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  • richardmitnick 5:23 pm on May 12, 2016 Permalink | Reply
    Tags: , , Found: surviving evidence of Earth’s formative years, Geology   

    From Carnegie: “Found: surviving evidence of Earth’s formative years” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 12, 2016
    Scientific Area:
    Earth & Planetary Science
    Reference to Person:
    Richard Carlson

    1
    Photographs from Baffin Island fieldwork, courtesy of Don Francis of McGill University.

    New work from a team including Carnegie’s Hanika Rizo and Richard Carlson, as well as Richard Walker from the University of Maryland, has found material in rock formations that dates back to shortly after Earth formed. The discovery will help scientists understand the processes that shaped our planet’s formative period and its internal dynamics over the last 4.5 billion years. It is published* by Science.

    Earth formed from the accretion of matter surrounding the young Sun. The heat of its formation caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.

    Over the subsequent 4.5 billion years of Earth’s evolution, convection in Earth’s interior, like water boiling on a stove, caused deep portions of the mantle to rise upwards, melt, and then separate once again by density. The melts, since they were less dense than the unmelted rock, rose to form Earth’s crust, while the denser residues of the melting sank back downward, altering the mantle’s chemical composition in the process.

    The mantle residues of crust formation were previously believed to have mixed back into the mantle so thoroughly that evidence of the planet’s oldest geochemical events, such as core formation, was lost completely.

    However, the research team—which also included Sujoy Mukhopadhyay and Vicky Manthos of University of California Davis, Don Francis of McGill University, and Matthew Jackson, a Carnegie alumnus now at University of California Santa Barbara—was able find a geochemical signature of material left over from the early melting events that accompanied Earth’s formation. They found it in relatively young rocks both from Baffin Island, off the coast of northern Canada, and from the Ontong-Java Plateau in the Pacific Ocean, north of the Solomon Islands.

    These rock formations are called flood basalts because they were created by massive eruptions of lava. The solidified lava itself is only between 60 and 120 million years old, depending on its location. But the team discovered that the molten material from inside the Earth that long ago erupted to create these plains of basaltic rock owes its chemical composition to events that occurred over 4.5 billion years in the past.

    Here’s how they figured it out:

    They measured variations in these rocks of the abundance of an isotope of tungsten—the same element used to make filaments of incandescent light bulbs. Isotopes are versions of an element in which the number of neutrons in each atom differs from the number of protons. (Each element contains a unique number of protons.) These differing neutron numbers mean that each isotope has a slightly different mass.

    Why tungsten? Tungsten contains one isotope of mass 182 that is created when an isotope of the element hafnium undergoes radioactive decay, meaning its elemental composition changes as it gives off radiation. The time it takes for half of any quantity of hafnium-182 to decay into tungsten-182 is 9 million years. This may sound like a very long time, but is quite rapid when it comes to planetary formation timescales. Rocky planets like Earth or Mars took about 100 million years to form.

    The team determined that the basalts from Baffin Island, formed by a 60-million-year-old eruption from the mantle hot-spot currently located beneath Iceland, and the Ontong-Java Plateau, which was formed by an enormous volcanic event about 120 million years ago, contain slightly more tungsten-182 than other young volcanic rocks.

    Because all the hafnium-182 decayed to tungsten-182 during the first 50 million years of Solar System history, these findings indicate that the mantle material that melted to form the flood basalt rocks that the team studied originally had more hafnium than the rest of the mantle. The likely explanation for this is that the portion of Earth’s mantle from which the lava came had experienced a different history of iron separation than other portions of the mantle (since tungsten is normally removed to the core along with the iron.)

    It was a surprise to the team that such material still exists in Earth’s interior.

    “This demonstrates that some remnants of the early Earth’s interior, the composition of which was determined by the planet’s formation processes, still exist today,” explained lead author Rizo, now at Université du Québec à Montréal.

    “The survival of this material would not be expected given the degree to which plate tectonics has mixed and homogenized the planet’s interior over the past 4.5 billion years, so these findings are a wonderful surprise,” added Carlson, Director of Carnegie’s Department of Terrestrial Magnetism.

    The team’s discovery offers new insight into the chemistry and dynamics that shaped our planet’s formative processes. Going forward, scientists will have to hunt for other areas showing outsized amounts of tungsten-182 with the hope of illuminating both the earliest portion of Earth’s history as well as the place in Earth’s interior where this ancient material is stored.

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    No descriptive captions present

    *Science paper:
    Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

    See the full article here .

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

     
  • richardmitnick 7:31 am on April 21, 2016 Permalink | Reply
    Tags: , , Geology   

    From ANU: “Stories in the stone: Geology students venture into the field” 

    ANU Australian National University Bloc

    Australian National University

    1

    If rocks could speak, they would have a lot to say. Even without a voice, they’re great story-tellers. So long as you know how to listen.

    “I didn’t really get interested in geology until the later years of high school, when I realised that you can tell a story from rocks,” says Eleni Ravanis, an ANU student who has just completed a nine-day geology field trip at Wee Jasper in NSW.

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    As part of the field trip students are learning how to map the type and structure of rocks to understand what has happened in past environments.

    In a limestone structure, students see a story that begins under the sea. In a fold or a fault, they understand the shifting of the Earth’s tectonic plates.

    “It’s pretty cool to infer that just from looking at a rock,” says Eleni.

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    The field trip was also the ultimate Aussie experience for Dutch exchange student, Jesse Zondervan.

    “We’re staying in Wee Jasper at a homestead in the bush with little sheep running around,” he says.

    Each morning the students leave the property and four-wheel drive across steep terrain to the upper reaches of Lake Burrinjuck. They drive past impressive folds and ripples in the Earth before arriving at a geological formation called the “Shark’s Mouth”.

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    The students learn a range of techniques in mapping and structural geology and they admit the course can be demanding.

    “It’s a steep learning curve but I’ve definitely improved my skills in the field,” says Jack Dennison, a former Sydney-sider who moved to Canberra for the well-regarded Earth sciences program.

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    But the best part about the course is the chance to interact with other students and make new friends.

    “It’s been a very intense few days but we’re all in it together,” says Eleni.

    “I’ve made better friends with people I didn’t really know before this course. We all help each other out.”

    And as the students retreat to their homestead to share the stories of the rocks, they have the chance to share some of their own.

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    f you would like to hone your geology skills you might like to try the Introduction to Structural and Field Geology course.

    See the full article here .

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    ANU Campus

    ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

    Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

     
  • richardmitnick 5:34 pm on April 6, 2016 Permalink | Reply
    Tags: , , Geology, ,   

    From phys.org: “Supernovae showered Earth with radioactive debris” 

    physdotorg
    phys.org

    April 6, 2016
    No writer credit found

    1
    Artist’s impression of supernova. Credit: Greg Stewart, SLAC National Accelerator Lab

    An international team of scientists has found evidence of a series of massive supernova explosions near our solar system, which showered the Earth with radioactive debris.

    The scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.

    The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr Anton Wallner from The Australian National University (ANU).

    “We were very surprised that there was debris clearly spread across 1.5 million years,” said Dr Wallner, a nuclear physicist in the ANU Research School of Physics and Engineering. “It suggests there were a series of supernovae, one after another.

    “It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.”

    The team from Australia, the University of Vienna in Austria, Hebrew University in Israel, Shimizu Corporation and University of Tokyo, Nihon University and University of Tsukuba in Japan, Senckenberg Collections of Natural History Dresden and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.

    Some theories suggest cosmic rays from the supernovae could have increased cloud cover.

    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech
    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The scientists believe the supernovae in this case were less than 300 light years away, close enough to be visible during the day and comparable to the brightness of the Moon.

    Although Earth would have been exposed to an increased cosmic ray bombardment, the radiation would have been too weak to cause direct biological damage or trigger mass extinctions.

    The supernova explosions create many heavy elements and radioactive isotopes which are strewn into the cosmic neighbourhood.

    One of these isotopes is iron-60 which decays with a half-life of 2.6 million years, unlike its stable cousin iron-56. Any iron-60 dating from the Earth’s formation more than four billion years ago has long since disappeared.

