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A seismologist at Washington University in St. Louis has made the first 3-D model of seismic wave damping — diminishing — deep in the Earth’s mantle and has revealed the existence of an underground water reservoir at least the volume of the Arctic Ocean.

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It is the first evidence for water existing in the Earth’s deep mantle.

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Michael E. Wysession, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, working with former graduate student Jesse Lawrence (now at the University of California, San Diego), analyzed 80,000 shear waves from more than 600,000 seismograms and found a large area in Earth’s lower mantle beneath eastern Asia where water is damping out, or attenuating, seismic waves from earthquakes.

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The traditional method seismologists use to image the Earth below us is to measure the speed of seismic waves. This will provide a sort of CAT scan of the Earth’s core and mantle. Using wave speeds alone is a problem, however, because they cannot distinguish between temperature and composition variations.

The research is described in a forthcoming monograph, Earth’s Deep Water Cycle, which is in press to be published by the American Geophysical Union.

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An increasingly popular method, which Wysession used, is to analyze the way waves damp out from their source. If you take a hammer and pound it hard on a desk, waves will go from the source to the end of the table with the mass of the table lessening, or attenuating, the power of waves. A picture near the striking point might topple, but a stapler two feet away might not even budge. Attenuation data tell seismologists how stiff a region is, which is a function of how hot it is and how much water it contains. Looking at the seismic wave speeds and attenuation at the same time can tell whether an anomaly is due to temperature or water.

In analyzing the data, Wysession first saw large patterns associated with known areas where the ocean floor is sinking down into the earth. Beneath Asia, the fallen Pacific sea floor piles up at the base of the mantle. Right above that he observed an “incredibly highly attenuating region, that is both very damping and slightly slow,” he said. “Water slows the speed of waves a little. Lots of damping and a little slowing match the predictions for water very well.”

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Previous predictions calculated that a cold ocean slab sinking into the earth at 1,200 to 1,4000 kilometers beneath the surface would release water in the rock that would escape the rock and rise up to a region above it, but this was never previously observed.

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“That is exactly what we show here, the exact depth and high attenuation amounts right above it,” Wysession said. “I call it the Beijing anomaly. Water inside the rock goes down with the sinking slab and it’s quite cold, but it heats up the deeper it goes, and the rock eventually becomes unstable and loses its water. The water then rises up into the overlying region, which becomes saturated with water.

“If you combine the volume of this anomaly with the fact that the rock can hold up to about 0.1 percent of water, that works out to be about an Arctic Ocean’s worth of water.”

In recent years, seismologists have become excited at the possibility of a feature like the Beijing anomaly. The availability of vast amounts of digital seismograms made possible the discovery by Wysession and Lawrence, who wrote many thousands of lines of computer codes to do the analyses.

Seventy percent of the earth is covered by water, which is very important for the earth’s geology, serving as a lubricant that allows efficient convection and plate tectonics and the continental collisions that form mountains.

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“Water is like a lubricant, constantly oiling the machine of mantle convection which then drives plate tectonics and causes the continents to move about Earth’s surface,” Wysession said. “Look at our sister planet, Venus. It is very hot and dry inside Venus, and Venus has no plate tectonics. All the water probably boiled off, and without water, there are no plates. The system is locked up, like a rusty Tin Man with no oil.”

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Tiny tremors and temblors recently discovered in fault zones from California to Japan are generated by slow-moving earthquakes that may foreshadow catastrophic seismic events, according to scientists at Stanford University and the University of Tokyo.

In a study published in the March 15 issue of the journal Nature, the research team focused on weak seismic signals known as “non-volcanic tremor” and “low-frequency earthquakes,” which seismologists say may be useful in forecasting the likelihood of potentially destructive mega-quakes of magnitude 8 or higher.

“Non-volcanic tremor is a weak shaking of the Earth that was discovered about five years ago in Japan,” said Gregory C. Beroza, professor of geophysics at Stanford and co-author of the Nature study. “It’s often accompanied by low-frequency earthquakes [LFEs]—small temblors of magnitude 1 or 2. Some people believe that LFEs and tremor are separate phenomena, but what we’ve shown in this paper is that they are actually the same thing. Tremor is simply a swarm of low-frequency earthquakes, but rather than happening quickly and impulsively like ordinary earthquakes, tremor shakes the Earth for hours, days or even weeks at a time.”
Destructive zones

To date, non-volcanic tremor and LFEs have been found primarily in subduction zones—seismically active faults where two tectonic plates meet and one plate constantly dives beneath the other. The most destructive earthquakes ever recorded have occurred in subduction zones, in places such as Chile, Japan, Alaska, Washington state and British Columbia. A recent example was the devastating 2004 earthquake near Sumatra, where a magnitude 9.2 temblor triggered powerful tsunamis that killed more than 200,000 people.

