How heavy and light isotopes separate in magma

In the crash-car derby between heavy and light isotopes vying for the coolest spots as magma turns to solid rock, weightier isotopes have an edge, research led by Case Western Reserve University shows.

This tiny detail may offer clues to how igneous rocks form.

As molten rock cools along a gradient, atoms want to move towards the cool end. This happens because hotter atoms move faster than cooler atoms and, therefore, hotter atoms move to the cool region faster than the cooler atoms move to the hot region.

Although all isotopes of the same element want to move towards the cool end, the big boys have more mass and, therefore, momentum, enabling them to keep moving on when they collide along the way.

“It’s as if you have a crowded, sealed room of sumo wrestlers and geologists and a fire breaks out at one side of the room,” said Daniel Lacks, chemical engineering professor and lead author of the paper. “All will try to move to the cooler side of the room, but the sumo wrestlers are able to push their way through and take up space on the cool side, leaving the geologists on the hot side of the room.”

Lacks worked with former postdoctoral researcher Gaurav Goel and geology professor James A. Van Orman at Case Western Reserve; Charles J. Bopp IV and Craig C. Lundstrum, of University of Illinois, Urbana; and Charles E. Lesher of the University of California at Davis. They described their theory and confirming mathematics, computer modeling, and experiments in the current issue of Physical Review Letters.

Lacks, Van Orman and Lesher also published a short piece in the current issue of Nature, showing how their findings overturn an explanation based on quantum mechanics, published in that journal last year.

“The theoretical understanding of thermal isotope separation in gases was developed almost exactly 100 years ago by David Enskog, but there is as yet not a similar full understanding of this process in liquids,” said Frank Richter, who is the Sewell Avery Distinguished Professor at the University of Chicago and a member of the National Academy of Sciences. He was not involved in the research. “This work by Lacks et al. is an important step towards remedying this situation.”

This separation among isotopes of the same element is called fractionation.

Scientists have been able to see fractionation of heavy elements in igneous rocks only since the 1990s, Van Orman said. More sensitive mass spectrometers showed that instead of a homogenous distribution, the concentration ratio of heavy isotopes to light isotopes in some igneous rocks was up to 0.1 percent higher than in other rocks.

One way of producing this fractionation is by temperature.

To understand how this happens, the team of researchers created a series of samples made of molten magnesium silicate infused with elements of different mass, from oxygen on up to heavy uranium.

The samples, called silicate melts, were heated at one end in a standard lab furnace, creating temperature gradients in each. The melts were then allowed to cool and solidify.

The scientists then sliced the samples along gradient lines and dissolved the slices in acid. Analysis showed that no matter the element, the heavier isotopes slightly outnumbered the lighter at the cool end of the gradient.

Computer simulations of the atoms, using classical mechanics, agreed with the experimental results.

“The process depends on temperature differences and can be seen whether the temperature change across the sample is rapid or gradual,” Lacks said.

Thermal diffusion through gases was one of the first methods used to separate isotopes, during the Manhattan Project. It turns out that isotope fractionation through silicate liquids is even more efficient than through gases.

“Fractionation can occur inside the Earth wherever a sustained temperature gradient exists,” Van Orman said. “One place this might happen is at the margin of a magma chamber, where hot magma rests against cold rock. Another is nearly 1,800 miles inside the Earth, at the boundary of the liquid core and the silicate mantle.”

The researchers are now adding pressure to the variables as they investigate further. This work was done at atmospheric pressure but where the Earth’s core and mantle meet, the pressure is nearly 1.4 million atmospheres.

Lacks and Van Orman are unsure whether high pressure will result in greater or lesser fractionation. They can see arguments in favor of either.

Study: Evolution of earliest horses driven by climate change

<IMG SRC="/Images/337210357.jpg" WIDTH="348" HEIGHT="450" BORDER="0" ALT="This is an artist's reconstruction of Sifrhippus sandrae (right) touching noses with a modern Morgan horse (left) that stands about 5 feet high at the shoulders and weighs about 1,000 pounds. Sifrhippus was the size of a small house cat (about 8.5 pounds) at the beginning of the Eocene (approximately 55.8 million years ago) and is the earliest known horse. – Danielle Byerley, Florida Museum of Natural History.”>
This is an artist’s reconstruction of Sifrhippus sandrae (right) touching noses with a modern Morgan horse (left) that stands about 5 feet high at the shoulders and weighs about 1,000 pounds. Sifrhippus was the size of a small house cat (about 8.5 pounds) at the beginning of the Eocene (approximately 55.8 million years ago) and is the earliest known horse. – Danielle Byerley, Florida Museum of Natural History.