    The iron-60 atoms reached Earth in minuscule quantities and so the team needed extremely sensitive techniques to identify the interstellar iron atoms.

    “Iron-60 from space is a million-billion times less abundant than the iron that exists naturally on Earth,” said Dr Wallner.

    Dr Wallner was intrigued by first hints of iron-60 in samples from the Pacific Ocean floor, found a decade ago by a group at TU Munich.

    He assembled an international team to search for interstellar dust from 120 ocean-floor samples spanning the past 11 million years.

    The first step was to extract all the iron from the ocean cores. This time-consuming task was performed by two groups, at HZDR and the University of Tokyo.

    The team then separated the tiny traces of interstellar iron-60 from the other terrestrial isotopes using the Heavy-Ion Accelerator at ANU and found it occurred all over the globe.

    The age of the cores was determined from the decay of other radioactive isotopes, beryllium-10 and aluminium-26, using accelerator mass spectrometry (AMS) facilities at DREsden AMS (DREAMS) of HZDR, Micro Analysis Laboratory (MALT) at the University of Tokyo and the Vienna Environmental Research Accelerator (VERA) at the University of Vienna.

    The dating showed the fallout had only occurred in two time periods, 3.2 to 1.7 million years ago and eight million years ago. Current results from TU Munich are in line with these findings.

    A possible source of the supernovae is an ageing star cluster, which has since moved away from Earth, independent work led by TU Berlin has proposed in a parallel publication. The cluster has no large stars left, suggesting they have already exploded as supernovae, throwing out waves of debris.

    More information: Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe, Nature, DOI: 10.1038/nature17196

    The science team:

    A. Wallner, J. Feige, N. Kinoshita, M. Paul, L. K. Fifield, R. Golser, M. Honda, U. Linnemann, H. Matsuzaki, S. Merchel, G. Rugel, S. G. Tims, P. Steier, T. Yamagata & S. R. Winkler

    Affiliations

    Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University (ANU), Canberra, Australian Capital Territory 2601, Australia
    A. Wallner, L. K. Fifield & S. G. Tims
    University of Vienna, Faculty of Physics—Isotope Research, VERA Laboratory, Währinger Straße 17, 1090 Vienna, Austria
    J. Feige, R. Golser, P. Steier & S. R. Winkler
    Institute of Technology, Shimizu Corporation, Tokyo 135-8530, Japan
    N. Kinoshita
    Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
    M. Paul
    Graduate School of Pure and Applied Sciences, University of Tsukuba, Ibaraki 305-8577, Japan
    M. Honda
    Senckenberg Collections of Natural History Dresden, GeoPlasmaLab, Königsbrücker Landstraße 159, Dresden 01109, Germany
    U. Linnemann
    MALT (Micro Analysis Laboratory, Tandem accelerator), The University Museum, The University of Tokyo, Tokyo 113-0032, Japan
    H. Matsuzaki
    Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Helmholtz Institute for Resource Technology, 01328 Dresden, Germany
    S. Merchel & G. Rugel
    Graduate School of Integrated Basic Sciences, Nihon University, Tokyo 156-8550, Japan
    T. Yamagata

    Contributions

    A.W. initiated the study and wrote the main paper together with J.F., M.P. and L.K.F.; all authors were involved in the project and commented on the paper. A.W., with J.F., L.K.F. and S.R.W., organized the Eltanin sediment samples. N.K. and M.P. organized the crust samples. S.M. and U.L. organized the nodules. J.F. and S.M. were primarily responsible for sample preparation of the sediment and nodules and N.K. was responsible for the crusts. A.W., L.K.F. and S.G.T. performed the AMS measurements for 60Fe at the ANU. P.S., S.R.W., J.F. and A.W. performed the 26Al and 10Be measurements at VERA. G.R., S.M. and J.F. performed 10Be measurements at HZDR. N.K., M.H., H.M. and T.Y. performed 10Be measurements at MALT. J.F., A.W. and N.K. performed the data analysis.

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 11:35 am on April 6, 2016 Permalink | Reply
    Tags: , , Geology, Rock falls   

    From Eos: “A Warm Day Can Trigger Rockfalls” 

    Eos news bloc

    Eos

    5 April 2016
    Lucas Joel

    Research on a cliff face in Yosemite National Park finds that when rockfalls happen without an obvious cause, ordinary warming in the Sun could be the culprit.

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    Researchers Brian Collins and Greg Stock download data that indicate how much partially detached granitic slabs on a mountain face have moved as a result of daily temperature variations. Such movement is a precursor to a rockfall. Credit: Valerie Zimmer, National Park Service

    Geologists have long known that earthquakes, along with precipitation and freeze-thaw cycles, can trigger giant slabs of rock to fall from mountain faces, to thunderous effect. Now a research team, following a clue from rock climbers at Yosemite National Park, has shed some light on why rockfalls will sometimes happen in the middle of a clear, sunny day without an obvious cause.

    The reason: Daily, seasonal, and annual temperature fluctuations can cause the granite slabs to slowly peel away, or exfoliate, then suddenly fracture and fall, the scientists reported last week in Nature Geoscience.

    “There’s this hypothesis that thermal stresses could cause rocks to fracture and break and fall. That isn’t anything new—people have been thinking about that for over a hundred years. But it hadn’t been measured,” said Brian Collins, a research civil engineer with the U.S. Geological Survey in Menlo Park, Calif., and a coauthor of the paper.

    Climbers Point the Way

    He and coauthor Greg Stock, who is Yosemite’s first-ever park geologist, had heard stories from Yosemite’s many rock climbers about their climbing gear getting stuck in the cracks of detached granite slabs—or “flakes” as Collins and Stock say—as hot days wore on into cool nights. This gave the duo the idea to climb to a flake and install “crackmeters”—instruments the researchers devised themselves that measure minute changes in crack width over time.

    “This isn’t just [one person who] put the gear in wrong and couldn’t get it back out; lots of people are going through this,” Collins said. “We thought, maybe it’s that the rock flakes are moving back into the cliff, and if that’s the case, maybe it’s measurable.”

    They specifically put the crackmeters in a gap behind a granite flake about 19 meters long, 4 meters wide, and about 15 meters above the park’s valley floor. After 1 month, the crackmeter data indicated the flake, from night to day, was moving “in and out of the wall by up to a centimeter each day,” said Collins. “That was a big huge ‘Wow!’—we had no idea it was going to move that much.”

    Thermal Weathering

    Ultimately, Collins and Stock monitored the crack for 3.5 years. Over that time, they found that crack widths vary seasonally, with the hot summer months producing the widest offsets. They also found that the rock’s outward expansion was cumulative: the flake would move forward more and more each year, building on the previous season’s progress.

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    An exfoliation-type rockfall cascades from Yosemite Valley’s El Capitan on a clear day in October 2010. Credit: Tom Evans

    Millions of people visit Yosemite every year, so the park’s staff has kept thorough records of rockfalls there. These records indicate that spontaneous rockfalls—the kind that happen for no obvious reason—occur most often during the hot summer months. “We discovered that these flakes actually deform quite a bit, much more than we had originally thought, and we’ve been able to link that to how the process of thermal heating can move a flake in and out,” Collins said. Such movement will “eventually lead to fracture,” he added.

    Still, because fracture propagation is nonlinear, it is not possible to predict how far off in the future a flake might pass its threshold and detach, Collins explained.

    “These results are scientifically wonderful, and they have implications for landscape evolution and rockfall hazards in other high mountain areas,” commented landslide expert David Petley of the University of East Anglia in the United Kingdom in a 30 March blog post about the new study.

    “Whilst higher than expected levels of rockfalls have been observed in the summer months in many mountain landscapes, in general I think it has been assumed that this is mostly associated with the melting of ice in cracks. Whilst this ice driven process is undoubtedly still important, Collins and Stock (2016) has given us cause to think about other processes too,” added Petley, whose editorially independent The Landslide Blog is hosted by the American Geophysical Union, publisher of Eos.org.

    In future work, Collins explains, it may be possible to determine “how many [thermal] cycles it takes to eventually fracture the rock,” which might help Yosemite’s staff identify slabs that may be close to collapsing and thus endangering park visitors.

