A replica of the pinky bone fragment found in a Siberian cave. Researchers used the bone bit to extract and sequence the genome of a girl who lived tens of thousands of years ago. Max Planck Institute for Evolutionary Anthropology hide caption

itoggle caption Max Planck Institute for Evolutionary Anthropology

A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/Wikimedia Commons

The Larsen B ice shelf, a large floating ice mass on the eastern side of the Antarctic Peninsula, shattered and separated from the continent 10 years ago. A NASA satellite captured the event in this image from Feb. 23, 2002. The 650 foot-thick, 1,250-square-mile ice shelf had existed since the last ice age. AP hide caption

itoggle caption AP

Childhood obesity is on the rise in many countries and overuse of antibiotics is now on the radar as a possible factor in the epidemic. Here 18-month-old twins are weighed in a nutritionist's office in Colombia. Raul Arboleda/AFP/Getty Images hide caption

itoggle caption Raul Arboleda/AFP/Getty Images

It may not be the best strategy to stay up late and cram. A new study finds that when teens don't get the sleep they need, all kinds of things can go poorly. iStockphoto.com hide caption

itoggle caption iStockphoto.com