back to top
27.8 C
New York
Friday, November 15, 2024
Home Blog Page 307

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

Covellite

Galactic Open Pit, Summitville, Summitville District (Summit District), Rio Grande Co., Colorado, USA Copyright © 2002 John H. Betts

Chemical Formula: CuS
Locality: Monte Somma, Vesuvius, Naples, Naples province, Campania, Italy.
Name Origin: Named after the Italian mineralogist, N. Covelli (1790-1829).

Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is ubiquitous in copper ores, it is found in limited abundance and is not an important ore of copper itself, although it is well known to mineral collectors.

The mineral is associated with chalcocite in zones of secondary enrichment (supergene) of copper sulfide deposits. Commonly found with and as coatings on chalcocite, chalcopyrite, bornite, enargite, pyrite, and other sulfides, it often occurs as pseudomorphic replacements after other minerals. Despite the very rare occurrence as a volcanic sublimate, the initial description was at Mount Vesuvius by Nicola Covelli (1790–1829).

Physical Properties

Cleavage: {0001} Perfect
Color: Indigo blue, Light blue, Dark blue, Black.
Density: 4.6 – 4.76, Average = 4.68
Diaphaneity: Opaque
Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals.
Hardness: 1.5-2 – Talc-Gypsum
Luminescence: Non-fluorescent.
Luster: Metallic
Magnetism: Nonmagnetic
Streak: black gray

Photos :

Chalcocite after Covellite – Butte District, Silver Bow Co., Montana, USA Size: 3.0 x 2.5 x 1.0 cm
These samples of covellite are displayed in the Smithsonian Museum of Natural History. The sample is about 18 cm across and is from Leonard mine, Butte, Montana.
COVELLITEEast Colusa Mine, Butte, Silver Bow Co., Montana, USA, North America Size: 4 x 3 x 2.3 cm (Miniature)
These samples of covellite are displayed in the Smithsonian Museum of Natural History. This covellite sample is from Sardegna, Italy. It is about 18 cm across.

‘Stunning’ tsunami record discovered in Indonesia cave

This undated handout photo taken in Lhonga Leupung, Aceh province, shows a cave that scientists found layers of sandy sediment, which had been washed in by tsunamis over thousands of years

Scientists said Friday they have discovered a cave on the Indonesian island of Sumatra that provides a “stunning” record of Indian Ocean tsunamis over thousands of years.They say layers of tsunami-borne sediments found in the cave in northwest Sumatra suggest the biggest destructive waves do not occur at set intervals—meaning communities in the area should be prepared at all times for a tsunami.
“It’s something that communities need to know,” research team leader Charles Rubin told AFP, adding that the team wanted to “promote safety of coastal communities”.

Professor Rubin and other researchers from a Singapore institute were working with scientists from an Indonesian university when they discovered the cave, south of Banda Aceh, the capital of Aceh province.

A quake-triggered tsunami devastated Aceh and areas across the Indian Ocean in 2004, leaving some 170,000 people dead in the province alone.

Inside the cave the researchers found layers of sandy sediment, which had been washed in by tsunamis thousands of years previously, Rubin said.

The layers, which contained small fossils from the seabed, were well-preserved and separated by droppings deposited by bats in the cave, he added.

“This is a beautiful, stunning record of tsunamis that you just don’t have very often,” Rubin said.

Only huge tsunamis and storm surges can get into the cave, which has a raised entrance—and afterwards the sediment is protected inside from erosion by wind or water.

Rubin said the scientists dated the layers and believe they show that between 2,800 and 3,300 years ago, some four to five tsunamis battered the area.

Before the 2004 tsunami, it had been hundreds of years since such a huge destructive wave had hit Aceh, the scientist said.

But he said the new discovery suggests that tsunamis are not evenly spaced through time, which should provide food for thought for those involved in policy and planning in the region.

“These don’t happen like clockwork, they have variations in time and variations in size,” he said.

Rubin works at the Earth Observatory of Singapore, an institute that forms part of Nanyang Technological University.

Scientists from the institute were working with researchers from Syiah Kuala University in Banda Aceh.

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

Corundum

Corundum, Rutile Locality: Emmelberg, Üdersdorf, Daun, Eifel, Rhineland-Palatinate, Germany Image width: 4 mm Copyright © Fred Kruijen

Chemical Formula: Al2O3
Locality: Tchainit and Yakutia, Russia.
Name Origin: Probably derived from the Sanskrit, kuruvinda, meaning “ruby.”

