Urey speculated that the early terrestrial atmosphere was composed of ammonia, methane, and hydrogen. One of his Chicago graduate students was Stanley L. Miller, who showed in the Miller–Urey experiment that, if such a mixture were exposed to electric sparks and water, it can interact to produce amino acids, commonly considered the building blocks of life. Work with isotopes of oxygen led to pioneering the new field of paleoclimatic research. In 1958, he accepted a post as a professor at large at the new University of California, San Diego (UCSD), where he helped create the science faculty. He was one of the founding members of UCSD's school of chemistry, which was created in 1960. He became increasingly interested in space science, and when Apollo 11 returned moon rock samples from the moon, Urey examined them at the Lunar Receiving Laboratory. Lunar astronaut Harrison Schmitt said that Urey approached him as a volunteer for a one-way mission to the Moon, stating "I will go, and I don't care if I don't come back."