Physical Properties of Cronstedtite

Cleavage: {001} Perfect
Color: Brownish black, Greenish black, Dark brown, Black.
Density: 3.34 – 3.35, Average = 3.34
Diaphaneity: Transparent to translucent
Hardness: 3.5 – Copper Penny
Luster: Vitreous – Resinous
Streak: dark olive green

Photo

Cronstedtite, Marcasite Locality: Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain Copyright © Enrico Bonacina
Locality: Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain FOV: 5 mm Copyright © Fontana Gianluca
Locality: Salsigne mine, Salsigne, Mas-Cabardès, Carcassonne, Aude, Languedoc-Roussillon, France Copyright © Germano Fretti

Earth’s crust was unstable in the Archean eon and dripped down into the mantle

Computer simulation of the processes in the Earth’s mantle Credit: Institute of Geosciences, JGU

Earth’s mantle temperatures during the Archean eon, which commenced some 4 billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle.
This is the conclusion reached by Dr. Tim Johnson who is currently studying the evolution of the Earth’s crust as a member of the research team led by Professor Richard White of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU). According to the calculations, this dense primary crust would have descended vertically in drip form. In contrast, the movements of today’s tectonic plates involve largely lateral movements with oceanic lithosphere recycled in subduction zones. The findings add to our understanding of how cratons and plate tectonics, and thus also the Earth’s current continents, came into being.

Because mantle temperatures were higher during the Archean eon, the Earth’s primary crust that formed at the time must have been very thick and also very rich in magnesium. However, as Johnson and his co-authors explain in their article recently published in Nature Geoscience, very little of this original crust is preserved, indicating that most must have been recycled into the Earth’s mantle. Moreover, the Archean crust that has survived in some areas such as, for example, Northwest Scotland and Greenland, is largely made of tonalite–trondhjemite–granodiorite complexes and these are likely to have originated from a hydrated, low-magnesium basalt source. The conclusion is that these pieces of crust cannot be the direct products of an originally magnesium-rich primary crust. These TTG complexes are among the oldest features of our Earth’s crust. They are most commonly present in cratons, the oldest and most stable cores of the current continents.

With the help of thermodynamic calculations, Dr. Tim Johnson and his collaborators at the US-American universities of Maryland, Southern California, and Yale have established that the mineral assemblages that formed at the base of a 45-kilometer-thick magnesium-rich crust were denser than the underlying mantle layer. In order to better explore the physics of this process, Professor Boris Kaus of the Geophysics work group at Mainz University developed new computer models that simulate the conditions when the Earth was still relatively young and take into account Johnson’s calculations.

These geodynamic computer models show that the base of a magmatically over-thickened and magnesium-rich crust would have been gravitationally unstable at mantle temperatures greater than 1,500 to 1,550 degrees Celsius and this would have caused it to sink in a process called ‘delamination’. The dense crust would have dripped down into the mantle, triggering a return flow of mantle material from the asthenosphere that would have melted to form new primary crust. Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to provide a source of the tonalite–trondhjemite–granodiorite complexes. The dense residues of these processes, which would have a high content of mafic minerals, must now reside in the mantle.

Note : The above story is based on materials provided by Universitaet Mainz

Crocoite

Kosminsky Mine, Dundas mineral field, Zeehan District, Tasmania, Australia © 2009 ROM
Chemical Formula: Pb(CrO4)
Locality: Tasmania.
Name Origin: From the Greek krokos, meaning “crocus” or “saffron.”

Crocoite is a mineral consisting of lead chromate, Pb(CrO4), and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment.

Crocoite is commonly found as large, well-developed prismatic crystals, although in many cases are poorly terminated. Crystals are of a bright hyacinth-red color, translucent, and have an adamantine to vitreous lustre. On exposure to UV light some of the translucency and brilliancy is lost.

The streak is orange-yellow; Mohs hardness is 2.5–3; and the specific gravity is 6.0.It was discovered at the Berezovskoe Au Deposit (Berezovsk Mines) near Ekaterinburg in the Urals in 1766; and named crocoise by F. S. Beudant in 1832, from the Greek κρόκος (krokos), saffron, in allusion to its color, a name first altered to crocoisite and afterwards to crocoite. In the type locality the crystals are found in gold-bearing quartz-veins traversing granite or gneiss and associated with crocoite are quartz, embreyite, phoenicochroite and vauquelinite.

Phoenicochroite is a basic lead chromate, Pb2CrO5 with dark red crystals, and vauquelinite a lead and copper phosphate-chromate, Pb2CuCrO4PO4OH, with brown or green monoclinic crystals. Vauquelinite was named after L. N. Vauquelin, who in 1797 discovered (simultaneously with and independently of M. H. Klaproth) the element chromium in crocoite.

Abundant masses with exceptional examples of crocoite crystals have been found in the Extended Mine at Mount Dundas as well as the Adelaide, Red Lead, West Comet, Platt and a few other Mines at Dundas, Tasmania; they are usually found in long slender prisms, usually about 10–20 mm but rarely up to 200 mm (4 inches) in length, with a brilliant lustre and color. Crocoite is also the official Tasmanian mineral emblem. Other localities which have yielded good crystallized specimens are Congonhas do Campo near Ouro Preto in Brazil, Luzon in the Philippines, Mutare in Mashonaland, near Menzies in Western Australia, plus Brazil, Germany and South Africa.

The relative rarity of crocoite is connected with the specific conditions required for its formation: an oxidation zone of lead ore bed and presence of ultramafic rocks serving as the source of chromium (in chromite). Oxidation of Cr3+ into CrO42− (from chromite) and decomposition of galena (or other primary lead minerals) are required for crocoite formation. These conditions are relatively unusual.

As crocoite is composed of lead(II) chromate, it is toxic, containing both lead and hexavalent chromium.

Physical Properties of Crocoite

Cleavage: {110} Distinct, {001} Indistinct, {100} Indistinct
Color: Yellow, Orange, Red, Red orange.
Density: 5.9 – 6.1, Average = 6
Diaphaneity: Translucent
Fracture: Sectile – Curved shavings or scrapings produced by a knife blade, (e.g. graphite).
Hardness: 2.5-3 – Finger Nail-Calcite
Luminescence: Non-fluorescent.
Luster: Adamantine
Streak: yellowish orange

Photos :

This sample is about 12×22 cm and is from Red Lead mine, Dundas, Tasmania, Australia. This sample is on display at the Smithsonian Museum of Natural History.
This sample is on display at the Smithsonian Museum of Natural History.
This sample of crocoite is about 20 cm wide and is from Adelaide, Dundas, Tasmania, Australia. This sample is on display at the Smithsonian Museum of Natural History.
Crocoite Adelaide Mine, Dundas, Tasmania, Australia Size: 5.3×2.8×1.1 cm Photo Copyright © SpiriferMinerals.
Crocoite Adelaide Mine, Dundas mineral field, Zeehan District, Tasmania, Australia Size: 6.0 x 4.0 x 3.0 cm Photo Copyright © danweinrich
Crocoite Adelaide Mine, Dundas, Tasmania, Australia Size: 5.8×0.6×0.4 cm Photo Copyright © SpiriferMinerals.