Corundum is a crystalline form of aluminium oxide (Al2O3) typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is one of the naturally transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., “green sapphire” for a green specimen.

The name “corundum” is derived from the Tamil word Kuruvindam or Sanskrit word Kuruvinda meaning ruby.Because of corundum’s hardness (pure corundum is defined to have 9.0 Mohs), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0.In addition to its hardness, corundum is unusual for its density of 4.02 g/cm3, which is very high for a transparent mineral composed of the low-atomic mass elements aluminium and oxygen.

Physical Properties

Cleavage: None
Color: Blue, Red, Yellow, Brown, Gray.
Density: 4 – 4.1, Average = 4.05
Diaphaneity: Transparent to translucent
Fracture: Tough – Difficult to break apart as shown by fibrous minerals and most metals.
Hardness: 9 – Corundum
Luminescence: Sometimes Fluorescent, Long UV=red.
Luster: Vitreous (Glassy)
Magnetism: Nonmagnetic
Streak: none

Photos :

Corundum var. Ruby – Ambahatraso- Hiosy – Madagascar Specimen weight:60 gr. Crystal size:1,2 cm tall Overall size: 42mm x 30 mm x 38 mm
Corundum, Hematite, Sanidine Locality: Wannenköpfe, Ochtendung, Polch, Eifel, Rhineland-Palatinate, Germany 0.6mm high Copyright © Fred Kruijen
Corundum, Pseudobrookite Locality: Emmelberg, Üdersdorf, Daun, Eifel, Rhineland-Palatinate, Germany Picture width 3 mm. Copyright © Stephan Wolfsried
Corundum (Var: Sapphire) Locality: Mogok Township, Pyin-Oo-Lwin District, Mandalay Division, Burma (Myanmar) Dimensions: 2.4 cm x 1 cm x 1 cm Copyright © Danny Jones

Volcano’s legacy still washing up on beaches

Pieces of pumice from the same volcanic eruption that caused the largest pumice raft seen in 50 years have continued to wash up on Queensland shores this week.The pumice was a result of the eruption of an underwater volcano known as Havre Seamount, 1000 km north of Auckland in July 2012. Dr Scott Bryan from QUT’s Science and Engineering Faculty has been collecting and studying the pumice since a raft of the porous volcanic rock was first spotted by a passenger while flying from Samoa to New Zealand two weeks after the eruption.

Pieces of pumice from the same volcanic eruption that caused the largest pumice raft seen in 50 years have continued to wash up on Queensland shores this week.The pumice was a result of the eruption of an underwater volcano known as Havre Seamount, 1000 km north of Auckland in July 2012.
Dr Scott Bryan from QUT’s Science and Engineering Faculty has been collecting and studying the pumice since a raft of the porous volcanic rock was first spotted by a passenger while flying from Samoa to New Zealand two weeks after the eruption.

“This volcano was discovered only a few years ago and so little is known about it,” he said.

“The summit sits about 700 m below sea level so it would have taken quite a lot of power to force the pumice up to the surface of the ocean. We are also looking at how big these pieces of pumice are and the amount that we are seeing washing up gives us an idea of the magnitude of the eruption.”

Since the discovery of the pumice raft, which was also seen early on via satellite imagery, pieces of the rock have washed up in New Zealand, Tonga, Fiji and along the eastern seaboard of Australia from as far north as the Torres Strait to Victoria. The most recent finds have been in South East Queensland, Townsville and the Whitsundays.

“It’s not unusual for pumice rafts to wash onto shore for up to a year after the first strandings which were in March this year,” Dr Bryan said.

“The pumice is essentially the only record we have of the eruption. It can help us to understand more about the nature of the volcano as well as how these volcanoes erupt explosively under so much water.”

While finding a piece of volcanic history on the beach is fun, Dr Bryan said the pumice does pose a safety issue for boats.

“The pumice can be a navigational hazard,” he said.

“We have had reports of it blocking and damaging water intakes for engine cooling systems on boats, which have had to be replaced, and so it can have a significant financial impact as well.”

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

Geologists report that risks of big earthquakes may be underestimated

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

Several geologists from around the world are presenting a case for missing or underreported earthquakes at this year’s American Geophysical Union Fall meeting being held in San Francisco. They suggest that faulty or missing data from before 1900 might be leading to underestimations of the numbers of big quakes to expect in the future.
One such speaker is Susan Hough—she’s with the US Geological Survey. She reported to those in attendance that prior to the invention and implementation of seismometers, evidence of earthquakes could be found only through earlier anecdotal writings. But such records, she notes, tended to underestimate the size of the quakes being described. Suddenly, she says, after 1900, earthquakes started getting bigger.

