News this Week

Science  10 Jun 2011:
Vol. 332, Issue 6035, pp. 1246

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  1. Around the World

    1 - Amazon Rainforest, Brazil
    'Monster Dam' Gets Green Light
    2 - Washington, D.C.
    Homeland Security Science Under Attack
    3 - Lyon, France
    WHO Weighs In on Cell Phones and Cancer
    4 - Geneva, Switzerland
    AIDS Turns 30

    Amazon Rainforest, Brazil

    'Monster Dam' Gets Green Light

    Brazil's environment agency gave final approval last week for the construction of the Belo Monte Dam, an immense hydroelectric station on the Xingu River in the Amazon rainforest.

    The dam, in planning for 30 years, is one of several large projects being built on tributaries of the Amazon River that are expected to damage pristine regions. Earlier this year, 20 Brazilian scientific societies wrote to Brazilian President Dilma Rousseff opposing the dam, saying it would violate the human rights of local indigenous groups.

    The new dam would straddle the Xingu River in the Amazon.


    But on 1 June, Brazil's environmental agency, Ibama, issued a license to the consortium Norte Energia SA to begin construction. The $16 billion dam would flood 516 square kilometers of forest while lowering water levels in the Xingu River, which locals say they depend upon for fishing.

    Designers say the 6-km-wide dam, slated for completion in 2015, would produce more than 11,233 MW of power, ranking it as the third largest in the world and helping Brazil stay in the top tier of renewable energy users. An analysis by antidam campaigners predicts 40,000 people could be displaced by the dam; the Brazilian government's estimate was 20,000.

    Washington, D.C.

    Homeland Security Science Under Attack

    Science and technology programs at the U.S. Department of Homeland Security (DHS) would be drastically downsized under a spending bill passed last week by the House of Representatives. The legislation would reduce funding for the science and technology directorate by 52%, from this year's $827 million to $398 million in fiscal year 2012, which begins on 1 October. By comparison, the Obama Administration requested $1.2 billion for those programs in 2012. The cuts are part of a $1.1 billion reduction in the agency's overall budget, now $43.4 billion, and are in line with a plan by House Republicans to rein in spending across the government.

    DHS officials say the cuts will wipe out dozens of programs, stalling the development of technologies for border protection, detection of biohazards, and cargo screening. Agency officials hope the Senate will restore some of the funds when it takes up the spending bill in the coming weeks. But a final number is unlikely until the White House and Congress agree on government-wide spending levels and raising the debt ceiling, contentious issues that may take months to resolve.

    Lyon, France

    WHO Weighs In on Cell Phones and Cancer

    Whether cell phones cause brain cancer has been debated for years, and last week the World Health Organization (WHO) stepped into the fray. A committee of 31 experts that had spent 8 days in Lyon, France, reviewing the literature concluded that radio-frequency electromagnetic fields, including those from cell phones, are “possibly carcinogenic” to people.


    The International Agency for Research on Cancer's (IARC's) uncertain classification already applies to more than 250 other agents, including lead and engine exhaust. In fact, it's so tough to show that something doesn't cause cancer that only one of the 900 or so agents that IARC has evaluated falls in the “probably not carcinogenic” category.

    The working group was swayed partly by a study called Interphone. It reported last year that although cell phones didn't seem to be linked to brain cancer in most people, for heavy cell users there were hints of risk.

    Reaching a more definitive answer won't be easy; one reason is that epidemiologic studies like Interphone depend on people recalling their cell phone use. A European effort called COSMOS is recruiting about 250,000 people and will track their cell phone use with help from phone company records. But it's years away from reporting results.

    Geneva, Switzerland

    AIDS Turns 30


    Thirty years after the epidemic first surfaced, just over 34 million people live with HIV. But by the end of last year, antiretroviral (ARV) drugs reached more people in resource-constrained countries—6.6 million—than ever before, says a new report from the Joint United Nations Programme on HIV/AIDS (UNAIDS), released 2 June. Infection rates, too, plummeted 25% worldwide between 2001 and 2009. But the report, titled AIDS at 30, warns that international funding needed to maintain progress has been declining.

    Even though the world now spends $15.9 billion a year combating the epidemic, 9 million people who need treatment still have no access to ARVs, says the report. And more than two dozen countries offer ARVs to just 20% or fewer of their citizens who need treatment. UNAIDS estimates that increaseing the number of people being treated to 15 million by 2015 will cost $22 billion a year.

    The report ushers in this week's U.N. General Assembly High-Level Meeting on AIDS, which will hammer out a new declaration about how best to address the epidemic. Michel Sidibé, executive director of UNAIDS, says that developing countries will be asked to shoulder more of the burden.

  2. Random Sample


    >Good news: You can now download that obscure National Academies report you wanted for free. The National Academies Press ( announced on 2 June that it was extending the new low price, currently available on 65% of its PDFs, to the rest of more than 4000 digitized books, as well as future reports.

