The Earth and the Role of Water

The Earth and the Role of Water — page 3 — Water is the only matter found naturally in three different forms solid as ice liquid as water and gas as water vapor Water freezes at 32 degrees Fahrenheit 0 degrees Celsius and boils at 212 degrees Fahrenheit 100 degrees Celsius Water changes form because of changes in temperature gas solid liquid Freezing water makes it become ice Warming ice changes it to a liquid again Boiling releases water as a gas or vapor into the air Cooling water vapor returns it to a liquid state water Water is needed for all life forms Human bodies are about 60 water People take in about two and a half quarts 2 4 liters of water per day Human brains are 70 water Blood is 83 water Cells in the human body move minerals and nutrients in water Water moves wastes from the human body

The Earth and the Role of Water — page 4 — Plants use water to transport nutrients and materials throughout the roots stems and leaves Water evaporates from plants through small openings under their leaves through transpiration They use water in photosynthesis their food transpiration water making process Transpiration pulls water upward into the plant's roots stems and leaves People use water in many different ways such as drinking cleaning and cooking Agriculture manufacturing and mining need water Water generates electricity and provides recreation Water is vital to life Yet one in eight people lack safe drinking water Careful use of the Earth's water will preserve this most needed resource People everywhere in the world need clean water Scientists think that water is the world's most important resource

The Earth and the Role of Water — page 5 — CHAPTER TWO The Water Cycle Water is found almost everywhere on Earth Even the Earth's atmosphere holds water in gas form This water vapor affects the Earth's climate and weather Changing temperatures cause water to change states like from rain to snow or lakes drying up in a drought Heat from the Sun drives the movement of water known as the water cycle or hydrologic cycle In the water cycle water molecules move from the Earth's surface water into the air Then they return to the surface Some of the water sinks into the ground The water continues to move in a cycle going from the oceans to the air and back to land The Water Cycle Transportation Transportation Condensation Precipitation Deposition Condensation Precipitation Snowmelt Runoff Evaporation Transpiration Surface Flow Evaporation Surface Flow Plant Uptake Percolation Groundwater Flow

The Earth and the Role of Water — page 6 — water vapor As water molecules warm they rise into the air as water vapor The Sun heats bodies of water Warmer water molecules move faster and bounce off one another This motion pushes some of them away and into the air as water vapor Evaporation occurs when a liquid changes to a gas Most of the Earth's atmospheric water evaporates from the oceans A tiny amount comes from rivers and lakes A small percentage of water vapor comes from plants releasing water Heat from the Sun causes ocean water to evaporate The water molecules heat up and move faster The motion spreads them out They rise into the air Air currents carry them higher where the air is much cooler The water vapor cools changing from a gas to a liquid This condensation forms little drops creating clouds Over time the collection of drops becomes too heavy for the air to support Water falls to the Earth as precipitation Precipitation can be rain snow sleet freezing rain or hail

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