The bdelloid rotifer Philodina gregaria. Bdelloid rotifers are tiny invertebrates that reproduce asexually. Courtesy of Micrographia hide caption

itoggle caption Courtesy of Micrographia

Water in the atmosphere traps heat, like glass in a greenhouse. When there's less water vapor in the atmosphere, less heat is trapped. Space Frontiers/Getty Images hide caption

itoggle caption Space Frontiers/Getty Images

An artist's rendition of two Sinosauropteryx dinosaurs, showing their short, bristle-like feathers along the midline of the head, neck, back and around the tail, forming irregular stripes. Chuang Zhao and Lida Xing hide caption

itoggle caption Chuang Zhao and Lida Xing

Tools like these ax heads from Vinelz, Switzerland, were used by Neolithic farmers and may have been part of their sex appeal to hunter-gatherer women. Sandstein via Wikimedia hide caption

itoggle caption Sandstein via Wikimedia

The red specks highlight where the integrity of the brain's white matter is significantly less in the teens who binge drink, compared to those who do not. Courtesy of Susan Tapert/Tim McQueeny/UCSD hide caption

itoggle caption Courtesy of Susan Tapert/Tim McQueeny/UCSD

Smog shrouds the Los Angeles skyline. New ozone standards from the EPA aim to reduce smog, but may actually increase global warming. David McNew/Getty Images hide caption

itoggle caption David McNew/Getty Images

Researchers dyed sperm from each deer mouse a different color; in this case, red represents one male and green another. The sperm joined together with their own kind, as seen here, allowing them to swim faster than those that did not cluster together. Heidi Fisher hide caption

itoggle caption Heidi Fisher

This decorative shell ornament, attributed to Neanderthals, shows signs of being painted with orange pigment. It's one of several examples of ornamentation that researchers have found in Spain, at sites that were used by Neanderthals as far back as 50,000 years ago. Courtesy of Joao Zilhao hide caption

itoggle caption Courtesy of Joao Zilhao