Science  04 Mar 2011:
Vol. 331, Issue 6021, pp. 1119

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  1. Visions From Africa


    On an African savanna 10 million years ago, our ancestors may have gazed upon a view much like this one. A new study suggests that this complex scenery influenced the mosaic in which the human retina's red, green, and blue light-sensitive cone cells are arranged.

    Studies in other species have suggested that cone cells evolve into a configuration that most efficiently takes in an animal's environment. To find out whether the same happened in human eyes, physicist Gasper Tkačik, neurobiologist Vijay Balasubramanian, and colleagues at the University of Pennsylvania created a database of more than 5000 high-resolution photographs, including this one, taken at various locations in a primate habitat in Botswana, the general region where humans likely evolved. The researchers measured the color information contained in these images and created an algorithm to predict which pattern of cone cells would extract the most information. That turns out to be the one found today in our retinas, which have an overabundance of red and green cones. The study and the image database, described in a paper on the preprint arXiv, may be useful for researchers trying to create machines with humanlike vision.

  2. Stage Set for Sixth Mass Extinction of Animals


    By consulting the fossil record to see how quickly different creatures have gone extinct in the past, a team of scientists has found that animals are going extinct so rapidly that we are on the brink of a mass extinction. Mass extinctions—in which more than three-quarters of the species on Earth disappear—have taken place five times in the past 540 million years. But if all of the animals that are currently endangered, critically endangered, or vulnerable actually go extinct, their loss will add up to a sixth mass extinction, according to a report published this week in Nature by paleobiologist Anthony Barnosky and his colleagues at the University of California, Berkeley. The researchers estimate that this mass extinction could arrive as soon as 300 years to 2200 years. But Barnosky says there's still time to fend it off by protecting these endangered animals from invasive species, habitat loss, disease, and global warming.

  3. Weird Matter Seen in Neutron Stars

    Astrophysicists have long speculated that nuclear matter inside neutron stars might flow without resistance—much as electricity does in superconductors. Now, two teams say they have direct evidence of such bizarre “superfluidity” in a neutron star.

    When a superconductor is cooled nearly to absolute zero, the electrons in it form hard-to-break “Cooper pairs” that flow without resistance. In theory, inside a neutron star—the superdense core of a massive star that exploded as a supernova—neutrons should pair in a similar way.

    Astronomers have seen indirect hints of such neutron superfluidity. Now, a team led by Dany Page, an astrophysicist at the National Autonomous University of Mexico in Mexico City, say NASA's orbiting Chandra X-ray Observatory has bolstered the case. Chandra's observations of the young neutron star Cassiopeia A show that its temperature of about 2 million kelvin plummeted 4% in 10 years. That huge cooling rate—the first ever measured in real time for a neutron star—shows that Cooper pairs are forming, the researchers reported online last week in Physical Review Letters. That's because when neutrons pair, they release energy that can increase the emission of neutrinos, the star's main cooling mechanism. A team led by Dmitry Yakolev of the Ioffe Physical-Technical Institute in St. Petersburg, Russia, has a similar paper in press at the Monthly Notices of the Royal Astronomical Society.

  4. Indonesia's Mud Volcano to Flow On and On

    Since it roared to life in May 2006, a mud volcano near Indonesia's coastal city of Sidoarjo has swallowed homes, rice paddies, factories, and roads, killing 15 people, displacing 40,000, and harming the livelihoods of many more. Will it ever stop? Not anytime soon. A new study online in the Journal of the Geological Society predicts the volcano, nicknamed Lusi, will continue spewing significant amounts of mud for at least another 2 decades.

    An aerial shot of Lusi.


    Richard Davies, a geologist at Durham University in the United Kingdom, believes that the eruption is driven by pressurized water from a deep aquifer beneath an impermeable rock layer. He argues that a well bore pierced the impermeable rock, allowing water to gush up and sweep overlying mud to the surface. Based on the volume of mud ejected after 1 year and 3 years, and assumptions about the size of the aquifer, Davies and colleagues estimate that mud will be flowing for 26 years and that the ground around Lusi will subside up to 475 meters. And that may be an underestimate—other researchers contend the flow could last even longer.