The World of Water - Science Textbook PDF

Okay, here's the markdown conversion of the document, formatted into sections, lists, and tables as appropriate. ### The World of Water **WARM UP** There is a popular saying in Hindi - 'Jal hi jiwan hai' which means, water is life. Water is an essential requirement for sustenance of life, making...

Okay, here's the markdown conversion of the document, formatted into sections, lists, and tables as appropriate. ### The World of Water **WARM UP** There is a popular saying in Hindi - 'Jal hi jiwan hai' which means, water is life. Water is an essential requirement for sustenance of life, making the Earth unique. The Earth is made up of 71% of water and 29% land. This means that water is more predominant than land on the Earth. However, of all the water that exists on the Earth, only 1% is potable. Most of the Earth's water is found in seas and oceans. Scientists, all over the world, are exploring the various celestial bodies for any trace of water as that would be an indicator for the possibility of life outside the Earth. We already know that the Earth's temperature varies according to the place, the water that is found in each of these places is also different. Water exists in three states - solid, liquid and gas. ### Introduction Water is one of nature's most precious gifts to all living things. Essential to life, a person's survival depends on drinking water. The human body consists of many minerals but nearly 55% of it is water. It is one of the most essential elements for good health. ### Our Hydrosphere The Earth is a unique planet largely due to the presence of the realm of water or the hydrosphere. The Blue Planet is a popular sobriquet used for the Earth due to abundance of water. Along with the atmosphere and lithosphere, the hydrosphere makes life possible on Earth. The hydrosphere comprises all forms of water bodies including solid, liquid and gaseous forms along with groundwater. The hydrosphere is sustained through the hydrological cycle involving numerous changes, which water undergoes on the sea, air and land. The water cycle involves four crucial phenomena: * Evaporation * Condensation * Precipitation * Collection The water in the oceans becomes water vapour through the process of evaporation which changes into clouds through condensation. Thereafter, the clouds precipitate as rain or snow that runs down into rivers and eventually goes back to the oceans. Therefore, the process by which water continuously changes its form and circulates between oceans, atmosphere and land is known as the water cycle. The amount of water that comes in, by way of precipitation, usually balances the amount that is lost by evaporation and transpiration. The availability of water varies from one place to another and from season to season. At times, the water cycle is affected by human activities such as deforestation, pollution of water bodies, etc. **Description of the Water Cycle Diagram:** There is a drawing consisting of clouds, the sun, and plants surrounding a body of water. The processes in the image are as follows: * Evaporation causes vapor from the water to form clouds.  * Condensation * Precipitation * Collection ### Fresh and Saline Water A huge amount of the evaporated water found in the atmosphere comes from the oceans. Around 97 per cent of all water from the oceans and seas is saline in nature and so is unsuitable for human consumption. It is saline because the rivers, while flowing over the land surface, dissolve and carry various salts with them which is deposited when the rivers merge into the oceans. The remaining 2 per cent is found in glaciers and icecaps while 1 per cent is found in groundwater, rivers, lakes, atmosphere and within life forms. Effectively, therefore, only 1 per cent of water is suitable for human consumption. **Distribution of Water** * Saltwater: 97.5% * Freshwater: 2.5% * Groundwater: 30.8% * Lakes and rivers: 0.3% * Locked in glacier: 68.9% ### Freshwater Water containing very little dissolved salts is known as freshwater. Rivers that carry freshwater from rain or melting of snow are among the most important and dominant sources of freshwater. The distribution of freshwater depends on the prevailing climatic conditions and is highly uneven. For instance, in the Northern Plains of India, where precipitation exceeds evaporation, there is surplus water, while in the Thar Desert, where evaporation is more, there is scarcity of water. Icecaps and glaciers are huge reservoirs of freshwater in a solid state. Large ice sheets are found all over Antarctica and Greenland. Glaciers are formed over a period of time due to the snowfall received in high mountain ranges above the snow line. Siachen in the Himalayas is one of the world's largest glaciers. Lakes are inland water bodies that are normally landlocked. These may vary in size from small ponds to big inland seas. The Caspian