Astrobiology is also known as exobiology.    

It is an interdisciplinary scientific field that studies the origins, early evolution, distribution and future of Life in the Universe.

It is the multidisciplinary field that investigates the deterministic conditions and contingent events with which life arises, distributes and evolves in the universe.

It considers the question of whether extraterrestrial life exists, and if it does, how humans can detect it.

Astrobiology makes use of the following scientific fields
- molecular biology
- biophysics
- biochemistry
- chemistry
- astronomy
- physical cosmology
- exoplanetology
- geology
- paleontology
- ichnology

It investigates the possibility of life on other worlds and it helps to recognize biospheres that might be different from that on Earth.

The origin and the evolution of life are basic components of Astrobiology.    Astrobiology concerns itself with interpretation of existing scientific data, and although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories.

It may have begun shortly after the bing bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10-17 million years old...

Panspermia hypothesis suggest microscopic life may exist throughout the universe since it may have been distributed by meteoroids, asteroids and other solar system bodies.

Very large galaxies may be more favorable to. the creation and development of habitable planets than our smaller Milky Way galaxy.

But so far we, humans, only know Earth to be harboring life.   Estimates of habitable zones around other stars, also known as 'Goldilocks zones', along with the discovery of thousands of extrasolar planets and new insights into extreme habitats here on Earth, suggest that there may be more habitable places in the universe than considered before.