Microbiology and Immunology

Miller, Stanley L. WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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The Miller-Urey experiment remains the subject of sci-

entific debate. Scientist continue to explore the nature and

composition of Earth’s primitive atmosphere and thus, con-

tinue to debate the relative closeness of the conditions of the

Miller-Urey experiment (e.g., whether or not Miller’s applica-

tion of electrical current supplied relatively more electrical

energy than did lightning in the primitive atmosphere).

Subsequent experiments using alternative stimuli (e.g., ultra-

violet light) also confirm the formation of amino acids from

the gases present in the Miller-Urey experiment. During the

1970s and 1980s, astrobiologists and astrophyicists, including

American physicist Carl Sagan, asserted that ultraviolet light

bombarding the primitive atmosphere was far more energetic

that even continual lightning discharges. Amino acid forma-

tion is greatly enhanced by the presence of an absorber of

ultraviolet radiation such as the hydrogen sulfide molecules

(H 2 S) also thought to exist in the early Earth atmosphere.

Although the establishment of the availability of the

fundamental units of DNA, RNA and proteins was a critical

component to the investigation of the origin of biological mol-

ecules and life on Earth, the simple presence of these mole-

cules is a long step from functioning cells. Scientists and

evolutionary biologists propose a number of methods by

which these molecules could concentrate into a crude cell sur-

rounded by a primitive membrane.

See also Biochemistry; DNA (Deoxyribonucleic acid);

Evolution and evolutionary mechanisms; Evolutionary origin

of bacteria and viruses; Mitochondrial inheritance

MMiller, Stanley L.ILLER, STANLEYL.(1930- )

American chemist

Stanley Lloyd Miller is most noted for his experiments that

attempted to replicate the chemical conditions that may have

first given rise to life on Earth. In the early 1950s he demon-

strated that amino acids could have been created under pri-

mordial conditions. Amino acids are the fundamental units of

life; they join together to form proteins, and as they grow more

complex they eventually become nucleic acids, which are

capable of replicating. Miller has hypothesized that the oceans

of primitive Earth were a mass of molecules, a prebiological

“soup,” which over the course of a billion years became a liv-

ing system.

Miller was born in Oakland, California, the younger of

two children. His father, Nathan Harry Miller, was an attorney

and his mother, Edith Levy Miller, was a homemaker. Miller

attended the University of California at Berkeley and received

his B.S. degree in 1951. He began his graduate studies at the

University of Chicago in 1951.

In an autobiographical sketch entitled “The First

Laboratory Synthesis of Organic Compounds under Primitive

Earth Conditions,” Miller recalled the events that led to his

famous experiment. Soon after arriving at the University of

Chicago, he attended a seminar given by Harold Ureyon the

origin of the solar system. Urey postulated that the earth was

reducing when it was first formed—in other words, there was

an excess of molecular hydrogen. Strong mixtures of methane

and ammonia were also present, and the conditions in the

atmosphere favored the synthesis of organic compounds.

Miller wrote that when he heard Urey’s explanation, he knew

it made sense: “For the nonchemist the justification for this

might be explained as follows: it is easier to synthesize an

organic compound of biological interest from the reducing

atmosphere constituents because less chemical bonds need to

be broken and put together than is the case with the con-

stituents of an oxidizing atmosphere.”

After abandoning a different project for his doctoral the-

sis, Miller told Urey that he was willing to design an experi-

ment to test his hypothesis. However, Urey expressed

reluctance at the idea because he considered it too time con-

suming and risky for a doctoral candidate. But Miller per-

sisted, and Urey gave him a year to get results; if he failed he

would have to choose another thesis topic. With this strict

deadline Miller set to work on his attempt to synthesize

organic compounds under conditions simulating those of

primitive earth.

Miller and Urey decided that ultraviolet light and elec-

trical discharges would have been the most available sources

of energy on Earth billions of years ago. Having done some

reading into amino acids, Miller hypothesized that if he

applied an electrical discharge to his primordial environment,

he would probably get a deposit of hydrocarbons, organic

compounds containing carbon and hydrogen. As he remem-

bered in “The First Laboratory Synthesis of Organic

Compounds”: “We decided that amino acids were the best

group of compounds to look for first, since they were the

building blocks of proteins and since the analytical methods

were at that time relatively well developed.” Miller designed

an apparatus in which he could simulate the conditions of pre-

biotic Earth and then measure what happened. A glass unit was

made to represent a model ocean, atmosphere, and rain. For

the first experiment, he filled the unit with the requisite “prim-

itive atmosphere”—methane, hydrogen, water, and ammo-

nia—and then submitted the mixture to a low-voltage spark

over night. There was a layer of hydrocarbons the next morn-

ing, but no amino acids.

Miller then repeated the experiment with a spark at a

higher voltage for a period of two days. This time he found no

visible hydrocarbons, but his examination indicated that

glycine, an amino acid, was present. Next, he let the spark run

for a week and found what looked to him like seven spots.

Three of these spots were easily identified as glycine, alpha-

alanine, and beta-alanine. Two more corresponded to a-amino-

n-butyric acid and aspartic acid, and the remaining pair he

labeled A and B.

At Urey’s suggestion, Miller published “A Production

of Amino Acids under Possible Primitive Earth Conditions” in

May of 1953 after only three-and-a-half months of research.

Reactions to Miller’s work were quick and startling. Articles

evaluating his experiment appeared in major newspapers;

when a Gallup poll asked people whether they thought it was

possible to create life in a test tube; seventy-nine percent of the

respondents said no.

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