Sea, Lake Superior and the Great Bear Lake are large lakes which are also used for transportation. Many smaller lakes, as in Great Britain, are also important for their water supply. Underground water, lying below the land surface, is another major source of freshwater. Rainwater seeps through cracks and permeable rocks into the ground, where it is stored in porous rocks, and collects here as groundwater above a layer of impermeable rock. ### Saline Water Water which contains a large amount of dissolved salts such as chlorine, sodium, sulphur, calcium, potassium and magnesium is known as saline water. The maximum concentration is of sodium chloride or common salt. The degree of concentration of salt in seawater is known as its salinity and it varies from one place to another. Salinity is expressed in terms of parts per thousand. Usually, the average salinity of seawater is 35 parts per thousand or 3.5% which means that 1000 grams of seawater contains 35 grams of salt. Salinity is contingent on the rate of evaporation, amount of precipitation and amount of freshwater added to the ocean. **Knowledge Zone** March 22 is celebrated as World Water Day. ### Temperature The temperature of ocean water, which is heated by the Sun, varies from one place to another. Wind, tides and waves mix the surface layer of the ocean water with its deeper layers. The temperature of the surface water varies with latitude, therefore, the tropical latitudes, which receive vertical rays of the Sun, have the warmest oceanic waters. The oceanic temperatures decrease steadily from the equator to the poles. The normal decrease in temperature from the equator to the poles is upset by ocean currents, which transfer vast quantities of water from one latitude to another. The temperature of ocean water also decreases with depth. The Sun's rays warm the surface waters more than the deeper waters. ### Terrarium: Artificial Atmosphere You must have heard about or seen an aquarium- an enclosed space normally of glass with an artificial environment in which aquatic animals are kept. The aquarium is fitted with an air-circulatory system (to provide oxygen to the water), a water filter, and a heater to maintain the temperature, some weeds to maintain the oxygen balance and fish which live in environment. Similarly there is a thing called terrarium which is for plants. A terrarium has soil, some plants are placed and water is provided and then it is closed. The water which evaporates from the soil and the plants, falls back in a form of water drops within the space. The Earth including its atmosphere is like a terrarium. Water keeps changing its form but its quantity remains the same. ### Major Water Bodies An ocean is a major body of saline water and constitutes a principal component of the hydrosphere. Ocean covers about 70 per cent of the surface area of the Earth with an average depth of about 3.8 km. The ocean trenches are the deepest part of the ocean and can reach a depth of nearly 11 km. The five major oceans of the world are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean. ### Oceans * Pacific ocean * Atlantic Ocean * Indian Ocean * Arctic Ocean ### Pacific Ocean It is the largest and deepest of all the five oceans covering an area of 30.5 per cent of the total surface area of the Earth. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bound by Asia and Australia in the west and North America and South America in the east. Roughly triangular in shape, the Pacific Ocean contains many islands which are volcanic in origin. ### Atlantic Ocean It is the second largest and busiest ocean. It is less than half the size of the Pacific Ocean. It covers 20.8 per cent of the Earth's total surface area. Shaped like the alphabet 'S', the ocean contains many shallow seas, e.g. the Caribbean Sea, Baltic Sea, North Sea, Black Sea and Gulf of Mexico. The highly indented coastline of this ocean provides many sites for natural harbours. The Mid-Atlantic Ridge is a spectacular underwater mountain range on the ocean floor, running roughly down to the centre of the ocean floor. Its total length is about 16,000 km from the Arctic Ocean in the north to the Bouvet Islands in the south. ### Indian Ocean It is located mostly in the southern hemisphere and is the only ocean named after a country. It covers 14.4 per cent of the total surface area of the Earth and is enclosed on three sides in the north by the landmasses of Africa, Asia and Australia while the Southern Ocean meets it on the southern side. The ocean is roughly triangular in shape and is important because of its high oil reserves. The Bay of Benegal and the Arabian Sea are the two northward extensions of the ocean. ### Antarctic or Southern Ocean It surrounds Antarctica and occupies about 4 per cent of the surface area of the Earth. Large ice sheets cover this ocean for most part of the year. Several seas lie adjacent to this ocean, for Instance, the Scotia Sea, Amundsen Sea, Ross Sea etc. ### Arctic Ocean It is the world's smallest ocean covering 2.8 per cent of the total surface area of the Earth. Enclosed by the landmasses of North America, Asia, Greenland and Europe, it is located north of the Arctic Circle. Many islands and marginal seas, for example, the White Sea, the Baffin Bay, the Kara Sea, etc., surround this ocean. **Spot Check:** 1. What do you mean by hydrosphere? 