A new synthesis by two Santa Fe Institute researchers offers a coherent picture of how metabolism, and thus all life, arose. The study, published December 12, 2012, in the journal Physical Biology, offers new insights into how the complex chemistry of metabolism cobbled itself together, the likelihood of life emerging and evolving as it did on Earth, and the chances of finding life elsewhere.

"We're trying to bring knowledge across disciplines into a unified whole that fits the essentials of metabolism development," says co-author Eric Smith, a Santa Fe Institute External Professor.

Creating life from scratch requires two abilities: fixing carbon and making more of yourself. The first, essentially hitching carbon atoms together to make living matter, is a remarkably difficult feat. Carbon dioxide (CO2), of which Earth has plenty, is a stable molecule; the bonds are tough to break, and a chemical system can only turn carbon into biologically useful compounds by way of some wildly unstable in-between stages.

As hard as it is to do, fixing carbon is necessary for life. A carbon molecule's ability to bond stably with up to four atoms makes it phenomenally versatile, and its abundance makes it suitable as a backbone for trillions of compounds. Once an organized chemical system can harness and manipulate carbon, it can expand and innovate in countless ways.

In other words, carbon fixation is the centerpiece of metabolism -- the basic process by which cells take in chemicals from their environments and build them into products they need to live. It's also the link between the geochemistry of Earth and the biochemistry of life.

In a paper earlier this year, Smith and Santa Fe Institute Omidyar Fellow Rogier Braakman mapped the most primitive forms of carbon fixation onto major, early branching points in the tree of life (PLoS Computational Biology, April 18, 2012). Now, the two researchers have drawn from geochemistry, biochemistry, evolution, and ecology to detail the likeliest means by which molecules lurched their way from rocks to cells.