Extraterrestrial Life

Extraterrestrial life is defined as life that does not originate from Earth. Various controversial claims have been made for evidence of extraterrestrial life. A less direct argument for the existence of extraterrestrial life relies on the vast size of the observable Universe. According to this argument, supported by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere other than Earth.