    Time Capsule From the Atomic Age


    On 2 June, a crowd watched as workers pried a large slab from the corner of the Research Institutes building at the University of Chicago (U of C) to reveal a small box, placed there in 1949 by the legendary physicist Enrico Fermi, pioneer of the nuclear reactor. The crowd waited, hushed. What had Fermi hidden away for the generations? Scientific secrets? Predictions for the future?

    Instead, master of ceremonies Roger Hildebrand, a U of C physicist and younger contemporary of Fermi's, held up a slim orange volume. “This is the telephone directory from the University of Chicago in 1948,” he announced. Next came a road map from a gas station, followed by a bundle of airline timetables (including a five-stop one-way flight to San Francisco for $113.75). And that was pretty much that.

    In a TV interview after the event, U of C physicist Riccardo Levi-Setti, who first met Fermi as a Ph.D. student in 1949, seemed stunned: “I'm a little surprised that there wasn't really”—he paused for a long time—“something very inspiring.” The building will be demolished in August to make way for the new Eckhardt Research Center.

    Mating of the Titans


    BEIJING—As the scalpel sliced into the towering celebrity, a crowd gathered to watch history in the making. A few cuts later, just before 9:00 p.m. on 28 May, Niu Xia removed a 5-centimeter-square chunk of green flesh and inserted a syringe. The operation was a success, but still the patient had only hours to live.

    The celebrity was titan arum, or corpse flower (Amorphophallus titanum), which boasts the tallest unbranched inflorescence on the planet, sometimes topping 3 meters. Famously hard to cultivate, the plant offers a noxious reward: When its flowerlike spathe opens, the tiny female flowers inside stink like a rotting corpse. That attracts its pollinators: carrion-eating beetles and flesh flies.

    In one respect, the corpse flower truly is the living dead. Cultivated individuals almost always begin dying hours after blooming. Sure enough, the night after the operation at Beijing Botanical Garden (BBG), the titan's spadix collapsed. That devastated Niu, who had raised the plant from when it was a mere tuber. “She cried all night,” says fellow BBG horticulturalist Guo Ling. “It was like it was her baby.”

    The withering titan arum may yet have babies of its own. Half a world away, scientists at the Royal Botanic Garden, Edinburgh, in the United Kingdom will attempt to pollinate their own first-time bloomer with the Chinese plant's pollen. As Niu sliced into the spathe and extracted the yellow sacs, BBG Director Zhao Shiwei hovered like an expectant father. In a few weeks, Zhao will learn whether the Scottish plant has borne a cluster of 500 or so dark-orange berries. Then he can break out the cigars.

    By the Numbers

    1,211,287 — Square kilometers of ice road–accessible Arctic lands that will be unreachable by 2050, a 14% decrease, according to a report online 29 May in Nature Climate Change. Iceland alone will lose 82%.

    8 — Points out of 72 that a U.K. university admissions exam devoted to a math problem later found to be unsolvable. Nearly 6800 students took the test on 26 May.

  3. Newsmakers

    Trailblazing Nobelist Passes


    “She is from New York. She is Jewish. She is a woman.” That's what a prominent U.S. university wrote about Rosalyn Yalow while denying her a spot in its graduate program decades ago. Yalow, who went on to win a Nobel Prize in physiology or medicine, died on 30 May in New York City. She was 89.

    Born to parents who never went to college, Yalow decided at age 8 to become a scientist. She became the first woman to earn a bachelor's degree in physics from NYC's Hunter College. But no graduate program accepted her until World War II, when the University of Illinois offered her a teaching assistantship. She got her doctorate in nuclear physics from Illinois in 1945.

    She began working at the Bronx Veterans Administration Hospital in 1950. There she and Solomon Berson developed the radioimmunoassay for measuring minute quantities of hormones in blood with radioactive tracers. The technique, which can also detect drugs and viruses, ushered in a “revolution in biological and medical research,” the Karolinska Institute in Sweden said when Yalow was awarded the Nobel Prize in 1977.

    Tracers of the Universe's Architecture

    In the early 1980s, scientists thought that dark matter, the mysterious stuff whose gravity binds galaxies, might actually consist of familiar, nearly massless particles called neutrinos. Then cosmologists Marc Davis of the University of California, Berkeley; George Efstathiou, now at the University of Cambridge in the United Kingdom; Carlos Frenk, now at Durham University in the United Kingdom; and Simon White, now at the Max Planck Institute for Astrophysics in Garching, Germany, proved that convenient idea untenable. Instead of “hot” neutrinos zipping about at near–light speed, dark matter had to consist of beefy, slow-moving, “cold” particles unlike any yet observed. That insight and the methods used to achieve it have won the quartet the 2011 Gruber Cosmology Prize and $500,000 to share.