2. What do you understand by the salinity of water? 3. What are the five major oceans of the world? 4. Name the shallow seas that are a part of the Atlantic Ocean. 5. Which is the largest and the deepest ocean in the world? ### Ocean Water Circulation Ocean water is dynamic and moves continuously, either in a vertical or horizontal way. These movements are caused by several factors such as difference in temperature and density of ocean water, variation in salinity and the effect of the prevailing winds. Waves, tides and currents are the major movements in oceans. ### Waves A wave is a regular rise and fall of ocean and sea water due to the action of the wind on the surface of water. The shape and size of waves depend on the speed of the wind and other weather conditions. The upper part of a wave is called a crest while the lower part is called a trough. The vertical distance between a crest and a trough is called wave height. The horizontal distance between two successive crests is called wavelength. ### Tsunami - The Earth's Pandemonium Tsunami or the harbour wave struck havoc in the Indian Ocean on the 26 December 2004. The wave was the result of the earthquake that had its epicenter close to the western boundary of Sumatra. The magnitude of the earthquake was 9.0 on the Richter scale. As the Indian plate went under the Burma plate, there was a sudden movement of the sea floor, causing the earthquake. The ocean floor was displaced by about 10-20m and tilted in a downwardly direction. A huge mass of ocean water flowed to fill in the gap that was being created by the displacement. This marked the withdrawal of the water mass from the coastlines of the landmasses in the south and southeast Asia. After thrusting of the Indian plate below the Burma plate, the water mass rushed back towards the coastline. Tsunami travelled at a speed of about 800 km/hour, comparable to speed of commercial aircraft and completely washed away some of the islands in the Indian ocean. The Indira point in the Andaman and Nicobar, islands that marks the southernmost point of India, got completely submerged. As the wave moved from earthquake epicenter from Sumatra towards the Andaman islands and Sri Lanka, the wave length decreased with decreasing depth of water. The travel speed also declined from 700-900km/hour to less than 70km/hour. Tsunami waves travelled up to a depth of 3 km from the coast killing more than 10,000 people and affected more than a lakh of houses. In India, the worst affected were the coastal areas of Andhra Pradesh, Tamil Nadu, Kerala, Puducherry, and the Andaman and Nicobar Islands. While the earthquake cannot be predicted in advance, it is possible to give a three-hour notice of a potential tsunami. Such early warning systems are in place across the Pacific Ocean, but not in the Indian Ocean. Tsunamis are rare in the Indian Ocean as the seismic activity is less as compared to the Pacific Ocean. ### Tides Sea water rises up the shore at a certain time of the day and then ebbs or recedes at regular intervals. This rhythmic rise and fall in the level of sea water is known as tides. Tides are caused due to the gravitational force exerted by the Moon, the Sun and the rotation of the Earth. The Moon, being closer to the Earth, exerts a greater gravitational force on water bodies closer to it. The height of tides varies every day since it is contingent on the relative positions of the Moon and the Sun with respect to the Earth. During the full Moon and the new Moon, the Earth, Moon and the Sun are in the same straight line, tides, known as spring tides, occur. If, in the first and last quarters, the ocean water is pulled in diagonally opposite directions by the gravitational force of the Sun and the Earth, it results in the occurrence of low tides called neap tides. ### **Importance of tides** * Tides clear mud and silt deposits from the mouth of rivers and so keep them open for ships. * Tides are of immense help in shipping and navigation. Ships leave the harbour when the tide goes out and enter when the tides come in. Spring tides are especially favourable for large ships. * Fishermen greatly benefit due to tides as fish come near the coast during high tide enabling a bountiful catch. * Tides are a very important source of renewable energy in the form of fast movement of water during inflow and outflow. In view of the predictability of tides, tidal power stations have been set up in Canada, France, China, Russia, South