Science  18 Nov 2011:
Vol. 334, Issue 6058, pp. 882

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  1. When the Bough Doesn't Break

    Leonardo da Vinci observed that when a tree's trunk splits into two branches, the total cross section of those secondary branches will equal the cross section of the trunk. Now, a new study suggests that trees may grow this way to resist wind damage.

    Christophe Eloy, a physicist at the University of California, San Diego, who is also affiliated with University of Provence in France, found the wind connection by modeling a tree as beams anchored at one end and assembled into a fractal, a shape that can be split into parts, each of which is a smaller version of the larger structure. So when a branch split into smaller branches, it split into the same number of branches, at approximately the same angles and orientations. Most natural trees grow in a fairly fractal fashion.

    Eloy modeled the force of wind blowing on a tree's leaves as a force pressing on the unanchored end of the beam. When he plugged that wind force equation into his model and assumed that the probability of a branch breaking due to wind stress is constant, he came up with Leonardo's rule, Eloy reveals in a paper soon to be published in Physical Review Letters.

  2. Biggest of Mass Extinctions Looking Even Worse

    The most detailed look yet at events at the end of the Permian Period 252 million years ago confirms a link between the biggest and baddest of eruptions and the most massive of extinctions. Paleontologist Shu-zhong Shen of Nanjing Institute of Geology and Palaeontology in China and his co-authors intensively sampled the fossil records at nine sites across South China and dated 300 mineral grains using the radioactive decay of uranium to lead.

    The extinction in the sea took no longer than 200,000 years and likely less than a geologically fleeting 100,000 years, the researchers report in a paper published online this week in Science. A similarly abrupt extinction struck rainy forests at exactly the same time. And the new, highly precise age for the extinction puts it within a mere tens of thousands of years of the great volcanic outpourings that formed the Siberian Traps, says geochronologist Paul Renne of the Berkeley Geochronology Center in California. Somehow, the nasty spewings of the eruptions—greenhouse gases and acid-generating sulfur among them—must have done in most of Permian life.