Which non-gaseous biogeochemical cycle is uniquely classified as a sedimentary cycle because its primary geological reservoir resides in rocks and ocean sediments rather than the atmosphere?

Answer and explanation

Correct answer: D. Phosphorus cycle

  1. Step 1: Biogeochemical cycles are classified into gaseous cycles (where the atmosphere serves as the main reservoir) and sedimentary cycles.
  2. Step 2: Phosphorus does not form a stable atmospheric gas under environmental temperatures; it is released slowly through the chemical weathering of phosphate minerals in apatite rocks, taken up by plants, and returned to marine sediments over millions of years.
Answer
Phosphorus cycle
Why not the others: 'Carbon cycle' The carbon cycle possesses a massive, highly dynamic atmospheric gaseous reservoir in the form of carbon dioxide (); 'Nitrogen cycle' The nitrogen cycle relies on Earth's atmosphere as its primary reservoir, where nitrogen gas constitutes 78% of air; 'Water (hydrological) cycle' The hydrological cycle moves trillions of tons of water through the atmosphere via evaporation, transpiration, and precipitation.

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