In 1953, Stanley Miller and Harold Urey built a model of Earth's early atmosphere by mixing gases that were thought to have been there. They exposed the gases to an electric current to simulate lightning. The liquid that condensed during the experiment contained amino acids. What was the significance of their results? A. Miller and Urey proved that biological molecules could have formed in a similar way. B. Miller and Urey proved that lightning was necessary for life to form on Earth. C. Miller and Urey proved the theory of spontaneous generation. D. Miller and Urey proved that all life evolved from a single common ancestor.