Life's First Scalding Steps

Science News, Jan 9, 1999 by Sarah Simpson

Around the vents, he theorizes, catalytic metallic ions first enabled the materials around them to fashion acetic acid. In the next step, the ions catalyzed the addition of a carbon molecule to the acetic acid to get three-carbon pyruvic acid, which is another key chemical in the citric acid cycle and also reacts with ammonia to form amino acids, which themselves link up to form proteins.

After writing the blueprint, Wachtershauser set out to prove each step. He produced the first important component of his assembly process 2 years ago. He and fellow German chemist Claudia Huber, of the Technical University of Munich, reported in the April 11, 1997 SCIENCE that they generated large quantities of activated acetic acid from basic raw materials at 100 [degrees] C. This is the temperature typical of the fringe of a hydrothermal vent, where the volcanic brines mix with near-freezing ocean water.

Critics complain that Wachtershauser's experimental temperature represents a limited zone in the vent environment. Toward the scalding core of a vent system, temperatures are nearer 350 [degrees] C.

A longtime supporter of the primordial soup hypothesis, Jeffrey L. Bada of the Scripps Institution of Oceanography in La Jolla, Calif., has conducted several experiments showing that certain life-critical chemicals could not survive in their scorching birthplace for more than a few minutes or days. By testing reactions at only a single temperature, Bada says, Wachtershauser is "not playing with a full deck of cards."

Such a rebuke doesn't apply to other experimentalists, such as the Carnegie Institution team, who are joining the game. The Carnegie researchers at times closely follow Wachtershauser's blueprint, but they're aiming for results much broader, and perhaps more convincing, than the German chemist has achieved to date.

They are trumping Bada's criticism by testing chemical reactions over a much wider range of temperatures. What's more, with their bomb apparatus, the team can perform experiments at the extreme pressures that are typical under thousands of meters of seawater, a factor Wachtershauser never explored.

Christopher Chyba of the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, Calif., is encouraged by the growing interest in this research. "A variety of ideas, many of them flowing out of Wachtershauser's hypothesis, are now leading to a kind of renaissance of experiments in the origins of life," he says.

It was another origins-of-life theorist who got the Carnegie team involved. About the same time that Wachtershauser began considering metabolism as the root of life, a similar idea came to biologist Harold J. Morowitz of George Mason University in Fairfax, Va. He also was drawn to the primitive power of the citric acid cycle. Unlike Wachtershauser, Morowitz's first ponderings were still steeped in the primordial soup.

It took prodding from his friend Corliss, now at the Central European University in Budapest, for Morowitz to move his envisioned birthplace of prebiotic metabolism out of the light and into the ocean depths. That's when he turned to his George Mason colleague Robert M. Hazen, who also holds a position at Carnegie's Geophysical Laboratory. Hazen had long studied what happens to the structures of mineral crystals buried deep inside the Earth, so his high-pressure expertise translated easily into methods for testing what might happen to chemicals at vents.