    Using large-scale simulations, pioneered by Efstathiou, they showed that only cold dark matter would lead to the distribution of galaxies observed in so-called red-shift surveys, pioneered by Davis. “Nobody took it [cold dark matter] seriously until the four of them did their first large-scale simulations,” says Julio Navarro, a cosmologist at the University of Victoria in Canada and a member of the prize committee. He adds: “They really started a whole industry in using this kind of simulation, … which has become a primary tool in cosmology.”

    Clockwise from top left: Davis, Efstathiou, White, and Frenk.


    Shaw Prizes

    The 2011 Shaw Prizes, announced this week, highlight achievements in astrophysics, immunology, and geometry. Enrico Costa of the Institute of Space Astrophysics and Cosmic Physics in Rome and Gerald Fishman of NASA's Marshall Space Flight Center in Huntsville, Alabama, share the astronomy prize for leading the development of space instruments that determined that gamma ray bursts—fleeting, energetic flashes of gamma rays—result from violent explosions in galaxies billions of light years from Earth. Discovering the molecular mechanism of innate immunity, which is the first line of defense against pathogens in all plants and animals, nets the life science and medicine prize for Jules Hoffmann of the University of Strasbourg in France, Ruslan Medzhitov of Yale University, and Bruce Beutler of the Scripps Research Institute in San Diego, California. And Demetrios Christodoulou of ETH Zurich and Richard Hamilton of Columbia University take the mathematics prize for their work on nonlinear partial differential equations in Lorentzian and Riemannian geometry and their applications to general relativity and topology.

    Hong Kong media mogul and philanthropist Run Run Shaw established the prizes in 2002. The winners in each category will split $1 million to be awarded at a ceremony in Hong Kong in September.

  4. A Bengali Recipe for Disaster

    1. Richard Stone

    Under a thick blanket of mud in the Bengal Basin, the crust is twisting and crumpling. A major earthquake is inevitable. Can the region's teeming, shoddily built cities avert calamity?

    Houses of cards.

    Sections of Dhaka are rising on reclaimed land that's prone to liquefaction.


    DHAKA—In the late afternoon of 12 June 1897 in Assam, northeastern India, the earth began to rumble. The eerie subterranean growl grew louder and louder and after a few minutes the ground began to shake, at first gently then with such violence that tombstones, masonry, and even people were flung into the air. The Great Assam Earthquake, estimated as high as magnitude 8.7, claimed 1626 lives. Several days later, a team from the Geological Survey of India set out to map the shattered land. “This was the first time someone had resurveyed after an earthquake,” says Philip England, a seismologist at the University of Oxford in the United Kingdom. Over months of wretched work in monsoon downpours, the surveyors measured an astounding 8-meter uplift on the northern edge of Assam's Shillong Plateau, extending through the area that today is Bangladesh. Incredulous superiors dismissed the results as erroneous and buried the report.

    The survey team would eventually be vindicated. And the more experts learn about the Great Assam Earthquake, the starker it stands as a warning to cities on the flood-plains of South Asia, including Bangladesh's densely populated capital, Dhaka. Perched on thick, alluvial sediments 200 kilometers south of the epicenter, Dhaka “was badly damaged” in 1897, says Syed Humayun Akhter, a seismologist at the University of Dhaka. The ground under much of the city liquefied, destabilizing foundations. Thanks to the earthquake's gradual buildup, most people in Dhaka managed to escape before buildings disintegrated. “It was a miracle there were so few deaths,” Akhter says.

    Dhaka may not be so lucky next time. Scientists are finding that both its social features and its geology, including a hidden fault that seismologists believe is gathering stress beneath the sediments, could make the area more vulnerable than appreciated. Few structures in this city of 13 million are built to resist shaking. Even when the ground is quiet, Akhter says, “you sometimes read reports of buildings falling down.” Shoddy construction is prevalent across Bangladesh and many other developing nations in seismic danger zones. “It's hard to see any realistic way to avoid the looming humanitarian disasters in places like this,” says Susan Hough, a seismologist with the U.S. Geological Survey in Pasadena, California. “The world is short on both resources and political will to make the necessary investments in risk mitigation.”

    Mud skipper.

    Michael Steckler (center) helps lower instruments into a well in northern Bangladesh.


    Among disasters waiting to happen, Bangladesh stands out for its unique geography, which is capable of transforming modest quakes into major calamities. A land of superlatives, the country is the world's most densely populated—more than 150 million people occupy an area the size of Iowa—and is home to the biggest delta and one of the heaviest sediment fluxes. Each year the Ganges, Brahmaputra, and Meghna rivers carry about 1 billion tons of sediment from the Himalayas, depositing much of it in the Bengal Basin. These sediments, a couple dozen kilometers thick in places, amplify seismic waves and hide active faults. Last February, Akhter and colleagues from Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, and other institutions embarked on a 5-year campaign to study the Ganges-Brahmaputra-Meghna delta. They will gauge the extent to which that heavy, wet blanket of sediment is ratcheting up seismic strain. They also hope to chart hidden faults, including what they call an “astonishing geologic event”: They hypothesize that the eastern Himalayan front—an area of folding, crumpling, and mountain building driven by India's collision into Asia—is jumping forward to a new front 200 kilometers to the south. The new front is raising the crust of the Shillong Plateau above a blind fault under the sediment in Bangladesh.