Korea and Japan. The Gulf of Kuchchh in Gujarat has been identified for the development of tidal power. ### Ocean Currents The continuous movement or drift of the ocean water in a definite direction is known as an ocean current. The water moves in the form of a river or broad stream flowing through the ocean, at a speed varying from 2 to 10 km per hour. The broad, \ slow moving masses of water are called drifts. On the basis of temperature, ocean currents are classified into two types-warm ocean currents and cold ocean currents. The warm currents flow from the equatorial region towards the polar region and their temperature is more than that of their surrounding areas while the temperature of cold currents is more than that of their surrounding areas and flow from the polar region towards the equatorial region. Ocean currents are caused by the winds, rotation of the Earth, the differences in density of ocean water depending on temperature and salinity, tides, interaction with other currents and shape of landmasses. Ocean currents flow in the direction of prevailing winds. Therefore, water from equatorial areas expands and flows towards the Polar regions while the water from the Polar regions flows towards the equatorial regions. Due to the effects of the Coriolis force of rotation, all oceanic currents generally move in a clockwise direction in the northern hemisphere and in an anti-clockwise direction in the southern hemisphere. Sometimes, a landmass may obstruct the flow of an ocean current causing it to change its direction. For example, the Equatorial current in the Atlantic Ocean divides into two branches when it meets the South American coast. The Gulf Stream goes north and the Brazil Current goes south. Warm and cold currents modify their temperature accordingly. When these winds blow over the coastal lands, they modify the temperatures there making the lands comparatively warmer or colder. * Winds that pass over warm currents become warm and absorb more moisture due to greater evaporation, thus bringing rainfall to coastal areas while cold currents decrease the moisture bearing capacity of winds. * The mixing of warm and cold currents causes heavy fog, hindering navigation since it reduces visibility and acts as a hazard to shipping. The best fishing grounds in the world with an abundance of plankton are also located where the warm and cold currents meet, e.g. Grand Banks, off the coast of Newfoundland, where the warm Gulf Stream meets the cold Labrador Current. * Warm currents melt dangerous icebergs, which they encounter, thus reducing danger to ships whereas cold currents often carry icebergs to the lower latitudes. * Ships prefer to sail along with the currents as they can move faster and hence, save on time and fuel. ### Importance of Hydrosphere The hydrosphere therefore sustains life in the biosphere in many ways. * Water from lakes and rivers is very important for domestic purposes as well as for irrigation. * It offers an important link in transport and communication between the continental masses. * The various water bodies existing on our planet are a vital source of diverse marine life and marine products. * Salt and other minerals are obtained from ocean waters. * Oceans and other water bodies also influence the weather and climate. * Tidal energy can be generated from ocean water while hydroelectricity is generated from rivers. Water is a precious resource and so we must use it judiciously and take adequate steps to prevent its pollution. Water conservation will go a long way in ensuring its availability forever. ### LET'S RECAP * The hydrosphere, also called the realm of water on Earth, helps sustain life in the biosphere. It is maintained by the hydrological cycle. * The four phenomena or processes involved in the hydrological cycle are evaporation, condensation, precipitation and collection. * The five oceans-Pacific, Atlantic, Indian, Arctic and the Antarctic-constitute the principal component of the hydrosphere. Each ocean has its own peculiar characteristics. * The major movements in oceans are in the form of waves, tides and currents. * Water conservation is crucial to the survival of mankind. ### KEY TERMS | Term | Definition | | :---------- | :--------------------------------------------------------------------------------------------------- | | Glacier | A huge mass of ice, slowly floating over landmass | | Icecap | The layer of ice which permanently covers parts of the Earth | | Permeable | A material which is penetrable, i.e. allows liquids to pass through | | Plankton | Tiny marine organisms which are an excellent source of food for fishes | | Transpiration | The process by which water absorbed by plants enters the atmosphere through the plant surface | ### **EXERCISES** **A. Multiple Choice Questions (MCQs):** 1. 71 percentage of the Earth's surface is covered with water. 