    Rockfall triggering by cyclic thermal stressing of exfoliation fractures

    Science team:
    Brian D. Collins, Greg M. Stock

    Affiliations

    US Geological Survey, Landslide Hazards Program, 345 Middlefield Road, MS-973, Menlo Park, California 94025, USA
    Brian D. Collins
    National Park Service, Yosemite National Park, El Portal, California 95318, USA
    Greg M. Stock

    See the full article here .

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  • richardmitnick 10:02 pm on April 5, 2016 Permalink | Reply
    Tags: , , Geology   

    From Eos: “Massive Ancient Tectonic Slab Found Below the Indian Ocean” 

    Eos news bloc

    Eos

    1 April 2016
    Cody Sullivan

    Scientists discover a surprisingly positioned tectonic plate, buried below the southern Indian Ocean, that spans the entire mantle.

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    Seismic wave velocity structure in the deep Earth revealed through seismic tomography. Earthquakes generate seismic energy near their epicenters (yellow markers), and the energy is recorded at seismic stations around the world (red markers). Seismic waves (depicted as yellow rays emanating from an earthquake beneath Spain) are disrupted as they travel through fast (blue) and slow (red) structures in the Earth. By mapping these anomalous structures on a global scale, researchers have uncovered a previously unidentified tectonic plate that sank into Earth’s mantle more than 130 million years ago beneath the southern Indian Ocean. Credit: Nathan Simmons, using MATLAB.

    A team of researchers recently discovered an ancient relic hidden within Earth: a tectonic plate resting beneath the southern Indian Ocean. Scientists have found other tectonic plates that sank below Eurasia and North America, but here Simmons et al. describe the unique structure of this newly discovered slab, which they named the Southeast Indian Slab (SEIS). The slab has at least one feature scientists have rarely seen before: It maintains its slab-like structure all the way from the upper mantle near Earth’s crust down to the region where the mantle meets the planet’s superheated core. The Farallon plate beneath North America is a well-known example of this—but it was expected to exist and sank much more recently than the SEIS. In addition, not only does the SEIS traverse the entire mantle, but it also becomes more vertical along one end, so much so that it stands almost vertically between the crust and core along the eastern edge, whereas the western portion is more horizontal.

    Researchers can make out structures beneath Earth’s crust by examining the speed at which seismic waves generated by earthquakes and similar Earth-shattering events—known as P and S waves—travel through Earth. Here the researchers used wave data from 12,607 seismic events dating back to the 1960s, collected by 7783 seismic stations around the world, to develop the model that identified the ancient slab.

    Once this tectonic slab was identified, the team looked at the region’s tectonic history over millions of years to determine where and when this plate was on the surface. They determined that the slab was once along the eastern portion of the early supercontinent of Gondwana. Then, sometime during the Triassic or Jurassic period, which stretched from 250 million years ago to 145 million years ago, the slab plunged underneath another plate. They further concluded that the subduction, or the sinking of the Southeast Indian Slab beneath another plate, terminated around 130 to 140 million years ago in the Mesozoic era, around the same time that the tectonic plates under eastern Gondwana began to separate and split up the continent.

    Tectonic plates usually sink down into the mantle at a rate of about 1 centimeter per year or more; they don’t necessarily melt but instead bunch up at the base of the mantle and eventually assimilate or become undetectable as their temperature increases. However, if the researchers accurately estimated the timing of their newly discovered slab’s subduction, this slab must have stalled in a transition zone before descending deeper down into the mantle, allowing the slab to persist in the mantle longer than any other known plate. (Geophysical Research Letters, doi:10.1002/2015GL066237, 2015)

    Citation: Sullivan, C. (2016), Massive ancient tectonic slab found below the Indian Ocean, Eos, 97, doi:10.1029/2016EO049219. Published on 1 April 2016.

    See the full article here .

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  • richardmitnick 5:09 pm on March 18, 2016 Permalink | Reply
    Tags: , , Geology   

    From Eos: “Antarctica Gets a New Gravity Map” 

    Eos news bloc

    Eos

    A comprehensive collection of variation in Earth’s gravity could aid studies of the Antarctic geoid and of Antarctica’s geology and ice sheet dynamics.

    Source: Geophysical Research Letters

    3.18.16
    Sarah Stanley
    Eos@agu.org

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    A new map of Antarctica’s gravity anomalies could help scientists study mountain building in the Transantarctic Mountains. Credit: NASA/Michael Studinger

    The pull of gravity is not even across Earth’s surface; in fact, your weight may change slightly depending on where you stand. The planet’s uneven density gives rise to these gravity anomalies—variations in the strength of gravity over Earth’s surface with respect to the smooth model of normal gravity. These data are much needed in geodesy to construct high-resolution models of Earth’s gravity field. Using these data, the undisturbed mean global sea level (the geoid) can be determined, and it serves as an important reference surface for height measurements and for inferring sea surface topography. Furthermore, by measuring those variations, scientists can glean important geophysical insights about subsurface structures and processes, including the structure of the upper mantle and the tectonic processes that shape Earth’s geological features.

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    Conducting terrestrial gravity measurements in Antarctica is time-consuming (as shown during an observation campaign in central Dronning Maud Land, East Antarctica). Therefore, airborne gravimetry provides the only viable and powerful method to survey extended areas in Antarctica. Credit: M. Scheinert

    Thanks to satellite data, maps of Earth’s gravity strength have become much more complete in recent years but are limited in resolution. However, terrestrial observations—made on the ground, from aircraft, or aboard ships—are still needed for high-resolution maps. But terrestrial observations can be difficult to collect, especially in remote, inhospitable regions of Antarctica.

    Now, by combining many terrestrial data sets, Scheinert et al. have constructed a modern map of gravity anomalies across Antarctica. The map covers 10 million square kilometers—about 73% of the continent—and has a resolution of 10 kilometers.

    To make the map, the team compiled all available terrestrial data from Antarctic gravity studies performed over the past 30 years. These studies employed a wide variety of analytical methods, making it impossible to blend their conclusions into a single product.

    Instead, the researchers focused on the original raw data, combining and processing it using consistent methods. To aid this analysis, they used a global gravity model based on observations made by the European Space Agency’s GOCE satellite.

    ESA/GOCE Spacecraft
    ESA/GOCE Spacecraft

    The resulting map is the most complete gravity map ever created for Antarctica. Shared publicly, it will help researchers complete the geodetic view of Earth’s gravity field and study the continent’s geophysical past and future. It will also enable scientists to gain a better understanding of how the continent’s geological features affect glacier and ice sheet dynamics.

    Additional terrestrial data are needed to close the remaining gaps in the map; for example, there is an especially large gap over the South Pole region. However, the authors say, aircraft data collection could fill in all the major gaps within the next few years. (Geophysical Research Letters, doi:10.1002/2015GL067439, 2016)

    Citation: Stanley, S. (2016), Antarctica gets a new gravity map, Eos, 97, doi:10.1029/2016EO047755. Published on 18 March 2016.

    See the full article here .

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  • richardmitnick 2:57 pm on March 15, 2016 Permalink | Reply
    Tags: , , Dr. Ellen Stofan NASA Chief Scientist, Geology   

    From AGU: “Geology and NASA: An Interview with Dr. Ellen Stofan, NASA Chief Scientist” 

    AGU bloc

    American Geophysical Union

    GeoSpace

    15 March 2016
    Mark Hilverda

    Dr. Ellen Stofan is a planetary scientist, STEM advocate and Chief Scientist at NASA. Her research interests include the geology of Venus, Mars, Titan and Earth and she’s been involved in several planetary missions including Cassini (Radar Team), the proposed Titan Mare Explorer mission, and the Magellan mission to Venus.

    NASA ESA ASI Cassini Spacecraft
    Cassini

    Titan Mare Explorer
    Titan Mare Explorer

    Magellan mission to Venus spacecraft
    Magellan mission spacecraft

    How did you become interested in a career in planetary science?

    I have an unusual story in that I grew up at NASA. My father worked at Glenn (then Lewis) Research Center in Cleveland working on the launch vehicle that sent the Viking and Voyager spacecraft into space.