They didn’t get bigger of course, what she meant was that the size perception of earlier earthquakes had been underestimated—many might not be in the historical record at all. Part of the problem, she explained, was that until fairly recently, it was believed that all earthquakes of a certain large size, produced tsunami’s, which of course tend to show up in written records.

The problem with relying on underestimated data, she also explained, is that it causes modern day planners to underestimate what is likely to happen in the future. She notes that one example was that of the Kamchatka quake that occurred in 1841 in Russia. The record shows it to have been an 8.3 magnitude quake, but closer scrutiny suggests that estimate was wrong—reports of a tsunami in Hawaii at the time, indicate it was almost certainly much stronger, perhaps as high as magnitude 9.2.

Roger Musson of the British Geological Survey concurred, noting that people were taken almost completely by surprise when the Fukushima quake struck in 2011. But, looking back, it’s clear that one almost exactly like it struck in the same place back in the 9th century. He noted virtually the same thing can be said for the Haiti quake that struck in 2010.

The overall point the geologists are trying to make is that it’s likely that the reported numbers and sizes of quakes described in the past are in error, and thus, using them as guides for the future is both risky and ill-advised as the lives of people in many at-risk areas may be depending on more accurate assessments.

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

Surprise: Duck-Billed Dinosaurs Had Fleshy ‘Cocks Comb’

This is an Edmontosaurus regalis reconstruction. Credit: Bell, Fanti, Currie, Arbour, Current Biology

A rare, mummified specimen of the duck-billed dinosaur Edmontosauraus regalis described in the Cell Press journal Current Biology on December 12 shows for the first time that those dinosaurs’ heads were adorned with a fleshy comb, most similar to the roosters’ red crest.

 

The most common dinosaurs in North America between 75 and 65 million years ago, duck-billed dinosaurs were gentle giants, about 12 meters long, and filled the same ecological role that kangaroos or deer play today. But no one had suspected that they — or other dinosaurs, for that matter — had fleshy structures on the tops of their heads.

“Until now, there has been no evidence for bizarre soft-tissue display structures among dinosaurs; these findings dramatically alter our perception of the appearance and behavior of this well-known dinosaur and allow us to comment on the evolution of head crests in this group,” says Phil Bell from Australia’s University of New England. “It also raises the thought-provoking possibility of similar crests among other dinosaurs.”

The dinosaur specimen in question was found in deposits west of the city of Grande Prairie in west-central Alberta, Canada. Bell, along with Federico Fanti from the University of Bologna, Italy, knew they had something special when they found skin impressions on parts of the mummified body. But it wasn’t until Bell put a chisel through the top of the crest that he realized they really had something incredible.

“An elephant’s trunk or a rooster’s crest might never fossilize because there’s no bone in them,” Bell explains. “This is equivalent to discovering for the first time that elephants had trunks. We have lots of skulls of Edmontosaurus, but there are no clues on them that suggest they might have had a big fleshy crest. There’s no reason that other strange fleshy structures couldn’t have been present on a whole range of other dinosaurs, including T. rex or Triceratops.”

Of course, it’s hard to tell what that cocks comb might have done for the duck-billed dinosaurs. In roosters and some other birds, bright red crests are a way to get the girls. “We might imagine a pair of male Edmontosaurus sizing each other up, bellowing, and showing off their head gear to see who was the dominant male and who is in charge of the herd,” Bell says.

We may never know exactly, but the new study is a useful reminder of just how bizarre and amazing dinosaurs really were, the researchers say. There is much left to discover.

Note : The above story is based on materials provided by Cell Press, via EurekAlert!, a service of AAAS. 

Cornetite

L’Etoile du Congo Mine (Star of the Congo Mine; Kalukuluku Mine), Lubumbashi (Elizabethville), Katanga Copper Crescent, Katanga (Shaba), Democratic Republic of Congo (Zaïre) © 2006 D. Schläfli
Chemical Formula: Cu3(PO4)(OH)3
Locality: Star of the Congo mine, near Lubumbashi, and at the Kalabi and Lukini mines, Katanga Province, Congo (Shaba Province, Zaire).
Name Origin: Named for Jules Cornet (1865-1929), Belgian geologist.

 

Cornetite is a rare secondary copper mineral that is noted for its deep blue, green-blue to green color. It is found in highly weathered, oxidation zones of copper sulfide ore bodies. It has a good deep color, nice crystal forms and an attractive sparkle, all the ingredients for a popular collection mineral.

