13. Gases used by Urey and Miller for experimentation support to Oparin and Haldane hypothesis for origin of life was
    (1) Hydrogen, methane and Ammonia
    (2) Hydrogen, methane and CO₂
    (3) Hydrogen, Ammonia, methane and CO₂
    (4) Hydrogen, Carboxylic acid and Amino acids

The Oparin-Haldane Hypothesis: A Foundation for Life’s Origins

Alexander Oparin and J.B.S. Haldane independently proposed that the early Earth had a reducing atmosphere—one lacking free oxygen but rich in gases such as hydrogen, methane, and ammonia. Under these conditions, they hypothesized, simple organic molecules could form spontaneously from inorganic precursors, given an energy source like lightning or ultraviolet radiation. Over time, these molecules could have assembled into more complex structures, eventually leading to the first living cells.

This hypothesis, now known as the Oparin-Haldane theory, provided a framework for experimental work on the origin of life. It suggested that the building blocks of life—amino acids, sugars, and nucleic acids—could arise naturally under the conditions of early Earth.

The Miller-Urey Experiment: Testing the Hypothesis

In 1953, Stanley Miller, a graduate student working under Harold Urey, set out to test the Oparin-Haldane hypothesis in the laboratory. The goal was to simulate the conditions of the early Earth’s atmosphere and ocean, and to observe whether organic molecules could form under these circumstances.

Design of the Experiment

Miller and Urey constructed a closed glass apparatus consisting of two main chambers:

• Lower Chamber: Contained water, representing the early oceans.

• Upper Chamber: Held a mixture of gases, simulating the early atmosphere.

The apparatus was designed so that water could be heated to produce water vapor, which would then mix with the gases in the upper chamber. Electrodes were used to generate electric sparks, mimicking lightning as an energy source. The water vapor and gases cycled continuously through the system, allowing for the condensation and collection of reaction products.

The Gases Used

The gases chosen by Miller and Urey were critical to the experiment’s success. They selected a mixture that reflected the hypothesized composition of the early Earth’s atmosphere, as proposed by Oparin and Haldane. The gases used were:

• Hydrogen (H₂)

• Methane (CH₄)

• Ammonia (NH₃)

• Water vapor (H₂O)

These gases were sealed inside the apparatus, and the experiment was run for several days.

Why These Gases?

The selection of hydrogen, methane, ammonia, and water vapor was based on the Oparin-Haldane hypothesis, which posited that the early atmosphere was reducing and rich in these simple compounds. This environment was thought to be favorable for the formation of organic molecules because:

• Reducing Atmosphere:

  • The absence of oxygen prevented the oxidation of organic molecules, allowing them to accumulate and interact.

• Availability of Carbon, Nitrogen, and Hydrogen:

  • Methane provided a source of carbon, ammonia a source of nitrogen, and hydrogen and water vapor provided hydrogen and oxygen atoms, respectively.

• Energy Source:

  • The electric sparks simulated lightning, providing the energy needed to drive chemical reactions.

Results and Significance

After running the experiment for about a week, Miller and Urey observed that the water in the apparatus had turned a reddish-brown color. Analysis revealed the presence of several amino acids, the building blocks of proteins, as well as other organic compounds.

This result was groundbreaking because it demonstrated that simple organic molecules could form spontaneously from inorganic precursors under conditions thought to resemble those of the early Earth. The experiment provided strong experimental support for the Oparin-Haldane hypothesis and suggested that the building blocks of life could have arisen naturally, without the need for living organisms.

Evaluating the Options

Let’s examine the options provided in the question and determine which combination of gases was used by Urey and Miller to support the Oparin-Haldane hypothesis:

• (1) Hydrogen, methane, and ammonia:

  • Correct, but incomplete. This combination was used, but water vapor was also a key component of the experiment.

• (2) Hydrogen, methane, and CO₂:

  • Incorrect. Carbon dioxide (CO₂) was not used in the original Miller-Urey experiment.

• (3) Hydrogen, ammonia, methane, and CO₂:

  • Incorrect. While the first three gases were used, CO₂ was not included in the original mixture.

• (4) Hydrogen, carboxylic acid, and amino acids:

  • Incorrect. Carboxylic acids and amino acids are organic compounds, not gases used in the experiment.

Note:
While option (1) lists the main gases (hydrogen, methane, and ammonia), it omits water vapor, which was a crucial part of the experimental setup. However, among the options provided, (1) is the closest to the gases actually used, but strictly speaking, the most accurate answer (if water vapor were listed) would be hydrogen, methane, ammonia, and water vapor. Since the question asks which gases “support to Oparin and Haldane hypothesis,” and water vapor is not always considered a “gas” in the strictest sense for such questions, option (1) is typically accepted as correct in most standard question formats.

Broader Implications

The Miller-Urey experiment had a profound impact on the field of origin-of-life research. It showed that the building blocks of life could form under plausible early Earth conditions, supporting the idea that life’s origins were a natural outcome of chemical and physical processes. The experiment also inspired further research into the chemical pathways that could lead from simple molecules to more complex biological structures.

Modern Perspectives

While the Miller-Urey experiment is celebrated for its pioneering approach, modern research has refined our understanding of the early Earth’s atmosphere. Some scientists now believe that the early atmosphere may have contained more carbon dioxide and nitrogen, and less methane and ammonia, than originally thought. Nevertheless, the experiment remains a foundational demonstration of how organic molecules could have arisen from inorganic precursors.

Key Takeaways

• The Oparin-Haldane hypothesis proposed that the early Earth’s atmosphere was reducing and rich in hydrogen, methane, ammonia, and water vapor.

• Miller and Urey used a mixture of hydrogen, methane, ammonia, and water vapor in their experiment to simulate these conditions.

• The experiment demonstrated that amino acids and other organic molecules could form spontaneously under these conditions, supporting the Oparin-Haldane hypothesis.

• Among the options provided, the combination of hydrogen, methane, and ammonia is the closest to the gases used, but water vapor was also a key component.

• The correct answer to the question is:

  (1) Hydrogen, methane, and Ammonia

Summary Table

Conclusion

The Miller-Urey experiment stands as a landmark in the study of life’s origins, providing experimental support for the Oparin-Haldane hypothesis. By using a mixture of hydrogen, methane, ammonia, and water vapor, Miller and Urey demonstrated that the building blocks of life could form under conditions thought to resemble those of the early Earth. Among the options provided, option (1) Hydrogen, methane, and Ammonia is the closest to the gases used, although water vapor was also essential to the experiment. This work remains foundational to our understanding of how life could have begun on our planet.

In summary, the correct answer is:

(1) Hydrogen, methane, and Ammonia
(Note: Water vapor was also used, but is not listed in the options. Option (1) is the standard accepted answer in most question formats.)