Experiment Supports Theory That Life Began in Volcanic Environment

July 31, 1998

Experiment Supports Theory That Life Began in Volcanic Environment

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By NICHOLAS WADE

he idea that life on Earth began in the furnace-like temperatures of a volcanic environment has received support from an experiment designed to reconstruct the chemical events that may have led to the first living cells.
The experiment, reported in Friday's issue of the journal Science, shows that peptides, short protein chains, can form naturally under conditions that might plausibly have existed on the early Earth some four billion years ago.
Dr. Carl R. Woese of the University of Illinois, a microbiologist who believes that life may have begun at high temperatures like those found near volcanoes and in the undersea vents where magma gashes through the ocean floor, described the result as "another step in the grand march."
But a dash of cold water was thrown by Dr. Stanley Miller of the University of California at San Diego, a leading advocate of the view that life evolved at temperatures similar to those of today.
The chief author of the experiment, a new voice in discussions of the origin of life, was Dr. Gunther Wachtershauser. Although his day job is as a patent lawyer in Munich, Germany, Wachtershauser (pronounced VEK-terz-hoi-zer) has a degree in organic chemistry, and his papers have been accepted by leading scientific journals.
The prevailing idea about the origin of life is that prebiotic chemistry -- the chemical reactions that led to the first living cell -- probably occurred in some kind of watery environment. As a graduate student in 1953, Miller provided striking evidence for this theory by showing that many chemicals used by living cells will form naturally from a mixture of water and gases subjected to electrical discharges that mimic lightning.
But it has proved very hard to take Miller's classic experiments much further. The problem is that a pinch of chemicals in watery solution do not bump into one another often enough to create the more complicated molecules of life.
Wachtershauser has developed a quite different concept: that prebiotic reactions occurred not in solution but on a surface, probably of some common catalyst like the ores of iron and nickel. Chemicals bound to a surface would be much more likely to meet and combine into the more complicated molecules typical of life, he believes. In other words, prebiotic chemistry started in 2-D, and only later did the first systems escape into three dimensions.
With a government grant and the help of a chemist colleague, Dr. Claudia Huber of the Munich Technical University, Wachtershauser has been conducting a series of experiments to test the elements of his theory.
Last year he showed that an active, carbon-based chemistry could get started in a simple mixture of iron ore, nickel and the volcanic gases hydrogen sulfide and carbon monoxide. In their latest paper, he and Dr. Huber show that in similar conditions, amino acids, the building blocks of today's proteins, can make the characteristic link known as a peptide bond that forms the backbone of proteins. In the conditions of their experiment, chains of two and three amino acids were assembled in a novel chemical reaction, they report.
This experiment started with amino acids already in the mixture. It showed, however, that had amino acids formed under these conditions, they could go on to form peptide bonds. Amino acids formed in space are thought to have been delivered to the early Earth by meteorites and comets. Wachtershauser is also trying to show how amino acids might have been generated under volcanic conditions.
Dr. Norman Pace, an expert on early life at the University of California at Berkeley, said the new reaction showed that it is relatively easy to make biological compounds from inorganic chemicals
. "Wachtershauser's concept of mineral-based chemistry being able to generate biologically active compounds is wonderful," Pace said. "I think the milieu of a geothermal environment is far superior to the sparking bottles of Stanley Miller."
Miller remains unconvinced by the proponents of a high-temperature origin of life. He has a forceful objection: Many of the essential components of living cells are unstable at high temperatures. In a paper published this month in The Proceedings of the National Academy of Sciences, he reported that constituents of DNA lasted as little as 19 days at the temperature of boiling water.
"We conclude that a high-temperature origin of life may be possible, but it cannot involve adenine, uracil, guanine or cytosine," he wrote with a touch of acerbity, referring to four of the five main components of the nucleic acids DNA and RNA.
In Wachtershauser's theory, however, the nucleic acids are a late adornment of the system.
"In the oldest days," he said, "all the molecules of life participated in the reproduction and inheritance process, and it is only later that the nucleic acids became enthroned."
Miller also said that carbon monoxide, an important ingredient of Wachtershauser's experiments, was not known to be produced by deep-sea vents and that an earlier report to the contrary was based on an erroneous measurement.
Woese, of the University of Illinois, said he considered this "a minor drawback compared with the drawbacks of the soup theory," the soup in question being the watery environments in which Miller seeks the origin of life.
"Since all this chemistry that Wachtershauser works with is novel," Woese said, "we have to cut him a little slack rather than close the door on it immediately."

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