Phanerozoic

The Phanerozoic is the current geologic eon in the geologic time scale, and the one during which abundant animal life has existed. It covers roughly 542 million years (541.0 ± 1.0) and goes back to the time when diverse hard-shelled animals first appeared. Its name derives from the Ancient Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean and Proterozoic eons.

The time span of the Phanerozoic includes the rapid emergence of a number of animal phyla; the evolution of these phyla into diverse forms; the emergence and development of complex plants; the evolution of fish; the emergence of insects and tetrapods; and the development of modern faunas. During this time span tectonic forces caused the continents to move and eventually collect into a single landmass known as Pangaea, which then separated into the current continental landmasses

Timing

The Proterozoic-Phanerozoic boundary happened 541.0 ± 1.0 million years ago. In the 19th Century, the boundary was set at the first abundant animal (metazoan) fossils. But several hundred groups (taxa) of metazoa of the earlier Proterozoic era have been identified since systematic study of those forms started in the 1950s. Most geologists and paleontologists would probably set the Proterozoic-Phanerozoic boundary either at the classic point where the first trilobites and reef building animals (archaeocyatha) such as corals and others appear; at the first appearance of a complex feeding burrow called Treptichnus pedum; or at the first appearance of a group of small, generally disarticulated, armored forms termed ‘the small shelly fauna’. The three different dividing points are within a few million years of each other.

The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. In the older literature, the term Phanerozoic is generally used as a label for the time period of interest to paleontologists, but that use of the term seems to be falling into disuse in more modern literature.

Biodiversity

It has been demonstrated that changes in biodiversity through the Phanerozoic correlate much better with the
During, the Phanerozoic biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera

Table of Contents

hyperbolic model (widely used in demography and macrosociology) than with exponential and logistic models (traditionally used in population biology and extensively applied to fossil biodiversity as well). The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a negative feedback arising from resource limitation. The hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the world population growth arises from a second-order positive feedback between the population size and the rate of technological growth.[1] The character of biodiversity growth in the Phanerozoic can be similarly accounted for by a feedback between the diversity and community structure complexity. It is suggested that the similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics.

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

Scientists show how deadly volcanic phenomenon moves

Green Tuff ignimbrite draping the outer caldera wall at Salto La Vecchia.

For the first time scientists have tracked how one of the deadliest volcanic hazards moves over time.Pyroclastic density currents are searing hot clouds of ash and gas released by volcanoes; they travel up to 450 miles per hour. Their speed and intense heat make it nearly impossible for humans to observe – anybody who got close enough to monitor one would be killed.
But scientists from the University of Leicester have developed a novel way of reconstructing how one of these currents flowed. Their technique showed for the first time that instead of flowing radially out from the volcano and covering everything in their path, these currents move initially in one direction, but that this direction then changes.

‘In the magma chamber under a volcano the chemistry of the magma at the top is different to the chemistry at the bottom. During an eruption these chemical zones are erupted at different times, so if something was erupted at the beginning it would show a record matching the chemical zone from the top of the magma chamber,’ explains Dr Rebecca Williams, now of the University of Hull, lead author on the project. ‘We realised that if I could find a chemical zoning in an ignimbrite I could use it as a proxy for time.’

The research, published in the journal Geology, looked at a deposit on the volcanic island of Panetelleria left by one of these pyroclastic density currents during an eruption 45,000 years ago.

‘The Green Tuff on Panetelleria was huge. It was much bigger than the ones that buried Pompeii and Herculaneum,’ says Williams. ‘It was very hot when it was deposited which means it welded and turned into a green volcanic glass that covers the entire island. It hasn’t really been weathered, which means it is incredibly well preserved. It is an incredible exposure.’

A close up of that caldera wall showing the Green Tuff draping over the older ignimbrites.

The chemical structure of this deposit, called the Green Tuff ignimbrite, varies from the bottom to the top, in a similar way to the variation in a magma chamber.

‘If you just look at a deposit you can’t tell it’s zoned. You can’t see it with the naked eye, although sometimes there may be an increase in the size or amount of some crystals. So I took closely spaced samples vertically through the deposit and did a chemical analysis of them to get the chemical compostion from it.’ Williams says.

The team matched the variation seen in the Green Tuff with the same layers in the magma chamber to assess at what point during the eruption they flowed.

They were surprised to discover that the circular deposits often left by these currents didn’t mean that they flowed out in a circle out from the eruption.

‘These really big currents tend to have circular deposit shapes to them so people often think deposits expand radially, going out in all directions at the same time. We’re actually able to show that didn’t happen, it’s only at the climatic phase of an eruption that it flows in all directions at the same time,’ Williams explains.

‘With the Green Tuff the current gradually went over the landscape, it was going off in one direction first and as it moved it was initially blocked by lots of topography, but as it continued moving it would start to creep around and eventually go over any barriers,’ she continues.

The team also showed for the first time that as the eruption tapered off, the pyroclastic density current couldn’t flow as far, so the leading edge appears to retreat over time.

‘This gives us a much better understanding of how pyroclastic density currents behave so it will be a huge help with hazard mapping. It’s really good to know that we can’t think of these phenomena as one very rapid event,’ concludes Williams.

Note : The above story is based on materials provided by PlanetEarth Online

Indonesia cave reveals history of ancient tsunamis

In this Monday, Dec. 2, 2013 photo, a guide stands at the entrance of a cave which scientists said reveals history of ancient tsunamis in Lhong, Aceh province, Indonesia. The cave discovered near the source of 2004’s massive earthquake-spawned tsunami in Indonesia contains the footprints of past gigantic waves dating up to 7,500 years ago, a rare natural record suggesting future generations living in the coastal area must stay prepared because disasters can occur in relatively short bursts or after long lulls. (AP Photo/Heri Juanda)

A cave discovered near the source of Indonesia’s massive earthquake-spawned tsunami contains the footprints of past gigantic waves dating up to 7,500 years ago, a rare natural record that suggests the next disaster could be centuries away—or perhaps only decades.

The findings provide the longest and most detailed timeline for tsunamis that have occurred off the far western tip of Sumatra island in Aceh province. That’s where 100-foot (30-meter) waves triggered by a magnitude-9.1 earthquake on Dec. 26, 2004, killed 230,000 people in several countries, more than half of them in Indonesia.