    NASA Viking 1 Lander
    NASA/Viking Lander

    NASA Voyager 1
    NASA/Voyager 1

    So space and NASA were always part of my life. My mother (a science teacher) took a geology class when I was about 11, and I thought wow- here is a career where you get paid to pick up rocks! Then during the Viking launches, I heard talks by the mission scientists, and realized you could combine geology and NASA- and I was sold.

    There’s a variety of worlds that your research covers including Venus, Mars, Earth and Titan. What fascinates you most about these worlds?

    In all of what I do, I am thinking about how can studying this place can help us to better understand Earth. It is really about comparative planetology. How can I study volcanoes around the solar system to better understand how a volcano works? Venus to me is so fascinating because it really is the Earth gone wrong. A runaway greenhouse planet with a surface covered by volcanoes, but you started out with a place that really wasn’t all that different from Earth. Mars is the place to go to really answer the question of whether or not life evolved off Earth. Titan is just cool- the only other place in the solar system where it rains—where rivers flow down to seas.

    You proposed a Discovery-class mission called Titan Mare Explorer that would explore one of the hydrocarbon seas on Titan. A floating lander on an extraterrestrial sea sounds incredible. Although it wasn’t selected, do you think a similar mission may be considered?

    We will one day sail on Titan’s seas! They are just too interesting and clearly a place to go to understand the limits of life in our solar system. You have a liquid, but not water, and extremely cold temperatures. Does this preclude life? Beyond the life question, they are the only other place to go in the solar system to study lacustrine/oceanographic processes like wave generation, air-sea interface processes, shoreline modification. So amazing!

    Earlier in 2015 you made an announcement that we should have definitive evidence of life outside of Earth within 20 to 30 years. How will we obtain the definitive evidence? Should we expect future missions to have more instrumentation designed specifically for detecting life?

    I think that rovers like Curiosity and 2020 are going to get us part of the way there.

    NASA Mars Curiosity Rover
    NASA/Mars Curiosity Rover

    NASA Mars 2020 orbiter
    NASA/Mars 2020 orbiter

    Curiosity has already found tantalizing evidence of organics and traces of methane. And it is my driver for why I want to see humans at Mars in the 2030s- microbial evidence of life is going to be hard to find, and as a geologist who spends part of my time in the field, I have a bias it is going to take astrobiologists and geologists on the surface looking at a lot of rocks to convince the community we have found definitive evidence of life. Then there is our planned mission to Europa- another prime target where life may have evolved beyond Earth.

    NASA Europa
    NASA Europa Clipper
    NASA/Europa

    And as we move out to beyond the 30 year mark, we will be increasingly analyzing planets in habitable zones around other stars, characterizing their atmospheres, assessing their potential habitability. So to me we are on the edge of this new era where we are so close to answering the question- are we alone?

    Any bets with colleagues on this timeline?

    No – some people think I am overly optimistic and some think I am overly conservative!

    Can you explain the role of the Chief Scientist at NASA? What does a typical day or week look like for you?

    My days are wonderfully varied. I might go work on a cross agency group assessing research in the Arctic, come back and have a meeting on diversity and inclusion at NASA, a meeting on how to get underrepresented groups more involved in STEM, on the latest work on research on the International Space Station to keep humans healthy on the long trip to Mars, then go get an update on exciting upcoming science missions like WFIRST or Europa. So never dull, but sometimes I do have to go to budget meetings!

    NASA WFIRST New
    NASA/WFIRST

    With a background in field geology, do you still sometimes get the opportunity to crack open some rocks with a hammer?

    I have been too busy to get out in the field, which makes me sad and stressed! I absolutely love getting out and studying volcanoes. My favorite is Mt. Etna – a really interesting and complex volcano. I also love the Icelandic volcanoes. So I am going to try to sneak off this fall and do some fieldwork!

    At the 2014 Fall Meeting, you gave the Shoemaker Lecture with a focus on comparative climatology. Do you find the general public is more receptive to exploring other worlds when they see how it contributes to understanding and protecting our own planet?

    I wanted to focus on comparative climatology because climate change is the key challenge that we face. When you look at the recently released temperature numbers and see the warming that is going on, especially in the Arctic, it is really alarming. As a geologist I am not accustomed to rapid change and that is what we are immersed in due to human induced climate change. I think that bringing in the fact that we study climates on other planets, where we look at how greenhouse gases affect those planetary climates, perhaps can help the public understand that we understand the role of greenhouse gases a lot better than they think we might. Also, studying specific issues, like the role of clouds and aerosols on other planets, can help us understand the complexities that go into climate modeling.

    Do you have any recommendations and advice for those considering careers in planetary science?

    Of course the simplest advice is to find something that really excites you. Graduate school is long and hard and you have to absolutely love what you are doing to get through it. But given that we are going from the situation that I had in the beginning of my career, when we had nine planets (sorry Pluto!) to the situation now – thanks in large part to Kepler – where we have thousands of planets to study, the field is going to be growing by leaps and bounds and becoming more and more interesting and complex!

    NASA Kepler Telescope
    NASA/Kepler

    What type of data would you be most interested in collecting from another world?

    I go back to this fundamental question of – is there life beyond Earth? We have the perfect places in this solar system, and the technology and ability, to go answer this question at Mars-Europa-Enceladus-Titan. In most of these places, we need to get down onto the surface or in the case of plumes at Enceladus and Europa we may be able to grab samples while flying by!

    See the full post here .

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  • richardmitnick 11:42 am on January 21, 2016 Permalink | Reply
    Tags: Geology, , , Sean_B._Carroll, The Day the Mesozoic Died   

    From Nautilus: “The Day the Mesozoic Died” 

    Nautilus

    Nautilus

    January 21, 2016
    Sean B. Carroll

    Temp 1

    “Understanding how we decipher a great historical event written in the book of rocks
    may be as interesting as the event itself.”
    —Walter Alvarez

    Built upon the slopes of Mount Ingino in Umbria, the ancient town of Gubbio boasts many well-preserved structures that document its glorious history. Founded by the Etruscans between the second and first centuries B.C., its Roman theater, Consuls Palace, and various churches and fountains are spectacular monuments to the Roman, Medieval, and Renaissance periods. It is one of those special destinations that draws tourists to this famous part of Italy.

    It was not the ancient architecture but the much longer natural history preserved in the rock formations outside the city walls that brought Walter Alvarez, a young American geologist, to Gubbio. Just outside the town lay a geologist’s dream—one of the most extensive, continuous limestone rock sequences anywhere on the planet (See Father and Son). The “Scaglia rossa” is the local name for the attractive pink outcrops found along the mountainsides and gorges of the area (“Scaglia” means scale or flake and refers to how the rock is easily chipped into the square blocks used for buildings, such as the Roman theater. “Rossa” refers to the pink color). The massive formation is composed of many layers that span about 400 meters in total. Once an ancient seabed, the rocks represent some 50 million years of Earth’s history.


    Watch and download mp4 video here .
    The Death of the Dinosaurs: The disappearance of the dinosaurs at the end of the Cretaceous period represented a long-standing scientific mystery. This three-act film tells the story of the extraordinary detective work that solved it. Howard Hughes Medical Institute

    Geologists have long used fossils to help identify parts of the rock record from around the world and Walter employed this strategy in studying the formations around Gubbio. Throughout the limestone he found fossilized shells of tiny creatures, called foraminifera or “forams” for short, a group of single-celled protists that can only be seen with a magnifying lens. But in one centimeter of clay that separated two limestone layers, he found no fossils at all. Furthermore, in the older layer below the clay, the forams were more diverse and much larger than in the younger layer above the clay (See Foraminifera). Everywhere he looked around Gubbio, he found that thin layer of clay and the same difference between the forams below and above it.

    Temp 2
    Father and Son: Luis (left) and Walter Alvarez at a limestone outcrop near Gubbio, Italy. Walter’s right hand is touching the top of the Cretaceous limestone, at the K-T boundary. Courtesy of Lawrence Berkeley National Laboratory

    Walter was puzzled. What had happened to cause such a change in the forams? How fast did it happen? How long a period of time did that thin layer without forams represent?

    These questions about seemingly mundane microscopic creatures and one centimeter of clay in a 1,300-foot-thick rock bed in Italy might appear to be trivial. But their pursuit led Walter to a truly Earth-shattering discovery about one of the most important days in the history of life.

