156 Evolution? The Fossils Say YES!
Recipe for Primordial Soup
It is often said that all the conditions for the first production of a living organism are
now present, which could ever have been present. But if (and oh! what a big if!) we
could conceive in some warm little pond, with all sorts of ammonia and phosphoric
salts, light, heat, electricity, &c., present, that a proteine [sic] compound was chemi-
cally formed ready to undergo still more complex changes, at the present day such
matter would be instantly absorbed, which would not have been the case before liv-
ing creatures were found.
—Charles Darwin, letter to Joseph HookerThe first scientific suggestions about the origin of life were made by several people, including
Darwin himself in this 1871 letter to his friend, botanist Joseph Hooker. Darwin speculated
that a “warm little pond” with the right combination of chemical compounds (usually called
the “primordial soup”) and the right sources of energy could produce proteins. But organic
chemistry was still in its infancy back then, so little could be done to follow this suggestion.
In the 1920s, the Russian biochemist A. I. Oparin and the British geneticist J. B. S. Haldane
(also one of the fathers of neo-Darwinism mentioned in chapter 4) independently suggested
that the earth with a reducing atmosphere of nitrogen, carbon dioxide, ammonia (NH 3 ), and
methane or “natural gas” (CH 4 ) would be the ideal primordial soup for producing simple
organic compounds.
The most important breakthrough occurred in 1953, when a young graduate student
at the University of Chicago named Stanley Miller heard about Oparin’s hypothesis from
his advisor, Nobel Prize–winning chemist Harold Urey. They decided to try an experiment
along the lines suggested by Oparin and Haldane to see whether such a primordial soup
could generate basic biochemicals. Miller built a simple apparatus (fig. 6.3) out of sealed
tubes that formed a continuous loop, with all the air removed by vacuum. A new atmo-
sphere rich in carbon dioxide, nitrogen, methane, ammonia, and water (but no free oxygen)
was placed in the evacuated tubes. Miller then put a source of heat below the “ocean” flask
at the base to start the steam circulating, and in another flask he used electrodes that cre-
ated sparks to simulate “lightning” as an energy source (fig. 6.3). Below the “lightning”
chamber, a condenser returned the gases to liquid state, where they recirculated back to
the “ocean.” This graduate student experiment (not even his original thesis topic) yielded
the most startling results. Within days, the ocean became brown with new chemicals, and
within a week, it was an organic-rich gunk. When Miller analyzed it, he had already pro-
duced 4 of the 20 amino acids that life uses to make proteins, plus many other organic mol-
ecules, such as cyanide (HCN) and formaldehyde (H 2 CO). As Knoll (2003:74) writes, “In
one remarkable experiment, Miller jump-started research on life’s origins. Powered by the
energy of nature, simple gas mixtures could give rise to molecules of biological relevance
and complexity.” Even though amino acids are much more complex than the chemicals
he started with, Miller showed they were remarkably easy to produce. Later experiments
produced 12 of the 20 amino acids found in life. Another experiment with a dilute cyanide
mixture produced seven amino acids. No matter how you cut it, it does not require divine
intervention or even more than a few days in the lab to make the basic building blocks
of life. Since Miller’s experiments, other scientists have found 74 different amino acids in
meteorites (including all 20 found in living systems), so apparently organic compounds