Abiogenesis is the development of living organisms from non-living precursors. The term was first applied by Thomas Huxley and comes from the Greek a "without" and bios "life." Gradual abiogenesis by chemical and biochemical evolution on the surface of the young Earth is the standard model of how terrestrial life arose (see life, origin), although evidence is accumulating that at least some of the early stages of abiogenesis may have taken place in space. According to a more extreme view, dense clouds of gas and dust in space may serve as the actual birthplace of primitive organisms (see life, in space). By contrast, some advocates of the panspermia hypothesis have maintained that there are no compelling reasons to believe that life originally came from non-living matter.
The old theory of instantaneous abiogenesis, known as spontaneous generation, was discredited over a period of two centuries by the experimental work of Redi, Spallanzani, de LaTour, Schwann, Pasteur, and Tyndall.