The limestone cave, located within a couple hundred yards (meters) of the coast near Banda Aceh, is about 3 feet (1 meter) above knee-high tide and protected from storms and wind. Only huge waves that inundate the coastal area are able to gush inside.

Researchers in 2011 uncovered seabed sand deposits that were swept into the cave over thousands of years and neatly layered between bat droppings like a geological cake. Radiocarbon analysis of materials, including clamshells and the remains of microscopic organisms, provided evidence of 11 tsunamis before 2004.

The disasters were by no means evenly spaced, said lead researcher Charles Rubin from the Earth Observatory of Singapore. The last one occurred about 2,800 years ago, but there were four others in the preceding 500 years.

And it’s possible there were others. Researchers know, for instance, that there were two mammoth earthquakes in the region around 1393 and 1450. Rubin said a big tsunami could have carried away evidence of other events through erosion.

The scientists are still working to determine the size of the waves that entered the cave.

“The take-home message is perhaps that the 2004 event doesn’t mean it won’t happen for another 500 years,” said Rubin, who added that the cave was discovered by chance and not part of planned field work. “We did see them clustered together closer in time. I wouldn’t put out a warning that we’re going to have an earthquake, but it shows that the timing is really variable.”

The quake that triggered the 2004 tsunami surprised scientists because the fault that unleashed the megathrust temblor had been quiet for hundreds of years. And since the last big earthquake had struck more than 500 years earlier, there was no surviving oral history that could have helped people understand the risk.

Since 2004, much research has been done to try to learn about the area’s past by examining sand deposits, uplifted coral and GPS data.

“The findings are very significant,” Katrin Monecke, a geosciences professor at Wellesley College in Massachusetts wrote in an email. She worked on tsunami sand deposits discovered in marshes in the area, but was not involved with the cave research, which was presented this month at an American Geophysical Union conference in San Francisco. “The sand sheets in the cave cover a very long time span and give an excellent idea about earthquake frequency.”

Despite the long record preserved in the cave, Rubin said it did not provide any clear clues about tsunami frequency or when events might happen in a relatively close period of time.

Geologist Kerry Sieh, director of the Singapore group and also part of the cave investigation, has predicted that another monster quake could rock the area in the next few decades. They tend to come in cycles and the 2004 temblor heaped more pressure on the fault. However, the history is so variable, it’s impossible to make an exact forecast.

“By learning about the type of tsunamis that happened in the past, maybe we can do planning for mitigation for the next tsunami,” said Nazli Ismail, head of the physics and geophysics department at Syiah Kuala University in Banda Aceh who worked on the project.

Indonesia is an archipelago located on the so-called “Ring of Fire,” a horseshoe of fault lines and volcanoes surrounding the Pacific Basin. It is home to some of the world’s biggest and deadliest seismic activity.

Note : The above story is based on materials provided by The Associated Press. All rights reserved.

Crocidolite

Granite Railway Quarry (Granite Rail Quarry), Quincy, Norfolk Co., Massachusetts, USA © 2004 Peter Cristofono
Riebeckite forms in two very different habits. The darker-colored forms which are individually crystallized are generally of igneous origin, such as volcanic rock and pegmatites. The finely fibrous variety, known as Crocidolite, usually originates from altered metamorphic rocks. The Crocidolite variety is a type of asbestos, and is sometimes also referred to as “blue asbestos”.

It is considered to be the most hazardous form of asbestos, and should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma. Symptoms of asbestosis do not arise until about 20 years after the inhalation. Due to the hazards, washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos minerals out of safety concerns.

Chemical Formula: [Na2][Z32+Fe23+]Si8O22(OH,F,Cl)2
Locality: Socotra island, Indian Ocean, Yemen.
Name Origin: Named after the German traveler, Emil Riebeck (1853-1885).

Physical Properties

Cleavage: {110} Perfect, {???} Perfect
Color: Blue, Black, Dark green.
Density: 3.4
Diaphaneity: Translucent to subtranslucent to opaque
Fracture: Brittle – Uneven – Very brittle fracture producing uneven fragments.
Hardness: 4 – Fluorite
Luminescence: Non-fluorescent.
Luster: Vitreous – Silky
Magnetism: Nonmagnetic
Streak: greenish brown

Photos :

This sample of the crocidolite variety of riebeckite is from Todos Santos, Cochabamba, Bolivia. The center bundle is about 25 cm high. These samples of crocidolite are displayed in the Smithsonian Museum of Natural History.
The sample is about 15 cm across and is from Carn Brea mine, Prieska district, Cape Province, South Africa. These samples of crocidolite are displayed in the Smithsonian Museum of Natural History.
Riebeckite Root Name (Var: Crocidolite), Pyrite Locality: Griqualand, Northern Cape Province, South Africa Dimensions: 5.2 cm x 3.2 cm x 2.9 cm Copyright © Jasun McAvoy & mineralman
Riebeckite Root Name (Var: Crocidolite), Hematite, Quartz, Tiger’s Eye Locality: Brockman Tiger eye mine (Marra Mamba), Mount Brockman, Ashburton Shire, Western Australia, Australia Dimensions: 185 mm x 80 mm Field of View: 180 mm Copyright © Andrew Tuma

Study faults a ‘runaway’ mechanism in intermediate-depth earthquakes

Local seismometers detect clusters of intermediate-depth earthquakes in and around the Colombian city of Bucaramanga. The epicenter of the quakes, more than 50 kilometers below the surface, is known as the “Nest.” Credit: MIT

Nearly 25 percent of earthquakes occur more than 50 kilometers below the Earth’s surface, when one tectonic plate slides below another, in a region called the lithosphere. Scientists have thought that these rumblings from the deep arise from a different process than shallower, more destructive quakes. But limited seismic data, and difficulty in reproducing these quakes in the laboratory, have combined to prevent researchers from pinpointing the cause of intermediate and deep earthquakes.

 

Now a team from MIT and Stanford University has identified a mechanism that helps these deeper quakes spread. By analyzing seismic data from a region in Colombia with a high concentration of intermediate-depth earthquakes, the researchers identified a “runaway process” in which the sliding of rocks at great depths causes surrounding temperatures to spike. This influx of heat, in turn, encourages more sliding—a feedback mechanism that propagates through the lithosphere, generating an earthquake.

German Prieto, an assistant professor of geophysics in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says that once thermal runaway starts, the surrounding rocks can heat up and slide more easily, raising the temperature very quickly.

