The Origin of Life
A case is made for the descent of electrons
The Origin of Origins
Most historians would say that the modern era of experimental research in origin-of-life studies began in a basement laboratory in the chemistry department of the University of Chicago in 1953. Harold Urey, a Nobel laureate in chemistry, and Stanley Miller, then a graduate student, put together a tabletop apparatus designed to look at the kinds of chemical processes that might have occurred on the planet soon after its birth. They showed that organic molecules (in this case amino acids) could be created from inorganic materials by natural environmental conditions such as acidic solution, heat and electrical discharge (lightning), without the mediation of enzymes. This finding triggered a wave of new thinking about both the origin and nature of life. (Today, the consensus is that Miller and Urey had the wrong atmospheric components in their apparatus, so the process they discovered was probably not representative of the emergence of life on Earth. It nevertheless pointed to the potential fecundity and diversity of nonenzymatic primordial chemistry.)
Since 1953, we have found many of the same simple organic molecules in meteorites, comets and even interstellar gas clouds. Far from being special, then, the simplest of the molecules we find in living systems—life’s building blocks—seem to be quite common in nature. To many, the real question was how these basic building blocks got put together into living systems, and, equally important, how the molecules that led to modern life were selected out of the messy molecular milieu in which they arose.
The ubiquity of simple molecules suggested an appealing scenario that had a profound effect on the way investigators approached the origin of life throughout the last half of the 20th century. The scenario went like this: After the Earth cooled enough to allow oceans to form, the Miller-Urey process or something like it produced a rain of organic matter. In a relatively short time, the ocean became a broth of these molecules, and given enough time, the right combination of molecules came together by pure chance to form a replicating entity of some kind that evolved into modern life.
Scientists called this scenario the Oparin-Haldane conjecture, but it was given a provocative nickname that endures in the popular consciousness—Primordial Soup.
The essential legacy of the Primordial Soup was twofold: It simplified the notion of the origin of life to a single pivotal event, and then it proposed that that event—the step that occurred after the molecules were made—was a result of chance. In the standard language, life is to be seen, in the end, as a “frozen accident.” In this view, many fundamental details about the structure of life are not amenable to explanation. The architecture of life is just one of those things. Although many modern theories are less extreme than this, frozen-accident thinking still influences what some of us ask about the origin of life and how we prioritize our experiments.