Earth Layers - Science Textbook PDF

layers are How many Earth? ur there in o 7 Chapter Earth By the end of this chapter, you should be able to:...

layers are How many Earth? ur there in o 7 Chapter Earth By the end of this chapter, you should be able to: make a model to explain the Earth’s internal structure by chemical composition based on collected information. describe the process of weathering, erosion and sedimentation from the model, including examples of the results of such processes that change the Earth’s surface. compare the formation process, properties and usage, and explain the effects of utilization of fossil fuels based on collected data. show awareness of the impacts of using fossil fuels by offering guidelines for fossil fuels usage. compare the advantages and disadvantages of each type of renewable energy by gathering information and present the guidelines for the use of renewable energy suited to local.  7.1 Layers of the Earth Our Earth consists of three layers – the crust, mantle and core. The crust is made up of rocks and minerals. Much of the crust is covered by water, sand, soil and ice. Below the loose layer of soil, sand and crumbled rocks found on Earth, is the bedrock, which is a solid rock. The crust makes up less than 1% of the Earth’s mass. There are 8 elements that make up 99% of the Earth’s crust. They are oxygen, magnesium, aluminium, silicon, calcium, sodium, potassium and iron. The continents are about 35 km thick and the ocean floors are about 8 km thick. Crust Mantle Outer core Inner core How are the layers of the Earth similar to an egg?  Crust = Egg shell The mantel is the layer below the crust. It is the solid casing of the Mantle = Egg white Earth and is about 2,900 km thick. It makes up about 70% of the Core = Egg yolk Earth’s mass. It is made of silicon, magnesium oxygen, aluminium and iron. Its temperature is between 500oC and 2,000oC. The core is the center of the Earth. It makes up about 30% of the Earth’s mass. The outer core is mainly made of molten iron and nickel, and it is about 2,200 km thick. Its temperature is between 4,000oC and 6,000oC. The inner core is about 1,270 km thick and is made of solid iron and nickel. This is mainly due to the extreme pressure. Its temperature can be as high as 7,000oC. Q1. How many layers are there in our Earth? Name them. Q2. Which layer is the hottest? Q3. Which layer is the thickest? 7.1 Chapter 7 133 Earth  7.2 Slow Processes that Change the Surface of the Earth Some changes on the Earth’s surface are caused by slow processes, such as weathering, erosion and deposition. These processes have occurred over billions of year ago. Weathering Weathering is the process where a rock is broken down into smaller pieces on the Earth’s surface. There are three types of weathering, namely physical, biological and chemical weathering. Physical weathering, also called mechanical weathering, breaks down rocks without changing their chemical composition. This process occurs mainly due to temperature changes when there is a big difference between the day and night temperatures.      During the day, the outer layer of a rock is hot while its center is cold. So, the outer layer of the rock expands slightly. At night, when the temperature drops, the outer layer cools faster than its center and contracts slightly. After some time, the outer layer of the rock cracks and breaks off. Ice    In very cold areas, weathering involves water. When water in the cracks of the rocks freezes, it expands. This expansion widens the cracks. After some time, the rocks are broken down into pieces. This process is known as ice wedging. 134 Science Focus Smart MATHAYOM 2 Living things contribute to biological weathering. Roots grow into cracks of rocks where water and nutrients might be. As the roots grow, they wedge the rocks apart. Sometimes, burrowing animals and even humans break down rocks into smaller pieces. Chemical weathering involves chemical reactions. Rain is naturally slightly acidic as carbon dioxide dissolves in it. Some rocks such as limestone have minerals in them that react with the acidic rainwater. The chemical reactions make the rock weathered.       When fossil fuels such as coal and gasoline are burnt, more acidic gases are released into the air. This makes the rainwater more acidic. This rain is known as acid rain. Acid rain speeds up chemical weathering. Erosion During weathering, large rocks are broken down into smaller and movable pieces. Then, they are transported through erosion. Erosion is the process of transportation of rocks and soil materials or sediments by natural agents, such as running water, waves, glaciers, and wind. Rain washes the sediments into streams. Wind may blow them away. Glaciers can carry them away too. Landslides and mudslides happen when the soil and rocks on a slope are unstable and tumble or slide down the slope.    
Chapter 7 135 Earth  Deposition Deposition occurs when movement of sediments slows or stops and the sediments are later dropped. This happens when the agents of erosion are losing their energy and slowing down. sually heavy and larger sediments are deposited first before less denser sediments. Deposition creates many types of landform on the Earth such as the sand dunes in deserts and deltas at river mouths.  