“What we predict is for medium-sized earthquakes, with magnitude 4 to 5, temperature can rise up to 1,000 degrees Centigrade, or about 1,800 degrees Fahrenheit, in a matter of one second,” Prieto says. “It’s a huge amount. You’re basically allowing rupture to run away because of this large temperature increase.”

Prieto says that understanding deeper earthquakes may help local communities anticipate how much shaking they may experience, given the seismic history of their regions.

He and his colleagues have published their results in the journal Geophysical Research Letters.

Water versus heat: two competing theories

The majority of Earth’s seismic activity occurs at relatively shallow depths, and the mechanics of such quakes is well understood: Over time, abutting plates in the crust build up tension as they shift against each other. This tension ultimately reaches a breaking point, creating a sudden rupture that splinters through the crust.

However, scientists have determined that this process is not feasible for quakes that occur far below the surface. Essentially, higher temperatures and pressures at these depths would make rocks behave differently than they would closer to the surface, gliding past rather than breaking against each other.

By way of explanation, Prieto draws an analogy to glass: If you try to bend a glass tube at room temperature, with enough force, it will eventually shatter. But with heating, the tube will become much more malleable, and bend without breaking.

So how do deeper earthquakes occur? Scientists have proposed two theories: The first, called dehydration embrittlement, is based on the small amounts of water in rocks’ mineral composition. At high pressure and heat, rocks release water, which lubricates surrounding faults, creating fractures that ultimately set off a quake.

The second theory is thermal runaway: Increasing temperatures weaken rocks, promoting slippage that spreads through the lithosphere, further increasing temperatures and causing more rocks to slip, resulting in an earthquake.

Probing the nest

Prieto and his colleagues found new evidence in support of the second theory by analyzing seismic data from a region of Colombia that experiences large numbers of intermediate-depth earthquakes—quakes whose epicenters are 50 to 300 kilometers below the surface. This region, known as the Bucaramanga Nest, hosts the highest concentration of intermediate-depth quakes in the world: Since 1993, more than 80,000 earthquakes have been recorded in the area, making it, in Prieto’s view, an “ideal natural laboratory” for studying deeper quakes.

The researchers analyzed seismic waves recorded by nearby surface seismometers and calculated two parameters: stress drop, or the total amount of energy released by an earthquake, and radiated seismic energy, or the amount of that energy that makes it to the surface as seismic waves—energy that is manifested in the shaking of the ground.

The stronger a quake is, the more energy, or heat, it generates. Interestingly, the MIT group found that only 2 percent of a deeper quake’s total energy is felt at the surface. Prieto reasoned that much of the other 98 percent may be released locally as heat, creating an enormous temperature increase that pushes a quake to spread.

Prieto says the study provides strong evidence for thermal runaway as the likely mechanism for intermediate-depth earthquakes. Such knowledge, he says, may be useful for communities around Bucaramanga in predicting the severity of future quakes.

“Usually people in Bucaramanga feel a magnitude 4 quake every month or so, and every year they experience a larger one that can shake significantly,” Prieto says. “If you’re in a region where you have intermediate-depth quakes and you know the size of the region, you can make a prediction of the type of magnitudes of quakes that you can have, and what kind of shaking you would expect.”

Prieto, a native Colombian, plans to deploy seismic stations above the Bucaramanga Nest to better understand the activity of deeper quakes.

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

Enormous aquifer discovered under Greenland ice sheet

Glaciologist Lora Koenig (left) operates a video recorder that has been lowered into the bore hole to observe the ice structure of the aquifer in April 2013. Credit: University of Utah/Clément Miège

Buried underneath compacted snow and ice in Greenland lies a large liquid water reservoir that has now been mapped by researchers using data from NASA’s Operation IceBridge airborne campaign.

A team of glaciologists serendipitously found the aquifer while drilling in southeast Greenland in 2011 to study snow accumulation. Two of their ice cores were dripping water when the scientists lifted them to the surface, despite air temperatures of minus 4 F (minus 20 C). The researchers later used NASA’s Operation Icebridge radar data to confine the limits of the water reservoir, which spreads over 27,000 square miles (69,930 square km) – an area larger than the state of West Virginia. The water in the aquifer has the potential to raise global sea level by 0.016 inches (0.4 mm).

“When I heard about the aquifer, I had almost the same reaction as when we discovered Lake Vostok [in Antarctica]: it blew my mind that something like that is possible,” said Michael Studinger, project scientist for Operation IceBridge, a NASA airborne campaign studying changes in ice at the poles. “It turned my view of the Greenland ice sheet upside down – I don’t think anyone had expected that this layer of liquid water could survive the cold winter temperatures without being refrozen.”

Southeast Greenland is a region of high snow accumulation. Researchers now believe that the thick snow cover insulates the aquifer from cold winter surface temperatures, allowing it to remain liquid throughout the year. The aquifer is fed by meltwater that percolates from the surface during the summer.

The new research is being presented in two papers: one led by University of Utah’s Rick Forster that was published on Dec. 22 in the journal Nature Geoscience and one led by NASA’s Lora Koenig that has been accepted for publication in the journal Geophysical Research Letters. The findings will significantly advance the understanding of how melt water flows through the ice sheet and contributes to sea level rise.

When a team led by Forster accidentally drilled into water in 2011, they weren’t able to continue studying the aquifer because their tools were not suited to work in an aquatic environment. Afterward, Forster’s team determined the extent of the aquifer by studying radar data from Operation IceBridge together with ground-based radar data. The top of the water layer clearly showed in the radar data as a return signal brighter than the ice layers.

Koenig, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Md., co-led another expedition to southeast Greenland with Forster in April 2013 specifically designed to study the physical characteristics of the newly discovered water reservoir. Koenig’s team extracted two cores of firn (aged snow) that were saturated with water. They used a water-resistant thermoelectric drill to study the density of the ice and lowered strings packed with temperature sensors down the holes, and found that the temperature of the aquifer hovers around 32 F (zero C), warmer than they had expected it to be.

Koenig and her team measured the top of the aquifer at around 39 feet (12 meters) under the surface. This was the depth at which the boreholes filled with water after extracting the ice cores. They then determined the amount of water in the water-saturated firn cores by comparing them to dry cores extracted nearby. The researchers determined the depth at which the pores in the firn close, trapping the water inside the bubbles – at this point, there is a change in the density of the ice that the scientists can measure. This depth is about 121 feet (37 meters) and corresponds to the bottom of the aquifer. Once Koenig’s team had the density, depth and spatial extent of the aquifer, they were able to come up with an estimated water volume of about 154 billion tons (140 metric gigatons). If this water was to suddenly discharge to the ocean, this would correspond to 0.016 inches (0.4 mm) of sea level rise.