    Some potential dangers are already known. The Shillong Plateau's southern edge has not slipped recently and could uncork a magnitude-8 or greater earthquake. Closer to Dhaka, a magnitude-7.5 quake on the Madhupur fault would level 72,000 buildings and kill more than 130,000 people, according to estimates published by the Bangladesh government in 2009. The biggest threat of all lurks in the east and offshore in the Bay of Bengal: the northern stretch of the Chittagong-Myanmar-Sumatra plate boundary. On 26 December 2004, some 2000 kilometers south of Bangladesh, the Sumatra-Andaman earthquake—at magnitude 9.3, the third largest ever recorded—ruptured as much as 1500 kilometers of plate boundary, triggering tsunami waves that killed more than 230,000 people.

    Bangladesh has been slow to come to terms with the seismic menace. “The nation is poor. This is reality,” Akhter says. But the government is strengthening the building code based on revised seismic maps, and its disaster agency is training 62,000 volunteers in earthquake response.

    Piling up the stress

    When the Geological Survey of India team struck out into the field in the summer of 1897, they were venturing into uncharted territory. Although the surveyors felt aftershocks, they did not realize that the entire plateau was still moving as they gauged its dimensions. As a standard accuracy check, the team would measure a triangle, at least 10 kilometers per side. By the time the third angle of a given triangle had been measured, days or weeks after the first, “all the angles had changed by an amount they had never hitherto encountered,” says seismologist Roger Bilham of the University of Colorado, Boulder. Supervisors derided what they deemed to be sloppy work. They were wrong, Bilham says: Shillong Plateau was adjusting to many thousands of aftershocks.

    Grim picture.

    New studies are shedding light on the Bengal Basin's complex tectonics. Most worrisome to geophysicists are the eerily calm Arakan and Tripura segments of the Chittagong-Myanmar-Sumatra plate boundary.

    Ferreting out faults.

    Syed Humayun Akhter hopes to uncover evidence of buried geology.


    Re-examining the data a century later in 2001, Bilham and England calculated that in the space of a few seconds, the Great Assam Earthquake had thrust up a 110-kilometer-long piece of Shillong about 10 meters. The crust beneath the plateau is pinched between massive forceps: the Indian Plate, crawling northeast toward the Himalayas at a rate of 6 centimeters per year, and the Burma Plate, grinding westward at 2 centimeters per year. When enough stress accumulates—perhaps every 3000 years or so—the plateau pops up, Bilham and England discovered.

    The seismic waves from the rupture of the northern fault in 1897 rippled across the Ganges-Brahmaputra-Meghna delta, jiggling alluvial sediments like a bowl of pudding. Hough and colleagues have calculated that the shaking was two to four times more intense in Dhaka and other cities built on sediments than on settlements a similar distance from the epicenter built on rock. This amplification “has been shown to significantly control shaking and damage in countless earthquakes, including the 1811–1812 New Madrid earthquakes,” Hough says. Because most terrain in Bangladesh is soft sediments, any local earthquake measuring magnitude 5 or more would be punishing, Akhter says.

    Another hazard is that when sediments are moist, they are primed to liquefy during an earthquake. Liquefaction of soil churned coast tracts on New Zealand's South Island during the magnitude-6.1 earthquake on 22 February, undermining foundations and leaving cars half-buried in sand, Hough says. In the Bengal Basin, during summer monsoon rains, the Ganges, Brahmaputra, and Meghna rivers deposit a sediment layer up to several centimeters thick across the delta. Surface flooding and groundwater recharge seasonally pile up 100 billion tons or more of water to the delta. The tremendous pressure can nudge a fault on the brink of rupture over the edge. “Most devastating earthquakes in this region have occurred during monsoon time,” including the 1897 Assam quake, Akhter says.

    Soft sediments are not uniformly bad news. Like a car's shock absorbers, they can soak up strain from faults. It takes more time for stress to build in faults overlain by sediments, and thus the period between large earthquakes is longer.

    To better understand how the Ganges-Brahmaputra-Meghna delta's thick sediments influence underlying faults, Akhter and colleagues have launched an ambitious research campaign. They will drill around 250 scientific wells to probe sedimentation and tectonics, gauge vertical shortening at two sites where well sets have been strung with optical fibers, measure electrical resistance of sediments, and use high-resolution seismic reflection to map sediments and underlying crust structure. “We will attempt to directly measure the compaction of sediments in the delta—how they squish as new sediments are piled on top,” says Columbia geophysicist Michael Steckler, the project's principal investigator. A GPS network will monitor strain and a seismic network will record earthquakes, while rock outcroppings near Shillong and along the Chittagong coast in the southeast will be analyzed for evidence of past earthquakes.

