Chapter 1Water on Earth

Why is water so important?Brainstorm the importance of water on: • Humans• Plants• Animals

Water as a resource• One of the reasons why water is so useful is that it can

dissolve many things.• Over long periods of time, water dissolves and wears

down rocks and mountains through processes called weathering and erosion.

Water as a resource

• The human body is 60% to 75% water.• When you eat food, water in

your body dissolves nutrients so they can be carried through your bloodstream.

The Water Cycle• Most of the fresh water on the Earth’s surface is found in moving and

in stand water.• Rivers, streams and springs are moving water.• Ponds, lakes, and swampy wetlands are standing water.

The Water Cycle• The hydrologic cycle or water cycle is the movement of water from

the oceans and freshwater sources to the air and land and finally back to the oceans.• The water cycle constantly renews the Earth’s supply of fresh water.

Steps of the Water Cycle• Evaporation• Condensation• Precipitation

Evaporation• The first step involves the heat energy given off by the sun. This

energy causes water on the surface of the Earth to change to water vapor.• This process is called evaporation.

Sources of Evaporation• Enormous amounts of water evaporate from the oceans.• Water also evaporates from freshwater sources and from the soil.• Animals and plants release water vapor into the air.

Condensation• The second step is condensation.• Condensation is the process by which water vapor changes back into

a liquid.

Condensation• For condensation to occur, the water vapor must be cooled.• This happens when the warm air close to the surface of the Earth

rises.• As it moves farther from the Earth, it cools.• Cool air holds less vapor and it condenses into droplets of water

known as clouds.

Water Vapor• When water evaporates from the ocean, it leaves the salts behind. • Water vapor is made of fresh water only.

Precipitation• The third step is precipitation.• Precipitation occurs when the water returns to the Earth in the form

of rain, snow, sleet or hail.

Precipitation• Precipitation occurs when the water droplets that form in clouds

become too numerous and heavy to remain afloat in the air.• It returns to the Earth as rain, snow, sleet or hail.• After it falls, some returns to the atmosphere through evaporation

and the cycle is complete.

Groundwater• Some of the water that falls as precipitation may run off into land,

ponds, streams, river or oceans.• Some may soak into the ground and become groundwater.• At some point, the groundwater flows underground to the oceans.

Places where water is found• Surface water on Earth refers to water that collects on

the ground.• This water includes oceans, lakes, rivers, streams, and

reservoirs.• A reservoir is a protected artificial or natural lake that is

used to store water.

Places where water is found• A glacier is a huge mass of ice that forms on land when

snow and ice accumulate faster than they melt. • Most of Earth’s fresh water is in the form of glacier ice.

Places where water is found• Groundwater is water that collects under ground. • Some of the water on Earth’s surface moves down

through the soil to the water table (the upper level of underground water).