Researchers think that the perennial aquifer is a heat reservoir for the ice sheet in two ways: melt water carries heat when it percolates from the surface down the ice to reach the aquifer. And if the trapped water were to refreeze, it would release latent heat. Altogether, this makes the ice in the vicinity of the aquifer warmer, and warmer ice flows faster toward the sea.

“Our next big task is to understand how this aquifer is filling and how it’s discharging,” said Koenig. “The aquifer could offset some sea level rise if it’s storing water for long periods of time. For example after the 2012 extreme surface melt across Greenland, it appears that the aquifer filled a little bit. The question now is how does that water leave the aquifer on its way to the ocean and whether it will leave this year or a hundred years from now.”

Note : The above story is based on materials provided by NASA’s Goddard Space Flight Center

Creedite

Santa Eulalia District, Mun. de Aquiles Serdán, Chihuahua, Mexico © A&M

Chemical Formula: Ca3SO4Al2F8(OH)2 · 2H2O
Locality: Wagon Wheel Gap, Creed Quadrangle, Colorado, USA.
Name Origin: Named after its locality.

Creedite is a calcium aluminium sulfate fluoro hydroxide mineral with formula: Ca3SO4Al2F8(OH)2 · 2H2O. Creedite forms colorless to white to purple monoclinic prismatic crystals. It often occurs as acicular radiating sprays of fine prisms. It is translucent to transparent with indices of refraction of nα = 1.461 nβ = 1.478 nγ = 1.485. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 2.7.

Creedite was first described in 1916 from the Creed Quadrangle in Mineral County, Colorado. It is a product of intense oxidation of ore deposits.

Geologic association

Creedite typically occurs with low-grade metamorphic rocks on a fluorite – calcite – quartz matrix or on a sulfide-matrix with its oxidized products. Creedite most commonly found in the form of creedite – carbonate – cyanotrichite – woodwardite – spangolite – kaolinite association. The other less common creedite association is creedite – limonite – kaolinite – hemimorphite – smithsonite – hydrozincite – aurichalcite. Creedite also occurs in skarn formation which usually has association with sulfides, spangolite, brochantite, linarite, limonite, cuprite, wad and kaolinite. In general, creedite usually found as two to three millimeters radial aggregates and less commonly as a single prismatic crystals up to one millimeters long.

Physical Properties

Cleavage: {100} Perfect
Color: Colorless, Violet, White.
Density: 2.71
Diaphaneity: Transparent to translucent
Fracture: Conchoidal – Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Hardness: 3.5 – Copper Penny
Luminescence: Non-fluorescent.
Luster: Vitreous – Greasy
Streak: white

Photos :

Creedite Abasolo Mine, Navidad, Durango, Mexico 143mm x 64mm x 62mm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Creedite Santa Eulalia, Chihuahua, Mexico 37mm x 23mm x 7mm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Creedite Qinglong (Dachang), Qinglong Co., Guizhou Province, China 42mm x 30mm x 16mm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com

Diamonds in Earth’s oldest zircons are nothing but laboratory contamination

This image explains how synthetic diamond can be distinguished from natural diamond. Credit: Dobrzhinetskaya Lab, UC Riverside.

This image explains how synthetic diamond can be distinguished from natural diamond.
Credit: Dobrzhinetskaya Lab, UC Riverside.

As is well known, the Earth is about 4.6 billion years old. No rocks exist, however, that are older than about 3.8 billion years. A sedimentary rock section in the Jack Hills of western Australia, more than 3 billion years old, contains within it zircons that were eroded from rocks as old as about 4.3 billion years, making these zircons, called Jack Hills zircons, the oldest recorded geological material on the planet.
In 2007 and 2008, two research papers reported in the journal Nature that a suite of zircons from the Jack Hills included diamonds, requiring a radical revision of early Earth history. The papers posited that the diamonds formed, somehow, before the oldest zircons—that is, before 4.3 billion years ago—and then were recycled repeatedly over a period of 1.2 billion years during which they were periodically incorporated into the zircons by an unidentified process.

Now a team of three researchers, two of whom are at the University of California, Riverside, has discovered using electron microscopy that the diamonds in question are not diamonds at all but broken fragments of a diamond-polishing compound that got embedded when the zircon specimen was prepared for analysis by the authors of the Nature papers.

“The diamonds are not indigenous to the zircons,” said Harry Green, a research geophysicist and a distinguished professor of the Graduate Division at UC Riverside, who was involved in the research. “They are contamination. This, combined with the lack of diamonds in any other samples of Jack Hills zircons, strongly suggests that there are no indigenous diamonds in the Jack Hills zircons.”

Study results appear online this week in the journal Earth and Planetary Science Letters.

“It occurred to us that a long-term history of diamond recycling with intermittent trapping into zircons would likely leave some sort of microstructural record at the interface between the diamonds and zircon,” said Larissa Dobrzhinetskaya, a professional researcher in the Department of Earth Sciences at UCR and the first author of the research paper. “We reasoned that high-resolution electron microscopy of the material should be able to distinguish whether the diamonds are indeed what they have been believed to be.”

Using an intensive search with high-resolution secondary-electron imaging and transmission electron microscopy, the research team confirmed the presence of diamonds in the Jack Hills zircon samples they examined but could readily identify them as broken fragments of diamond paste that the original authors had used to polish the zircons for examination. They also observed quartz, graphite, apatite, rutile, iron oxides, feldspars and other low-pressure minerals commonly included into zircon in granitic rocks.

“In other words, they are contamination from polishing with diamond paste that was mechanically injected into silicate inclusions during polishing” Green said.

The research was supported by a grant from the National Science Foundation.

Green and Dobrzhinetskaya were joined in the research by Richard Wirth at the Helmholtz Centre Potsdam, Germany.

Dobrzhinetskaya and Green planned the research project; Dobrzhinetskaya led the project; she and Wirth did the electron microscopy.

Note : The above story is based on materials provided by University of California – Riverside

Scientists explore world’s largest undersea canyon

3D seafloor bathymetry map of upper Agadir Canyon

A joint British-German team has returned from a five-week research expedition, mapping and sampling a giant submarine canyon off northwest Morocco. The expedition was on the German research vessel, Maria S Merian.

Dr Russell Wynn of the National Oceanography Centre led the British contribution to the expedition, which was in partnership with Professor Sebastian Krastel at University of Kiel. He said, “Agadir Canyon is remarkably similar in size to the Grand Canyon in Arizona, and yet until now it has barely been explored. We discovered that this huge valley is the source for the world’s largest submarine sediment flow 60,000 years ago. Up to 160 cubic kilometres of sediment was transported to the deep ocean in a single catastrophic event.”