    Seismic sleuth.

    Columbia geologist Leonardo Seeber inspects river sediment layers and a rare intact rock (right) in northern Bangladesh.


    Planning for the worst

    On 26 December 2004, in the hours after the Sumatra-Andaman earthquake, Akhter watched at the University of Dhaka as aftershocks marched up the plate boundary toward Bangladesh. “People were extremely tense and frightened,” he recalls. University officials called an emergency meeting that evening on how to cope in the event that the northern segment of the plate boundary were to rupture. According to campus policy, dormitory doors were locked at midnight. “We needed to change this without creating panic,” Akhter says. Resident teachers were asked to discreetly unlock the doors.

    Although a northern rupture never materialized, the threat hasn't gone away. The last major earthquake at that end of the fault occurred on 2 April 1762, along the Chittagong coast. The rupture of the Arakan fault segment, estimated to have exceeded magnitude 8, submerged islands just off the coast, triggered mud volcanoes, and caused seiches, inland tsunami waves, that capsized boats on the Buriganga River in Dhaka. Since then, Akhter says, a 600-kilometer stretch of the subduction fault from Myanmar to the Andaman Islands has been a seismic gap: in other words, strangely calm. There are no known ruptures of the onshore Tripura segment, north of Arakan. “We have no idea how much strain is building up in these segments,” Akhter says.

    The subduction fault, he and others believe, is due for a major temblor. The Arakan segment would surely unleash a tsunami. Cyclones occasionally score a direct hit on Bangladesh, and the country's low-lying, funnel-shaped coastline makes storm surges all the more deadly. Cyclone shelters dotting the coastline in principle could offer a haven from tsunami waves. But a tsunami would make landfall within an hour after a quake on the Arakan or Tripura segments. “We would not be able to send a warning in time,” Akhter says. A major quake on the Tripura segment, meanwhile, would deal a crippling blow to Dhaka and much of Bangladesh. “This is the segment that most worries me,” Steckler says.

    The biggest hazard in Bangladesh may be poor construction. Before Bangladesh's independence in 1971, Akhter says, most buildings had at most three stories. Since then, to accommodate a constant influx of migrant workers, landlords have added floors to many buildings helter-skelter without shoring up foundations, he says. And new housing developments in Dhaka are rising on unconsolidated sediments augmented by fill—a recipe for liquefaction. There's little the cash-strapped country can do about existing structures, Akhter says. But he hopes that new building projects will incorporate earthquake-resistant design. “We are now trying to convince architects and builders that they have to follow building codes,” he says.

    Adhering to the current Bangladesh National Building Code may not offer sufficient protection. It is based on a seismic zone map prepared by the Geological Survey of Bangladesh in 1979. The zones were drawn up “on very scanty data,” Akhter says. He calls up a map of the zones on his laptop; a small area of northeast Bangladesh is designated as high risk. “To me now, this whole area should be high risk, including Dhaka,” Akhter says, tracing out the eastern half of the country, anchored by the Tripura fault segment.

    The picture is similar in neighboring countries in a seismic belt stretching from northern India across Nepal and Bhutan and down through Bangladesh and Myanmar. The 26 January 2001 earthquake that leveled Gujarat, India, killing 20,000 people, happened in a region long known to be at high risk for shocks, Bilham says. But the code was so unevenly applied, he says, that the same percentage of the population was killed in collapsed buildings in 2001 as in an earthquake in 1819—when earthquake-resistant construction was unknown.

    “There's no magic wand that will make a vulnerable city in the developing world safe,” Hough says. Bilham argues that it is essential to replace the ancient building stock of cities. That would substantially reduce the carnage, he says, and it would “make politicians and urban planners look less culpable than they do now.” It would take decades to gird cities in the developing world against earthquakes. In the meantime, Hough says, cash-strapped nations can take discrete steps. One “realistic goal,” she says, is to shore up critical facilities like hospitals, schools, and airports. Toward that end, politicians need advice, and pressure, from experts. “One of the most important things the international community can do is to help train and support local communities of earthquake professionals,” Hough says.

    The task is daunting. “Many decades will pass before the developing world can hope to approach the levels of resilience that are potentially achievable,” England and James Jackson of the University of Cambridge in the United Kingdom warn in this month's issue of Nature Geoscience. “During this time millions of people will be affected by earthquakes on faults that have not been recognized,” they write. The highest scientific priority, they argue, is to map with precision where the level of seismic hazard is increasing in the regions of greatest risk: the 10 million square kilometers of the Alpine–Himalayan belt, which stretches from Italy, Greece, and Turkey, across the Middle East, Iran, and central Asia, to India, China, and, of course, Bangladesh.