    Temp 3
    Foraminifera : Walter Alvarez was puzzled by the rapid, dramatic change in foram size between the end of the Cretaceous (pictured at the bottom here) and the beginning of the Tertiary (top) periods, which is seen worldwide. These specimens are from a different location (not Gubbio). Images courtesy of Brian Huber, Smithsonian Museum of Natural History

    The K-T Boundary

    From the distribution of fossils and other geological data, it was known that the Gubbio formation spanned parts of both the Cretaceous [usually abbreviated K for its German translation Kreide (chalk)] and Tertiary periods. The names of these and other geological time periods come from early geologists’ ideas about the major intervals in Earth history, and from some of the features that mark particular times. In one scheme, the history of life is divided into three eras—the Paleozoic (“ancient life,” the first animals), the Mesozoic (“middle life,” the age of dinosaurs), and the Cenozoic (“recent life,” the age of mammals). The Cretaceous period, named after characteristic chalky deposits, forms the last third of the Mesozoic era. The Tertiary period (which has been renamed and subdivided into the Paleogene and Neogene) begins at the end of the Cretaceous 65 million years ago and ends at the beginning of the Quaternary period 2.6 million years ago.

    Temp 4
    Geologic time scale: Geologists organize Earth’s history into eras and periods. The KT boundary falls right at the border of the Cretaceous period and the Tertiary period, around 65 million years ago.

    Walter and his colleague Bill Lowrie spent several years studying the Gubbio formation, sampling up from the Tertiary and down through the Cretaceous. They were first interested in trying to correlate reversals in the Earth’s magnetic field with the fossil record as a way of deciphering the time-scale of Earth’s history. They learned to figure out where they were in the rock formation by the forams characteristic of certain deposits, and by learning to recognize the boundary between the Cretaceous and Tertiary rocks. That boundary was always right where the dramatic reduction in foram diversity size occurred. The rocks below were Cretaceous and the rocks above were Tertiary, and the thin layer of clay was in the gap between (See The K-T Boundary at Gubbio). The boundary is referred to as the K-T boundary.

    One thousand kilometers from Gubbio, at Caravaca on the southeast coast of Spain, a Dutch geologist, Jan Smit, had noticed a similar pattern of changes in forams in rocks around the K-T boundary. Smit knew that the K-T boundary marked the most famous extinction of all—the dinosaurs. When a colleague pointed out that fact to Walter, he became even more interested in those little forams and the K-T boundary.

    Temp 5
    The K-T boundary at Gubbio: The white Cretaceous limestone is separated from the reddish Tertiary limestone by a thin clay layer (marked with coin). Courtesy of Frank Schonian, Museum of Natural History, Berlin

    Walter was relatively new to academic geology. After he received his Ph.D. he had worked for the exploration arm of a multinational oil company in Libya, until Colonel Qaddafi expelled all of the Americans out of the country. His work on magnetic reversals had gone well but he realized that the abrupt change in the Gubbio forams and the K-T extinction presented a much bigger mystery that he became determined to solve.

    One of the first questions Walter wanted to answer, naturally, was how long it took for that thin clay layer to form? To answer this he would need some help. It is very common for children to get help from their parents with their science projects. However, it is extremely unusual, as it was in Walter’s case, that the “child” is in their late 30s. But few children of any age had a Dad like Walter’s.

    From A-Bombs to Cosmic Rays

    Luis Alvarez knew very little about geology or paleontology but he knew a lot about physics. He was a central figure in the birth and growth of nuclear physics. He received his Ph.D. in physics in 1936 from the University of Chicago and worked at the University of California, Berkeley under Ernest Lawrence, the recipient of the 1939 Nobel Prize in Physics for the invention of the cyclotron.

    His early work in physics was interrupted by the onset of World War II. During the first years of the war, Luis worked on the development of radar and systems that would help airplanes land safely in poor visibility. He received the Collier Trophy, the highest honor in aviation, for developing the Ground Controlled Approach (GCA) system for bad weather landings.

    In the middle of the war, he was recruited into the Manhattan Project, the top secret national effort to develop atomic weapons. Alvarez and his student Lawrence Johnston designed detonators for the bombs. Robert Oppenheimer, the director of the Manhattan Project, then put him in charge of measuring the energy released by the bombs. Luis was one of the very few to witness the first two atomic blasts. He flew as a scientific eyewitness to the first test of the atomic bomb in the New Mexico desert and then shortly thereafter to the bomb dropped on Hiroshima, Japan.

    After the war, Luis returned to physics research. He developed the use of large liquid hydrogen bubble chambers for tracking the behavior of particles. Luis received the Nobel Prize in Physics in 1968 for his work in particle physics.

    That would seem to be a nice capstone to an illustrious career. But several years later his son Walter moved to Berkeley, where Luis had worked for many years, to join the university’s geology department. This gave father and son the chance to talk often about science. One day, Walter gave his dad a small polished cross-section of Gubbio K-T boundary rock and explained the mystery within it. Luis, then in his late 60s, was hooked and started thinking about how to help Walter crack it. They started brainstorming about how to measure the rates of change around the K-T boundary. They needed some kind of atomic timekeeper.

    Luis, obviously an expert on radioactivity and decay, first suggested that they measure the abundance of beryllium-10 (10Be) in the K-T clay. This isotope is constantly created in the atmosphere by the action of cosmic rays on oxygen. The more time the clay represented, the more 10Be would be present. Luis put Walter in touch with a physicist who knew how to do the measurements. But just as Walter was set to work, he learned that the published half-life of 10Be was wrong, The actual half-life was shorter, and too little 10Be would be left after 65 million years to measure it.

    Fortunately, Luis had another idea.

    Space Dust

    Luis remembered that meteorites are 10,000 times richer in elements from the platinum group than is the Earth’s crust. He figured that the rain of dust from outer space should be falling, on average, at a constant rate. Therefore, by measuring the amount of space dust (platinum elements) in rock samples, one could calculate how long they had taken to form.

    These elements are not abundant, but they are measurable. Walter figured that if the clay bed had been deposited over a few thousand years, it would contain a detectable amount of platinum group material, but if it had been deposited more quickly, it would be free of these elements.

    Luis decided that iridium, not platinum itself, was the best element to measure because it was more easily detected. He also knew the physicists to do the measurements, the two nuclear chemists Frank Asaro and Helen Michel at the Berkeley Radiation Laboratory.

    Walter gave Asaro a set of samples from across the Gubbio K-T boundary. For months he heard nothing back. The analytical techniques Asaro was using were slow, his equipment was not working, and he had other projects to work on.

    Nine months later Walter got a call from his dad. Asaro wanted to show them his results. They had expected iridium levels on the order 0.1 parts per billion (ppb) of sample. Asaro found 3 ppb of iridium in the portion of the clay bed, about 30 times more than expected and than the level found in other layers of the rock bed.

    Temp 6
    The iridium anomaly: The levels of iridium across the Gubbio formation are plotted. Note the spike in the K-T boundary clay.Data redrawn from Alvarez, et al. 1980 by Leanne Olds

    Why would that thin layer have so much iridium?

    Before they got too carried away with speculation, it was important to know if the high level of iridium was an anomaly of rocks around Gubbio, or a more widespread phenomenon. Walter went looking for another exposed K-T boundary site that they could sample. He found a place called Stevns Klint, south of Copenhagen, Denmark. Walter visited the clay bed there and could see right away that “something unpleasant had happened to the Danish sea bottom” when the clay was deposited. The cliff face was almost entirely made of white chalk, full of all kinds of fossils. But the thin K-T clay bed was black, stunk of sulfur, and had only fish bones in it. Walter deduced that during the time this “fish clay” was deposited, the sea was an oxygen-starved graveyard. He collected samples and delivered them to Frank Asaro.

    In the Danish fish clay, iridium levels were 160 times background levels.

    Walter suggested to Jan Smit that he also look for iridium in his clay samples. The Spanish clay also contained a spike of iridium. So did a sample taken from a K-T boundary in New Zealand, confirming that the phenomenon was global.

    Something very unusual, and very bad, had happened at the K-T boundary. The forams, the clay, the iridium, the dinosaurs were all signs—but of what?