Agadir Canyon is over 1,000 metres deep and 450 kilometres long, and is potentially the world’s largest undersea canyon. The researchers collected seafloor images and sediment cores that provide evidence for powerful sediment flows originating from the canyon head, transporting gravel and sand derived from the onshore Atlas Mountains to deep offshore basins over three miles below the sea surface. These flows deposited sediment over an area of deep seafloor exceeding 350,000 square kilometres, roughly the size of Germany. This is the first time individual sediment flows of this scale have been tracked along their entire flow pathway.

The survey team also discovered a new giant landslide south of Agadir Canyon that covers an area of seafloor in excess of 5,000 square kilometres, larger than the county of Hampshire. However, initial data suggest it is a relatively ancient feature, at least 130,000 years old. Significant biological discoveries were also made within and around the canyon, including samples of the first living deep-water corals to be recovered from the Atlantic Moroccan margin, and an amazing aggregation of hundreds of Loggerhead Turtles basking at the surface.

Dr Wynn added, “To be the first people to explore and map this extensive and spectacular area of seafloor is a rare privilege, especially on the doorstep of Europe. It is hoped that our findings will inform further work on geological hazards and marine conservation in this region.”

Note : The above story is based on materials provided by National Oceanography Centre, Southampton

Rock points to potential diamond haul in Antarctica

View looking southeast from the locality of the kimberlite samples on the slopes of Mt Meredith, across the Lambert Glacier, towards the Fisher Massif, northern Prince Charles Mountains, Antarctica. Credit: Dr Geoff Nichols

Australian geologists on Tuesday opened up the tantalising but controversial prospect that Antarctica could be rich in diamonds.

In a scientific paper published in the journal Nature Communications, a team said they had found a telltale rock called kimberlite in the Prince Charles Mountains in East Antarctica.

No diamonds were found in the samples, taken from Mount Meredith, and the study—focusing only on the region’s geology, not on mining possibilities—was not designed to quantify how many could be there.

But, it said, the mineral’s signature is identical to that in other locations in the world where diamonds have been found.

“The samples are texturally, mineralogically and geochemically typical of Group 1 kimberlites from more classical localities,” said the probe, led by Greg Yaxley at the Australian National University in Canberra.

Kimberlite, a rock that is rarely found near Earth’s surface, is believed to be formed at great depths in the mantle, where conditions are right for forming diamonds—carbon atoms that are squeezed into lattice shapes under extreme pressure and temperature.

The study suggested kimberlite was thrust towards the surface around 120 million years ago, when present-day Africa, the Arabian peninsula, South America, the Indian sub-continent, Australia and Antarctica were glommed together in a super-continent called Gondwana.

Outcrops of kimberlite studded the centre of Gondwana at this time.

The component continents then drifted apart, which explains why diamonds have been found in such diverse and distant locations, from Brazil to southern Africa and India, according to this theory.

Mining banned – for now

Independent experts were divided as to whether the discovery could unleash a diamond rush that would ravage the world’s last pristine continent.

A treaty protecting Antarctica was signed in 1961 and was updated with an environmental protocol in 1991 whose Article 7 expressly prohibits “any activity relating to mineral resources.”

The 1991 pact comes up for review in 2048, 50 years after it came into effect following ratification. It has been ratified by 35 nations.

Robert Larter, a geophysicist with the British Antarctic Survey (BAS), said “the default assumption” was that the protocol will continue.

“Any change would require agreement of the majority of parties at a review conference, including three-quarters of the states which were Antarctic Treaty Consultative Parties at the time of adoption of the protocol,” he said in comments to Britain’s Science Media Centre.

Teal Riley, a BAS survey geologist, said the discovery of kimberlite was “not unsurprising” given that the local geology in East Antarctica has a feature called cratons, a telltale of this rock.

“However, even amongst the Group 1 kimberlites, only 10 percent or so are economically viable, so it’s still a big step to extrapolate this latest finding with any diamond mining activity in Antarctica,” where extraction would be tougher and costlier.

But Kevin Hughes, a senior officer at an international panel called the Scientific Committee on Antarctic Research (SCAR), was more cautious.

More than three decades from now, “we do not know what the treaty parties’ views will be on mining… or what technologies might exist that could make extraction of Antarctic minerals economically viable,” he said.

“An additional issue is that nations outside the protocol are not bound by its provisions, including the ban on mineral resource activities.”

Kimberlite takes its name from the town of Kimberley, in South Africa, which was created by a diamond rush.

In 1871, a cook found a huge stone while digging on a farm, and within a year 50,000 prospectors were there, digging feverishly and living in a makeshift tented city.

Note : The above story is based on materials provided by © 2013 AFP

Exmouth stalagmites reveal more climatic history

More than 300 caves are scattered across WA’s Cape Range Peninsula along with spectacular gorges like Yardie Creek.Credit: Salleelee

Paleoclimatic reconstructions from West Australian stalagmites have demonstrated how historic climatic events still determine Australia’s current climate variability.

Researchers from across Australia and the United States have profiled stalagmites from cave C126 in WA’s Cape Range Peninsula to produce a high-resolution, continental paleoclimate record from the Indian Ocean sector of Australia.
Lead researcher Rhawn Denniston of Cornell College, USA, says the record, which spans the Last Glacial Maximum, deglaciation, and early to mid-Holocene, is the first of its kind.

“It goes without saying that Australian societies are closely tied to climate,” Prof Denniston says.

“The more we understand about how things have occurred in the past, the better we can develop a frame of reference for current and future climate.

“The first thing the results illustrate is how much we still don’t know about the nature, timing, and drivers of climate variability in this part of the world over the last glacial period.

“However, we do see events that are synchronous to and consistent with other regional events, some of which have ties to far-flung regions such as the North Atlantic.”

The stalagmite analysis found evidence of such an event which had global significance.

“A climate anomaly occurred at the site during a period called Heinrich Stadial 1, about 16,000 years ago,” he says.

The event was likely driven by changes in ocean circulation originating in the North Atlantic.

Prof Denniston says the impact of Heinrich Stadial 1 has been felt in other parts of the world too including the Indo-Pacific, China, Brazil, and parts of Africa and Europe and has been tied to climate variability in southern Australia.

“It is the most prominent event in our record, and in other recently published records from the Kimberley, suggesting that it had a widespread impact across much of Australia,” he says.

The stalagmite samples were sliced in half vertically, with material milled out for dating and chemical analysis.

The dating involved extracting and measuring tiny abundances of uranium and its radioactive daughter thorium.

The research builds on previous studies on stalagmites in China, which show variability in the east Asian summer monsoon over decades to hundreds of thousands of years.

“Other work, largely from lake records and ocean sediments, conducted in and around areas of southern Australia suggest that precipitation moving north from high latitudes was also highly dynamic and influenced the climate there over the last several tens of thousands of years,” he says.

