A classic experiment exploring the origin of life has, more than a half-century later, yielded new results.

In 1953, Stanley L. Miller, then a graduate student of Harold C. Urey at the University of Chicago, put ammonia, methane and hydrogen  the gases believed to be in early Earth’s atmosphere  along with water in a sealed flask and applied electrical sparks to simulate the effects of lightning. A week later, amino acids, the building blocks of proteins, were generated out of the simple molecules.

Enshrined in high school textbooks, the Miller-Urey experiment raised expectations that scientists could unravel the origins of life with simple chemistry experiments.

The excitement has long since subsided. The amino acids never grew into the more complex proteins. Scientists now think the composition of air on early Earth was much different from what Dr. Miller used, leading some to question whether the Miller-Urey experiment had any relevance to the still unsolved problem of the origin of life.