These violent mega-thrusts occur every 100 to 600 years, depending on the location. Recent studies suggest that giant quakes, which form at relatively shallow depths, are preceded by a series of much deeper events called slow (or silent) earthquakes, which displace the ground without shaking it. A slow earthquake can last days, months or years without being felt at the surface.

“In Japan, the deep section of the fault where slow earthquakes form is particularly significant, because it lies next to the shallower locked portion of the fault, where big quakes periodically strike,” Beroza said. “So each time a slow earthquake happens, it adds stress to the locked section and increases the likelihood of a magnitude 8 mega-thrust. Therefore, knowing when a slow earthquake has occurred could be useful in seismic hazard forecasting.”
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But detecting slow quakes is a difficult task, he added. That’s one reason why seismologists were particularly excited by the recent discovery of non-volcanic tremor and LFEs in the subduction zone near Shikoku, Japan.

“Shikoku experiences a big earthquake every 100 years or so,” said Stanford graduate student David R. Shelly, lead author of the Nature study. “The last one happened in 1946, a magnitude 8.1 event that killed 1,330 people, and the next big one could strike in less than 40 years.”

Seismologists believe that since the violent 1946 fault rupture, Shikoku has experienced a series of slow earthquakes every six months or so. These events, which can last a few days or up to two weeks, cause an imperceptible shift in the Earth’s crust equivalent to the ground displacement produced by an ordinary earthquake of magnitude 6. Although harmless on the surface, these slow-slip events may be causing stress to accumulate in the adjacent locked section of the fault, scientists say.

Concerned about the hazards posed by earthquakes, the Japanese government installed a network of highly sensitive seismic instruments 10 years ago throughout the region. This advanced technology soon led to the discovery of slow earthquakes accompanied by LFEs and non-volcanic tremor in the Shikoku fault zone. Since then, some seismologists have proposed using LFEs and tremor to monitor slow earthquakes and assess seismic hazard. Others maintain that these weak signals are of little use in earthquake forecasting.

“Some people draw an analogy between non-volcanic and volcanic tremor,” Beroza said. “In volcanoes, fluids moving through shallow conduits cause the Earth to vibrate. But in earthquakes, waves are generated by slip on a fault. That’s the fundamental earthquake mechanism.”
Fluids vs. slip

Is non-volcanic tremor a vibration caused by fluids moving deep in the subduction zone, or is it a seismic signal produced when the fault slips during a silent earthquake? To find out, Shelly pored over hundreds of seismograms recorded in the Shikoku region between 2002 and 2005. His analysis revealed an almost perfect correlation between tremor events and low-frequency earthquakes.

“David found that the wiggles that tremor makes on seismographs matches the wiggles of the low-frequency earthquakes,” Beroza explained. “This demonstrates that tremor is actually a swarm of hundreds of thousands of LFEs, each of which is caused by slip on the deep part of the fault—the same mechanism by which regular earthquakes are generated but with a twist. The slip in deep tremor happens more slowly than in ordinary earthquakes.”

This insight may open new avenues of research for predicting earthquake hazards, Shelly said. “We now understand that tremor is generated directly by slip on the deep extension of the fault,” he said. “Combining this understanding with our new ability to locate tremor precisely in time and space, we can now track the details of how slip evolves during a weeklong slow-slip event. This could also improve our ability to predict the effects on the shallower, earthquake-generating portion of the subduction fault and potentially lead to an improved ability to forecast a major earthquake there.”

Besides Japan, non-volcanic tremor also has been detected under California’s San Andreas Fault and in the Cascadia subduction zone, which stretches from northern California to British Columbia. Cascadia includes four heavily populated urban areas—Portland, Seattle, Vancouver and Victoria, B.C. In 2003, Canadian scientists discovered that slow quakes and tremors in Cascadia occur like clockwork every 13 to 15 months. Scientists worry that these predictable slow events are loading stress on the locked portion of the fault, where a devastating magnitude 9 earthquake is expected to strike sometime in the next 300 years.