When Sifrhippus, the earliest known horse, first appeared in the forests of North America more than 50 million years ago, it would not have been mistaken for a Clydesdale. It weighed in at around 12 pounds — and it was destined to get much smaller over the ensuing millennia.

Sifrhippus lived during the Paleocene-Eocene Thermal Maximum, a 175,000-year interval of time some 56 million years ago in which average global temperatures rose by about 10 degrees Fahrenheit, caused by the release of vast amounts of carbon into the atmosphere and oceans.

About a third of mammal species responded with significant reduction in size during the PETM, some by as much as one-half. Sifrhippus shrank by about 30 percent to the size of a small house cat (about 8.5 pounds) in the PETM’s first 130,000 years and then rebounded to about 15 pounds in the final 45,000 years of the PETM.

Scientists have assumed that rising temperatures or high concentrations of carbon dioxide primarily caused the phenomenon in mammals during this period, and new research led by Ross Secord of the University of Nebraska-Lincoln and Jonathan Bloch of the Florida Museum of Natural History at the University of Florida in Gainesville offers new evidence of the cause-and-effect relationship between temperature and body size. Their findings also offer clues to what might happen to animals in the near future from global warming.

In a paper to be published in the Feb. 24 issue of the international journal Science, Secord, Bloch and colleagues used measurements and geochemical composition of fossil mammal teeth to document a progressive decrease in Sifrhippus‘ body size that correlates very closely to temperature change over a 130,000-year span.

Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History, said multiple trails led to the discovery.

One was the fossils themselves, recovered from the Cabin Fork area of the southern Bighorn Basin near Worland, Wyo. Stephen Chester, then an undergraduate student at Florida, now an anthropology Ph.D. candidate at Yale and a co-author on the paper, had the task of measuring the horses’ teeth. What he found when he plotted them through time caught Bloch and Secord by surprise.

“He pointed out that the first horses in the section were much larger than those later on,” Bloch recalled. “I thought something had to be wrong, but he was right — and the pattern became more robust as we collected more fossils.”

A postdoctoral researcher in Bloch’s lab for the first year of the project, Secord performed the geochemical analysis of the oxygen isotopes in the teeth. What he found provided an even bigger surprise.

“It was absolutely startling when Ross pulled up the first oxygen isotope data,” Bloch said. “We looked at the curve and we realized that it was exactly the same pattern that we were seeing with the horse body size.

“For the first time, going back into deep time — going back tens of millions of years — we were able to show that indeed temperature was causing essentially a one-to-one shift in body size within this lineage of horse. Because it’s over a long enough time, you can argue very strongly that what you’re looking at is natural selection and evolution — that it’s actually corresponding to the shift in temperature and driving the evolution of these horses.”

Secord, who came to UNL in 2008 as an assistant professor of Earth and atmospheric sciences and curator of vertebrate paleontology at the University of Nebraska State Museum, said the finding raises important questions about how plants and animals will respond to rapid change in the not-too-distant future.

“This has implications, potentially, for what we might expect to see over the next century or two, at least with some of the climate models that are predicting that we will see warming of as much as 4 degrees Centigrade (7 degrees Fahrenheit) over the next 100 years,” he said.

Those predictions are based largely on the 40 percent increase of atmospheric carbon dioxide levels (from 280 to 392 parts per million) since the start of the Industrial Revolution in the mid-19th century.

Ornithologists, Secord said, have already started to notice that there may be a decrease in body size among birds.

“One of the issues here is that warming (during the PETM) happened much slower, over 10,000 to 20,000 years to get 10 degrees hotter, whereas now we’re expecting it to happen over a century or two,” Secord said. “So there’s a big difference in scale and one of the questions is, ‘Are we going to see the same kind of response?’ Are animals going to be able to keep up and readjust their body sizes over the next couple of centuries?”

