Did life start with a replicating molecule or a metabolism?

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Early biologists may have been at a loss when they wondered how life on Earth could ever have possibly arisen. Modern biochemists face the opposite quandary. They know of many possible prebiotic chemistries that could have produced cells and therefore life; the challenge lies in figuring out which one actually occurred.

The idea of a primordial "RNA world" was proposed 50 years ago, and it has since been demonstrated that biological compounds—i.e. DNA, proteins, and membranes that can enclose vesicles—can be generated with prebiotic means. That's a lot of progress. But these prebiotic means require minerals like boron and molybdenum that are only present in the requisite quantities on Mars. And there is still a big gap between the synthesis of such compounds and their organization into Life As We Know It: understanding how those biological compounds, once synthesized, became capable of replication.

According to Science's latest perspective on the origin of life, "biochemistry occurred on geological time scales, in which millions of years of a poor replicator (a blink on the geological time scale) might well have been necessary to craft a feedback cycle that led to a slightly better replicator."