How did Louis Pasteur's experiments support the idea of biogenesis?

Louis Pasteur provided definitive evidence against the theory of spontaneous generation through his experiments with "swan-neck" flasks.

To test whether life could arise from nonliving matter, Pasteur boiled beef broth in flasks with long, curved necks. These necks allowed air to enter but trapped dust particles and other potential microbial contaminants in the bend, preventing them from reaching the broth. As long as the broth remained isolated from these contaminants, it stayed sterile, demonstrating that life did not spontaneously generate within the liquid.

However, when Pasteur broke the necks of the flasks, exposing the broth directly to the air and its associated particles, the broth eventually became cloudy with microbial growth. These results proved that microorganisms were present in the environment and were responsible for contamination, rather than arising spontaneously from the broth itself. By establishing that life must come from pre-existing life, Pasteur’s work provided the foundation for the science of bacteriology and validated the principles of germ theory.1