Increased temperatures are not the only change animals will have to adapt to, Secord said. Greenhouse experiments show that increased atmospheric carbon dioxide lowers the nutritional content of plants, which he said could have been a secondary driver of dwarfism during the PETM.

From Bass Strait to the Indian Ocean — tracking a current

Deep-diving ocean “gliders” have revealed the journey of Bass Strait water from the Tasman Sea to the Indian Ocean.

Deployed in 2010 and 2011, the gliders have also profiled a 200-metre tall wall of water at the core of long-lived ocean eddies formed from the East Australian Current.The study, by University of Technology Sydney and CSIRO oceanographers, revealed the value of new sensors being deployed by Australia’s Integrated Marine Observing System.

“We’re getting a terrific amount of data that is opening up a very big window on Australia’s oceans,” UTS scientist Dr Mark Baird said.

Dr Baird was the lead author of a paper published this week in Geophysical Research Letters. Dr Baird is a Research Fellow with UTS Plant Functional Biology and Climate Change Cluster.

“In this case, we have seen for the first time a 200-metre tall, 40 kilometre wide disc formed from water that originated in Bass Strait that amazingly remains undiluted as it travels hundreds of kilometres,” he said.

“This new discovery is a clear example of the benefits arising from a significantly enhanced technical ability to explore our oceans and identify features relevant to marine ecosystems and climate.”Scientists have known that salty Bass Strait water, with its unique chemical signature, flows into the Tasman Sea north-east of Flinders Island, sinking to a depth of 400-800 metres in a feature referred to as the Bass Strait Cascade.

However, the porpoising action of the $200,000 pre-programmed ocean gliders has given scientists data to a depth of 1000 metres and a detailed insight into anti-clockwise rotating warm-core eddies that regulate ocean conditions and influence the ocean food chain.

Co-author and leader of these Integrated Marine Observing System deployments, CSIRO Wealth from Oceans scientist Ken Ridgway, said the gliders were programmed to sample across the East Australian Current and through long-lived ocean eddies up to 200 kilometres across that form off New South Wales.

“East of Tasmania, we found bodies of water entrained in the ocean eddies that were originally formed six months previously in Bass Strait and that were up to 40 kilometres wide and 200-300 metres in height,” Mr Ridgway said.

“Further measurements show that at least some of this Bass Strait water makes the journey past southern Tasmania and possibly thousands of kilometres into the Indian Ocean.”

The $230M Integrated Marine Observing System has successfully deployed a range of observing equipment in the oceans around Australia, and is making all of the data freely and openly available through the IMOS Ocean Portal [external link] for the benefit of Australian marine and climate science as a whole.

The Bass Strait study was part-funded through the Australian Climate Change Science Program, a joint initiative of CSIRO, the Bureau of Meteorology and the Department of Climate Change and Energy Efficiency with further support from the Australian Research Council and the Sydney Institute of Marine Science.

IMOS is supported by the Australian Government through the National Collaborative Research Infrastructure Strategy and the Super Science Initiative.

Geological cycle causes biodiversity booms and busts every 60 million years, research suggests

A mysterious cycle of booms and busts in marine biodiversity over the past 500 million years could be tied to a periodic uplifting of the world’s continents, scientists report in the March issue of The Journal of Geology.

The researchers discovered periodic increases in the amount of the isotope strontium-87 found in marine fossils. The timing of these increases corresponds to previously discovered low points in marine biodiversity that occur in the fossil record roughly every 60 million years. Adrian Melott, a Professor of Physics and Astronomy at the University of Kansas and the study’s lead author, thinks these periodic extinctions and the increased amounts Sr-87 are linked.

“Strontium-87 is produced by radioactive decay of another element, rubidium, which is common in igneous rocks in continental crust,” Melott said. “So, when a lot of this type of rock erodes, a lot more Sr-87 is dumped into the ocean, and its fraction rises compared with another strontium isotope, Sr-86.”

An uplifting of the continents, Melott explains, is the most likely explanation for this type of massive erosion event.

