“WATER ON EARTH”

The Big Idea Water is a dominant feature on Earth’s surface and is essential for life.

Main Idea 1: Salt water and freshwater make up Earth’s water supply. Water covers some two-thirds of the planet. Salt Water About 97 percent of the Earth’s water is salty. Unsafe to drink because of high levels of salt. In general, found in Earth’s oceans, which cover some 71 percent of the planet’s surface Also found in some of Earth’s lakes

Main Idea 1: Salt water and freshwater make up Earth’s water supply. Water without salt. Makes up only 3 percent of our water supply Much of Earth’s freshwater is locked in glaciers, large areas of slow moving ice, and in the ice of the Arctic and Antarctic regions. Surface water is water that is found in Earth’s streams, rivers, and lakes and makes up less than one percent of Earth’s water supply.

Main Idea 1: Salt water and freshwater make up Earth’s water supply. Freshwater (continued) Precipitation is water that falls to Earth’s surface as rain, snow, sleet, or hail. Streams form when precipitation collects in a narrow channel and flows toward the ocean. Most available freshwater is groundwater, water found below Earth’s surface. Some naturally bubbles from the ground to the surface as a spring. Most groundwater is obtained by digging wells.

Main Idea 2: In the water cycle, water circulates from Earth’s surface to the atmosphere and back again. Water is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas, or water vapor. The water cycle is the movement of water from Earth’s surface to the atmosphere and back; it is driven by the sun’s energy. Evaporation - water turns from liquid to gas. Condensation - the rising gas cools and condenses, or changes from a vapor into tiny liquid droplets, to form clouds. Precipitation - if the droplets in clouds become heavy enough, they fall back to Earth as rain, snow, sleet, or hail. Runoff - excess water that isn’t absorbed as groundwater flows over land and collects in streams, rivers, and oceans.

Main Idea 3: Water plays an important role in people’s lives. Water Problems Lack of available freshwater, which can be caused by droughts or overuse. Contaminated, or polluted, water can harm humans, plants, and animals. Flooding can damage property and threaten lives. Water Benefits Provides us with food to eat Important source of energy Provides us with recreation, including swimming, fishing, surfing, and sailing.