Why is the Hydrologic Cycle considered a closed system?

• A. Water is always recycled
• B. Water never evaporates
• C. Water disappears into space
• D. Water becomes permanently trapped in rocks

Answer: (A)

The hydrologic cycle describes the continuous movement of water through evaporation, condensation, precipitation, and runoff among the oceans, atmosphere, land, and underground. Because the total amount of water on Earth stays essentially constant, water is always recycled within the planet’s system. Evaporation lifts water into the atmosphere, it cools and condenses into clouds, and it returns as rain or snow, replenishing oceans, rivers, soil, and groundwater. Water may be stored briefly in ice caps or deep aquifers, but it remains part of the cycle and can re-enter circulation. Only an extremely small amount escapes to space over very long timescales, which is negligible for everyday hydrologic processes. So the best way to describe the cycle is that water is continually recycled within Earth, making it a closed system for matter.