What term describes the idea that simple life forms appeared spontaneously through chemical reactions long ago?

The term that accurately describes the idea that simple life forms originated spontaneously through chemical reactions in the distant past is abiogenesis. This concept suggests that life arose naturally from non-living chemical compounds without the involvement of pre-existing living organisms.

Essentially, abiogenesis posits that under certain conditions, certain combinations of elements and molecules could lead to the formation of complex structures that eventually gave rise to the earliest forms of life. This idea is supported by various scientific theories and experimental evidence that focus on the conditions present on early Earth and how they might have facilitated the emergence of life.

Other terms listed in the choices refer to different concepts in biology. For instance, biogenesis is the principle that living organisms arise from pre-existing life, opposing the idea of abiogenesis. Cell theory is a fundamental concept stating that all living organisms are composed of cells, and spontaneous generation is a historical and now-discredited concept suggesting that living organisms could arise from non-living matter in a fast and unregulated manner. Understanding these distinctions clarifies why abiogenesis is the most appropriate term for describing the origin of simple life forms from chemical reactions.