Early life: in the soup or on the rocks?

In most scenarios of the origin of life, precursors of biological molecules formed in a rich brew of amino acids. Then, on the beaches of primitive Earth, these raw materials of life somehow linked into longer, self-replicating molecules. Reproducing these events in the laboratory has proved challenging, however.

In experiments designed to mimic primordial chemistry, scientists have demonstrated that biological precursors form when simple organic compounds are blended and cooked. Yet these prebiotic molecules rarely combine into chains of more than 10 to 20 links. To replicate, researchers believe, molecules must contain close to 60 molecular segments-the minimum necessary to sustain a primitive genetic code.

Now, James P. Ferris, a chemist at Rensselaer Polytechnic Institute in Troy, N.Y., and his colleagues have shown that long, chainlike molecules called oligomers can assemble themselves on mineral surfaces. Describing the chemical feat in the May 2 Nature, the researchers contend that "the minerals on the primitive Earth would have provided a 'library' of surfaces for the exploration of molecular evolution."

Ferris' group mimicked conditions in which a warm broth of prebiotic molecules repeatedly splashed up on rocks and dried in the sun. The researchers poured solutions of amino acids and nucleotides over each of three materials: a clay called montmorillonite and two porous, bonelike minerals known as illite and hydroxylapatite. Many cycles of incubation, evaporation, and replenishment yielded oligomers up to 55 units long.

From those molecules, the scenario continues, others would have emerged-still larger molecules capable of carrying enough information to replicate.

Eventually, these prebiotic molecules could have mutated into more advanced forms, including, ultimately, the nucleic acids and proteins that make life possible.

Ferris' results represent "quite an achievement," says Andrew D. Ellington, a chemist at Indiana University in Bloomington. "In terms of the chemistry, it's a significant step ahead of what's been achieved before."

If organic molecules solidified on warm stone, says chemist Gunter von Kiedrowski of the University of Ruhr in Germany, "the polymers of life were more likely to have been baked like prebiotic crepes than cooked in a prebiotic soup."

"The message," he adds in a commentary accompanying the report in Nature, "is that the earliest forms of life may have proliferated by spreading on surfaces."