    It Came From Outer Space

    The Alvarez’s concluded right away that the iridium must have been of extraterrestrial origin. They thought of a supernova, the explosion of a star that could shower earth with its elemental guts. The idea had been kicked around before in paleontological and astrophysics circles.

    Luis knew that heavy elements are produced in stellar explosions, so if that idea was right, there would be other elements besides iridium in unusual amounts in the boundary clay. The key isotope to measure was plutonium-244 with a half-life of 75 million years. It would be still present in the clay layer, but decayed in ordinary earth rocks. Rigorous testing proved there was no elevated level of plutonium. Everyone was at first disappointed, but the sleuthing continued.

    Luis kept thinking of some kind of scenario that could account for a worldwide die-off. He thought that maybe the solar system passed through a gas cloud, that the sun had become a nova, or that the iridium could have come from Jupiter. None of these ideas held up. An astronomy colleague at Berkeley, Chris McKee, suggested that an asteroid could have hit the earth. Luis at first thought that would only create a tidal wave, and he could not see how a giant tidal wave could kill the dinosaurs in Montana or Mongolia.

    Then he started to think about the volcanic explosion of the island of Krakatoa, in 1883. He recalled that miles of rock had been blasted into the atmosphere and that fine dust particles had circled the globe, and stayed aloft for two years or more. Luis also knew from nuclear bomb tests that radioactive material mixed rapidly between hemispheres. Maybe a large amount of dust from a large impact could turn day into night for a few years, cooling the planet and shutting down photosynthesis?

    If so, how big an asteroid would it have been?

    From the iridium measurements in the clay, the concentration of iridium in so-called chondritic meteorites and the surface area of the Earth, Luis calculated the mass of the asteroid to be about 300 billion metric tons. He then used various methods to infer that the asteroid had a diameter of 10 ± 4 kilometers (km).

    That diameter might not seem enormous with respect to the 13,000-km diameter of the Earth. But now consider the energy of the impact. Such an asteroid would enter the atmosphere traveling at about 25 km per second—over 50,000 miles per hour. It would punch a hole in the atmosphere 10 km across and hit the planet with the energy of 108 megatons of TNT. (The largest atomic bomb ever exploded released the equivalent of about one megaton—the asteroid was 100 million times more powerful.) With that energy, the impact crater would be about 200 km across and 40 km deep, and immense amounts of material would be ejected from the impact.

    The team had their foram- and dinosaur-killing scenario.

    Hell on Earth

    The asteroid crossed the atmosphere in about one second, heating the air in front of it to several times the temperature of the sun. On impact, the asteroid vaporized, an enormous fireball erupted out into space, and rock particles were launched as far as halfway to the moon. Huge shock waves passed through the bedrock, then curved back up to the surface and shot melted blobs and bedrock out to the edge of the atmosphere and beyond. A second fireball erupted from the pressure on the shocked limestone bedrock. For a radius of a few hundred kilometers or more from ground zero, life was annihilated. Further away, matter ejected into space fell back to earth at high speeds—like trillions of meteors—heated up on re-entry, heating the air and igniting fires. Tsunamis, landslides, and earthquakes further ripped apart landscapes nearer to the impact.

    Elsewhere in the world, death came a bit more slowly.

    The debris and soot in the atmosphere blocked out the sun, and the darkness may have lasted for months. This shut down photosynthesis and halted food chains at their base. Analysis of plant fossils and pollen grains indicate that half or more plant species disappeared in some locations. Animals at successively higher levels of the food chain succumbed. The K-T boundary marks more than the end of the dinosaurs, it is also the end of belemnites, ammonites, and marine reptiles. Paleontologists estimate that more than half of all the planet’s species went extinct. On land, nothing larger than 25 kilograms in body size survived.

    It was the end of the Mesozoic world.

    Where Is the Hole?

    Luis, Walter, Frank Asaro, and Helen Michel put together the whole story—the Gubbio forams, the iridium anomaly, the asteroid theory, the killing scenario—in a single paper published in the journal Science in June 1980.1 It is a remarkable, bold synthesis across different scientific fields, perhaps unmatched in scope by any other single paper in the modern scientific literature. Jan Smit and Jan Hertogen published their study based on Spanish rocks in the journal Nature, and reached a similar conclusion.2

    They were concerned, however, that the scientific community was not well prepared to accept the impact hypothesis. They had good reason to be worried. For the previous 150 years, since the beginning of modern geology, the emphasis had been on the power of gradual change. The science of geology had supplanted biblical stories of catastrophes. The idea of a catastrophic event on Earth was not just disturbing, it was considered unscientific. Until the asteroid impact papers, explanations for the disappearance of the dinosaurs usually invoked gradual changes in climate or in the food chain to which the animals could not adapt.

    Some geologists scoffed at the catastrophe scenario and some paleontologists were not at all persuaded by the asteroid theory. It was pointed out that the highest dinosaur bone in the fossil record at the time was 3 meters below the K-T boundary. Some suggested that perhaps the dinosaurs were already gone when the asteroid hit.3 Other paleontologists rebutted that dinosaur bones are so scarce, one should not expect to find them right up against the boundary.4 Rather, they argued the rich fossil record of forams and other creatures is the more revealing record, and forams and ammonites do persist right up to the K-T boundary.

    Of course, there was a somewhat larger problem that begged explanation: Where on Earth was that huge crater? To the skeptics and proponents this was an obvious weakness of the hypothesis, and so the hunt was on to find the impact zone, if it existed.

    At the time, there were only three known craters on Earth 100 km or more in size. None were the right age. If the asteroid had hit the ocean, which, after all, covers more than two-thirds of the planet’s surface, then searchers might be out of luck. The deep ocean was not well mapped, and a substantial part of the pre-Tertiary ocean floor has been swallowed up into the deep Earth in the continual movement of tectonic plates.

    In the decade following the proposal of the asteroid theory, many clues and trails were pursued, often to dead ends. As the failures mounted, Walter began to believe that the impact had in fact been in an ocean.

    Then a promising clue emerged from a riverbed in Texas. The Brazos River empties into the Gulf of Mexico. The sandy bed of the river is right at the K-T boundary. When examined closely by geologists familiar with the pattern of deposits left by tsunamis, the sandy bed was found to have features that could only be accounted for by a giant tsunami, perhaps more than 100 meters high. Moroever, mixed in with the tsunami debris were tektites—small bits of glassy rock that were ejected from the impact crater in molten form and cooled as they rained back down to Earth.5,6

    Temp 7
    Tektites: Tektites from Dogie Creek, Wyoming (top) and Beloc, Haiti (bottom). Note the bubbles within the glassy sphere—these formed in the vacuum of space as the particles were ejected out of the atmosphere.Top figure courtesy of Geological Society of Canada; bottom figure from Smit, J. [5]

    Many scientists were on the hunt for the impact site. Alan Hildebrand, a graduate student at the University of Arizona was one of the most tenacious. Alan concluded that the Brazos River tsunami bed was a crucial hint to the crater’s location—that it was in the Gulf of Mexico or the Caribbean. He looked at available maps to see if there might be any candidate craters around. He found some rounded features on maps of the sea floor north of Colombia. He also learned of some circular-shaped “gravity anomalies,” places where the concentration of mass varies, on the coast of Mexico’s Yucatan Peninsula.

    Alan searched for any other hints that he was on the right track. Alan noticed a report of tektites in late Cretaceous rocks from a site on Haiti. When he visited the lab that had made the report, he recognized the material as impact tektites. He then went to Haiti and discovered that the deposits there included very large tektites, along with shocked quartz grains—another signature of impacts. He and his advisor William Boynton surmised that the impact site was within 1,000 km of Haiti.

    When Hildebrand and Boynton presented their findings at a conference, they were contacted by Carlos Byars, a reporter for the Houston Chronicle. Byars told Hildebrand that geologists working for the state-owned Mexican oil company PEMEX might have discovered the crater many years earlier. Glen Penfield and Antonio Camargo had studied the circular gravity anomalies in the Yucatan. PEMEX would not allow them to release company data but they did suggest at a conference in 1981—just a year after the Alvarez’s asteroid proposal—that the feature they mapped might be the crater. Penfield had even written to Walter Alvarez with that suggestion.

