Miller Urey Experiment: Definition, Purpose, Results & Facts

The Miller-Urey experiment is one of the most significant experiments in the study of the origin of life on Earth under prebiotic conditions. It was conducted by Stanley Miller and Harold Urey in 1953. In the experiment, they used a mixture of gases like methane, ammonia, hydrogen, and water vapor to represent an early Earth's atmosphere exposed to electrical sparks to stimulate lightning. This experiment provided the foundation for theories of biological evolution by demonstrating that organic molecules formed from non-living substances.

This Story also Contains

1. What is the Miller-Urey Experiment?
2. Setup of the Experiment
3. Miller-Urey Experiment Procedure
4. Result of the Miller-Urey Experiment
5. Criticism of the Miller-Urey Experiment
6. Recommended video for "Miller Urey Experiment"
7. MCQs on Miller Urey Experiment

This experiment helped us to understand how life could have evolved naturally. It shows that life on Earth originated from simple chemical compounds through natural processes, a concept closely tied to evolution. The Miller-Urey experiment opened the door to further research and helped to explain chemical origins of life.

What is the Miller-Urey Experiment?

The Miller-Urey experiment was one of the key studies that Stanley Miller and Harold Urey conducted in 1953. It simulated the early Earth environment to test abiogenesis associated with the spontaneous eruption of simple life forms from non-living matter.

The importance of this experiment lies in the fact that it offers a basis where simple organic compounds could be built up from inorganic precursors under conditions that might have existed on primordial Earth.

Before the Miller-Urey experiment, several theories on evolution were mostly unproven. The works by Alexander Oparin and J.B.S. Haldane speculated that early Earth atmospheres could have caused spontaneous generation of organic compounds from simple molecules. This was not tested until Miller and Urey came up with their experiment.

The scientific environment of the early 1950s was a question about life's origin. Advances in chemistry and biological research set the stage for Miller and Urey to test the abiogenesis theory by simulating a controlled laboratory experiment.

Setup of the Experiment

The main purpose of the Miller-Urey experiment was to find if the conditions of primitive Earth gave rise to the living world. The setup was kept running for several days. This allowed observation of chemical reactions.

Apparatus and Materials

The Miller-Urey experiment used specially designed glass apparatus to mimic early Earth conditions. It included a boiling flask to produce water vapor, a chamber filled with gases and electrodes to supply electrical sparks that simulated lightning. The setup was sealed to maintain a controlled environment during the experiment.

Miller-Urey Experiment Procedure

In the experiment, water in boiling flask was heated to produce water vapor. This vapor was mixed with other gases in a closed chamber. Electric sparks were passed to generate lightning. The vapors were cooled and the condensed water was collected and analyzed. The detailed procedure of the Miller-Urey experiment is:

1. Gas Mixture Introduction: A mixture of gases such as methane gas (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapour (H₂O) was introduced into a closed system of glass tubes and flasks.
2. Electrical Stimulation: Electrical sparks were created with electrodes, mimicking lightning storms that are believed to have been common on primitive Earth.
3. Cooling and Condensation: The mixture is allowed to cool, and the gases condensed back into the liquid water were trapped.
4. Collection and Analysis: After a week, the liquid collected was analysed, and the presence of organic compounds was detected.

Result of the Miller-Urey Experiment

The experiment produced a wide array of organic compounds including amino acids, which are the very building blocks of proteins and prime constituents of living cells. This was an important discovery in terms of providing strong evidence that life originated from simple inorganic molecules under the right conditions.

Organic Compound Detected

Criticism of the Miller-Urey Experiment

One of the major criticisms against the Miller-Urey experiment lies in the composition of the atmosphere that was used. Miller and Urey held that the primitive atmosphere was highly reducing, rich in CH₄, NH₃, H₂, and H₂O. However, subsequent experiments suggested that early Earth's atmosphere might have been less reducing and probably made of carbon dioxide, nitrogen, and water vapour, with a trace of hydrogen. This might then radically affect the kinds of organic molecules produced as a result of the different atmospheric compositions.

