medium · GMAT Verbal

Passage: The phosphorus cycle differs from other major biogeochemical cycles, such as the nitrogen and carbon cycles, in that it does not include a significant atmospheric phase. Phosphorus is primarily found in rock formations and ocean sediments, from which it is released through the slow process of weathering. Once in the soil, it is absorbed by plants and moved through the food web. Because the natural release of phosphorus is so slow, it is often the limiting nutrient for primary productivity in terrestrial and freshwater ecosystems. However, the intensive use of phosphorus fertilizers—derived from mined phosphate rock—has significantly accelerated the movement of phosphorus into the environment. Unlike nitrogen, which can be fixed from the atmosphere, phosphate rock is a finite resource. Current projections suggest that the world's highest-quality phosphate deposits may be depleted within a century. This looming 'peak phosphorus' crisis has prompted calls for more efficient fertilizer use and the development of technologies to recover phosphorus from wastewater and animal manure, emphasizing that nutrient security is as vital to global stability as energy security. The main idea of the passage is to:

1. Predict that all freshwater ecosystems will experience algal blooms due to excess phosphorus by 2100.
2. Argue that energy security is more important than nutrient security for global stability.
3. Describe the chemical process by which weathering releases phosphorus from rock formations.
4. Explain the unique characteristics of the phosphorus cycle and the risks associated with its depletion.
5. Contrast the biological roles of phosphorus and nitrogen in terrestrial ecosystems.

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