U.S. Marines board a C-130 transport plane as they withdraw from Camp Leatherneck, their huge base in southern Afghanistan. This marked the biggest handover yet to the Afghan army, which is facing a tough fight with the Taliban in Helmand province and other parts of southern Afghanistan. Wakil Koshar/AFP/Getty Images hide caption

IBM's Watson supercomputer is most famous for winning at Jeopardy! Now it's been called in to come up with recipe ideas. Bob Goldberg/AP/IBM hide caption

We asked you to send in your embarrassing instant messenger handles from days gone by. Thanks for sharing, Blondsoccerplyr, AgentGiggleChunk and absofsteel3616! iStockphoto hide caption

A woman on the L train in New York City last week covers her face, fearful because a doctor with Ebola rode the train days earlier. Epidemiologists say people on the subway were not at risk. Stephen Nessen /WNYC hide caption

Caribous doing their business in mountain ice have left a viral record hundreds of years old. Courtesy of Brian Moorman hide caption

W.H. Auden at the 92nd Street Y Poetry Center in 1966. Diane Dorr-Dorynek/Courtesy of the 92nd Street Y hide caption

Proponents of the taxes say that if the measures pass, the money would be directed, in San Francisco, toward childhood nutrition and recreation and, in Berkeley, into the city's general fund. Joel Saget /AFP/Getty Images hide caption

Companies from Jordan, Pakistan, Turkey, Saudi Arabia and Iran were among the more than 100 Internet startups at this year's Startup Istanbul event on Sept. 30. It was Iranian entrepreneurs' first time competing on an international stage. Courtesy of Startup Istanbul hide caption

Caltech biochemical engineer Frances Arnold was awarded a National Medal of Technology and Innovation by President Obama in 2013. Jason Reed/Reuters/Landov hide caption

In 2011, Glen Campbell announced that he had been diagnosed with Alzheimer's disease. Courtesy of the artist hide caption