“Continental uplift increases erosion in several ways,” he said. “First, it pushes the continental basement rocks containing rubidium up to where they are exposed to erosive forces. Uplift also creates highlands and mountains where glaciers and freeze-thaw cycles erode rock. The steep slopes cause faster water flow in streams and sheet-wash from rains, which strips off the soil and exposes bedrock. Uplift also elevates the deeper-seated igneous rocks where the Sr-87 is sequestered, permitting it to be exposed, eroded, and put into the ocean.”

The massive continental uplift suggested by the strontium data would also reduce sea depth along the continental shelf where most sea animals live. That loss of habitat due to shallow water, Melott and collaborators say, could be the reason for the periodic mass extinctions and periodic decline in diversity found in the marine fossil record.

“What we’re seeing could be evidence of a ‘pulse of the earth’ phenomenon,” Melott said. “There are some theoretical works which suggest that convection of mantle plumes, rather like a lava lamp, should be coordinated in periodic waves.” The result of this convection deep inside the earth could be a rhythmic throbbing-almost like a cartoon thumb smacked with a hammer-that pushes the continents up and down.

Melott’s data suggest that such pulses likely affected the North American continent. The same phenomenon may have affected other continents as well, but more research would be needed to show that, he says.

Tohoku grim reminder of potential for Pacific Northwest megaquake

The March 11, 2011 Tohoku earthquake is a grim reminder of the potential for another strong-motion mega-earthquake along the Pacific Northwest coast, geophysicist John Anderson of the University of Nevada, Reno told members of the American Association for the Advancement of Science in a lecture at their annual conference in Vancouver, B.C. Sunday.

“The Cascadia fault line, which runs from southern Canada all the way to Northern California, could have much stronger ground-motions than those observed in Japan,” Anderson, a professor of geophysics, said. “The Tohoku earthquake, while only half the length of Cascadia, is an analog for an earthquake that could happen here in the northwestern United States and southwestern British Columbia.”

Both Japan and Cascadia sit above subduction zones that dip at a low angle beneath the land. One might consider them roughly mirror images, he said.

“In this mirror image, one can see that if the same earthquake occurred in Cascadia, the fault would rupture to a significant distance inland, since the Cascadia trench sits much closer to the coastline than the trench off the coast of Japan, Anderson said. “Some models predict that a Cascadia earthquake will not rupture so far under the land, but if it does, the data from the Tohoku earthquake predict stronger ground motions along our west coast than those seen in Japan. In any case, the ground motions from Tohoku are critical for understanding the seismic hazard here in Vancouver, and in Seattle, and Portland, and Eureka and all points in between.”

In Cascadia, the last great earthquake occurred on January 26, 1700. Based on the size of the tsunami, the magnitude of that earthquake was about magnitude 9.0.

“Although the average interval is apparently larger, earthquakes of this size in the past may have recurred with intervals of as small as about 300 years. So it would not be a scientific surprise if such an event were to occur in the near future,” Anderson said. “If you live in the Pacific northwest, look at the videos of Tohoku as a reminder to be prepared for an earthquake and tsunami.”

Anderson, who studies strong ground-motions, spent nine months recently as a visiting research professor at the prestigious Tokyo University, home of one of the world’s premier seismology programs. Before coming to the Universtiy of Nevada, Reno in 1998, he earned his doctorate in geophysics from Columbia University and has held appointments at the California Institute of Technology, University of Southern California and the University of California at San Diego.

In his presentation at the AAAS conference, about the strong ground motions in the Tohoku earthquake, he discusses the significance of the data, the effects of the source on the nature of the data, the effects of site response, and some discussion of the engineering effects.

“There have of course been other mega-earthquakes, but this is by far the best-recorded,” he said. “The Japanese event will undoubtedly stand as the best-recorded megaquake for a long time to come, both because megaquakes are rare and because no place is as well instrumented as the islands of Japan.”

For instance, the strong ground motions that could be generated along Cascadia, unfortunately, might not be observed nearly as thoroughly, since the strong motion instrumentation in most of the Cascadia region is sparse compared to Japan.

Anderson said that in spite of the occasional records with high accelerations, damage to structures from the shaking in Tohoku was reduced by high building standards, and because the ground velocities caused by the earthquake were not high enough to cause damage even at sites with peak acceleration over 1g.

