Health & Science

Did a comet lay waste to North America?

Scientists have long known that dozens of large species in North America, including the continent’s earliest human inhabitants, were suddenly wiped out some 13,000 years ago. But debate has raged over what caused the extinction, with explanations ranging from climate change to overhunting. Now, the discovery of microscopic diamonds deep in the Arizona soil has boosted one of the theories: that a comet exploded on or above North America, producing tremendous fires and floods from melting glaciers, followed by a cataclysmic ice age when smoke and sediment blocked the sun. The “nanodiamonds,” which are produced under intensely hot, high-pressure conditions, provide compelling evidence of enormous “cosmic impacts,” researchers say. The comet theory could explain the disappearance of such mammals as the saber-tooth tiger and the mammoth, as well as of the Clovis people, believed to be the first humans to migrate to the Americas from Siberia. The diamond discovery does not settle the debate, but it points researchers in a new direction. “This is an event that happened on one day,” lead researcher Doug Kennett of the University of Oregon tells Scientific American. “We’re going to need high-resolution climate records, archaeological records, and paleontological records to try to explore the effects.”

Memories we can live without

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How do older people manage to live with all the setbacks and losses that life inevitably deals them? A new study suggests that as people age, they learn to process and remember negative experiences differently, so those ordeals have less long-term impact. Researchers at Duke University scanned the brains of people in their 20s and 70s as they looked at various images, some of them disturbing. Later, when they were asked to try to recall the images, the older subjects remembered far fewer of the negative images than the younger ones did. The brain scans showed that young adults have stronger neural connections between the emotional and memory-storing parts of the brain, especially when the memories are of negative experiences. But older people process intense experiences in the “higher thinking” area of the brain called the frontal cortex. As a result, older people are essentially diluting the emotional punch of negative experiences, researchers say, making them less likely to be remembered. A survival mechanism appears to be in play. “They may be suppressing negative emotions to maintain emotional well-being,” neuroscientist Roberto Cabeza tells USA Today.

When ignorance is not bliss

Your choice of a surgeon may determine whether you live or die, yet most people tend to treat that decision as almost an afterthought, says The New York Times. A survey by the American College of Surgeons found that the average patient devotes an hour or less to researching his surgeon or surgical procedure. More than a third of those operated on in the past five years made no attempt at all to review the credentials of the doctor who cut them open. In fact, the study found, people are likely to spend more time researching a job change (10 hours, on average) or a new car (eight hours) than an upcoming operation. This laissez-faire approach is not in the patient’s best interests, says Dr. Thomas Russell, executive director of the surgeons association. “Today, medicine and surgery are really team sports,” Russell says. “The patient, as the ultimate decision-maker, is the most important member of the team and must understand what’s going on.”

When alcohol beckons

The closer teens live to places alcohol is sold, the greater their risk of binge drinking and drunken driving, says the Los Angeles Times. Researchers from the Pardee RAND Graduate School in Santa Monica, Calif., studied the relationship between drinking among children ages 12 to 17 and their proximity to liquor stores. They found a sharp increase in alcohol abuse among kids who lived within a half-mile of places that sell alcohol. The statewide study also found that alcohol is far more readily available in predominantly minority neighborhoods than in mostly white ones, which could contribute to higher rates of crime and drunken driving in the minority areas. While other factors besides “opportunity” are at work, researchers say that living within walking distance of a liquor store clearly presents a “risk factor for youth.”

How ads get inside our heads

Advertising can persuade consumers to want a product, but too much of it may backfire, says LiveScience.com. Cognitive scientist Mark Changizi of Rensselaer Polytechnic Institute has studied how traditional advertising works, and he’s found that our unconscious minds are constantly weighing the cost of obtaining an item against its value or benefit. Advertising establishes that a product is available and desirable—an important first step. But if we then conclude that the item is too available, we’ll suspect it’s not that valuable, so we’ll want it less. This “cost-benefit” analysis happens unconsciously, Changizi says, but advertisers who inundate us with images of their products may actually be detracting from the items’ desirability. The newest kind of advertising—product placements in TV shows and films—on the other hand, signals to us that a product is available without triggering the negative feelings that come from overexposure. So it’s probably more effective than traditional ads.