Electrical sparks imitated lightning as the energy source in the experiment. Other possible sources of energy include ultraviolet radiation, volcanic activity, and hydrothermal vents. Such alternative energy sources have been tested in other experiments, with similar results, suggesting that pathways for the origin of life can be much more diverse than that indicated by this classic experiment.

Given its controlled conditions, this experiment in the laboratory does not account for the impurities, catalytic surfaces, and variety of minerals found on early Earth. Under realistic conditions, several variables would have existed that could have affected the actual synthesis and stability of the organic molecules.

Alexander Oparin and J.B.S. Haldane postulated that life on early Earth began through a gradual chemical evolution of carbon-based molecules in a "primordial soup." While growing organic molecules in the lab under prebiotic conditions, the Miller-Urey experiment provided evidence for this hypothesis. However, it only tested a very small part of what Oparin and Haldane had in mind. Their theories generally envisioned a longer time frame and a much broader set of chemical processes.

Recommended video for "Miller Urey Experiment"

MCQs on Miller Urey Experiment

Q1. Which of the following is formed in Miller’s experiment?

1. Amino acids

2. Nucleic acids

3. UV radiation

4. Microspheres

Correct Answer: 1) Amino acids

Explanation:

The Miller-Urey experiment is an in vitro simulation performed in 1953 by Stanley Miller, assisted by Harold Urey, and used early earth conditions in their quest for finding the origins of life. This experiment involves the combination of methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water (H₂O), to be applied as a form of an electric arc, simulating lightning. As a result, amino acids emerged from the above experiment showing organic molecules as the resultant of chemical building blocks thereby supporting the argument over abiogenesis and chemical evolution view.

Hence, the correct answer is Option 1) Amino acids.

Q2. Directions: In the following questions, a statement of Assertion (A) is followed by a statement of reason (R).

Assertion – The strongest Evidence in favor of chemical evolution was proposed by Stanley Miller.

Reason – Simple amino acids were formed by the reaction of CH4, NH3, H2 & Electric discharge in the Laboratory.

1. If both assertion and reason are true and reason is correct explanation of assertion

2. If both assertion and reason are true but the reason is not the correct explanation of the assertion

3. If the assertion is true but the reason is false

4. If both assertion and reason are false

Correct answer: 1) If both assertion and reason are true and the reason is the correct explanation of the assertion

Explanation:

The Miller-Urey Experiment - The theory given by Miller and Urey about the formation of simple organic molecules

The early compound interacted and produced simple organic compounds such as sugars, and nitrogenous bases. The setup is explained in

Stanley Miller created similar conditions at Laboratory scale which were thought to be on primitive Earth. He took CH4, NH3, and Hydrogen gas (2: 1: 2 ratio) along with water vapor at 800℃ in a flask. He created Electric discharge by using two tungsten electrodes as a source of energy. At the end of the experiment, he got simple amino acids like Glycine, Alamine, and aspartic acid.

Hence, the correct answer is option 1) If both assertion and reason are true and the reason is the correct explanation of the assertion.

Q3. All of the following gases were present in the Miller-Urey experiment except

1. Methane

2. Oxygen

3. Ammonia

4. Hydrogen

Correct answer: 2) Oxygen

Explanation:

A pioneering experiment, the Miller-Urey experiment (1953) was intended to test the theory that organic molecules may originate under early Earth conditions by simulating such conditions. To replicate lightning and volcanic activity in the early Earth's atmosphere, a combination of gases was circulated over a heated water flask. The following gases were utilized in the experiment:

Methane: Denotes the existence of methane, a crucial element believed to have been in the early Earth's atmosphere.

Ammonia: Ammonia was utilized to replicate the early Earth's nitrogen-rich environment.

Hydrogen: The early makeup of the atmosphere contained hydrogen.

However, as it is believed that oxygen was mostly missing in the early Earth's atmosphere, O2 (oxygen) was not included in the experiment. Because oxygen is reactive and would have broken down organic molecules, its presence would have prevented the synthesis of organic compounds.

Hence, the correct answer is option 2)Oxygen.

Also read:

• MCQs on Miller-Urey Experiment

• Darwin Theory of Natural Selection

• Adaptive Radiation