Expert panel deliberates hydraulic fracturing in shale gas development

The use of hydraulic fracturing in shale gas development took center stage Friday as a panel of U.S. and Canadian experts discussed the contentious practice in a three-hour symposium hosted by the American Association for the Advancement of Science (AAAS).

The panel, moderated by Dr. Raymond L. Orbach, former Under Secretary for Science in the U.S. Department of Energy, addressed concerns related to the role of hydraulic fracturing in shale gas production, which has at once been heralded as a game-changer for North American energy supplies and a threat to drinking water and air quality.

Hydraulic fracturing involves the high-pressure injection of water, sand and chemicals into a shale seam, which causes the rock to shatter, releasing natural gas. The process is conducted after a well bore has been drilled and lined with concrete to prevent communication between the deep, gas-bearing shale and shallow freshwater aquifers.

The practice, often used in tandem with horizontal drilling, has been in use for decades, but has come under scrutiny from environmentalists and others who fear it poses a threat to public health.

Orbach, now Director of the Energy Institute at The University of Texas at Austin, decried the divisive tone of public discourse over hydraulic fracturing, which he characterized as “driven largely by fear and emotion, rather than by science and facts.”

Dr. Charles “Chip” Groat, a geology professor at The University of Texas at Austin and an associate director at the Energy Institute, presented findings from a new study of shale gas development in the Barnett, Marcellus and Haynesville Shales.

The study, which the Institute funded, found no evidence of a direct link between hydraulic fracturing and groundwater contamination.

“Many reports of groundwater contamination occur in conventional oil and gas operations, often caused by poor well-bore casing or cement construction,” Groat said. “These problems are not unique to hydraulic fracturing.”

Researchers also determined that natural gas found in water wells often can be traced to natural sources, and likely was present before the onset of shale gas operations, Groat added.

Other participants in Friday’s AAAS symposium included Dr. John Clague, a professor at Simon Fraser University who studies earthquakes and other natural hazards; Dr. David Layzell, Executive Director of the Institute for Sustainable Energy, Environment and Economy (ISEEE) at the University of Calgary; and Dr. Danny Reible, an engineering professor at The University of Texas at Austin who studies the fate of contaminants and devises risk mitigation measures.

While panelists acknowledged numerous concerns related to hydraulic fracturing, and agreed that additional scientific research on the practice is warranted, the consensus view was that none of the problems identified thus far are insurmountable.

“Certainly, there are some trouble spots, especially with respect to surface issues, such as the handling of flow-back water,” said Reible. “But most of these problems are manageable.”

Dr. John Clague, from Simon Fraser University, said the re-injection of waste water produced from hydraulic fracturing likely triggered seismic activity in the Horn River area in northeastern British Columbia, but that the threat to Vancouver and other populated areas was “negligible.”

Still, Clague said he supports a temporary suspension of shale gas operations until scientists complete additional research on hydraulic fracturing’s effect on the environment.

The University of Calgary’s Layzell said the public debate over shale gas development “raises the bar” about the impact of hydraulic fracturing on the environment.

“We need to ask ourselves, ‘What is required to get hydraulic fracturing right?’ ” Layzell said.

Moreover, the issue presents an opportunity to share knowledge and build consensus on how to achieve a more sustainable energy future, he added.

Building blocks of early Earth survived collision that created moon

This is a photograph of a complete section of a komatiite lava flow that solidified on an ocean floor 2.82 billion years ago. Komatiites can provide extremely valuable evidence of the distant geological past of our planet. -  Igor Puchtel, UMD
This is a photograph of a complete section of a komatiite lava flow that solidified on an ocean floor 2.82 billion years ago. Komatiites can provide extremely valuable evidence of the distant geological past of our planet. – Igor Puchtel, UMD

Unexpected new findings by a University of Maryland team of geochemists show that some portions of the Earth’s mantle (the rocky layer between Earth’s metallic core and crust) formed when the planet was much smaller than it is now, and that some of this early-formed mantle survived Earth’s turbulent formation, including a collision with another planet-sized body that many scientists believe led to the creation of the Moon.

