Water on Earth

Water on Earth: ● Three fourths of the Earth is water! ● Most of Earth’s water—roughly 97 percent—is salt water found in oceans. Only 3 percent is fresh water - Of that 3 percent, about three quarters is frozen in huge masses of ice near the North and South poles. - A tiny fraction of Earth’s fresh water occurs in underground and in lakes and rivers. - An even tinier fraction is found in the atmosphere. Oceans (97% Salt water) ● Earth’s oceans are all connected. - include: Pacific, Atlantic, Arctic, & Indian - Make up one big ocean! Ice (76% of the 3% freshwater) ● Icebergs are huge floating chunks of ice made from fresh water. ● Some icebergs have broken off from massive sheets of ice on land, called glaciers. ● The most freshwater is found in icebergs, however it is inaccessible to humans because it is frozen and because of its location. *Groundwater (shallow 12%, deep 11% of the 3% fresh) ● To find some of the freshwater on Earth, you would have to go underground. ● Groundwater is water that fills the cracks and spaces in underground soil and rock layers. ● This is humans main water source! Rivers and Lakes (0.34% of the 3% fresh) ● The Great Lakes contain the majority of Earth’s fresh lake water. The Water Cycle ● Earth’s water is naturally recycled through the water cycle. ● The water cycle is the continuous process by which water moves from Earth’s surface to the atmosphere and back. ● In the water cycle, water moves from bodies of water, land, and living things on Earth’s surface to the atmosphere and back to Earth’s surface. The water cycle has three major steps—evaporation, condensation, and precipitation. The cycle itself has no real beginning or end. But it is driven by an energy source—the sun. (transpiration is water evaporating from plants, perspiration is water evaporating from humans) Water Evaporates ● Evaporation is the process by which molecules at the surface of a liquid absorb enough energy to change to a gaseous state ● Water is constantly evaporating from the surfaces of oceans and large lakes. ● Smaller amounts evaporate from the soil, puddles, and even from your skin. Condensation forms Clouds ● When water evaporates, warm air carries the water molecules upward. ● At higher altitudes, air tends to become much colder and cold air cannot hold as much water vapor as warm air can. ● As a result, some of the water vapor cools and condenses into liquid water. ● Condensed droplets of water clump together around tiny dust particles in the air, forming clouds. Water falls as Precipitation ● As more water vapor condenses, the water droplets in a cloud grow larger and larger. ● Eventually, they become so heavy that they fall back to Earth. ● Water that falls to Earth as rain, snow, hail, or sleet is called precipitation. ● The water cycle renews the usable supply of fresh water on Earth. ● For millions of years, the total amount of water on Earth has remained fairly constant—rates of evaporation and precipitation are balanced. Distribution of Earth’s Water – 1. What are the four main sources of water on Earth? - oceans, icebergs, groundwater, rivers/lakes 2. Which of the four main water sources contain salt water? Which contain fresh water? - oceans are salt water - icebergs, rivers/lakes, and groundwater are all fresh water 3. Which freshwater resource is most accessible to people? - groundwater is the most accessible 4. What three major steps make up the water cycle? - evaporation, condensation, precipitation 5. Starting with a puddle on a sunny day, describe how water might move through the water cycle and eventually fall back as rain. - Water will evaporate into the air as it absorbs heat and turns to a gaseous state. Then as the water reaches a higher altitude and becomes colder, it begins to condense forming clouds. Once the water droplets become heavy enough, then they will fall back to earth as rain (precipitation).