formation of “protocells” from the proteinoids. The first step was achieved in the gas
phase by passing methane through a concentrated ammonium hydroxide solution,
heating it to 1000°C in a bed of sand, lava, or other matrix, then rapidly quenching it
in cold ammonia solution. The heating produced a racemic mixture of amino acids,
including some not found in biological systems. Polymerization of amino acids was
also achieved by heating, but because the reaction is an elimination of water, it was
carried out anhydrously, just dry amino acids mixed and heated (175°C) in a tube.
Using a mixture of several amino acids was essential; polymerization does not occur
with just, say, glycine. This produced fairly long chains of somewhat organized
“proteinoid”, various conditions giving different but crudely repeatable order and
residue composition to the amino acid sequence. Finally, he tossed some hot
proteinoid into boiling water, producing little vesicles that he called protocells. These
had a membrane-like structure, and a mass of them could inefficiently catalyze some
simple metabolic reactions like decarboxylation of pyruvic acid.
(^) The dry, then wet, then dry, then wet sequence of the Fox “synthesis” would be hard
to reproduce anywhere, and especially so in hydrothermal vents, where wet would be
persistent. Nevertheless, Hoffman argued that small, constituent organic molecules
might be generated from reduced species (CH 4 , NH 3 , H 2 , H 2 S, all found abundantly
in venting waters) deep in the hottest part of the vent (>600°C), convectively lifted
and cooled by mixing with surrounding waters to levels (>250°C) where
polymerization might be favored, then cooled further to form structures like Fox’s
protocells. From that point a sort of metabolism would develop, eventually becoming
subject to selection for stability, most rapid growth, and division at sufficient sizes as
a precursor to reproduction.
(^) Hoffman and Corliss were both experts on Archean geology, on rocks and deposits
of the very greatest ages. They noted that a number of structures in rocks greater than
3 billion years in age, structures containing microscopic bits long interpreted as the
earliest fossil traces of life (bits that Fox & Dose had noted looked identical to
protocells) could best be interpreted as having been formed in once-submerged
hydrothermal vents. Thus, the age of the earliest traces of possible microbial life was
not greater than ages likely for remains of submerged hydrothermal sites. The overall
fit certainly suggested further examination of the possibility. Part of the evidence
suggesting an origin in hydrothermal vents is that evolutionary trees (Woese & Fox
1977) developed from DNA sequences for SSU rRNA sequences, phylogenies based
mostly on the assumption that evolutionary advance will be accompanied by
increased molecular complexity, tend to root among thermophilic Archaea. The most
primitive of those microbes are chemoautotrophic and found in or near deep-sea
hydrothermal vents (Kandler 1998).
(^) The subsequent history is complex, involving personality conflicts as well as
objective evaluations of the chemistry involved. However, hydrothermal vents have