“It is believed that Earth grew to its current size by collisions of bodies of increasing size, over what may have been as much as tens of millions of years, yet our results suggest that some portions of the Earth formed within 10 to 20 million years of the creation of the Solar System and that parts of the planet created during this early stage of construction remained distinct within the mantle until at least 2.8 billion years ago.” says UMD Professor of Geology Richard Walker, who led the research team.

Prior to this finding, scientific consensus held that the internal heat of the early Earth, in part generated by a massive impact between the proto-Earth and a planetoid approximately half its size (i.e., the size of Mars), would have led to vigorous mixing and perhaps even complete melting of the Earth. This, in turn, would have homogenized the early mantle, making it unlikely that any vestiges of the earliest-period of Earth history could be preserved and identified in volcanic rocks that erupted onto the surface more than one and a half billion years after Earth formed.

However, the Maryland team examined volcanic rocks that flourished in the first half of Earth’s history, called komatiites, and found that these have a different type of composition than what they, or anyone, would have, expected. Their findings were just published in the journal Science: “182W Evidence for Long-Term Preservation of Early Mantle Differentiation Products,” by Mathieu Touboul, Igor S. Puchtel, and Richard J. Walker, University of Maryland. Their laboratory and work are supported by funding from the National Science Foundation and NASA.

An Isotopic Signature

“We have discovered 2.8 billion year old volcanic rocks from Russia that have a combination of isotopes of the chemical element tungsten that is different from the combination seen in most rocks — different even from the tungsten filaments in incandescent light bulbs,” says the first author, Touboul, a research associate in the University of Maryland’s Department of Geology. “We believe we have detected the isotopic signature of one of the earliest-formed portions of the Earth, a building block that may have been created when the Earth was half of its current mass.”

As with many other chemical elements, tungsten consists of different isotopes. All isotopes of an element are characterized by having the same number of electrons and protons but different numbers of neutrons. Therefore, isotopes of an element are characterized by identical chemical properties, but different mass and nuclear properties. Through radioactive decay, some unstable (radioactive) isotopes spontaneously transform from one element into another at a specific, but constant, rate. As a result, scientists can use certain radioactive isotopes to determine the age of certain processes that happen within the Earth, as well as for dating rocks.

For the Maryland team the tungsten isotope182-tungsten (one of the five isotopes of tungsten) is of special interest because it can be produced by the radioactive decay of an unstable isotope of the element hafnium, 182-hafnium.

According to the UMD team, the radioactive isotope 182-hafnium was present at the time our Solar System formed, but is no longer present on Earth today. Indeed, decay of 182-hafnium into 182-tungsten is so rapid (~9 million year half-life) that variations in the abundance of 182-tungsten relative to other isotopes of tungsten can only be due to processes that occurred very early in the history of our Solar System, they say.

The Maryland geochemists found that the 2.8 billion year old Russian komatiites from Kostomuksha have more of the tungsten isotope 182-W than normal. “This difference in isotopic composition requires that the early Earth formed and separated into its current metallic core, silicate mantle, and perhaps crust, well within the first 60 million years after the beginning of our 4.57-billion-year-old Solar System,” says Touboul.

“In itself this is not new,” he says, “but what is new and surprising is that a portion of the growing Earth developed the unusual chemical characteristics that could lead to the enrichment in 182-tungsten; that this portion survived the cataclysmic impact that created our moon; and that it remained distinct from the rest of the mantle until internal heat melted the mantle and transported some of this material to the surface 2.8 billion years ago, allowing us to sample it today.”

Higher Precision Yields New Findings, Insights

The UMD team explained that they were able to conduct this research because they have developed new techniques that allow the isotopic composition of tungsten to be measured with unprecedented precision. “We do this by chemically separating and purifying the tungsten from the rocks we study. We then use an instrument termed a mass spectrometer to measure the isotopic composition of the tungsten”

According to the researchers their new findings have far reaching implications for understanding how Earth formed; how it differentiated into a metallic core, rocky mantle and crust; and the dynamics of change within the mantle.

“These findings indicate that the Earth’s mantle has never been completely melted and homogenized, and that convective mixing of the mantle, even while Earth was growing, was evidently very sluggish,” says Walker. “Many questions remain. The rocks we studied are 2.8 billion years old. We don’t know whether the portion of the Earth with this unusual isotopic composition or signature can be found in much younger rocks. We plan to analyze some modern volcanic rocks in the near future to assess this.”

