Miller Urey Experiment


The basic requirements for the origin of life were created by the formation of the earth and its initial environment. These provided the initial raw material and the essential conditions that were needed to interact together and to form organic molecules that favour life. It was believed that our universe came into existence some 15 billion years ago with a big bang that was a thermonuclear expansion of a huge entity. Scientists believe that our solar system came into existence around 4-5 billion years ago and that the planets were formed by the spinning cloud of cosmic dust and gas. Some state that life has begun from non-living matter, some suggest that life has arisen by the power of the divine, while some suggest that there was spontaneous creation, and many more.

The Miller and Urey Experiment

  • The Miller and Urey experiment was based on the statement that was given by two other scientists that were working on the theory of the origin of life. Their experiment provided a demonstration based on the statement that first life arises from abiogenesis and that spontaneous generation of life is not possible in today’s environmental conditions. The Earth’s initial atmosphere was a reducing atmosphere with little or no oxygen at that time.

  • Stanley L Miller and Harold C Urey conducted an experiment to test the conditions put forward by other scientists to check if the origin of life was spontaneous or not.

  • Miller created a glass device that consists of a gas flask, a condenser, and a liquid flask that are all connected by tubes and equipped with an energy source. The apparatus simulated the same conditions that were present on primitive Earth, including the reducing atmosphere.

  • In the apparatus, he circulated a 2:2:1 mixture of methane, ammonia, hydrogen, and water vapor. All these gases were believed to be present in the primitive reducing atmosphere of the earth. For the energy that was needed for the interaction of gases that were present in the mixture, he provided electric sparks from electrodes at 75000 volts in the gas flask. These electric sparks imitate lightning.

  • To stimulate the volcanic conditions, he passed the gases in a narrow tube through a liquid flask, and energy was provided as heat with an electric heater.

  • He kept the experiment running for 18 days after recreating the conditions.

  • The gas flask produced a mixture of small organic molecules, which were then transferred by condensation to the liquid flask. He then analyzed the chemical composition of these molecules that were produced in the chemical reaction and found many organic compounds such as amino acids.

Experimental setup diagram

The original uploader was Carny at Hebrew Wikipedia., MUexperiment, CC BY 2.5


  • Some scientists argue that the gases that were used by Miller in his experiment were not as abundant as shown in the experiment.

  • Larger macromolecules that are responsible for the life form such as DNA and proteins were missing in the experiment.

  • Complex and complicated experiments should be carried out in a sealed, inert, and sterilized environment to eliminate the chances of contamination. But Miller’s experiment was carried out in a glass apparatus. The borosilicate glass dissolved roughly in the experimental broth and changed the number of amino acids formed, which is not seen when experiments are performed in teflon apparatus.

  • The major point was that the conditions of primitive earth were only hypothesized and that may not be accurate.

Oparin and Haldane Theory

The theory given by Oparin and Haldane is also called a chemical theory or modern theory. This theory is based on the idea of Charles Darwin that the origin of life from non-living materials was possible on the primitive earth because the environmental conditions prevailing then were different from the present conditions on the earth, which do not permit abiogenesis to occur. Oparin and Haldane elaborated this idea in their modern theory independently.

According to their modern theory-

  • In present conditions, the spontaneous generation of life is not possible.

  • Earth’s primitive atmosphere was totally different from today’s conditions, as it was a reducing one.

  • The first life originated from a mixture of chemicals through a series of chemical reactions in which atoms came together to form inorganic molecules, inorganic molecules evolved into simple organic molecules or monomers, which then evolved into complex organic molecules or polymers, and polymers eventually crystallized into aggregates to form living matter.

  • Solar radiation and lightning provide the energy needed for molecules to evolve.

The Oparin Haldane theory was not accepted immediately as there was no supporting evidence. However, it was experimentally supported by the Miller and Urey experiments.


The ability of organisms to use external resources like light, water, and gas for energy, growth, and reproduction through carefully regulated chemical reactions is what scientists refer to as life. For this, various theories were given by various scientists all around the world. They have estimated the prerequisites for life, which were the earth’s and its initial atmosphere. Miller and Urey provide experimental proof for one such theory by creating the primitive environment of the earth’s atmosphere in the glass apparatus and providing all the factors that were believed to be there at that time when life originated.


Q1. What is the Big Bang theory?

Ans. This is a widely accepted theory, first proposed by Abbe Lemaitre in 1931. According to this theory, the universe was created by a big bang, or thermonuclear explosion of a dense object, approximately 15 billion years ago. This massive explosion threw out a lot of cosmic debris known as nebulae, which gradually organized into a collection of stars known as galaxies.

Q2. What is the difference between the primitive atmosphere and the modern atmosphere of Earth?

Ans. Differences include −

Primitive Atmosphere Modern Atmosphere
It was reducing in nature. It is oxidizing in nature.
It lacks free oxygen and its most common element is hydrogen. Contains about 21% oxygen and less than 0.04% hydrogen.
It had no ozone layer, so UV radiation reached the earth. It is surrounded by a thick ozone layer that minimizes the UV radiation reaching the earth.
It was very hot. It maintains a moderate temperature.
It favored chemical evolution. It disallows chemical evolution.

Q3. What is the significance of the Miller and Urey Experiment?

Ans. The main significance of Miller’s experiment was that it provides evidence that supports the origin of life on Earth was due to abiogenesis, or life arising from nonliving matter. Since then, biogenesis has occurred.

Q4. Name all the theories that have been given for the origin of life.

Ans. There were six main theories put forward by different scientists.

  • Theory of Special Creation.

  • Theory of Spontaneous Generation.

  • Theory of Catastrophism.

  • Cosmozoic or interplanetary Theory.

  • Theory of Eternity of Life or Steady State Theory.

  • Modern or Oparin-Haldane Theory.