    Back in his office, Akhter calls up a map of Bangladesh with red dots indicating major earthquakes. From 1869 to 1930, five temblors with a magnitude of seven or higher rattled the country. “It's been 80 years since the last big earthquake,” he says. In that time, Dhaka's population has grown 10-fold.

    The perils are incalculable.

  5. Planetary Science

    Enceladus Now Looks Wet, So It May Be ALIVE!

    1. Richard A. Kerr

    Accumulating evidence from a Saturn orbiter points to liquid water in a distant moon, but further investigation of this likely habitable zone may be out of reach.


    An icy plume with solar halo blasts from a fissure on Saturn's moon Enceladus.


    Liquid water—and the life it may permit—has been the goal of planetary exploration for decades, with not much of the sloshy stuff to show for the effort. Jupiter's moon Europa has a global ocean, but unfortunately, it's out of reach beneath many kilometers of ice. So the sight in 2005 of ice and water vapor jetting hundreds of kilometers above Saturn's icy little moon Enceladus, like Yellowstone geysers gone ballistic, warmed the hearts of astrobiologists everywhere. But as terrestrial geologists soon pointed out, water plumes needn't mean liquid water. Enceladus might be frozen solid and still be spouting water ice and vapor.

    With new observations, the “Enceladus: Oasis or Iceball?” debate is now coming down on the side of a wet interior for the moon—and a chance for life. “Everything seems to point to some amount of liquid water,” says cosmochemist Jonathan Lunine of the University of Arizona, Tucson. “It's hard to argue for a completely frozen moon.”

    The science team operating instruments on the Cassini Saturn orbiter had suggested that subsurface liquid water was boiling to form the plumes. But Susan Kieffer of the University of Illinois, Urbana-Champaign, a geological fluid dynamicist who has studied Yellowstone's Old Faithful geyser, saw a problem (Science, 15 December 2006, p. 1668). The Cassini mass spectrometer showed that the plumes contained considerable amounts of carbon dioxide, nitrogen, and methane, far more nitrogen and methane than could have been dissolved in liquid water. Kieffer noted that only clathrates, water ice with various gas molecules trapped in the “cages” of its own crystal structure, could deliver so much of the gases once heating decomposes the clathrates. Enceladus could be solid, lifeless ice throughout.

    Since Kieffer's 2006 challenge, Cassini team members have been accumulating more evidence for liquid water from more and closer flybys of Enceladus. In 2009, planetary scientist Frank Postberg of the University of Heidelberg in Germany and his colleagues reported having detected sodium salts in 6% of the particles that make up Saturn's faint outer E ring, which is created by the plumes (Science, 23 January 2009, p. 458). The composition of the ring particles resembled that of seawater, so Postberg and his colleagues argued that water from a deep ocean was reaching the fractures of the south pole region, where the plumes originate, and blasting salty droplets into space.

    In May, at a meeting of the Enceladus Focus Group, Postberg and his colleagues reported that an extra-close flyby through the densest parts of the plumes had detected sodium salts in particles that account for more than 95% of the mass of particles. Liquid water, not solid clathrates, looks like the best bet for producing salty plume particles (although clathrates could still be producing the nitrogen, carbon dioxide, and methane).

    Cassini infrared measurements of the temperature of Enceladus's plume-emitting south polar region are also pointing more strongly toward liquid water. Last March, planetary scientists Carly Howett and John Spencer of Southwest Research Institute in Boulder, Colorado, and their colleagues reported in the Journal of Geophysical Research-Planets that improved observations had almost doubled the best estimate of the emitted heat energy to 15.8 gigawatts. “That's quite a lot of power,” Spencer says. It's enough to drive liquid-derived plumes, which require higher subsurface temperatures than clathrates do. “Once you have temperatures that high, you don't need clathrates as a driving mechanism” for the plumes, Spencer says.

    The great abundance of heat energy also points to liquid water. The only known way Enceladus could generate heat is for Saturn to raise tides in solid parts of the moon the way Earth's moon raises tides in the oceans. Repeated tidal flexing of Enceladus's ice would produce heat the way repeatedly bending a paper clip makes it warm. But Enceladus's interior would be too stiff for tidal heating to work if it were solid ice throughout, notes planetary physicist David Stevenson of the California Institute of Technology in Pasadena. A layer of ice overlying a sea of water would be flexible enough, he says. So would ice over a layer of water-filled cracks.

    All in all, liquid water in Enceladus is “pretty likely,” “most likely,” or “almost inescapable,” scientists told Science. Most would agree with Spencer that the chances for liquid water are something like 90%. And all agree that at least some clathrates could be decomposing in order to explain the gases, especially methane.