    In 1991, Hildebrand, Boynton, Penfield, Camargo, and colleagues formally proposed that the 180-km-diameter crater (almost exactly the size predicted by the Alvarez team) one-half mile below the village of Chicxulub [Cheech-zhoo-loob] on the Yucatan Peninsula was the long-sought K-T impact crater.7,8

    Temp 8
    Location of Chicxulub crater and key impact evidence sites: The map shows locations of various impact evidence—the tsunami bed in the Brazos River, tektites in Haiti, the Ocean Drilling Site 1049, and the crater and surrounding ejected material on the Yucatan Peninsula. Leanne Olds

    There were still crucial tests to be done to determine if Chicxulub was truly the “smoking gun.” Another important issue was the age of the rock. This was no easy task to determine because the crater was buried. The best approach would be to test the core rock samples from the wells drilled by PEMEX in the region decades earlier. At first, it was feared that all of the core samples had been destroyed in a warehouse fire. They were eventually located and the rock that was melted by the impact could be dated by a number of laboratories. The results were spectacular. One lab obtained a figure of 64.98 + 0.05 million years, another a value of 65.2 + 0.4 million years. Right on the button—the melt rock was the same age as the K-T boundary.

    The Haitian tektites were also dated to this age, as was a deposit of material ejected from the impact. Detailed chemical analysis showed that the Chicxulub melt rock contained high levels of iridium9 and that it and the Haitian tektites came from the same source. Furthermore, the Haitian tektites had extremely low water content and the gas pressure inside was nearly zero, indicating that the glass solidified while in ballistic flight outside the atmosphere.

    Within a little more than a decade, what had at first seemed to be a radical and, to some, outlandish idea, had been supported by all sorts of indirect evidence, and then ultimately confirmed by direct evidence. Geologists subsequently identified ejected material that covers most of the Yucatan and is deposited at more than 100 K-T boundary sites around the world.10 We now understand that the history of life on Earth has not been the steady, gradual process envisioned by generations of geologists since Lyell and Darwin.

    The identification of the huge crater, while a great advance for the asteroid theory, was bittersweet for Walter. Luis Alvarez had passed away in 1988, just before its discovery.

    Temp 9
    K-T boundary sites: At left, a core sample, drilled at a site about 500km east of Florida (Ocean Drilling Project Site 1049), beautifully depicts the K-T event. Note the very large layer of ejected material on top of which the iridium-containing layer settled. On the right, an exquisitely well-preserved site near Tbilisi, Republic of Georgia, reveals a graded layer of spherules (smaller particles at the top, larger at the bottom) ejected from the impact that is also highly enriched in iridium (86 ppb). Left image courtesy of Integrated Ocean Drilling Program; right image from Smit, J. [5]

    One Punch or Two?

    The discovery of the K-T asteroid impact prompted extensive examination of whether other extinctions were due to impacts. It appears that none of the other four major extinctions of the past 500 million years is attributable to an impact. Yet, there have been many sizable asteroid or comet impacts on Earth over the same period, although none as large as the K-T strike. Since most impacts do not cause extinctions, and most extinctions are not due to impacts, the question has been raised of why the K-T asteroid was so devastating?

    Some scientists have suggested that where the asteroid struck was important. The target rock that was vaporized included a large amount of gypsum, which liberated a large amount of sulfur aerosols that could exacerbate the blockage of the sun, as well as produce acid rain that would alter bodies of water as well as soils. In addition, the impact liberated a large amount of chlorine sufficient to destroy today’s ozone layer.11

    But other evidence has accumulated that a period of massive volcanic eruptions might have weakened Earth’s ecosystems before the K-T impact. The so-called Deccan Traps in present-day western India have been shown to have poured massive amounts of carbon dioxide and sulfur dioxide into the atmosphere in episodic eruptions beginning several hundred thousand years prior to the K-T impact.12 Indeed, for many years, there has been an ongoing debate among some scientists as to whether the Deccan Traps or the K-T impact were the primary cause of the mass extinction. Because of the temporal coincidence between the K-T impact and the onset of the mass extinction, the consensus view has been that the K-T impact was the primary cause of extinction.13 Very recently, new geological evidence has suggested a scenario that may reconcile both viewpoints. It now appears that the largest Deccan eruptions occurred very close to the time of the impact.14,15 This has led some scientists to suggest that the seismic effect of the impact rocking the Earth’s mantle may have been sufficient to trigger enormous, climate-altering eruptions. In this scenario, the asteroid would be the first punch, and volcanism the knockout blow.

    Sean B. Carroll is a professor of molecular biology and genetics at the University of Wisconsin-Madison and Vice President for Science Education at the Howard Hughes Medical institute. His new book The Serengeti Rules will be published in March by Princeton University Press.

    References

    1. Alvarez, L.W., Alvarez, W., Asaro, F., & Michel, H.V. Extraterrestrial cause for the Cretaceous-Tertiary extinction: Experimental results and theoretical interpretation. Science 208, 1095–1108 (1980).

    2. Smit, J. & Hertogen, J. An extraterrestrial event at the Cretaceous-Tertiary boundary. Nature 285, 198–200 (1980).

    3. Clemens, W.A., Archibald, J.D. & Hickey, L.J. Out with a whimper not a bang. Paleobiology 7, 293–98 (1981).

    4. Signor, P.W. & Lipps, J.H. Sampling bias, gradual extinction patterns and castastrophes in the fossil record. Geological Society of America Special Papers 190, 291–96 (1982).

    5. Smit, J. The global stratigraphy of the Cretaceous-Tertiary boundary impact ejecta. Annual Review of Earth and Planetary Sciences 27, 75–113 (1999).

    6. Simonson, B.M. & Glass, B.P. Spherule layers—Records of ancient impacts. Annual Review of Earth and Planetary Sciences 32, 329–361 (2004).

    7. Hildebrand, A.R., et al. Chicxulub crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico. Geology 19, 867–71 (1991).

    8. Pope, K.O., Ocampo, A.C., & Duller, C.E. Mexican site for K/T impact crater? Nature (Scientific Correspondence) 351, 105 (1991).

    9. Schuraytz, B.C., et al. Iridium metal in Chicxulub impact melt: Forensic chemistry on the K-T smoking gun. Science 271, 1573–1576 (1996).

    10. Claeys, P., Kiessling, W., & Alvarez, W. Distribution of Chicxulub ejecta at the Cretaceous-Tertiary Boundary. In Koeberl, C., & MacLeod, K.G., (Eds.) Catastrophic Events and Mass Extinctions: Impacts and Beyond Geological Society of America Special Paper, Boulder, CO (2002).

    11. Kring, D.A. The Chicxulub impact event and its environmental consequences at the Cretaceous-Tertiary boundary. Palaeogeography, Palaeoclimatology, Palaeoecology 255, 4-21 (2007).

    12. Schoene, B., et al. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science 347, 182-184 (2015).

    13. Schulte, P., et al. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science 327, 1214–1218 (2010).

    14. Richards, M.A., et al. Triggering of the largest Deccan eruptions by the Chicxulub impact. Geological Society of America Bulletin (2015). Retrieved from doi: 10.1130/B31167.1

    15. Renne, P.R., et al. State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact. Science 350, 76-78 (2015).

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 4:08 pm on January 13, 2016 Permalink | Reply
    Tags: , Geology, , What is under the East Antarctic Ice Sheet   

    From GIZMODO: “There’s Something Enormous Buried Beneath the East Antarctic Ice Sheet” 

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    GIZMODO

    1.13.16
    Maddie Stone

    Temp 1

    Every week, we’re bombarded with images of dazzling terrains on Mars and Pluto, but there are still geologic wonders to be discovered right here on Earth. Case in point: a new study suggests there could be a canyon system more than twice as long as the Grand Canyon buried beneath an ice sheet in Antarctica. If confirmed, the frozen chasm would be the world’s longest by a wide margin.

    Faint traces of a ravine system stretching across the remote Princess Elizabeth Land in East Antarctica were first spotted by satellite images. A team of geologists then used radio-echo sounding, wherein radio waves are sent through the ice to map the shape of the rock beneath it. The results of this analysis, published recently in the journal Geology, reveal a chain of winding features over 600 miles long and half a mile deep buried beneath miles of ice.

