Earth's Water and the Water Cycle

• Earth is called the Blue Planet because about 75% of its surface is covered with water.
• Water exists on Earth as a liquid, solid (ice), and gas (water vapor).
• Water is essential for life.
• Water is found in bodies, lakes, rivers, oceans, plants, animals, air, and ground.
• The water cycle is the constant movement of water through the land, air, oceans, and living things.
• The energy from light and the force of gravity move water between oceans, the atmosphere, living organisms, and the land.
• Solar energy heats surface water causing evaporation into water vapor.
• Water vapor cools in the atmosphere and condensation occurs into clouds or crystallizes into snow or ice.
• Precipitation falls to the ground by the force of gravity and becomes surface runoff.
• Plants absorb water and release water vapor back into the air through transpiration.
• Animals use water and release water vapor through respiration.
• Surface water freezes by crystallization or is stored in land in bodies of water or in underground aquifers.
• The water cycle has no beginning or end, it is continuous.
• Water can come from anywhere in the world because all of Earth’s water is recycled in the water cycle.

Water States

• Water changes states of matter as it moves through the water cycle.
• Solar energy drives melting and evaporation.
• Earth’s gravity drives precipitation, groundwater penetration, and downhill flow.
• Water created on Earth billions of years ago is continually being cycled.
• Water flows down rivers and slopes into oceans.
• Ocean currents carry water around the globe.
• Water evaporates, condenses into clouds, and falls as rain potentially anywhere in the world.
• Solar energy increases temperature, liquid water molecules change into water vapor and move into the atmosphere through evaporation.
• Ocean water is a mixture of salt and water; during evaporation, only water evaporates, leaving the salt behind.
• Evaporation happens from lakes, rivers, puddles, soil, and bodies.
• Sweat comprises salt water; when sweat evaporates, salt is left behind on the skin.
• Water vapor loses energy and cools as it rises in the atmosphere.
• Water vapor molecules change state from gas to liquid and form small droplets of water through condensation.
• Condensation is the opposite of evaporation.
• Water vapor molecules need condensation nuclei to grab onto, like dust, dirt, or smoke.
• The atmosphere is the layer of gases that surrounds Earth.

Crystallization and Precipitation

• Liquid water molecules lose energy and cool to become a solid through crystallization.
• Crystallization is when liquid molecules form an orderly, geometric solid (snow).
• The geometric shape of a water molecule when it freezes is hexagonal.
• Gravity pulls snow down to Earth.
• Raindrops freeze into sleet when cloud temperatures are not freezing, but temperatures closer to the ground are.
• Ice pellets form in storm clouds, and strong updrafts add more layers of ice to form hail.
• Gravity pulls hail to earth.
• Precipitation is when water droplets or ice in the atmosphere become larger and heavier.
• Gravity pulls precipitation from the cloud to the surface of Earth.
• Types of precipitation include rain, snow, hail, and sleet.

Water Distribution

• The Dry Valleys in Antarctica are the driest places on Earth and have not seen rain for nearly 2 million years.
• The Atacama Desert in Chile and Peru is the next driest place on the planet.
• Water moves via downhill flow to return to the ocean.
• Water percolates through the ground to replenish groundwater and aquifers.
• The water table is the top of the surface where groundwater occurs.
• The saturated zone is the ground below the water table that is filled with water.
• Aquifers are replenished by the seepage of precipitation.
• An aquifer is a layer of permeable rock that retains and filters water.

Transpiration

• Plants absorb water from the soil, and animals drink from streams.
• Living things take in water and release it.
• Plants release water into the atmosphere through their leaves during transpiration.
• Animals release water through sweat (perspiration) and urination.
• Solar energy causes water to evaporate, continuing the water cycle.
• Transpiration is the evaporation of water through openings on the leaves of plants.

75% of Earth's surface is water, existing as liquid, solid, and gas. Water is constantly moving through the land, air, oceans, and living things in the water cycle. Solar energy, gravity, evaporation, condensation, precipitation, transpiration, and respiration are all part of the water cycle.