“In early February, Cascadia experienced one of those slow events, and the Canadian Geological Survey issued a public warning based on increased tremor activity,” Shelly noted. “The survey announced that there was a greater likelihood of a major earthquake in the next two or three weeks based on the activity of the tremor. Fortunately, the earthquake didn’t happen, but the real utility of the warning was to get people thinking about earthquake hazard in that region. It shows that tremor is starting to be used for earthquake forecasting.”

Seismologist Satoshi Ide of the University of Tokyo is the third co-author on the Nature study, which was supported by the National Science Foundation.

From Stanford University

Scientists at The Scripps Research Institute and the Salk Institute for Biological Studies are reporting a possible answer to a longstanding question in research on the origins of life on Earth–how did the first amino acids form the first peptides?

Peptides and proteins are strings of amino acid building blocks, and they are one of the most important classes of biological molecules found in living things today. Fifty years of chemical research on the origins of life has shown that amino acids could have formed spontaneously on the early Earth environment or could have been introduced onto the early Earth from meteorites.

”There are lots of ways to make amino acids,” says Professor M. Reza Ghadiri, Ph.D., who is a member of The Skaggs Institute for Chemical Biology at Scripps Research. ”But the question is, how do you couple them together?”

Ghadiri and Luke Leman, who is a member of the Kellogg School of Science and Technology at Scripps Research, worked out one possible solution with Leslie Orgel of the Salk Institute. In the latest issue of the journal Science, Leman, Ghadiri, and Orgel suggest that the missing link is a chemical component of volcanic gas known as carbonyl sulfide.

Carbonyl sulfide is present in volcanic gasses and deep sea vent emissions today, and since these geological phenomena were prominent features on the early Earth, it is reasonable to assume that the gas was present.

In their report, the scientists demonstrate that the gas can bring about a vigorous chemical reaction that forms peptides under mild aqueous conditions. Within a few minutes of introducing the gas to a reaction vessel containing amino acids, they observed high yields of di-, tri-, and tetra-peptides. They carried out the reaction in the presence of air, without air, and with and without other ingredients like metal ions, and they found peptides formed readily under all these conditions.

”It’s really efficient, actually,” says Ghadiri. ”This addresses a very important question that we did not have a real good answer for.”

Life–What We Know, and What We Don’t

The question of how life originated is one of the most interesting gaps in our knowledge–interesting perhaps because we know approximately when it occurred, but we do not know how it occurred.

The earliest fossils scientists have found are stromatolites–large clumps of cyanobacteria that grew in abundance in the ancient world over 3.5 billion years ago in what is now western Australia. These most likely evolved from some simpler life forms because, like all modern life, cyanobacteria are highly sophisticated living organisms–with cell walls, complex metabolism, and DNA genes. The question of the origins of life is: what came before the stromatolites?

Research on the origins of life has suggested the notion of an ancient RNA world–one in which RNA genes stored genetic information (something done by DNA today), carried out the chemistry necessary for life, and formed the essential physical structures of life (something done primarily by proteins today).

But how did that RNA world come about?

”Anybody who thinks they know the solution to this problem [of the origin of life] is deluded,” says Orgel.

”But,” he adds, ”anybody who thinks this is an insoluble problem is also deluded.”

One possible approach to the problem of life’s origins is to ask the question scientifically rather than historically– how can life emerge rather than how did life emerge. In order to address this, scientists try to determine experimentally what is chemically feasible and what could have occurred on the prebiotic earth.

One possibility, which was suggested in the 1920s by the Russian scientist A.I. Oparin, is that life emerged in its most primitive forms from minerals, metals, and the elements carbon, hydrogen, oxygen, and nitrogen, which were combined into amino acids, nucleotides, and the other the building blocks of life under the violent energy of lightning, solar radiation, comet impacts, and volcanic events that were present.

In 1953, this theory was given a boost when a paper was published in Science by Stanley L. Miller, who is Professor Emeritus at the University of California, San Diego. In the paper, Miller described an experiment he devised with Harold C. Urey–now called the Miller and Urey experiment–that gave experimental underpinnings to Oparin’s ideas.

In the experiment, Miller boiled H2O, CH4,H2, and NH3 gases in a glass apparatus containing a pair of tungsten electrodes. He subjected the chemicals to an electric discharge, intended to simulate conditions on the early Earth, and he collected and analyzed the molecules that formed–which included the amino acids alanine, glycine, and a few others. In the years since, several other investigators have expanded on the Miller–Urey experiment to demonstrate the formation and chemistry of many of the common biological amino acids, sugars, and nucleotides. Orgel, who is a long-time investigator in the field, has done pioneering research on the prebiotic chemistry of nucleotides.