Physical Properties of Cornetite

Color: dark blue, green-blue to green.
Luster: vitreous.
Transparency: Specimens are translucent.
Crystal System: orthorhombic; 2/m2/m2/m
Crystal Habits: include crystals that are short, rounded, nearly diamond-shaped prisms that are terminated by a dome with trapezohedral faces, also as tiny crystalline druzes, fibrous masses and crusts.
Cleavage: absent.
Fracture: uneven.
Hardness: 4.5
Specific Gravity : approximately 4.1 (above average for translucent minerals)
Streak: blue.

Photos :

Locality: L’Etoile du Congo Mine (Star of the Congo Mine; Kalukuluku Mine), Lubumbashi (Elizabethville), Katanga Copper Crescent, Katanga (Shaba), Democratic Republic of Congo (Zaïre) Picture width 3 mm. Copyright © Stephan Wolfsried
Locality: L’Etoile du Congo Mine (Star of the Congo Mine; Kalukuluku Mine), Lubumbashi (Elizabethville), Katanga Copper Crescent, Katanga (Shaba), Democratic Republic of Congo (Zaïre) Image is 6 mm wide. Copyright © Dominik Schläfli
Locality: Manto Ruso Mine (Manto Russo), Mantoverde district, El Salado, Chañaral Province, Atacama Region, Chile FOV: 0.95 mm Copyright © Chinellato Matteo
Locality: L’Etoile du Congo Mine (Star of the Congo Mine; Kalukuluku Mine), Lubumbashi (Elizabethville), Katanga Copper Crescent, Katanga (Shaba), Democratic Republic of Congo (Zaïre) FOV: 1.7 cm Copyright © Tony Peterson

What the Past Tells Us About Modern Sea-Level Rise

Glacier Bay. Calving glacier. (Credit: © jeffong / Fotolia)

Researchers from the University of Southampton and the Australian National University report that sea-level rise since the industrial revolution has been fast by natural standards and — at current rates — may reach 80cm above the modern level by 2100 and 2.5 metres by 2200.

The team used geological evidence of the past few million years to derive a background pattern of natural sea-level rise. This was compared with historical tide-gauge and satellite observations of sea-level change for the ‘global warming’ period, since the industrial revolution. The study, which was funded by the Natural Environment Research Council (iGlass consortium) and Australian Research Council (Laureate Fellowship), is published in the journal Scientific Reports.

Lead author Professor Eelco Rohling, from the Australian National University and formerly of the University of Southampton, says: “Our natural background pattern from geological evidence should not be confused with a model-based prediction. It instead uses data to illustrate how fast sea level might change if only normal, natural processes were at work. There is no speculation about any new mechanisms that might develop due to human-made global warming. Put simply, we consider purely what nature has done before, and therefore could do again.”

Co-author Dr Gavin Foster, a Reader in Ocean and Earth Science at the University of Southampton, who is based at the National Oceanography Centre, Southampton (NOCS), explains: “Geological data showed that sea level would likely rise by nine metres or more as the climate system adjusts to today’s greenhouse effect. But the timescale for this was unclear. So we studied past rates and timescales of sea-level rise, and used these to determine the natural background pattern.”

Co-author Dr Ivan Haigh, lecturer in coastal oceanography at the University of Southampton and also based at NOCS, adds: “Historical observations show a rising sea level from about 1800 as sea water warmed up and melt water from glaciers and ice fields flowed into the oceans. Around 2000, sea level was rising by about three mm per year. That may sound slow, but it produces a significant change over time.”

The natural background pattern allowed the team to see whether recent sea-level changes are exceptional or within the normal range, and whether they are faster, equal, or slower than natural changes.

Professor Rohling concludes: “For the first time, we can see that the modern sea-level rise is quite fast by natural standards. Based on our natural background pattern, only about half the observed sea-level rise would be expected.

“Although fast, the observed rise still is (just) within the ‘natural range’. While we are within this range, our current understanding of ice-mass loss is adequate. Continued monitoring of future sea-level rise will show if and when it goes outside the natural range. If that happens, then this means that our current understanding falls short, potentially with severe consequences.”

