Question

Would you mind explaining what Urey and Miller's experiment actually was, and what they concluded from their experiment?

The Miller-Urey experiment is a famous milestone toward understanding the origin of life on Earth, and detailed descriptions can be found on a number of websites (use your search engine); it is also described in many high-school and college textbooks on biology and astronomy. Under the guidance of his advisor, Nobel-laureate Harold Urey, graduate student Stanley Miller at the University of Chicago carried out a series of laboratory experiments to determine if complex organic compounds could be synthesized under conditions that were chemically similar to those of the early Earth. These conditions were then thought to involve a reducing or hydrogen-rich chemistry, so Miller used compounds such as methane and ammonia as well as water in his experiment. He discovered that many carbon-bearing or organic compounds were formed under these circumstances, thus providing considerable support for the concept that life (or at least the chemical building blocks of life) originated on Earth through naturalistic chemical processes. The term "Miller-Urey experiment" also refers to many subsequent laboratory studies of increasing complexity, including those that involve a less-reducing chemistry, which we now think was more representative of the atmosphere of the early Earth. The key questions for each of these experiments are (1) what was the actual set-up, especially the nature of the gases used, (2) what were the chemical products, or more properly what was the yield of the experiment for various compounds of interest, and (3) what was the interpretation in terms of the chemical evolution of the Earth and other planets.

David Morrison
NAI Senior Scientist
October 1, 2003