2. d. oceans A huge amount of the evaporated water found in the atmosphere comes from the 3. triangular The Pacific Ocean is roughly in shape containing many islands of volcanic origin. 4. crest. The upper part of a wave is called something. 5. Ocean currents flow in the direction of prevailing winds. 6. b. and c. The hydrosphere comprises all forms of water bodies including those in liquid and solid states, and gaseous state, including groundwater. 7. The water cycle involves four crucial phenomena which are evaporation, condensation, precipitation and collection. 8. The oceanic temperature decreases steadily from the Equator to the Poles region 9. The Mid Atlantic Ridge is an underwater mountain range on the ocean floor of the Atlantic Ocean. 10. Tides are caused due to the gravitational force exerted by the Moon and rotation of the earth. **C. Write T for True or F for False:** 1. True 2. True 3. False 4. False 5. True **Match the following:** 1. Tsunami - b. Earthquake in the ocean 2. Precipitation - d. Snow 3. Plankton - e. Grand Banks 4. Spring tide - a. High tide 5. Neap tide - c. Low tide **E. Short Answer Type Questions:** 1. Define the water cycle. Explain it with the help of a diagram. 2. How is water distributed on Earth? 3. Name the inland water bodies that are used for transportation. 4. How does groundwater get collected? 5. How are waves formed? **F. Long Answer Type Questions:** 1. The distribution of freshwater depends on the prevailing climatic conditions. It is highly uneven. Give an example to support this statement. 2. How are the glaciers formed? Give an example. 3. What are the factors that cause the horizontal as well as the vertical movement of ocean water? 4. Define wave height. What are the factors that decide the size of the wave? 5. Define Tide. How is it Influenced by the gravitational force of the Sun and the Moon? **G. Distinguish between:** 1. Waves and Tides 2. Crest and Trough 3. Evaporation and Condensation 4. High tide and Low tide **H. Give reasons:** 1. Tides are considered important. 2. Fog over the ocean is considered dangerous for ships. 3. Ships prefer to sail with the current. 4. The ocean water is salty. **DO AND LEARN** **ASSERTION AND REASONING** In the following questions, there are two statements marked as Assertion (A) and Reason (R). Read them and choose the appropriate option for each part. 1. Assertion (A): Oceans are very important. Reason (R): They regulate the Earth's temperature and climate. * a. Both A and R are true, and R is the correct explanation of A. 2. Assertion (A): Warm and cold currents modify their temperature accordingly. Reason (R): Winds that pass over warm currents become warm and absorb more moisture due to greater evaporation, thus bringing rainfall to coastal areas while cold currents decrease the moisture bearing capacity of winds. * a. Both A and R are true, and R is the correct explanation of A. **APPLICATION/COMPETENCY BASED QUESTIONS** 1. Water is one of the most precious natural resources. But unfortunately, our present lifestyle is based on excessive use of water. It is the need of the hour that we adopt water- **HOTS** 1. In the coastal areas, the tsunami appears as a huge wall of water. Explain. 2. Sun's rays warm the surface waters more than the deeper waters. Why? 3. Atlantic Ocean has many natural harbors. Why? **PICTURE BASED QUESTIONS** Observe the picture given alongside and answer the following questions: 1. What does this picture show? 2. Name the natural disaster being depicted in the given picture? 3. In which year did this natural disaster occur on a large scale? 4. Name the coastal areas of India that were affected by it. 5. What are the early indications of approaching of this disaster? **DIGITAL LITERACY** 1. Collect pictures and newspaper cutting of the Indian Ocean tsunami of 2004 and paste them in a scrapbook. Write about the nature of the tsunami, why it occurred, and its after effects in the form of a flowchart. 2. Find out about Alexander Von Humboldt who was the first to discover the cold currents along the coast of Peru. Share your findings with the rest of the class. **ACTIVITY** 1. Make a model of terrarium and observe the water cycle. 2. Make a PowerPoint presentation on the importance of water. **PROJECT** Explore the Internet and find out about five disasters caused by water. Make a chart of the same. **LIFE SKILLS** Water pollution is gaining gigantic proportions with its terrifying impact on aquatic life. Imagine that you are at a beach where there are a group of people who are littering the place with plastic bottles, wrapping papers, cellophane wrappers and aluminum foils What will you do? * Ask them to clean up the place as soon as possible. * Ignore them as they are adults and are unlikely to listen to you. * Click pictures and circulate around to shame the group. * Call for help, preferably from the patrolling vehicles on the beach and notify about the situation.