Origin of life in a hot iron-sulphur environment

In 1953 Stanley Millar produced carboxylic acids and amino acids by shooting sparks through a glass vessel containing an atmosphere of water, methane, hydrogen and ammonia (Miller, 1953). This was a ground-breaking experiment, which has been used as the basis for much theorizing on the origin of life in a warm (but not hot) shallow sea-water broth. It is now quite widely believed, however, that the early atmosphere did not contain a significant amount of methane, hydrogen or ammonia, but instead was dominated by carbon dioxide, nitrogen and water (Huber and Wachtershauser, 1997) - a mixture which would be non-productive in a Miller-type experiment.

The origin-of-life pendulum is now swinging clearly away from the warm broth environment, towards a hydrothermal ("hot water") environment - with temperatures between 100 and 250° C and depths of several km below surface - in which iron, nickel and/or cobalt sulphide minerals act as critical catalysts in the construction of pre-biotic organic molecules. This connection between life and metal-sulphide compounds is no surprise. As described by Beinert et al. (1997), "Iron-sulphur proteins are found in all life forms", and "are common to the most ancient components of living matter".

German chemist Gunter Wachtershauser is a leader in the research on the hydrothermal origin of life, and has conducted numerous experiments which demonstrate how complex organic molecules can be formed from simple starting compounds - such as carbon monoxide (CO) - when metal sulphides are present as catalysts (Huber and Wachtershauser, 1997, Huber and Wachtershauser, 1998). It appears that the surfaces of metal sulphides can catalyze the binding of simple carbon molecules into new and more complex carbon molecules.

Researchers from the Carnegie Institution in Washington have recently taken this idea a step further by synthesizing the critical compound pyruvic acid (CH₃-CO-COOH) from CO in the presence of iron-sulphide at 250° C and pressures equivalent to a depth of 7 km within the rock (Cody et al., 2000). They suggest that this process may have taken place at depth in the oceanic crust, and that the compounds formed could have been moved by groundwater to the upper crust, where the critical life-forming processes might have taken place at lower temperatures (100 to 150° C) and pressures.

The important components of this process are CO, Fe and/or Ni sulphides at high temperatures and pressures. All of these could have existed in proximity to volcanism in an early oceanic crust (Wachtershauser, 2000)

References

Beinert, H, Holm, R and Munck, E, Iron-sulfur clusters: nature's modular, multipurpose structures, Science, V. 277, p. 653, (August 1997)

Cody, G, Boctor, N, Filley, T, Hazen R, Scott, J, Sharma, A, and Yoder, H, Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate, Science, V. 289, p. 1337-1340, (August 2000)

Huber, C and Wachtershauser, G, Peptides by activation of amino acids with CO on (Ni,Fe)S surfaces: implications for the origin of life, Science, V. 281, p. 670, (July, 1998)

Huber, C and Wachtershauser, G, Activated acetic acid by carbon fixation on (Ni,Fe)S under primordial conditions, Science, V. 276, p. 245-247, (April, 1997)

Miller, S, Science, V. 117, p. 528 (1953)

Wachtershauser, G, Life as we don't know it, Science, V. 289, p. 1307-1308, (August 2000)

Steven Earle, 2000. Return to Earth Science News