26. Origin of Life on Earth
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       The Oparin-Haldane Theory of the Origin of Life

According to their theory, life evolved in the oceans during a period when the atmosphere was reducing - containing H2, H2O, NH3, 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.


  Page 11 of 36 Glossary