Alternative biology is the study of theoretical or non-traditional life forms such as acellular life, non-carbon-based life, extraterrestrial life, cyborg life, or artificial life.
It also considers the earliest theoretical forms of life on Earth, such as RNA life or iron-sulfur life which may have been the earliest organisms.
Known biological entities which may not always be considered life may also be considered in alternative biology such as viruses and plasmids.