President Obama speaks during a campaign event at University of Colorado Boulder Sept. 2. He and his Republican challenger, Mitt Romney, will have their first debate at the University of Denver on Wednesday.
Pablo Martinez Monsivais/AP
Vice President Richard Nixon listens as Sen. John F. Kennedy talks during their televised presidential race debate. This photo was made from a television screen in New York, Oct. 21, 1960.
Plankton make up 98 percent of the biomass of ocean life and provide half of the oxygen on the planet. Scientists are working to figure out how climate change may be affecting these important microorganisms.
M. Ormestad/Tara Oceans