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

Runaway Process Drives Intermediate-Depth Earthquakes

A 3D rendering of the tectonic plates (multicolored regions) in northern South America (coastline shown in yellow) shows the underlying Bucaramanga Nest, which experiences more intermediate-depth earthquakes than any place in the world. (Credit: Image courtesy of German Prieto)

Stanford researchers have uncovered a vital clue about the mechanism behind a type of earthquake that originates deep within Earth and accounts for a quarter of all temblors worldwide, some of which are strong enough to pose a safety hazard.

Stanford scientists may have solved the mystery of what drives a type of earthquake that occurs deep within Earth and accounts for one in four quakes worldwide.

Known as intermediate-depth earthquakes, these temblors originate farther down inside Earth than shallow earthquakes, which take place in the uppermost layer of Earth’s surface, called the crust. The kinds of quakes that afflict California and most other places in the world are shallow earthquakes.

“Intermediate-depth earthquakes occur at depths of about 30 miles down to about 190 miles,” said Greg Beroza, a professor of geophysics at Stanford and a coauthor of a new study that will be published in an upcoming issue of the journal Geophysical Research Letters.

Unlike shallow earthquakes, the cause of intermediate quakes is not well-understood. Part of the problem is that the mechanism for shallow earthquakes should not physically work for quakes at greater depths.

“Shallow earthquakes occur when stress building up at faults overcomes friction, resulting in sudden slip and energy release,” Beroza said. “That mechanism shouldn’t work at the higher pressures and temperatures at which intermediate depth earthquakes occur.”

A better understanding of intermediate-depth quakes could help scientists forecast where they will occur and the risk they pose to buildings and people.

“They represent 25 percent of the catalog of earthquakes, and some of them are large enough to produce damage and deaths,” said study first author Germán Prieto, an assistant professor of geophysics at the Massachusetts Institute of Technology.

A tale of two theories

There are two main hypotheses for what may be driving intermediate depth earthquakes. According to one idea, water is squeezed out of rock pores at extreme depths and the liquid acts like a lubricant to facilitate fault sliding. This fits with the finding that intermediate quakes generally occur at sites where one tectonic plate is sliding, or subducting, beneath another.

“Typically, subduction involves oceanic plates whose rocks contain lots of water,” Beroza said.

A competing idea is that as rocks at extreme depths deform, they generate heat due to friction. The heated rocks become more malleable, or plastic, and as a result slide more easily against each other. This can create a positive feedback loop that further weakens the rock and increases the likelihood of fault slippage.

“It’s a runaway process in which the increasing heat generates more slip, and more slip generates more heat and so on,” Prieto said.

To distinguish between the two possible mechanisms, the scientists studied a site near the city of Bucaramanga in Colombia that boasts the highest concentration of intermediate quakes in the world. About 18 intermediate depth temblors rattle Bucaramanga every day. Most are magnitude 2 to 3, weak quakes that are detectable only by sensitive instruments.

But about once a month one occurs that is magnitude 5 or greater — strong enough to be felt by the city’s residents. Moreover, past studies have revealed that most of the quakes appear to be concentrated at a site located about 90 miles beneath Earth’s surface that scientists call the Bucaramanga Nest.

A natural laboratory

This type of clustering is highly unusual and makes the Bucaramanga Nest a “natural laboratory” for studying intermediate depth earthquakes. Comparison studies of intermediate quakes from different parts of the world are difficult because the makeup of Earth’s crust and mantle can vary widely by location.

In the Bucaramanga Nest, however, the intermediate quakes are so closely packed together that for the purposes of scientific studies and computer models, it’s as if they all occurred at the same spot. This vastly simplifies calculations, Beroza said.

“When comparing a magnitude 2 and a magnitude 5 intermediate depth earthquake that are far apart, you have to model everything, including differences in the makeup of the Earth’s surface,” he said. “But if they’re close together, you can assume that the seismic waves of both quakes suffered the same distortions as they traveled toward the Earth’s surface.”

By studying seismic waves picked up by digital seismometers installed on Earth’s surface above the Bucaramanga Nest, the scientists were able to measure two key parameters of the intermediate quakes happening deep underground.

One, called the stress drop, allowed the team to estimate the total amount of energy released during the fault slips that caused the earthquakes. The other was radiated energy, which is a measure of how much of the energy generated by the fault slip is actually converted to seismic waves that propagate through Earth to shake the surface.

Two things immediately stood out to the researchers. One was that the stress drop for intermediate quakes increased along with their magnitudes. That is, larger intermediate quakes released proportionally more total energy than smaller ones. Second, the amount of radiated energy released by intermediate earthquakes accounted for only a tiny portion of the total energy as calculated by the stress drop.