Mother of pearl tells a tale of ocean temperature, depth

Nacre — or mother of pearl, scientists and artisans know, is one of nature’s amazing utilitarian materials.

Produced by a multitude of mollusk species, nacre is widely used in jewelry and art. It is inlaid into musical instruments, furniture and decorative boxes. Fashioned into buttons, beads and a host of functional objects from pens to flatware, mother of pearl lends a lustrous iridescence to everyday objects.

In recent years, subjecting the material to the modern tools of scientific analysis, scientists have divined the fine points of nacre architecture and developed models to help explain its astonishing durability: 3,000 times more fracture resistant than the mineral from which it is made, aragonite.

Now, in a new report (Thursday, Feb. 16) in the Journal of the American Chemical Society (JACS), scientists from the University of Wisconsin-Madison show that nacre can also be deployed in the interest of science as a hard-wired thermometer and pressure sensor, revealing both the temperature and ocean depth at which the material formed.

“We found a strong correlation between the temperature at which nacre was deposited during the life of the mollusk and water temperature,” explains Pupa Gilbert, a UW-Madison professor of physics and chemistry and the senior author of the new JACS report. “All other (temperature) proxies are based on chemical analyses and the relative concentration of different elements or isotopes. This could be our first physical proxy, in which the microscopic structure of the material tells us the maximum temperature and maximum pressure at which the mollusk lived.”

The new study was conducted using mother of pearl from modern mollusks, but Gilbert notes that nacre is widespread in the fossil record going back 450 million years. If the techniques used by the Wisconsin group can be applied to fossil nacre, scientists can begin to accurately reconstruct a global record of ancient environments and environmental change.

“If the correlation holds, we would have a thermometer that goes back in time, a paleothermometer of how hot or cold water temperatures were when the nacre formed,” says Gilbert.

The material also holds a distinctive signature-the thickness of the nacre layers – for the water depth at which the material was assembled by a mollusk, potentially providing even more insight into environmental conditions of the present and past.

“These are two independent parameters, measured by different aspects of nacre structure,” the Wisconsin physicist explains. “The maximum temperature can be measured by how disordered the nacre crystal orientations are, while the maximum pressure can be taken from the thickness of the nacre layers.”

Working with UW-Madison graduate student Ian C. Olson, the lead author of the JACS report, Gilbert subjected nacre from eight mollusk species from different environments to a technique capable of mapping the orientation of nacre crystals. From the different shells, they observed uneven thicknesses, widths and angles of the crystalline “bricks” that, together with an organic mortar, are laid down by the mollusk to form mother of pearl.

“We wondered why the shells were so different and concluded that the key parameters to test were the environmental ones, including maximum, minimum and mean annual temperatures as well as maximum and minimum water pressure, which depends on water depth,” says Gilbert.

Comparing the structural maps of nacre from the different mollusks and environmental data from the places where the animals were collected, Olson, Gilbert and their collaborators found an extremely high correlation between the microscopic structural characteristics of their nacre specimens and the temperature and pressure data obtained from the various environments where they were collected.

Microbial oasis discovered beneath the Atacama Desert

Microbes grow in salt crystals below the Atacama Desert. -  Parro et al./CAB/SINC
Microbes grow in salt crystals below the Atacama Desert. – Parro et al./CAB/SINC

Two meters below the surface of the Atacama Desert there is an ‘oasis’ of microorganisms. Researchers from the Center of Astrobiology (Spain) and the Catholic University of the North in Chile have found it in hypersaline substrates thanks to SOLID, a detector for signs of life which could be used in environments similar to subsoil on Mars.

Life is bustling under the driest desert on Earth. A Spanish-Chilean team of scientists have found bacteria and archaea (primitive microorganisms) living two metres below the hypersaline substrates in the Atacama Desert in Chile, according to the journal Astrobiology.

“We have named it a ‘microbial oasis’ because we found microorganisms developing in a habitat that was rich in halite (rock salt) and other highly hygroscopic compounds (anhydrite and perchlorate) that absorb water” explained Victor Parro, researcher from the Center of Astrobiology (INTA-CSIC, Spain) and coordinator of the study.