This latest study is an advance because previous attempts to demonstrate the formation of peptides on early Earth depended on reaction schemes that were less plausible or were not as efficient. Next, the team plans to examine carbonyl sulfide’s reactive properties further and see if the gas can bring about other chemical reactions that are relevant to prebiotic chemistry.

From The Scripps Research Institute

Just as explorers once searched the vast reaches of Africa’s Nile River for clues to its behavior and ultimate source, modern-day scientists are searching Antarctica for its hidden lakes and waterways that can barely be detected at the surface of the ice sheet. In a new study, researchers have unearthed how water from this vast subglacial system contributes to the formation of ice streams, and how it plays a crucial role in transporting ice from the remote interior of Antarctica toward the surrounding ocean. Water flowing from this network of under-ice lakes, they say, ultimately affects climate and global sea level.

A research team led by geophysicists Robin Bell and Michael Studinger from the Lamont-Doherty Earth Observatory of Columbia University in New York City, discovered four large, subglacial lakes miles beneath the Antarctic ice sheet’s surface. The team was able to link these lakes for the first time to a fast flowing ice stream above and establish that within this 170-mile wide area the lakes contribute to the creation of a major ice stream. The team, which includes scientists from NASA, the University of New Hampshire, Durham, and the University of Washington, Seattle, published their results in the Feb. 22 issue of Nature.

“This connection of major subglacial lakes to the accelerated pace of ice movement deep in Antarctica’s interior is a key piece of the ice sheet stability puzzle,” said co-author Christopher Shuman, a physical scientist in the Cryospheric Science Branch at NASA’s Goddard Space Flight Center, Greenbelt, Md. “Given the remoteness of the area, we could not have put the picture together without multiple types of satellite data.”

Ice streams are large, fast-flowing features within ice sheets that transport land-based ice and meltwater to the ocean. One such stream, the Recovery Glacier ice stream, annually drains the equivalent of eight percent of the huge East Antarctic Ice Sheet, an area larger than the continental United States. The associated Recovery drainage basin, virtually unexplored since an American-led Antarctic ice sheet research trek over 40 years ago, funnels an estimated 35 billion tons of ice into the Weddell Sea annually.

The scientists used a remote sensing technology called interferometric synthetic aperture radar from the Canadian Space Agency’s RADARSAT instrument to measure the speed of the ice flow. They also used visible imagery from sensors aboard NASA’s Terra and Aqua satellites and high-resolution laser data from NASA’s Ice Cloud and Land Elevation Satellite to capture small changes in the landscape characteristics of the ice stream indicating the presence of subglacial lakes beneath the ice.

Not only did the scientists find four new lakes, they discovered that the lakes coincide with the origin of tributaries of the Recovery Glacier ice stream. Upstream of the lakes, the ice sheet moves at just a few feet a year; downstream the flow increases to a third of a mile each year. The research team concluded that the lakes provide a reservoir of water that lubricates the bed of the stream, which speeds the flow of ice, and prevents the base of the sheet from freezing to the bedrock.

“It’s almost as if the lakes are capturing the geothermal energy from the entire basin and releasing it to the ice stream,” said lead author Bell, a senior research scientist at the Lamont-Doherty Earth Observatory. “They power the engines that drive ice sheet collapse. The more we learn about the lakes, the more we realize how important they are to ice sheet stability.”

The team’s work also suggests that subglacial lakes play a role in sea-level rise as well as regional and global climate change. “Here we found that meltwater at the base of the ice sheet speeds the flow of Recovery ice to the oceans. In turn, that contributes to higher sea levels worldwide,” said Shuman. “Floods have been known to originate from the interior of the ice sheet in the past, possibly from systems like these subglacial lakes. These sudden outbursts of fresh water could potentially interfere with nearby ocean currents that redistribute heat around the globe and could disrupt the Earth’s climate system.”

From NASA

Researchers at Rensselaer Polytechnic Institute have discovered what likely triggered the eruption of a “supervolcano” that coated much of the western half of the United States with ash fallout 760,000 years ago.

Using a new technique developed at Rensselaer, the team determined that there was a massive injection of hot magma underneath the surface of what is now the Long Valley Caldera in California some time within 100 years of the gigantic volcano’s eruption. The findings suggest that this introduction of hot melt led to the immense eruption that formed one of the world’s largest volcanic craters or calderas.

The research, which is featured in the March 2007 edition of the journal Geology, sheds light on what causes these large-scale, explosive eruptions, and it could help geologists develop methods to predict such eruptions in the future, according to David Wark, research professor of earth and environmental sciences at Rensselaer and lead author of the paper.

