Perhaps the leading theory focuses on a much more prosaic realm: the slimy interface where the sea laps against land. If early oceans carried organic molecules—and they most likely did—the porous surfaces of shoreline minerals could have helped organize such building blocks into primitive structures. Eventually, these units could have replicated, forming thin films on the seashore rocks, says Robert Hazen, a researcher at the Carnegie Institution in Washington.
Scientists favoring one or another theory have tried to boost their case by attempting to re-create the elements of life—and even life itself—from the bottom up. Such work sparked to life in 1953, when two researchers cooked up a "primordial soup" of amino acids. In their University of Chicago lab, they applied simulated lightning to a pair of flasks that contained, respectively, an oceanlike solution and an atmosphere rich in methane, water vapor, ammonia, and hydrogen. That experiment and subsequent ones showed that simple chemistry can transform nonorganic molecules into the building blocks of life.
"The classic experiments done over a period of 50 years give us confidence that the building blocks would have been present," says Andrew Knoll, a paleontologist at Harvard University. "The big question is how do you go from there to something that can replicate itself." A pile of lumber, after all, is not a house.
To understand how the transition might have occurred, a handful of scientists are striving to re-enact it in the lab. Jack Szostak of Harvard Medical School is at the forefront of this work. In his lab, researchers fill test tubes with the barest ingredients of life, then watch the elements self-assemble into what look like primitive cells, hoping that they will begin replicating. "Sooner or later, life will be made in the lab," says Joyce, who performs similar experiments.
While none of these primitive cells have yet "gone critical" and started to copy themselves, the research has already paid real-world divi-dends, including one blockbuster pharmaceutical and perhaps more to come. The drug Macugen treats macular degeneration, the leading cause of blindness in the elderly, with a tiny snippet of the genetic molecule RNA. Since scientists like Szostak think RNA preceded DNA, they've invented ways of pushing RNA to evolve in test tubes. Under the right conditions, that process can produce an RNA molecule that's evolutionarily "fit" for a task like treating the biological cause of macular degeneration.
Hazen says that origins-of-life experiments may also help create synthetic cells that can churn out biofuels, which would be a boon in these days of energy crunches and concerns about climate change. "Life takes things like carbon dioxide and water and makes useful compounds, including fuels," he says. "If we understand in a basic way how that's done," he adds, then scientists might be able to build a primitive, fuel-producing protocell.
Such a self-replicating system, Joyce and Szostak contend, would constitute life. And while such a feat may not exactly recapitulate how biology began, it would be example No. 2—the first being the entire panoply of plants, animals, and other organisms that now dominate our planet.