Q. Which one of the following sets of elements was primarily responsible for the origin of life on the Earth? (UPSC Prelims 2012)
Answer:
Carbon, Hydrogen, Nitrogen
Notes: The correct answer is
[B] Carbon, Hydrogen, Nitrogen. These three elements, along with Oxygen, Phosphorus, and Sulfur, are often referred to as the "CHNOPS" elements—the fundamental building blocks of all known life.Why these elements are primary:The origin of life on Earth (the transition from "chemistry" to "biology") required the formation of complex organic molecules like amino acids, proteins, and nucleic acids (DNA/RNA).
- Carbon: The "backbone" of life. Due to its four valence electrons, it can form stable covalent bonds with many elements, including itself, allowing for the creation of long, complex chains and rings that form the structure of organic molecules.
- Hydrogen: The most abundant element in the universe. It is a key component of water (H2O) and organic compounds, and it plays a critical role in energy transfer within cells.
- Nitrogen: A vital component of amino acids (the building blocks of proteins) and nitrogenous bases (the "letters" that make up the genetic code in DNA and RNA).
The Oparin-Haldane Hypothesis and the Miller-Urey ExperimentIn the early 1950s, the
Miller-Urey experiment famously simulated the conditions of the "primordial soup" of early Earth. By subjecting a mixture of water (H
2O), methane (CH
4), ammonia (NH
3), and hydrogen (H
2) to electric sparks (simulating lightning), they successfully synthesized
amino acids.Note the components used:
- Methane (CH4): Provided Carbon and Hydrogen.
- Ammonia (NH3): Provided Nitrogen and Hydrogen.
- Water (H2O): Provided Oxygen and Hydrogen.
Analysis of Other Options:
- Sodium, Calcium, Potassium (Options A, C, D): While these are essential "macro-minerals" for modern biological functions (like nerve signaling and bone structure), they were not the primary elements responsible for the initial formation of organic life-forms.
- Oxygen (Option C): While essential for life today, the early Earth's atmosphere was reducing (oxygen-poor). Life actually originated in an environment where free oxygen was scarce; it only became abundant later due to photosynthesis by cyanobacteria.