Q1. What is weathering? Q2. How are weathering and erosion different? Q3. Describe weathering, erosion and deposition in changing the surface of the Earth. 7.2 7.3 Sources of Energy We use energy to do work. There are many sources of energy on our Earth. We can classify them into non-renewable energy sources and renewable enery sources. Non-renewable energy sources Non-renewable energy sources are energy sources that will not replenish quickly and may run out soon. Most non-renewable energy sources are fossil. Fossil fuels are hydrocarbon compounds formed from the decay of organic matter over 300 millions years ago. Coal, petroleum and oil shale are the types of fossil fuels currently in use. These materials are made into fuels for different kinds of equipment and are used in manufacturing. 136 Science Focus Smart MATHAYOM 2 Coal The coal we use today began to form millions of years ago in swampy areas where plentiful huge plants grew. When they died and fell in the swamps, they were covered by mud, soil and other plants. Layers after layers of sediments piled up. Over millions of years, the intense heat and pressure of the Earth converted the plant matter into a mixture of carbon and hydrocarbon compounds, known as coal. There are four types of coal which are classified according to their age. Bituminous coal and anthracite coal are the oldest types of coal and they contain the highest carbon content. This makes them useful for fueling power plants. Sub-bituminous coal and lignite coal are the youngest types of coal and they contain less carbon. They are not as useful as fuels because of their lower carbon content.   èê Coal comes in different forms, from hard black  
rocks to soft brown dirt. Some forms burn hotter and cleaner than others. Coal is used to produce electricity. Many coal beds are near the ground’s surface. We get coal by mining for it. Most coal is used by power plants where it is burned to make steam. The steam turns turbines to produce electricity. Coal is also used in steel manufacturing. It is refined to produce a substance called coke which burns at very high temperatures to smelt the iron into steel. Petroleum Petroleum is formed over millions of years from the decay of algae and tiny ocean animals known as plankton. The tiny animals and plants were buried in the sediments on the ocean floor. These sediments and organic matter are buried deeper into the Earth, under pressure and heat to become oil bearing shale and finally crude oil. Petroleum refers to the bituminous deposits that include crude oil, natural gas and tar. It is a thick, black, gooey liquid found way down in the ground, usually between layers of rocks. These products are aided in their Å     
formation by anaerobic bacteria and form methane. Petroleum is a major source of energy for transportation. It is refined by fractional distillation into gasoline, diesel, and kerosene. Oil products are also used as raw materials in the manufacture of plastics. ç   
Chapter 7 137 Earth  Oil shale Oil shale generally refers to any sedimentary rocks that contain solid bituminous materials (called kerogen) that are released as petroleum-like liquid when the rocks are heated in the chemical process of pyrolysis. Oil shale was formed over millions of years by deposition of silt and organic debris on lake beds and sea bottoms. Over long periods of time, heat and pressure transformed the materials You may use into oil shale in a process similar to the process that forms this animation to petroleum; however, the heat and pressure were not as great. understand better the formation of coal and Oil shale contains enough oil that will burn without any petroleum. additional processing. It is known as “the rock that burns”. It can be mined and processed to generate petroleum similar to those pumped from conventional oil wells. However, extracting oil from oil shale is more complex than conventional oil refineries and is currently more expensive. The oil in oil shale is solid and cannot be pumped out directly of the ground. The oil shale must first be mined and then heated to high temperature in the proses called retorting and the resultant liquid is then separated and collected. Disadvantages of using fossil fuels Non-renewable energy resources – The supply of fossil fuels is limited. Fossil fuels do not replenish themselves and the formation of fossil fuels takes millions of years and specific conditions. At our current consumption rate, we will simply run out of fossil fuels in 50 to 100 years later. Global warming – Combustion of fossil fuels gives out a large amount of carbon dioxide which is a greenhouse gas. It is responsible for global warming, the rising of the overall temperature of the Earth. This phenomenon is associated with frequent heavy rainfalls, floods and droughts. Pollution – Combustion of fossil fuels also releases carbon monoxide, nitrogen oxides, sulfur oxide and some heavy metals into the air. Carbon monoxide is a poisonous gas. Oxides of nitrogen and sulphur create acid rain when they are mixed with water. Acid rain is harmful to plants, animals and stone and metal artworks. Nitrogen oxides contribute to the formation of smog too. 138 Science Focus Smart MATHAYOM 2  There are a few ways to reduce the negative impact of using fossil fuels. Lowering fossil fuel consumption – We can do so by conserving energy. We can turn off electrical appliances not in use. We can carry out carpooling. We can practice the 3Rs to reduce waste materials and the need for raw materials to make new things. n e in e e fi ien – We need to make sure the fuel combustion is very efficient, producing the most energy with minimum waste. Nowadays, many house appliances come in with a range of energy-efficiency models. We can replace the regular light bulbs with compact florescent light (CFL) bulbs. Replacing with renewable energy sources – Renewable energy sources such as the Sun and wind offer many advantages from reliability to lower costs to small environmental impact. Renewable energy sources Renewable energy sources are energy sources that can be replaced after being used. Examples of renewable energy sources are the Sun, wind, running water, waves, biomass, heat from inside the Earth and hydrogen. In the ‘Thailand 4.0’ policy, renewable energy The Sun is a key priority for innovation. We intend to The Sun gives out heat and light energy for billions of years. reduce dependency on We use it to keep ourselves warm and to dry our food. Now, we imported energy sources have devices to collect solar energy for water heating. Some and increase the share of renewable energy devices convert it directly into electricity. This energy can be consumption from the used to heat water, and power homes, buildings and even current 12% to 30% in cars. The advantages of using solar energy are: 2036. Free of pollution Low maintenance cost ù          
