Astrobiology is the study of the origin, evolution and distribution of life in the universe. It seeks to answer two important scientific questions: how did we get here and are we alone in the universe? Scientists begin by studying life on Earth and its limits. The discovery of extremophiles on Earth capable of surviving extremes encourages the idea of life beyond our planet. Astrobiologists search for microbial life on rocky planets and moons in our solar system and on Earth-like planets orbiting other stars in the universe, looking for evidence of any biological activity that would indicate the presence of life.