Note : The above story is based on materials provided by Science Network WA

Global Map Predicts Locations for Giant Earthquakes

Andaman Sea. “For the Australian region subduction zones of particular significance are the Sunda subduction zone, running from the Andaman Islands along Sumatra and Java to Sumba, and the Hikurangi subduction segment offshore the east coast of the North Island of New Zealand. Our research predicts that these zones are capable of producing giant earthquakes,” Dr Schellart said. (Credit: © vichie81 / Fotolia)

A team of international researchers, led by Monash University’s Associate Professor Wouter Schellart, have developed a new global map of subduction zones, illustrating which ones are predicted to be capable of generating giant earthquakes and which ones are not.

The new research, published in the journal Physics of the Earth and Planetary Interiors, comes nine years after the giant earthquake and tsunami in Sumatra in December 2004, which devastated the region and many other areas surrounding the Indian Ocean, and killed more than 200,000 people.

Since then two other giant earthquakes have occurred at subduction zones, one in Chile in February 2010 and one in Japan in March 2011, which both caused massive destruction, killed many thousands of people and resulted in billions of dollars of damage.

Most earthquakes occur at the boundaries between tectonic plates that cover the Earth’s surface. The largest earthquakes on Earth only occur at subduction zones, plate boundaries where one plate sinks (subducts) below the other into the Earth’s interior. So far, seismologists have recorded giant earthquakes for only a limited number of subduction zone segments. But accurate seismological records go back to only ~1900, and the recurrence time of giant earthquakes can be many hundreds of years.

“The main question is, are all subduction segments capable of generating giant earthquakes, or only some of them? And if only a limited number of them, then how can we identify these,” Dr Schellart said.

Dr Schellart, of the School of Geosciences, and Professor Nick Rawlinson from the University of Aberdeen in Scotland used earthquake data going back to 1900 and data from subduction zones to map the main characteristics of all active subduction zones on Earth. They investigated if those subduction segments that have experienced a giant earthquake share commonalities in their physical, geometrical and geological properties.

They found that the main indicators include the style of deformation in the plate overlying the subduction zone, the level of stress at the subduction zone, the dip angle of the subduction zone, as well as the curvature of the subduction zone plate boundary and the rate at which it moves.

Through these findings Dr Schellart has identified several subduction zone regions capable of generating giant earthquakes, including the Lesser Antilles, Mexico-Central America, Greece, the Makran, Sunda, North Sulawesi and Hikurangi.

“For the Australian region subduction zones of particular significance are the Sunda subduction zone, running from the Andaman Islands along Sumatra and Java to Sumba, and the Hikurangi subduction segment offshore the east coast of the North Island of New Zealand. Our research predicts that these zones are capable of producing giant earthquakes,” Dr Schellart said.

“Our work also predicts that several other subduction segments that surround eastern Australia (New Britain, San Cristobal, New Hebrides, Tonga, Puysegur), are not capable of producing giant earthquakes.”

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

When Will Earth Lose Its Oceans?

Numerical simulations of the Earth’s surface temperatures at the spring equinox, with an increasingly luminous Sun in the future. The first two diagrams are obtained with the global climate model. The second one shows the situation just before the complete evaporation of the oceans. The last one (380 W/m2) is an extrapolation showing temperatures after the complete evaporation of the oceans. The dates, expressed in Myr (millions of years), indicate the Sun’s evolution: in reality, the continents and topography will be totally different in this distant future. (Credit: © Jérémy Leconte)

The natural increase in solar luminosity-a very slow process unrelated to current climate warming-will cause the Earth’s temperatures to rise over the next few hundred million years. This will result in the complete evaporation of the oceans. Devised by a team from the Laboratoire de Météorologie Dynamique[1] (CNRS / UPMC / ENS / École polytechnique), the first three-dimensional climate model able to simulate the phenomenon predicts that liquid water will disappear on Earth in approximately one billion years, extending previous estimates by several hundred million years. Published on December 12, 2013 in the journal Nature, the work not only improves our understanding of the evolution of our planet but also makes it possible to determine the necessary conditions for the presence of liquid water on other Earth-like planets.

Like most stars, the Sun’s luminosity very slowly increases during the course of its existence. It is therefore expected that, due to higher solar radiation, the Earth’s climate will become warmer over geological timescales (of the order of hundreds of millions of years), independently of human-induced climate warming, which takes place over decades. This is because the amount of water vapor in the atmosphere rises as the oceans become warmer (the water evaporates faster). However, water vapor is a greenhouse gas that contributes to the warming of the Earth’s surface. Scientists therefore predict that runaway climate warming will occur on Earth, causing the oceans to boil and liquid water to disappear from the surface. Another consequence is that the greenhouse effect will enter a runaway state and become unstable, making it impossible to maintain a mild mean temperature of 15 °C on Earth. This phenomenon may explain why Venus, which is a little nearer to the Sun than the Earth, turned into a furnace in the distant past. It also sheds light on the climate of exoplanets.

When might this runaway state occur on Earth? Until now, this was difficult to estimate as the phenomenon had only been investigated using highly simplified astrophysical (one-dimensional) models, which considered the Earth to be uniform and failed to take into account key factors such as the seasons or clouds. Yet the climate models used to predict the climate over the coming decades are not suited to such high temperatures. According to some of these one-dimensional models, the Earth would start to lose all its water to space and turn into a new Venus within a mere 150 million years.

A team from the Laboratoire de Météorologie Dynamique (CNRS / UPMC / ENS / École polytechnique) has now designed a three-dimensional model able to predict how the terrestrial environment would change under the effect of a significant increase in solar flux causing evaporation of liquid water into the atmosphere. According to this sophisticated model, the tipping point should occur when mean solar flux reaches approximately 375 W/m2, with a surface temperature of around 70 °C (present-day flux is 341 W/m2), i.e. in approximately one billion years. The oceans will then start to boil and the greenhouse effect will increase until it enters a runaway state. This result pushes back earlier predictions for the complete evaporation of the oceans by several hundred million years.

This difference is due to atmospheric circulation: while transporting heat from the equator to the mid-latitudes, it dries these warm regions and reduces the greenhouse effect in the areas where it is most likely to enter a runaway state. Increased solar flux appears to intensify this atmospheric circulation, drying sub-tropical regions even more and stabilizing the climate for several hundred million years before it reaches the point of no return. In addition, this work shows that the parasol effect of clouds, in other words their ability to reflect solar radiation-which helps to cool the present-day climate-tends to decrease over millions of years compared to their greenhouse effect. The parasol effect is therefore likely to contribute to climate warming and destabilization.