However, the disadvantages of using solar energy are: High initial cost for materials and installation Weather dependent Expensive energy storage Chapter 7 139 Earth  Wind Wind is the moving air. Wind can be used to turn the blades of large windmills to produce electricity or to pump water from the ground. The advantages of using wind energy are: Free of pollution Low maintenance cost The disadvantages of using wind energy are: Not consistent High installation cost Threat to aerial animals Running water Running water in streams and waterfalls has energy. This water energy can be used as a source of energy in different ways. Hydroelectric energy is the energy released when water rushing from a dam into a turbine. The fast-moving water turns the turbine to generate electricity. Here are some advantages of using hydroelectric energy: Reliable and efficient Flexible as we can control the flow of water Recreation and tourism attraction The disadvantages of using hydroelectric energy are: Environmental impact – changes in river levels, flow patterns and water temperature Displacement of people as the large area is be flooded Expensive to build Limited places to built Waves Winds blowing over the oceans produce the vertical movement of the surface water known as waves. We can capture the wave energy by using special floating devices on the water. However, the technologies to harness the wave energy are still at an early stage of development. Here are some advantages of using wave energy: Free of pollution Relative consistent and predictable Low operation cost The disadvantages of using wave energy: High cost of investment Difficult to transmit wave energy May disturb vessels on the oceans 140 Science Focus Smart MATHAYOM 2 Biomass Biomass is the organic materials that come from plants and animals. Wood, unwanted agricultural waste such as dried plants and husks, animal manure, vegetable oils and food waste are examples of biomass. When biomass is burned directly or converted to liquid biofuels or biogas that can be burned as fuels, biomass energy is released. Here are some advantages of using biomass energy: Widely available Cheaper than fossil fuels Reduces landfills Here are some disadvantages of using biomass energy: Not entirely clean Risk of deforestation Large space is needed to produce and store biomass Heat from inside the Earth Power station Geothermal energy is the heat energy beneath the surface of the Earth. This energy can be drawn from the hot water below the Earth’s surface or by pumping cold water onto the hot rocks and returning the heated water to the surface. This can drive steam turbines to produce electricity. Here Steam up Cold water are some advantages of using geothermal energy: down Hot region Free of pollution Constant supply †  Here are some disadvantages of using geothermal energy: Can lead to release of greenhouse gases High investment cost Instability of ground as these sites are usually prone to earthquakes Location specific Hydrogen Electricity Hydrogen is one of the most abundant elements on Earth. However, hydrogen gas is not found Hydrogen Oxygen naturally and has to be manufactured. We can gas gas convert the hydrogen energy into electricity using a fuel cell. A fuel cell combines hydrogen with oxygen to produce electricity and water. Membrane Here are some advantages of using hydrogen electrolyte energy: Free of pollution More powerful and high efficiency, even used to power rockets and spaceships Water Here are some disadvantages of using hydrogen energy: †   Expensive Difficult to transport and store hydrogen gas Dangerous as hydrogen gas is flammable Chapter 7 141 Earth  Q1. What are non-renewable energy sources and renewable energy sources? What are their differences? Q2. Why are coal, petroleum and oil shale known as fossil fuels? Q3. Why is it not likely to find deposits of coal and petroleum at the same 7.3 location? Q4. List three disadvantages of using fossil fuels. Q5. List the renewable energy sources. Inner core Outer core Biological weathering Crust Mantle Core Physical Chemical weathering weathering Layers of Earth Weathering Slow processes Earth that change Erosion the Earth’s surface Deposition Energy sources Renewable Non-renewable energy sources energy sources Running Heat from The Sun Hydrogen Coal Petroleum Oil shale water inside the Earth Wind Biomass Waves 142 Science Focus Smart MATHAYOM 2  1. The Earth is made of layers. (a) How many layers are there? Name them in the correct sequence starting from the outmost one. (b) Which is the thinnest layer? (c) Which is the thickest layer? (d) Why is the inner core in solid state when it has the highest temperature? (e) What are the two main metals that make up the outer and inner core? 2. Sources of energy can be categorized into two groups. (a) Name the two groups. (b) Hydrogen energy is one of the new sources of energy. (i) What is hydrogen? (ii) What device is used to obtain electrical energy from hydrogen gas? (iii) What is the other product produced by this device? (c) Burning of fossil fuels produces heat energy. (i) What are fossil fuels? (ii) Give three examples of fossil fuels. (iii) What are the disadvantages of burning fossil fuels? 146 Science Focus Smart MATHAYOM 2