“For these intermediate-depth earthquakes in Colombia, the amount of energy converted to seismic waves is only a small fraction of the total energy,” Beroza said.

The implication is that intermediate earthquakes are expending most of their energy locally, likely in the form of heat.

“This is compelling evidence for a thermal runaway failure mechanism for intermediate earthquakes, in which a slipping fault generates heat. That allows for more slip and even more heat, and a positive feedback loop is created,” said study coauthor Sarah Barrett, a Stanford graduate student in Beroza’s research group.

Note : The above story is based on materials provided by Stanford University. The original article was written by Ker Than. 

RAVAN to Help Solve an Earth Science Mystery

Artist rendering of the Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) satellite, a new, low-cost cubesat mission led by the Johns Hopkins Applied Physics Laboratory in Laurel, Md. RAVAN will demonstrate technology needed to measure the absolute imbalance in the Earth’s radiation budget for the first time; the cubesat is scheduled for launch in 2015. (Credit: JHU/APL)

A new, low-cost cubesat mission led by the Johns Hopkins Applied Physics Laboratory in Laurel, Md. will demonstrate technology needed to measure the absolute imbalance in Earth’s radiation budget for the first time, giving scientists valuable information to study our climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) satellite, scheduled for launch in 2015, will demonstrate how accurate and wide-ranging measurements of Earth’s outgoing radiation can be made with a remarkably small instrument. The RAVAN team includes partners at Draper Laboratory in Cambridge, Ma.; L-1 Standards and Technology in New Windsor, Md.; and NASA’s Goddard Space Flight Center in Greenbelt, Md.

“Under stable climate conditions, the energy from the sun reaching the top of Earth’s atmosphere and that being reflected or radiated to space are equal,” explains Bill Swartz, an atmospheric scientist at APL and RAVAN principal investigator. “There is substantial evidence that they are not equal, and that difference is known as Earth’s radiation imbalance (ERI). It’s a really small number — a difference thought to be less than one percent — but that imbalance drives the future of climate change. RAVAN will demonstrate how ERI can be unambiguously and affordably quantified from space, enabling a huge leap in our ability to predict the future climate.”

RAVAN will use a small, accurate radiometer, developed at L-1 Standards and Technology and not much larger than a deck of cards, to measure the strength of Earth’s outgoing radiation across the entire spectrum of energy — from the ultraviolet to the far infrared. “ERI is too small to be measured by previous, current, or planned future space assets,” says co-investigator Warren Wiscombe, a climate scientist at Goddard.

The secret to RAVAN’s precise measurements is a “forest” of carbon nanotubes, grown at APL, that serve as the radiometer’s light absorber. “The carbon nanotubes are a very deep black across the energy spectrum, which will let the radiometer gather virtually all the light reflected and emitted from the planet,” says Swartz.

RAVAN represents the first step toward a constellation of cubesats, each no larger than a loaf of bread, that would provide global coverage of Earth’s total outgoing radiation throughout the day and night, and data to answer long-standing questions about Earth’s climate future.

“RAVAN is unique because it’s not only a technology demonstration, but a manufacturing and economic demonstration,” says Draper Laboratory’s Lars Dyrud, RAVAN project lead. “Resolving climate uncertainty and improved prediction of future climate change requires 30 to 40 RAVAN sensors. The cubesat revolution and advanced manufacturing offer the best hope for affordably achieving these urgent goals.” Draper Laboratory is responsible for process engineering for RAVAN, with the goal of ensuring that the instrument design can be manufactured in a cost-effective manner.

RAVAN is the first Earth science cubesat built by APL. It is part of the Lab’s ongoing development and refinement of these small, adaptable and cost-effective platforms for operational use. APL’s first two cubesats carried technology demonstration payloads, and launched Nov. 19, 2013, aboard a Minotaur rocket from Wallops Island. The RAVAN mission is sponsored by NASA’s Earth Science Technology Office, located at Goddard.

Note : The above story is based on materials provided by Johns Hopkins University Applied Physics Laboratory. 

Rising mountains dried out Central Asia, scientists say

Stanford researchers visited the Nemegt Basin in Mongolia’s Gobi Desert in search of clues to Central Asia’s extreme aridity. Credit: Hari Mix

A record of ancient rainfall teased from long-buried sediments in Mongolia is challenging the popular idea that the arid conditions prevalent in Central Asia today were caused by the ancient uplift of the Himalayas and the Tibetan Plateau.

