The Inner Life of the Cell

The process of life arising naturally from non-life is called "abiogenesis." From the fourth century BC through the nineteenth century AD, some scientists and philosophers believed that certain forms of life arise spontaneously (e.g., that maggots arise from decaying meat). This theory, called "Spontaneous Generation," was decisively refuted in a series of experiments by Louis Pasteur (and others). 

Nevertheless, many scientists became convinced that, under certain conditions, a living cell can arise from nonliving molecules. However, this view only became popular because scientists believed (incorrectly) that living cells were relatively simple structures (little blobs of protoplasm). The following video shows how unimaginably mistaken this assumption was:

Of course, most biologists continue to believe that life arose from non-life. But this simply shows how reluctant people are to give up established theories (even when those theories only became established because of false assumptions).