    Despite the general agreement, Cassini's set of instruments is unlikely to clinch the case for liquid water. Enceladus advocates are calling for another, more capable, mission to finish the job. Liquid, salty water laced with organic compounds “points strongly to a habitable zone beneath the south polar terrain,” Carolyn Porco of the Space Science Institute in Boulder, who leads the Cassini camera team and co-organized the Focus Group meeting, writes in an e-mail. And whatever is inside the moon is continually ejected for close inspection. “So, Enceladus is THE most promising place for investigation of things astrobiological,” she writes.

    But the spotlight has been on Jupiter's moon Europa so long (Science, 19 December 2008, p. 1780) that a mission to Enceladus was little more than an afterthought in March's Planetary Science Decadal Survey, which recommended a Europa mission (Science, 11 March, p. 1254). Moving Enceladus up the priority list would be a daunting task, liquid water or not.

  6. Archaeology

    South African Cave Slowly Shares Secrets of Human Culture

    1. Michael Balter

    In the hands of a skilled archaeologist, a South African site serves as a laboratory for testing ideas about early human culture and cognition.

    Prime location.

    Sibudu is a “perfect place” to study very early human culture.


    SIBUDU CAVE, SOUTH AFRICA—“Did you remember to put your insect repellent on?” It's a question archaeologist Lyn Wadley asks of every visitor to her excavations at Sibudu Cave, chiseled into a cliff face high above the Tongati River in South Africa's KwaZulu-Natal province. To get to Sibudu, Wadley and her team members have to drive down a dusty dirt road, wade across the knee-deep, swiftly flowing river, hike through tick-infested brush along the river bank, and scramble up a steep slope strewn with loose rocks to the ledge of this rock shelter, located about 40 kilometers north of Durban.

    There on a broad, flat rock shelf, under the shade of a towering Natal elm tree, lies what has kept Wadley coming back to Sibudu for the past 12 years: an 8-meter-thick mound, a record of prehistoric human occupation that extends back at least 77,000 years and probably much longer. These multilayered, human-made sediments, which cover most of the 55-by-19-meter cave floor, are crammed with thousands of artifacts left behind by Homo sapiens during our species' formative years, culturally speaking. There are sophisticated stone tools, skillfully made bone implements, deep hearths, and the charred bones of large and small mammals; there are swatches of bedding made of sedges and grass, chunks of red ochre, and sparkling ornamental beads made from the shells of sea snails.

    Under Wadley's trowel, this site has become a powerful tool for testing hypotheses about the cognitive prowess of early modern humans. The excavations “have provided a powerful database,” says archaeologist Paola Villa of the University of Colorado, Boulder. For example, Wadley, of the University of the Witwatersrand (Wits), Johannesburg, and her team have pushed back the first signposts for what she calls “complex cognition,” producing evidence for the earliest known bows and arrows as well as the precocious use of snares and traps to catch small animals, both of which require the ability to plan ahead.


    A stream of papers from Wadley's team about early H. sapiens' activities at Sibudu has made her one of archaeology's most influential theorists and thrust Sibudu into the archaeological limelight. “Sibudu is probably the most important site in southern Africa at the moment,” says archaeologist Alex MacKay of Australian National University in Acton.

    And yet the next chapter in the site's history won't include Wadley: She retired from fieldwork at the end of the spring field season. But given Sibudu's importance—and the fact that Wadley has dug through only 3 of 8 meters of human occupation—the dig will go on. Wadley has passed the torch to a new crew chief, Nicholas Conard of the University of Tübingen in Germany, to uncover the rest of Sibudu's riches, which may stretch back to 100,000 years ago or more. Wadley could have taken a peek at those earlier layers; other archaeologists urged her to dig a small, deep test pit to see what was there. But she decided against this shortcut, because then she wouldn't have context for the oldest layers. “How would I make sense of it without knowing what was in between?”

    The road to Sibudu

    The hominins who repeatedly visited Sibudu may have been drawn by its protective setting and an abundance of flowing water, fruit trees, and animals. But for Wadley, 64, the road to Sibudu was long and winding. She grew up in a small town in what is now Zimbabwe, an only child who loved to read, write, and paint, and she attended a teacher's college in Bulawayo. There she was inspired to become an archaeologist, but she spent many years teaching before finally earning a Ph.D. in archaeology from Wits.

    Wadley began to explore the Middle Stone Age (MSA), which ranges from about 300,000 to 40,000 years ago and includes Sibudu and other well-known South African cave sites such as Blombos. She started out working at Rose Cottage Cave, an MSA site on South Africa's Caledon River, where she began to formulate her ideas about “complex cognition.” This concept, Wadley insists, “is a lot more empirical” and testable than the more commonly used notion of “modern human behavior,” because complex cognition focuses on actual cognitive tasks, such as toolmaking or hunting strategies, rather than on vague notions of modernity and symbolism.

    After 11 years working at Rose Cottage Cave, Wadley had an “extremely large and excellent” stone tool collection but no organic preservation of animal bones or plant materials that could tell her more about how the people lived.

    Making it stick.

    Traces of red ochre on stone tools like this one may have been used to haft the tools to handles.


