Early metabolism may have begun as a mix of metal and enzyme catalysis before bacteria and archaea independently evolved into free-living cells. The study, published in Science Advances, examined the chemical network early cells used to produce essential components of life and investigated how those reactions could have been powered. The researchers conclude that the transition to free-living bacteria and archaea may have occurred independently, even though both lineages share the same underlying genetic code. That result suggests that early metabolism may have depended directly on the chemistry of its surroundings. Only free-living cells are alive.