Furthermore, the substrates where the microbes live favour deliquescence, which means they can attract the limited moisture in the air, condensing it on the surface of the salt crystals. Thin films of water that are a few microns thick are thereby formed.

In this environment, the underground microorganisms grow with everything they need to live: food and water. The species are not very different from others in similar hypersaline environments, but the peculiar thing is that they were discovered at a depth of between 2 and 3 metres, without any oxygen or sunlight.

To carry out this investigation, scientists used an instrument called SOLID (Signs of Life Detector), which was developed by the research team with the aim of using it for future missions on Mars.

The core of SOLID is a biochip -called LDChip- which includes up to 450 antibodies to identify biological material, such as sugar, DNA and protein. Samples can be taken, incubated and processed automatically and the results can be observed in an image with shiny points that show the presence of certain compounds and microorganisms.

Using this technique, the researchers in collaboration with Catholic University of the North in Chile have confirmed the presence of underground archaea and bacteria in the desert. They also took samples from a depth of up to 5 metres and took them to the laboratory, where not only were they able to photograph the microorganisms with the electron microscope, but also ‘brought them into life’ when supplied with water.

Lessons for Mars

“If there are similar microbes on Mars or remains in similar conditions to the ones we have found in Atacama, we could detect them with instruments like SOLID” Parro highlighted.

The researcher explained that saline deposits have been found on the red planet, therefore it is possible to think that there maybe hypersaline environments in its subsoil. “The high concentration of salt has a double effect: it absorbs water between the crystals and lowers the freezing point, so that they can have thin films of water (in brine) at temperatures several degrees below zero, up to minus 20 C.”

The high salt level and lack of water help preserve biological molecules, so that it was possible to find biological products in materials of this type, even though there were no live microorganisms since millions of years ago.

Lava formations in western US linked to rip in giant slab of Earth

Like a stream of air shooting out of an airplane’s broken window to relieve cabin pressure, scientists at Scripps Institution of Oceanography at UC San Diego say lava formations in eastern Oregon are the result of an outpouring of magma forced out of a breach in a massive slab of Earth. Their new mechanism explaining how such a large volume of magma was generated is published in the Feb. 16 issue of the journal Nature.

For years scientists who study the processes underlying the planet’s shifting tectonic plates and how they shape the planet have debated the origins of sudden, massive eruptions of lava at the planet’s surface. In several locations around the world, such “flood basalts” are marked by immense formations of volcanic rock. A famous example is India’s Deccan flood basalt, a formation widely viewed as related to the demise of the dinosaurs 65 million years ago.

Such eruptions are thought to typically occur when the head of a mantle plume, a mushroom-shaped upwelling of hot rock rising from deep within the earth’s interior, reaches the surface. Now Scripps postdoctoral researcher Lijun Liu and geophysics professor Dave Stegman have proposed an alternative origin for the volcanic activity of Oregon’s Columbia River flood basalt.

Liu and Stegman argue that around 17 million years ago the tectonic plate that was subducting underneath the western United States began ripping apart, leading to massive outpourings of magma. Their proposed model describes a dynamic rupture lasting two million years-a quick eruption in geological terms- across the so-called Farallon slab, where the rupture spread across 900 kilometers (559 miles) along eastern Oregon and northern Nevada.

“Only with a break of this scale inside the down-going slab can we reach the present day geometry of mantle we see in the area,” said Liu, “and geochemical evidence from the Columbia River lavas can also be explained by our model.”

“When the slab is first opened there’s a little tear, but because of the high pressure underneath, the material is able to force its way through the hole. It’s like in the movies when a window breaks in an airplane that is at high altitude-since the cabin is at higher pressure, everything gets sucked out the window,” said Stegman, an assistant professor with Scripps’ Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics.

Liu and Stegman came upon their new mechanism by attempting to describe how the complicated structure of the earth’s mantle under the western U.S. developed during the past 40 million years. The final state of their model’s time-evolution matches the present day structure as imaged by the USArray, the National Science Foundation’s transportable seismic network of 400 sensor stations leapfrogging across the United States.

“This paper highlights the importance of interdisciplinary efforts in Earth sciences,” Liu added.