The 20-mile-long Long Valley Caldera was created when the supervolcano erupted. The geologists focused their efforts on Bishop Tuff, an expanse of rock that was built up as the hot ash cooled following the eruption. The researchers studied the distribution of titanium in quartz crystals in samples taken from Bishop Tuff.

A team from Rensselaer previously discovered that trace levels of titanium can be analyzed to determine the temperature at which the quartz crystallized. By monitoring titanium, Wark and his colleagues confirmed that the outer rims of the quartz had formed at a much hotter temperature than the crystal interiors. The researchers concluded that after the interiors of the quartz crystals had grown, the magma system was “recharged” with an injection of fresh, hot melt. This caused the quartz to partly dissolve, before starting to crystallize again at a much higher temperature.

Analyses of titanium also revealed that the high-temperature rim-growth must have taken place within only 100 years of the massive volcano’s eruption. This suggests that the magma recharge so affected the physical properties of the magma chamber that it caused the supervolcano to erupt and blanket thousands of square miles with searing ash.

“The Long Valley Caldera has been widely studied, but by utilizing titanium in quartz crystals as a geothermometer we were able to provide new insight into the reasons for its last huge eruption,” Wark said. “This research will help geologists understand how supervolcanoes work and what may cause them to erupt, and this in turn may someday help predict future eruptions.”

From Rensselaer Polytechnic Institute

Scientists using NASA satellite and rainfall data have linked the recent El Nino to the greatest rise in wildfire activity in Indonesia since the record-breaking 1997-98 El Nino.

As rainfall sharply decreased during the last quarter of 2006 across the dense tropical rainforests of Sumatra, Kalimantan, and Malaysia, the land became exceptionally dry. This allowed wildfires to quickly spread, releasing large amounts of soot and tiny dust particles called aerosols that brought unhealthy pollution levels to the area.

The Measurements of Pollution in the Troposphere (MOPITT) instrument aboard NASA’s Terra satellite tracked the wildfire pollution plumes as they spread from the Indonesian islands into the Indian Ocean from September through November 2006, and measured the associated increases in atmospheric carbon monoxide levels.

“Droughts over Indonesia are often brought on by a shift in the atmospheric circulation over the tropical Pacific associated with El Nino conditions,” said David Edwards, MOPITT project leader at the National Center for Atmospheric Research, Boulder, Colo. “Although the current El Nino is rather weak compared to that of 1997-98, we have found dramatic increases in wildfire activity and corresponding pollution.”

Using MOPITT, Edwards and his team noted a distinct spike in carbon monoxide levels across much of the Southern Hemisphere from the large number of Indonesian fires at the end of 2006, greater than that associated with any El Nino event since 1997-98. The recent increase in wildfires was also captured by another instrument, the Moderate Resolution Imaging Spectroradiometer, on NASA’s Terra and Aqua satellites, while NASA’s Global Precipitation Climatology Project confirmed a decline in Indonesian rainfall during the period.

Despite the number of factors that influence air quality across the region, wildfires play a very significant role. “Even though fires in South America and southern Africa typically produce the greatest amount of carbon monoxide, the pollution from Indonesian fires is likely responsible for most of the year-to-year variation in pollution levels throughout the Southern Hemisphere,” Edwards said. Carbon monoxide is also involved in raising the concentration of ground-level “bad” ozone.

Some burning takes place every year in Indonesia, but the number and intensity of fires depends largely on rainfall and soil moisture conditions during the fire season, which usually runs September through November. Regional forest clearing practices also heighten the risk for wildfire development and spread. As lands are cleared, peat deposits – thick layers of partially decayed vegetation matter – build up. These deposits are vulnerable to wildfire and once ignited often result in a smoldering burn that releases copious amounts of smoke and carbon into the atmosphere until monsoon rains begin, typically in December.

“MOPITT is an especially valuable tool because it monitors carbon monoxide, a good indicator of pollution from combustion that remains in the atmosphere for several weeks, often traveling vast distances,” said Edwards. “Fires also produce large relative changes in atmospheric carbon monoxide levels that are detected quite well by satellites, so that we can easily assess the impact of fires on air quality and pollution levels.”

Carbon monoxide released from wildfires is a major player in regional air quality conditions, but significant amounts of carbon dioxide -the primary greenhouse gas – are also released. As a result, wildfires also have the potential to impact long-term climate.

From NASA