According to their theory, life evolved in the oceans during a
period when the atmosphere was reducing - containing H2,
CH4, and CO2,
but no free O2.
Organic compounds were synthesized nonbiologically by ultraviolet
light energy, which in the absence of an ozone shield would penetrate
the upper layers of the ocean.
Without free O2 to oxidize them,
these organic molecules would be stable, and would accumulate in
a warm, dilute broth that has been nicknamed "Haldane soup."
The first living organism would be little more than a few chemical
reactions wrapped up in a film or membrane to keep them from being
diluted and destroyed. These organelles would absorb chemicals,
grow, divide, and obtain energy by fermenting the available organic
molecules around them.
Photosynthesis would arise eventually as an alternative energy
source when natural foods ran short. The oxygen released by photosynthesis
would have the side effect of screening out the ultraviolet radiation
with an ozone layer in the upper atmosphere, and eventually would
turn the atmosphere from reducing to oxidizing. Free oxygen would
lead to the evolution of respiration and to modern eucaryotic metabolism.
This Oparin-Haldane theory was a remarkably complete blueprint
for the ideas still held today. It was especially remarkable because
in 1929 virtually none of the biochemical details of the previous
chapters were known.
None of the chemistry of glycolysis, respiration, or photosynthesis
was understood, aside from the overall reactions.
Enzymes were a mystery, and were not even thought to be proteins.
The nature of the genetic machinery was unknown - scientists were
as likely to choose proteins as they were nucleic acids for the
carriers of genetic information.
The Oparin-Haldane theory was an accurate extrapolation far beyond
the limits of chemical knowledge of the time, which undoubtedly
contributed to its general neglect.
It is to the credit of both men that much of what we have learned
since then has been a filling in of the blanks in their proposals.