Instead, Stanford scientists say the formation of two lesser mountain ranges, the Hangay and the Altai, may have been the dominant drivers of climate in the region, leading to the expansion of Asia’s largest desert, the Gobi. The findings will be presented on Thursday, Dec. 12, at the annual meeting of the American Geophysical Union (AGU) in San Francisco.

“These results have major implications for understanding the dominant factors behind modern-day Central Asia’s extremely arid climate and the role of mountain ranges in altering regional climate,” said Page Chamberlain, a professor of environmental Earth system science at Stanford.

Scientists previously thought that the formation of the Himalayan mountain range and the Tibetan plateau around 45 million years ago shaped Asia’s driest environments.

“The traditional explanation has been that the uplift of the Himalayas blocked air from the Indian Ocean from reaching central Asia,” said Jeremy Caves, a doctoral student in Chamberlain’s terrestrial paleoclimate research group who was involved in the study.

This process was thought to have created a distinct rain shadow that led to wetter climates in India and Nepal and drier climates in Central Asia. Similarly, the elevation of the Tibetan Plateau was thought to have triggered an atmospheric process called subsidence, in which a mass of air heated by a high elevation slowly sinks into Central Asia.

“The falling air suppresses convective systems such as thunderstorms, and the result is you get really dry environments,” Caves said.

This long-accepted model of how Central Asia’s arid environments were created mostly ignores, however, the existence of the Altai and Hangay, two northern mountain ranges.

Searching for answers

To investigate the effects of the smaller ranges on the regional climate, Caves and his colleagues from Stanford and Rocky Mountain College in Montana traveled to Mongolia in 2011 and 2012 and collected samples of ancient soil, as well as stream and lake sediments from remote sites in the central, southwestern and western parts of the country.

The team carefully chose its sites by scouring the scientific literature for studies of the region conducted by pioneering researchers in past decades.

“A lot of the papers were by Polish and Russian scientists who went there to look for dinosaur fossils,” said Hari Mix, a doctoral student at Stanford who also participated in the research. “Indeed, at many of the sites we visited, there were dinosaur fossils just lying around.”

The earlier researchers recorded the ages and locations of the rocks they excavated as part of their own investigations; Caves and his team used those age estimates to select the most promising sites for their own study.

At each site, the team bagged sediment samples that were later analyzed to determine their carbon isotope content. The relative level of carbon isotopes present in a soil sample is related to the productivity of plants growing in the soil, which is itself dependent on the annual rainfall. Thus, by measuring carbon isotope amounts from different sediment samples of different ages, the team was able to reconstruct past precipitation levels.

An ancient wet period

The new data suggest that rainfall in central and southwestern Mongolia had decreased by 50 to 90 percent in the last several tens of million of years.

“Right now, precipitation in Mongolia is about 5 inches annually,” Caves said. “To explain our data, rainfall had to decrease from 10 inches a year or more to its current value over the last 10 to 30 million years.”

That means that much of Mongolia and Central Asia were still relatively wet even after the formation of the Himalayas and the Tibetan Plateau 45 million years ago. The data show that it wasn’t until about 30 million years ago, when the Hangay Mountains first formed, that rainfall started to decrease. The region began drying out even faster about 5 million to 10 million years ago, when the Altai Mountains began to rise.

The scientists hypothesize that once they formed, the Hangay and Altai ranges created rain shadows of their own that blocked moisture from entering Central Asia.

“As a result, the northern and western sides of these ranges are wet, while the southern and eastern sides are dry,” Caves said.

The team is not discounting the effect of the Himalayas and the Tibetan Plateau entirely, because portions of the Gobi Desert likely already existed before the Hangay or Altai began forming.

“What these smaller mountains did was expand the Gobi north and west into Mongolia,” Caves said.

The uplift of the Hangay and Altai may have had other, more far-reaching implications as well, Caves said. For example, westerly winds in Asia slam up against the Altai today, creating strong cyclonic winds in the process. Under the right conditions, the cyclones pick up large amounts of dust as they snake across the Gobi Desert. That dust can be lofted across the Pacific Ocean and even reach California, where it serves as microscopic seeds for developing raindrops.

The origins of these cyclonic winds, as well as substantial dust storms in China today, may correlate with uplift of the Altai, Caves said. His team plans to return to Mongolia and Kazakhstan next summer to collect more samples and to use climate models to test whether the Altai are responsible for the start of the large dust storms.

“If the Altai are a key part of regulating Central Asia’s climate, we can go and look for evidence of it in the past,” Caves said.