    According to the researchers, the scarred landscape was probably carved out by liquid water long before the ice sheet grew. Satellite images also suggest that the canyon might be connected to a previously undiscovered subglacial lake, one that could cover up to 480 square miles.

    “It’s astonishing to think that such large features could have avoided detection for so long,” lead study author Steward Jamieson of Durham University said in a statement.

    Astonishing, yes—but not quite confirmed. We won’t know for sure that this canyon really exists until Jamieson’s preliminary results are verified by a comprehensive radio-echo sounding analysis of the entire landscape. That airborne survey is scheduled to take place later this year.

    If its existence is confirmed, the canyon system will become the world’s longest, handily stealing the title from Greenland’s Grand Canyon, which covers over 460 miles. Astonishingly, that canyon wasn’t discovered until 2013, when remote sensing data allowed scientists to peer through thick ice and reconstruct the rugged topography below. If one thing is clear from this recent spate of geologic finds, it’s that the age of discovery is far from over.

    Read the full scientific paper. at Geology.

    See the full article here .

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    “We come from the future.”

    GIZMOGO pictorial

     
  • richardmitnick 6:02 pm on October 1, 2015 Permalink | Reply
    Tags: , , , Geology, , U Kansas   

    From Kansas: “Scientists refine hunt for Mars life by analyzing rock samples in Western U.S” 

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    University of Kansas

    LAWRENCE — The search for life beyond Earth is one of the grandest endeavors in the history of humankind — a quest that could transform our understanding of our universe both scientifically and spiritually.

    1
    Petrographic thin section made from core sample. This 30 micron thin slice of rock allows a view of the types of features thought to be microbial. Here, the blue layers are an epoxy added in to see void-space in the rock, and the grey is sediment. The morphology of the orange-brown layers are suggestive of microbial activity, such as they way they roll over themselves in the bottom left and smoothly drape over the triangular feature. This type of deposition demonstrates that the sediment had to have a degree of cohesive stickiness, such as that provided by the presence of microbial mats.

    With news coming this week that NASA has confirmed the presence of flowing saltwater on the surface of Mars, the hunt for life on the Red Planet has new momentum.

    “One of the many reasons this is exciting is that life as we currently know it requires water,” said Alison Olcott-Marshall, assistant professor of geology at the University of Kansas. “So the fact that it’s present at Mars means that the most basic and universal requirement for life was fulfilled.”

    In the journal Astrobiology, Olcott-Marshall recently has published an analysis of Eocene rocks found in the Green River Formation, a lake system extending over parts of Colorado, Utah and Wyoming.

    Marshall and co-author Nicholas A. Cestari, a masters student in her lab, found these Green River rocks have features that visually indicate the presence of life, and they argue that probes to Mars should identify similar indicators on that planet and double-check them through chemical analysis.

    “Once something is launched into space, it becomes much harder to do tweaks — not impossible, but much, much harder,” Olcott-Marshall said. “Scientists are still debating the results of some of the life-detection experiments that flew to Mars on the Viking Missions in the late ’70s, in a large part because of how the experiments were designed. Looking at Earth-based analogs lets us get some of these bumps smoothed out here on Earth, when we can revise, replicate and re-run experiments easily.”

    2
    Petrographic thin section made from core sample. This 30 micron thin slice of rock allows a view of the types of features thought to be microbial, such as the layers that fold over themselves in the middle of the sample marked 2534.8’. This demonstrates that the sediment had to have a degree of cohesive stickiness, such as that provided by the presence of microbial mats.

    The researchers examined cored samples of rock from 50 million years ago that included sections of “microbial mats.”

    “Microbial mats are essentially the microbial world’s version of apartment buildings — they are layered communities of microbes, and each layer represents a different metabolic strategy,” Olcott-Marshall said. “Generally, the photosynthetic microbes are at the top, and then every successive layer makes use of the waste products of the level above. Thus, not only does a microbial mat contain a great deal of biology, but a great number of chemicals, pigments and metabolic products are made, which means lots of potential biosignatures.”

    At times during the Eocene, the Green River Formation’s water chemistry purged fish and other organisms from the lake, providing room for these microbes to thrive.

    “During these times, ‘microbialites’ formed — these are rocks thought to be made by microbial processes, essentially the preserved remnants of microbial mats. The Green River Formation has a wide variety of these structures, and these features are why we went looking in these rocks, as microbialites are one life-detection target on Mars.”

    First, the researchers visually inspected the cored samples for signs of biology by identifying geological signs associated with microbialites — such as “stromatolites.”

    “These are things like finely laminated sediments, where each lamination follows the ones below, or signs of cohesive sediment, things like layers that roll over onto themselves or are at an angle steeper than what gravity would allow,” Olcott-Marshall said. “These are all thought to be signs that microbes are helping hold sediment together.”

    If visual examination pointed to the presence of biology in sections of the rock cores, the researchers looked to confirm the presence of life. They powdered those rock samples in a ball mill, and then used hot organic solvents like methanol to remove any organic carbons that might have been preserved in the rocks. That solvent was then concentrated and analyzed with gas chromatography/mass spectroscopy.

    “GC/MS allows an identification of compounds, including organic molecules, preserved in a rock,” Olcott-Marshall said. “Viking was the first time that a GC/MS was sent to Mars, and there is one up there right now on Curiosity collecting data.”

    NASA Viking 2
    NASA/Viking 2

    NASA Mars Curiosity Rover
    NASA/Mars Curiosity Rover

    Through GC/MS, the researchers determined that rock structures appearing to be biological indeed hosted living organisms millions of years ago: analysis showed the presence of lipid biomarkers.

    “A lipid biomarker is the preserved remnant of a lipid, or a fat, once synthesized by an organism,” Olcott-Marshall said. “These can be simple or very complex. Different organisms make different lipids, so identifying the biomarker can often allow a deeper understanding of the biota or the environment present when a rock was formed. These are a type of biosignature.”

    The researchers said their results could be a powerful guide for sample selection on Mars.

    “There is a GC/MS on Curiosity right now, but there are only nine sample cups dedicated for looking for biomarkers like these,” Olcott-Marshall said. “It’s crucial those nine samples are ones most likely to guarantee success. Additionally, one of the goals of the planned 2020 rover mission is to identify samples for caching for eventual return to Earth. The amount of sample that can be returned is likely very small, thus, once again, doing our best to guarantee success is very important. What this shows is that we can use visual inspection to help us screen for these samples that are likely to be successful for further biosignature analysis.”

    She said microbial and non-microbial rocks are found in similar environments, with identical preservation histories for millions of years, and many of the same chemical parameters, such as amounts of organic carbon preserved in the rocks.

    “The only difference is that one rock is shaped in a way people have associated with biology, and sure enough, those rocks are the ones that seem to preserve the biosignatures, at least in the Green River,” she said.

    See the full article here.

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    U Kansas campus

    Since its founding, the University of Kansas has embodied the aspirations and determination of the abolitionists who settled on the curve of the Kaw River in August 1854. Their first goal was to ensure that the new Kansas Territory entered the union as a free state. Another was to establish a university.

    Nearly 150 years later, KU has become a major public research and teaching institution of 28,000 students and 2,600 faculty on five campuses (Lawrence, Kansas City, Overland Park, Wichita, and Salina). Its diverse elements are united by their mission to educate leaders, build healthy communities, and make discoveries that change the world.

    A member of the prestigious Association of American Universities since 1909, KU consistently earns high rankings for its academic programs. Its faculty and students are supported and strengthened by endowment assets of more than $1.44 billion. It is committed to expanding innovative research and commercialization programs.

    KU has 13 schools, including the only schools of pharmacy and medicine in the state, and offers more than 360 degree programs. Particularly strong are special education, city management, speech-language pathology, rural medicine, clinical child psychology, nursing, occupational therapy, and social welfare. Students, split almost equally between women and men, come from all 50 states and 105 countries and are about 15 percent multicultural. The University Honors Program is nationally recognized, and KU has produced 26 Rhodes Scholars, more than all other Kansas schools combined.

     
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