These findings can also be used to determine the extent of the habitable zone around the Sun. They show that a planet can be as close as 0.95 astronomical units[3] to a star similar to our Sun (i.e. 5% less than the distance from the Earth to the Sun) before losing all its liquid water. In addition, they demonstrate yet again that a planet does not need to be exactly like the Earth to have oceans. The researchers are now planning to apply this model to extrasolar planets in order to determine which environments could help them retain liquid water.

[1] The Laboratoire de Météorologie Dynamique is part of the Institut Pierre-Simon Laplace (IPSL). The project was granted an Ile-de-France Region post-doctoral research allowance. 2 It is estimated that at the origin of the Solar System 4.5 billion years ago, the Sun’s luminosity was 70% of today’s value, which implies an increase of around 7% every billion years. 3 1 astronomical unit (AU) = 150 million kilometers.

Note : The above story is based on materials provided by CNRS. 

Precambrian

The Precambrian (Pre-Cambrian) is the large span of time in Earth’s history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4600 million years ago (Ma) to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of geologic time.

Overview

Relatively little is known about the Precambrian, despite its making up roughly seven-eighths of the Earth’s history, and what is known has largely been discovered in the past 50 years. The Precambrian fossil record is poorer than that for the succeeding Phanerozoic, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.

It is thought that the Earth itself coalesced from material in orbit around the Sun roughly 4500 Ma, or 4.5 billion years ago (Ga), and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that came together to form the Moon (see Giant impact hypothesis). A stable crust was apparently in place by 4400 Ma, since zircon crystals from Western Australia have been dated at 4404 Ma.

The term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. It was briefly also called the Cryptozoic eon.

Life before the Cambrian

It is not known when life originated, but carbon in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved bacteria older than 3.46 billion years have been found in Western Australia. Probable fossils 100 million years older have been found in the same area. There is a fairly solid record of bacterial life throughout the remainder of the Precambrian.

Excluding a few contested reports of much older forms from USA and India, the first complex multicellular life forms seem to have appeared roughly 600 Ma. The oldest fossil evidence of complex life comes from the Lantian formation, at least 580 million years ago. A quite diverse collection of soft-bodied forms is known from a variety of locations worldwide between 542 and 600 Ma. These are referred to as Ediacaran or Vendian biota. Hard-shelled creatures appeared toward the end of that time span. By the middle of the later Cambrian period a very diverse fauna is recorded in the Burgess shale, including some which may represent stem groups of modern taxa. The rapid radiation of lifeforms during the early Cambrian is called the Cambrian explosion of life.

While land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas.

Planetary environment and the oxygen catastrophe

Evidence illuminating the details of plate motions and other tectonic functions in the Precambrian has been

The atmosphere of the early Earth is not well understood. Most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, lacking in free oxygen. This has been disputed with evidence in support of an oxygen-rich atmosphere since the early Archean.

Weathered Precambrian pillow lava in the Temagami greenstone belt of the Canadian Shield

poorly preserved. It is generally believed that small proto-continents existed prior to 3000 Ma, and that most of the Earth’s landmasses collected into a single supercontinent around 1000 Ma. The supercontinent, known as Rodinia, broke up around 600 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, roughly 2200 Ma. The best studied is the Sturtian-Varangian glaciation, around 600 Ma, which may have brought glacial conditions all the way to the equator, resulting in a “Snowball Earth”.

Molecular oxygen was not present as a significant fraction of Earth’s atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism. This radical shift from an inert to an oxidizing atmosphere caused an ecological crisis sometimes called the oxygen catastrophe. At first, oxygen would quickly combine with other elements in Earth’s crust, primarily iron, as it was produced. After the supply of oxidizable surfaces ran out, oxygen began to accumulate in the atmosphere, and the modern high-oxygen atmosphere developed. Evidence for this lies in older rocks that contain massive banded iron formations, laid down as iron and oxygen first combined.

Subdivisions

An established terminology has evolved covering the early years of the Earth’s existence, as radiometric dating allows plausible real dates to be assigned to specific formations and features.[10] The Precambrian Supereon is divided into three Precambrian eons: the Hadean (4500-3950 Ma), Archean (4000-2500 Ma) and Proterozoic (2500-541.0 ± 1.0 Ma). See Timetable of the Precambrian.
  • Proterozoic: this eon refers to the time from the lower Cambrian boundary, 541.0 ± 1.0 Ma, back through 2500 Ma. As originally used, it was a synonym for “Precambrian” and hence included everything prior to the Cambrian boundary. The Proterozoic eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.

– Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary (541.0 ± 1.0 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American geology.

–  Ediacaran: The youngest geologic period within the Neoproterozoic Era. The “2012 Geologic Time Scale” dates it from 541.0 ± 1.0 to ~635 Ma. In this period the Ediacaran fauna appeared.
– Cryogenian: The middle period in the Neoproterozoic Era: ~635-850 Ma.
– Tonian: the earliest period of the Neoproterozoic Era: 850-1000 Ma.
– Mesoproterozoic: the middle era of the Proterozoic Eon, 1000-1600 Ma. Corresponds to “Precambrian Y” rocks of older North American geology.
– Paleoproterozoic: oldest era of the Proterozoic Eon, 1600-2500 Ma. Corresponds to “Precambrian X” rocks of older North American geology.
  • Hadean Eon: 3950-4500 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites.[11]
It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs. The Precambrian could be divided into five “natural” eons, characterized as follows.[12]
  1. Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event.
  2. Hadean: dominated by heavy bombardment from about 4.51, (possibly including a Cool Early Earth period) to the end of the Late Heavy Bombardment period.
  3. Archean: a period defined by the first crustal formations (the Isua greenstone belt) until the deposition of banded iron formations due to increasing atmospheric oxygen content.
  4. Transition: a period of continued iron banded formation until the first continental red beds.
  5. Proterozoic: a period of modern plate tectonics until the first animals.

Precambrian supercontinents

The movement of plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent that contains most or all of the continents. The earliest known supercontinent was Vaalbara. It formed from proto-continents and was a supercontinent by 3.1 billion years ago (3.1 Ga). Vaalbara broke up ~2.8 Ga ago. The supercontinent Kenorland was formed ~2.7 Ga ago and then broke sometime after 2.5 Ga into the proto-continent Cratons called Laurentia, Baltica, Australia, and Kalahari. The supercontinent Columbia or Nuna formed during a period of 2.0–1.8 billion years and broke up about 1.5–1.3 billion years ago The supercontinent Rodinia is thought to have formed about 1 billion years ago and to have embodied most or all of Earth’s continents, and broken up into eight continents around 600 million years ago.
Note : The above story is based on materials provided by Wikipedia
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