Which statement best explains why the phosphorus cycle lacks a gaseous phase?

• A. Phosphorus frequently vaporizes and cycles through the atmosphere as a gas
• B. Phosphorus primarily cycles through rocks and organisms without a gaseous phase
• C. Phosphorus is only found in detergents and fertilizers
• D. Phosphorus cycles through the atmosphere via sulfur-like processes

Answer: (B)

Phosphorus has no significant gaseous phase on Earth, so its cycle is essentially sedimentary. Most phosphorus exists in minerals such as phosphate in rocks. Weathering releases phosphate into soils and water, plants and other organisms take it up and incorporate it into biological molecules, and when they die or excrete waste it returns to the environment to be recycled through soils, waters, and sediments. Over long timescales, phosphate from the surface is buried and can become rock again, closing the loop. Because there isn’t a sizable atmospheric reservoir for phosphorus, there isn’t a true gas-phase component to the cycle, which is why the statement describing the cycle as primarily through rocks and organisms without a gaseous phase is the best explanation.

The idea that phosphorus frequently vaporizes and cycles through the atmosphere isn’t supported by how phosphorus behaves under Earth surface conditions. The notion that phosphorus is only found in detergents and fertilizers ignores its natural presence in rocks and soils and its essential biological role. And the suggestion that phosphorus cycles through the atmosphere via sulfur-like processes isn’t accurate, since sulfur–gas cycles involve distinct compounds and pathways that don’t apply to phosphorus.