Extraterrestrial life is life that is not from the planet Earth. It is alien life. The word 'Terra' in Latin refers to our planet - Earth. Thus, Extraterrestrial Life refers to the life forms not originating on or from the planet Earth.
It is not a new idea. Quite a few philosophers have speculated on the existence of other planets like ours, with the idea that what happened here could also happen there. One thing we do know is that many other star systems do have exoplanets.
- Sagan, Carl & Shklovskii I.S. 1966. Intelligent life in the Universe. Random House.
- Sagan, Carl 1973. Communication with extraterrestrial intelligence. MIT Press. ISBN 0-262-19106-7
- Crowe, Michael J. 1986. The Extraterrestrial life debate, 1750–1900. Cambridge. ISBN 0-521-26305-0
- Crowe, Michael J. 2008. The extraterrestrial life debate Antiquity to 1915: a source book. University of Notre Dame Press. ISBN 0-268-02368-9