The Origins Divide: Reconciling Views on How Life Began

Abstract

F our and a half billion years ago, the planet Earth coalesced out of the gas and dust left over from the formation of the sun. For the next several hundred million years, the young planet was bombarded by comets and meteorites, volcanic eruptions raged across its surface, and its heat boiled the nascent oceans. But within about a billion years—and perhaps much earlier—life had arisen. How nonliving chemicals transformed into living molecules is one of the biggest mysteries in science, and we might never know for sure how it happened. Deep divides in opinion are found in almost all areas of origin-of-life research. Did life begin in extreme heat or relative cold? Were its essential molecules synthesized in the prebiotic ocean, at the mouths of churning deep-sea vents, or did they rain down from space? Did the first life-form get its energy from the sun or from the chemical energy of minerals? Were inherited genetic molecules essential to the first life-form, or could life simply have been a chain of chemical reactions taking place on a rock? “If we’re going to make any progress, we really have to be critically life couldn’t arise out of nothing, then where did it come from? A few years later, Darwin speculated about chemical reactions in a “warm little pond,” and Alexander Oparin and J. B. S. Haldane independently took that idea a step further by proposing that life began in a primordial ocean of organic molecules. Origin-of-life research didn’t get its experimental start, however, until the famed chemical synthesis experiments of Stanley Miller and Harold Urey, of the University of Chicago, were published in 1953. By sending an electrical current through a mixture of water, methane, ammonia, and hydrogen, they simulated what might have happened when lightning struck the oceans and atmosphere of ancient Earth. What they got—a mixture of key amino acids and other organic molecules—profoundly changed views of the origin of life. The origin of biology was now experimentally approachable. Other groups soon conducted similar experiments, and in the following years, researchers managed to synthesize not only additional amino acids but also other essential biomolecules, including sugars, metabolic acids, and lipids. honest about what we don’t know,” says geochemist George Cody, of the Carnegie Institution for Science in Washington, DC. “And that’s just about everything.” The questions surrounding life’s origins are indeed vast and, for the most part, unanswered. A comprehensive explanation of the origin of life will require pinning down the beginnings of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), of proteins and lipid membranes, of genetic coding and metabolic machinery. In modern life, all of these molecules and processes are so intertwined that it’s difficult to imagine how any of them could have arisen without the others already in place. Chicken-andegg problems abound. But new technologies, hypotheses, and experiments are constantly surfacing, and each step reveals a bit more of the way the inanimate chemistry of Earth’s beginnings may have morphed into the remarkable variety of life we see today.