Earth Science

Water on Earth

Processes of the Water Cycle

Study Tip
Based on your knowledge and observations of water in our atmosphere, create a flow chart depicting water’s movement on the Earth. Then compare your sketch to the water cycle figure shown below.

The Water Cycle

The hydrological (water) cycle is the movement of water around Earth’s surface. Water inhabits reservoirs, such as ponds, oceans, or the atmosphere, within the cycle. Molecules move between these reservoirs by certain processes including condensation and precipitation.

  • Solar Energy
  • The Sun provides the energy that drives evaporation and ultimately the water cycle
Study Tip
Based on your knowledge and observations of water in our atmosphere, create a flow chart depicting water’s movement on the Earth. Then compare your sketch to the water cycle figure shown below.
  • Oceans
  • Most of Earth’s water is stored in the oceans
  • Water can remain here for hundreds or thousands of years
  • Atmosphere
  • Evaporation: water changes from liquid to gaseous water vapor, supplied with energy from the Sun
  • Condensation: water vapor becomes tiny droplets of liquid, which gather in clouds
  • Precipitation: after water droplets in clouds collide and grow, they fall as rain, sleet, hail, or snow
the water cycle
Because it is a cycle, the water cycle has no beginning and end.
  • Streams and lakes
  • When water falls from the sky as rain, it may enter streams and rivers that flow downwards to oceans and lakes
  • Snow may sit on a mountain for several months and may become part of the ice in a glacier, where it remain for hundreds or thousands of years
  • Sublimation: process by which a solid changes directly into a gas without first becoming a liquid (snow and ice goes back into the air)
  • Snow and ice gradually melt to become liquid water which provides a steady flow of fresh water to streams, rivers, and lakes below
  • A water droplet falling as rain could become part of a stream or lake

Earth Science

  • Soil
  • Soil moisture is an important reservoir, as this water is necessary for plant development
  • Groundwater
  • Water may seep through dirt and rock below soil and then through pores infiltrating the ground, into Earth’s groundwater system
  • Enters aquifers that may store fresh water for centuries
  • Biosphere
  • Plants and animals depend on water to live and also play a role in the water cycle
  • Transpiration: plants take up water from soil and release large amounts of water vapor into the air through their leaves
Pont  du  Gard  in  France
Pont du Gard in France is an ancient aqueduct and bridge that was part of a well-developed system that supplied water around the Roman Empire.

Human Uses

People also depend on water as a natural resource.

  • Humans create canals, aqueducts, damns, and wells to collect water and direct it as they desire
Concept Check
  • What is transpiration?
  • Describe when and how sublimation occurs?
  • What is the role of the major reservoirs in the water cycle?