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

Ancient Crater Could Hold Clues About Moon’s Mantle

Among the largest known craters in the solar system. Red areas on the topographic image indicate high elevations, and blue or purple areas indicate low elevation. The South Pole Aitken basin could hold clues about the composition of the Moon’s mantle. (Credit: NASA/GSFC)

A massive impact on the Moon about 4 billion years ago left a 2,500-mile crater, among the largest known craters in the solar system. Smaller subsequent impacts left craters within that crater. Comparing the spectra of light reflected from the peaks of those craters may yield clues to the composition of the Moon’s lower crust and mantle — and would have implications for models of how the Moon formed.

Researchers from Brown University and the University of Hawaii have found some mineralogical surprises in the Moon’s largest impact crater.

Data from the Moon Mineralogy Mapper that flew aboard India’s Chandrayaan-1 lunar orbiter shows a diverse mineralogy in the subsurface of the giant South Pole Aitken basin. The differing mineral signatures could be reflective of the minerals dredged up at the time of the giant impact 4 billion years ago, the researchers say. If that’s true, then the South Pole Aitken (SPA) basin could hold important information about the Moon’s interior and the evolution of its crust and mantle.

The study, led by Brown graduate student Dan Moriarty, is published in online early view in the Journal of Geophysical Research: Planets.

At 2,500 kilometers across, the SPA is the largest impact basin on the Moon and perhaps the largest in the solar system. Impacts of this size turn tons of solid rock into molten slush. It has been assumed generally that the melting process would obliterate any distinct signatures of pre-existing mineralogical diversity through extensive mixing, but this latest research suggests that might not be the case.

The study looked at smaller craters within the larger SPA basin made by impacts that happened millions of years after the giant impact that formed the basin. Those impacts uncovered material from deep within the basin, offering important clues about what lies beneath the surface. Specifically, the researchers looked at the central peaks of four craters within the basin. Central peaks form when material under the impact zone rebounds, forming an upraised rock formation in the middle of the crater. The tops of those peaks represent pristine material from below the impact zone.

Using Moon Mineralogy Mapper data, the researchers looked at the light reflected from each of the four central peaks. The spectra of reflected light give scientists clues about the makeup of the rocks. The spectra showed substantial differences in composition from peak to peak. Some crater peaks were richer in magnesium than others. One of the four craters, located toward the outer edge of the basin, contained several distinct mineral deposits within its own peak, possibly due to sampling a mixture of both upper and lower crust or mantle materials.

The varying mineralogy in these central peaks suggests that the SPA subsurface is much more diverse than previously thought.

“Previous studies have suggested that all the central peaks look very similar, and that was taken as evidence that everything’s the same across the basin,” Moriarty said. “We looked in a little more detail and found significant compositional differences between these central peaks. The Moon Mineralogy Mapper has very high spatial and spectral resolution. We haven’t really been able to look at the Moon in this kind of detail before.”

The next step is figuring out where that diversity comes from.

It’s possible that the distinct minerals formed as the molten rock from the SPA impact cooled. Recent research from Brown and elsewhere suggests that such mineral formation in impact melt is possible. However, it’s also possible that the mineral differences reflect differences in rock types that were there before the giant SPA impact. Moriarty is currently undertaking a much larger survey of SPA craters in the hope of identifying the source of the diversity. If indeed the diversity reflects pre-existing material, the SPA could hold important clues about the composition of the Moon’s lower crust and mantle.

“If you do the impact scaling from models, [the SPA impact] should have excavated into the mantle,” Moriarty said. “We think the upper mantle is rich in a mineral called olivine, but we don’t see much olivine in the basin. That’s one of the big mysteries about the South Pole Aitken basin. So one of the things we’re trying to figure out is how deep did the impact really excavate. If it melted and excavated any material from the mantle, why aren’t we seeing it?”

If the impact did excavate mantle material, and it doesn’t contain olivine, that would have substantial implications for models of how the Moon was formed, Moriarty said.

Much more research is needed to begin to answer those larger questions. But this initial study helps raise the possibility that some of the original mantle mineralogy, if excavated, may be preserved in the Moon’s largest impact basin.

Carle Pieters, professor of geological sciences at Brown, and Peter Isaacson from the University of Hawaii were also authors on the paper. The work was supported by NASA’s Lunar Advanced Science and Exploration Research (LASER) program and the NASA Lunar Science Institute (NLSI).

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

1...306307308...333Page 307 of 333

Related Articles

All
Facebook Instagram Linkedin TikTok Twitter Youtube
© © 2011-2024. All Rights Reserved.