CHAP 1.2 – WATER ON EARTH

Facts About Water on Earth The Earth is the only planet that has most of its surface covered in water. Oceans cover about 70% of the Earth surface. Hence, Earth has the nickname the “blue planet”.

I. All Living Things Need Water Water makes up nearly 2/3 of the human body mass. For living organisms, water is needed to carry all the body processes such as digestion and circulation of oxygen. Also, many living organisms use water and shelter.

A. Body Processes We need water to carry necessary body processes. For example, water allows living organisms to: 1. obtain chemicals from their surroundings; 2. break down food; 3. grow; 4. reproduce; and 5. move substances around the body.

We obtain water by drinking it directly or eating indirectly through certain foods like watermelon. Plants need water to carry out photosynthesis. Photosynthesis is the process by which plants take in water, carbon dioxide, and energy from the sun to make their own food (glucose). Photosynthesis is important to us because we eat plants or eat the animals that eat plants.

Photosynthesis

B. SHELTER Bodies of water provide shelter or a habitat for many living organisms. Def. of habitat: a place where living organisms live and obtain all the things they need to survive. There are more aquatic living organisms in a habitat than land living organisms.

II. DISTRIBUTION OF EARTH’S WATER 97% of the Earth’s water is saltwater. Only 3% is freshwater (the water we drink). Of the 3% of freshwater, ¾ of it is in frozen ice masses near the South and North Poles. The other ¼ is underground. A very small fraction of the 3% freshwater is in lakes, rivers, and water vapor in the atmosphere.

A. OCEANS There are 4 major oceans: Artic Ocean, Atlantic Ocean, Indian Ocean, and Pacific Ocean. The largest ocean is the Pacific Ocean. All the ocean waters are connected.

B. ICE Icebergs are present by the South and North Poles. Icebergs are massive sheets of ice that broken of the main ice plate. Icebergs are made of freshwater only.

C. RIVERS AND LAKES The Great Lakes of North America contain nearly 20% of all the freshwater in the world. The Great Lakes are Lake Michigan, Lake Erie, Lake Huron, Lake Ontario, and Lake Superior.

D. GROUNDWATER Fresh water from rain or snow can soak into the ground. The water trickles down through particles of rock and soil to reach a layer of solid rock which it cannot go through. Def. of Groundwater: The water the fills the cracks and spaces in underground soil and rock layers. There is more freshwater underground than in lakes and rivers.

Groundwater Flow

III. THE WATER CYCLE Earth’s water is constantly renewed through the water cycle. Def. of Water Cycle: the continuous process by which water moves from the Earth’s surface to the atmosphere and back to the Earth’s surface. The main steps in the water cycle are evaporation, condensation, and precipitation.

A. WATER EVAPORATES Def. of evaporation: Water molecules at the surface of a liquid absorb enough energy to break free and change into a gas. Water is constantly evaporating from the surfaces of oceans and lakes. It also evaporates from soil, puddles, and your skin. Plants evaporate water from their leaves through a process called transpiration.

B. CONDENSATION FORMS CLOUDS Warm air rises and carries the water vapor with it to the atmosphere. However, the atmosphere is much colder than land temperatures. As a result, the water vapor cools and condenses by to liquid. Some of this liquid clumps around tiny dust particles to form clouds.

C. WATER FALLS AS PRECIPITATION Water droplets in a cloud grow larger until it is too heavy for the cloud to hold. The water droplets come back to Earth in the form of precipitation. Precipitation can be snow, sleet, hail, or rain. Most of the precipitation falls in the oceans.

If precipitation falls on land, three things can happen: 1. It can evaporate immediately. 2. It can run off land surfaces and go into lakes or rivers. From the lakes or rivers, it can evaporate or head to the oceans. 3. It can be absorbed as ground water. If the groundwater becomes too much, it will flow to a river, lake, or ocean.

The Water Cycle

IMPORTANT FACTS: Precipitation is where we get our fresh water. The amount of water on Earth has stayed the same for millions of years due to the balance of evaporation and precipitation.