The molecule was not alive, at least not in any conventional sense. Yet its behavior was astonishingly lifelike. When it appeared last April at the Scripps Research Institute in La Jolla, California, scientists thought it had spoiled their experiment. But this snippet of synthetic rna — one of the master molecules in the nuclei of all cells — proved unusually talented. Within an hour of its formation, it had commandeered the organic material in a thimble-size test tube and started to make copies of itself. Then the copies made copies. Before long, the copies began to evolve, developing the ability to perform new and unexpected chemical tricks. Surprised and excited, the scientists who witnessed the event found themselves wondering, Is this how life got started? See the top 10 scientific discoveries of 2009. It is a question that is being asked again and again as news of this remarkable molecule and others like it spreads through the scientific world. Never before have the creations of laboratories come so close to crossing the threshold that separates living from nonliving, the quick from the dead. It is as if the most fundamental questions about who we are and how we got here are being distilled into threadlike entities smaller than specks of dust. In the flurry of research now under way — and the philosophical debate that is certain to follow — scientists find themselves confronting anew one of earth’s most ancient mysteries. What, exactly, is life, and how did it get started? See TIME’s special report on the environment.