A study published in the journal Science last December suggested that a bacterium found in California's Mono Lake was able to substitute arsenic for phosphorous. But that conclusion has many critics.
Miss Bliss 55 via Flickr
Shoppers crowd a narrow street outside Tsukiji market in Tokyo on Dec. 31, 2010. Japan has relatively tight social rules. And that makes sense, according to researchers. When people are squeezed together, they have an incentive to cooperate.
Toru Yamanaka/AFP/Getty Images
CT scans of fossil Hadrocodium skulls allowed scientists to reconstruct its brain. The olfactory bulbs, located at the front of the brain, grew steadily larger as millions of years passed.
Matt Colbert/University of Texas at Austin