An open flame or burning flame
There are lots:
Biology and Medicine - cloning and expression of human insulin in bacteria (stopped having to produce it from pig pancreases); Watson & Crick discovery of the structure of DNA; gene therapy in humans
Chemistry - determination of the exact number of molecules in a mole (Avagadro's number); discovery of radioactivity (Rutherford); the invention of nylon (DuPont); Boyle's law (behavior of gases)
