Which one of the following sets of elements was primarily responsible for the origin of life on…

Answer: (b) Carbon, Hydrogen, Nitrogen

The answer is (b). Life arose through chemical evolution, in which simple gas molecules of the early Earth reacted to form organic molecules. Those gases were methane (CH4), ammonia (NH3), hydrogen (H2) and water vapour, and together they supply carbon, hydrogen and nitrogen. Only option (b) has all three.

• ✓ (b) Methane gives carbon and hydrogen, and ammonia gives nitrogen and hydrogen. In Miller's 1953 experiment, an electric discharge in a closed flask of CH4, H2, NH3 and water vapour produced amino acids, the building blocks of proteins.
• ✗ (a) Sodium was not one of the simple gases (CH4, NH3, H2, water vapour) from which the first organic molecules formed. Carbon and nitrogen are missing from this set.
• ✗ (c) The early atmosphere had very little free oxygen. Calcium and phosphorus were not part of the simple gases that gave rise to the first organic molecules. Carbon, hydrogen and nitrogen are all missing from this set.
• ✗ (d) Carbon and hydrogen fit, but potassium does not. Nitrogen, which is needed for amino acids, is missing.

Remember · The early atmosphere had methane, ammonia and water vapour, with very little free oxygen. Miller (1953) made amino acids from CH4, NH3, H2 and water vapour, so carbon, hydrogen and nitrogen were the key elements.

📘 Read it in NCERT: Class 12 Biology, Ch 6 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 2 (practise this chapter)

Question: UPSC Civil Services (Preliminary) 2012, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). · Report an error