What energy source drives the water cycle?

• A. Sun
• B. Moon
• C. Wind
• D. Gravity

Answer: (A)

The Sun powers the water cycle. Solar radiation heats surface water in oceans, rivers, and soils, causing evaporation. Plants also contribute through transpiration, adding water vapor to the air. As this water vapor rises and cools, it condenses into clouds, and when the clouds become saturated, precipitation falls back to Earth, continuing the cycle. Gravity plays a supporting role by pulling rain downward and driving infiltration and runoff, but it isn’t the energy source that drives evaporation and cloud formation. Wind results from temperature differences created by solar heating and helps transport moisture, yet the energy behind the cycle comes from the Sun’s heat.