The Science Book

FUNDAMENTAL BUILDING BLOCKS 275

Recreating Earth’s
early atmosphere
In 1953, Urey and Miller carried out
the first prolonged experiment to
test the Oparin–Haldane theory. In
a closed series of connected glass
flasks, sealed from the atmosphere,
they put water and a mixture of
gases thought to have been present
in Earth’s primitive atmosphere—
hydrogen, methane, and ammonia.
The water was heated so that water
vapor formed and wafted its way
around all the flasks in the closed
loop. In one of the flasks was a pair
of electrodes, between which sparks
were passed continuously to
represent lightning—one of the
hypothetical triggers for primordial
reactions. The sparks provided
enough energy to break up some of
the molecules, and generate highly
reactive forms that would go on to
react with other molecules.
Within a day, the mixture had
turned pink, and after two weeks
Urey and Miller found that at least
10 percent of the carbon (from the
methane) was now in the form of
other organic compounds. Two
percent of the carbon had formed
amino acids, which are the vital

building blocks of the proteins in all

living things. Urey encouraged

Miller to send a paper about the

experiment to the journal Science,

which published it as “Production

of amino acids under possible

primitive earth conditions.” The

world could now imagine how

Darwin’s “warm little pond” may

have generated the first life forms.

In an interview, Miller said that

“just turning on the spark in a basic

prebiotic experiment will yield

amino acids.” Scientists later found,

using better equipment than was

available in 1953, that the original

experiment had produced at least

25 amino acids—more than are

found in nature. Since Earth’s early

atmosphere almost certainly

contained carbon dioxide, nitrogen,

hydrogen sulphide, and sulfur

dioxide released from volcanoes,

a much richer mixture of organic

compounds might well have been

created then—and was indeed

formed in subsequent experiments.

Meteorites containing dozens of

amino acids, some found on Earth

and others not, have also spurred

on the search for signs of life on

planets beyond the solar system. ■

See also: Jöns Jakob Berzelius 119 ■ Friedrich Wöhler 124–25 ■
Charles Darwin 142–49 ■ Fred Hoyle 270

Harold Urey and

Stanley Miller

Harold Clayton Urey was born

in Walkerton, IN. His work on

the separation of isotopes led

to the discovery of deuterium,

which won him the Nobel Prize

in Chemistry in 1934. He went

on to develop enrichment of

uranium-235 by gaseous

diffusion which was crucial for

the Manhattan Project’s

development of the first atomic

bomb. After his prebiotic

experiments with Stanley

Miller in Chicago he moved to

San Diego and studied the

Moon rocks brought back by

Apollo 11.

Stanley Lloyd Miller was

born in Oakland, CA. After

studying chemistry at the

University of California at

Berkeley, he was a teaching

assistant at the University of

Chicago, and worked with

Urey. Later, he became a

professor in San Diego.

Key work

1953 Production of Amino

Acids under Possible Primitive

Earth Conditions

My study [of the universe]

leaves little doubt that life has

occurred on other planets. I

doubt if the human race is the

most intelligent form of life.

Harold C. Urey

Laboratory apparatus replicated
the effect of lightning on early Earth’s
primitive atmosphere, in a continual
loop of chemical reactions.

Vapor (cloud

formation)

Boiling water

(Earth’s oceans)

Cooled water (containing

organic molecules)

Power

supply

Spark

(lightning)

Gases (Earth’s atmosphere)

Condensing

column

Heat source