Year-end lists inevitably leave room for debate and criticism, and ours is no exception. It was an eventful year, and we relied on voting among Scientific American editors to cull our candidates. Any of these notable achievements were certainly worthy but didn't make the final cut. The runners-up were:
• The discovery in South Africa of a new hominid, called Australopithecus sediba, that could be a lost member of our family tree
• The emergence of hydraulic fracturing, or “fracking,” a controversial way to recover natural gas trapped in deep rocks
• The detection of an atmosphere of a “super-Earth” and other signs of potentially habitable worlds around other stars