The Great Hydrologic Engine: How the Water Cycle Works
Earthâs water is in a state of constant motion, moving seamlessly between the surface, the atmosphere, and subterranean reservoirs. Known as the water cycle, or hydrologic cycle, this continuous process relies on energy from the sun to transform water through its three primary physical states: liquid, gas, and solid. Without this perpetual dynamic system, life on Earth could not exist, as fresh water would remain trapped in isolated locations rather than circulating across the globe.
The cycle begins with solar energy heating the surfaces of oceans, lakes, and rivers. This thermal energy causes liquid water to transform into water vaporâan invisible gasâin a process known as evaporation. Simultaneously, vegetation plays a critical role through transpiration, where plants absorb water through their roots and release excess moisture as vapor through tiny pores in their leaves. Together, these processes uplift massive amounts of water vapor into the atmosphere every day.
As warm water vapor ascends, it encounters cooler temperatures in the upper atmosphere. This cooling causes the gas to condense back into microscopic liquid droplets or ice crystals, forming clouds and fog. When these droplets accumulate and become too dense to remain suspended by atmospheric currents, gravity pulls them back toward Earth as precipitation. Depending on regional atmospheric temperatures, precipitation can take the form of rain, snow, sleet, or hail.
- evaporation:
- The process by which liquid water changes into an invisible gas called water vapor when heated.
- transpiration:
- The process by which plants absorb water through roots and release vapor through leaf pores.
- precipitation:
- Water falling from clouds to Earth's surface as rain, snow, sleet, or hail.
- infiltration:
- The process of water soaking deep into the soil from the surface.
- aquifers:
- Underground layers of rock or soil that hold and supply fresh groundwater.
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Preview questions from this passageShowHide
- 1What powers the water cycle and drives the transformation of water through its physical states?
- 2What are the three primary physical states of water described in the passage?
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About this informational passage for 7th Grade
âThe Great Hydrologic Engine: How the Water Cycle Worksâ is a informational reading passage about Water Cycle, written for 7th Grade. It takes about 2 minutes to read (297 words) and comes with an interactive quiz and a printable worksheet with comprehension questions and an answer key.