    So she began looking for a site that could better test her ideas about the technological abilities of early modern humans. Tipped off by another archaeologist who had briefly excavated the top layers of Sibudu, Wadley visited the rock shelter in 1998 and saw its thick MSA layers and excellent organic preservation. “I knew this was going to be good even before I put my trowel into the earth for the first time.”

    Wadley and her team headed to Sibudu that same season, and as the years went by, they encountered, as she puts it, one “pleasant surprise” after another. So far, the team has determined that Sibudu was occupied intermittently between 38,000 and at least 77,000 years ago. “It's a long and very complete sequence of occupation,” says new dig leader Conard. “No other site has a better record of human activity.”

    This extremely long occupation record includes two sophisticated stone tool industries found across southern Africa, called the Still Bay and the Howieson's Poort and dated to about 71,000 to 72,000 years ago and 60,000 to 65,000 years ago, respectively (Science, 6 May, p. 658). Wadley and her team have microscopically analyzed residues on the Howieson's Poort tools and uncovered important clues about how they were used. Archaeologist Marlize Lombard of the University of Johannesburg found traces of tree gum and wood on the tools. That, along with patterns of wear that suggest the tools were not used for cutting or scraping, led her to conclude that they had been hafted to handles of wood or bone and probably used for hunting.

    And in a paper published last year in the journal Antiquity, Lombard went even further, suggesting from the wear patterns and other evidence that some tools from layers dated to 64,000 years ago might have been used as arrowheads. That's the earliest claim for bow-and-arrow hunting, which other archaeologists have argued was key to the success of our species, because it allows humans to take down large animals from a distance with less risk to themselves. “I find their paper quite convincing,” says anthropologist Alison Brooks of George Washington University in Washington, D.C.

    Making art, or making glue?

    Meanwhile, Wadley had been noticing that some Howieson's Poort segments had traces of ochre on the edges that apparently had been hafted into wood or bone handles. She launched a series of experiments in which she mixed Acacia tree gums, beeswax, and ochre—which is also known to have good adhesive properties—in various combinations. She found that when she got the recipe right, the mixture had all the properties needed to tightly haft tools to handles.

    In a widely read 2009 paper in the Proceedings of the National Academy of Sciences, Wadley and her colleagues detailed the multiple steps involved in this procedure: getting the ingredients ready ahead of time, heating them to the right temperature, and holding the entire hafting plan in one's mind while carrying it out over time. They argued that this was better evidence for abstract reasoning and advanced cognition than some other indications of symbolic behavior, such as the mere presence of ochre itself. “Lyn did a great job discovering and describing the steps involved in hafting [segments] onto shafts,” says archaeologist Thomas Wynn of the University of Colorado, Colorado Springs, who agrees that this process is a sign of advanced cognition. “But this needs to be weighed against the evidence that ochre probably had other roles,” he adds, citing abstract designs etched onto ochre pieces at Blombos 75,000 years ago.

    A woman and her cave.

    Lyn Wadley has spent 12 years excavating at Sibudu.


    Wynn says he is even more convinced by Wadley's contention that the hominins at Sibudu probably used snares and traps to catch small animals at least 65,000 years ago. In a 2010 paper in the Journal of Human Evolution, Wadley argued that archaeological sites containing a high proportion of animals that are difficult to capture in any other way present circumstantial evidence of the use of snares and traps, which do not preserve well.

    Indeed, the faunal record at Sibudu is dominated by small, forest-dwelling mammals such as a tiny antelope called the blue duiker and the very aggressive bushpig, animals not easily hunted but vulnerable to falling into human-laid traps. Wadley notes that recent hunter-gatherer populations in Africa use snares and traps to catch similar animals. If early H. sapiens at Sibudu were using snares and traps, Wynn says, “this would be strong evidence” for advanced cognition, because it would require planning over a span of several days and inhibiting the impulse to grab whatever food was immediately at hand.

    Yet despite the progress Wadley and her team have made at Sibudu, there are many unanswered questions. Why did early humans return again and again to the site, leaving behind such a thick mound of evidence for their presence? What was so special about this place? The team has uncovered strong evidence that the hominins who frequented the cave stayed for extended periods, including traces of bedding made from sedges and grass. “They even ate breakfast in bed,” Wadley says, citing the numerous animal bones found among the plant remains.

    It will now fall to Conard to answer those questions, if he can. Conard says “it was hard to say no” when Wadley asked him to take over the site: “Sibudu is a perfect place to study how human behavior evolved during the MSA.”

    Even when retired, Wadley says she will never stop thinking about the hominins who returned repeatedly to Sibudu. Perhaps the artist in her is speaking when she says: “I like to imagine that they would stand here and look at the river and the lovely forest around it and think this was a very beautiful place. And since they had language, they would say to each other, ‘When the fruits next appear on the trees, let's meet here again.’ ”

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