TOEFL Experts Reading Practice 29
Coal is an ignitable, or burnable, black or dark brown rock that is generally found within deep layers of sedimentary rock. Coal is formed from peat bogs, or bogs containing dead plant material, that became buried due to flooding, landslides, or earthquakes. Over many years, additional soil and mud gradually layer on top of them, causing both the pressure upon and the temperature of the trapped material to rise. This process eventually transforms it into the hard rock known as coal.
As coal forms, it progresses through a series of stages, called grades, ranging from peat, which is considered the predecessor to coal, to lignite, bituminous, and finally anthracite coal. Each grade of coal is progressively harder and blacker, with a higher carbon content and a lower hydrogen and oxygen content. Peat and lignite coal have a few special applications, while bituminous coal is mostly used in electric power generation and the production of coke, a low-impurity fuel that burns very hot and is thus suitable for smelting metals. Anthracite coal is primarily used as an indoor heating fuel.
For at least 6,000 years, coal has been used for various purposes, starting with the use of black lignite for carving into ornaments in China. In Britain, coal has been used at least to some extent as a fuel source for over 5,000 years. Today, about half of the coal produced globally comes from China, with most of the rest produced in the United States, India, Australia, and Europe. In total, about 8 billion metric tons (8 trillion kilograms) of coal is produced and consumed annually worldwide.
Coal is extracted from the ground via coal mining, which can be divided into two categories: surface mining and underground mining. Strip, or “open cut,” mining is primarily used for surface mining, because it recovers a larger proportion of the available coal deposits. With this method, deep chunks of earth are razed, with the “overburden,” or rock and soil covering the deposits, removed via explosives, power shovels, and trucks. Once the coal is exposed, it is then ruptured into strips and transported to coal refineries or directly to sites where it will be consumed. Contour mining and mountaintop removal mining are surface mining techniques that are comparable to strip mining, but are typically directed toward coal deposits found underneath the slope of a hill or inside a mountain.
Underground mining is more prevalent than strip mining, as most coal deposits are too far below the surface to make strip mining practical. In underground mining, deep vertical shafts are drilled, with coal miners and equipment descending down the shafts to extract the coal in the horizontal deposits found between and around the shafts. As coal is removed, the weight of the rock and soil above the coal deposits, known as the “mine roof,” becomes supported more and more tenuously. Thus, hydraulic “roof supports” are positioned to buttress the ground above the mines in order to prevent dangerous cave-ins. Once the mining operation is completed, these roof supports are removed, and in most cases the mine roof eventually collapses.
While safety measures have evolved considerably over the past century, coal mining is still considered a dangerous occupation. Between 1900 and 1999, over 100,000 coal miners perished in the United States alone. Roof collapse, gas explosions, gas poisoning, wall failure, coal dust explosions, and suffocation are among the many reasons for these deaths. Moreover, the use of coal causes a number of serious health and environmental problems. Lung cancer and “black lung” can be caused by the burning and mining of coal, while the ashes from burnt coal contain poisonous heavy metals that can leak into the ground and atmosphere. Coal-fired power plants contaminate soil and groundwater and can lead to acid rain, which can harm ecosystems hundreds of miles away. Coal is also a primary contributor to the rise of “greenhouse gases,” such as carbon dioxide, which can lead to global climate change. While “clean coal” technologies can reduce or remove some of these threats, many such technologies will take decades to implement, and questions remain about whether it will ever be economically or politically possible to do so.
Coal is an ignitable, or burnable, black or dark brown rock that is generally found within deep layers of sedimentary rock. Coal is formed from peat bogs, or bogs containing dead plant material, that became buried due to flooding, landslides, or earthquakes. Over many years, additional soil and mud gradually layer on top of them, causing both the pressure upon and the temperature of the trapped material to rise. This process eventually transforms it into the hard rock known as coal.
As coal forms, it progresses through a series of stages, called grades, ranging from peat, which is considered the predecessor to coal, to lignite, bituminous, and finally anthracite coal. Each grade of coal is progressively harder and blacker, with a higher carbon content and a lower hydrogen and oxygen content. Peat and lignite coal have a few special applications, while bituminous coal is mostly used in electric power generation and the production of coke, a low-impurity fuel that burns very hot and is thus suitable for smelting metals. Anthracite coal is primarily used as an indoor heating fuel.
For at least 6,000 years, coal has been used for various purposes, starting with the use of black lignite for carving into ornaments in China. In Britain, coal has been used at least to some extent as a fuel source for over 5,000 years. Today, about half of the coal produced globally comes from China, with most of the rest produced in the United States, India, Australia, and Europe. In total, about 8 billion metric tons (8 trillion kilograms) of coal is produced and consumed annually worldwide.
Coal is extracted from the ground via coal mining, which can be divided into two categories: surface mining and underground mining. Strip, or “open cut,” mining is primarily used for surface mining, because it recovers a larger proportion of the available coal deposits. With this method, deep chunks of earth are razed, with the “overburden,” or rock and soil covering the deposits, removed via explosives, power shovels, and trucks. Once the coal is exposed, it is then ruptured into strips and transported to coal refineries or directly to sites where it will be consumed. Contour mining and mountaintop removal mining are surface mining techniques that are comparable to strip mining, but are typically directed toward coal deposits found underneath the slope of a hill or inside a mountain.
Underground mining is more prevalent than strip mining, as most coal deposits are too far below the surface to make strip mining practical. In underground mining, deep vertical shafts are drilled, with coal miners and equipment descending down the shafts to extract the coal in the horizontal deposits found between and around the shafts. As coal is removed, the weight of the rock and soil above the coal deposits, known as the “mine roof,” becomes supported more and more tenuously. Thus, hydraulic “roof supports” are positioned to buttress the ground above the mines in order to prevent dangerous cave-ins. Once the mining operation is completed, these roof supports are removed, and in most cases the mine roof eventually collapses.
While safety measures have evolved considerably over the past century, coal mining is still considered a dangerous occupation. Between 1900 and 1999, over 100,000 coal miners perished in the United States alone. Roof collapse, gas explosions, gas poisoning, wall failure, coal dust explosions, and suffocation are among the many reasons for these deaths. Moreover, the use of coal causes a number of serious health and environmental problems. Lung cancer and “black lung” can be caused by the burning and mining of coal, while the ashes from burnt coal contain poisonous heavy metals that can leak into the ground and atmosphere. Coal-fired power plants contaminate soil and groundwater and can lead to acid rain, which can harm ecosystems hundreds of miles away. Coal is also a primary contributor to the rise of “greenhouse gases,” such as carbon dioxide, which can lead to global climate change. While “clean coal” technologies can reduce or remove some of these threats, many such technologies will take decades to implement, and questions remain about whether it will ever be economically or politically possible to do so.
→(P3) For at least 6,000 years, coal has been used for various purposes, starting with the use of black lignite for carving into ornaments in China. In Britain, coal has been used at least to some extent as a fuel source for over 5,000 years. Today, about half of the coal produced globally comes from China, with most of the rest produced in the United States, India, Australia, and Europe. In total, about 8 billion metric tons (8 trillion kilograms) of coal is produced and consumed annually worldwide.
→(P3) For at least 6,000 years, coal has been used for various purposes, starting with the use of black lignite for carving into ornaments in China. In Britain, coal has been used at least to some extent as a fuel source for over 5,000 years. Today, about half of the coal produced globally comes from China, with most of the rest produced in the United States, India, Australia, and Europe. In total, about 8 billion metric tons (8 trillion kilograms) of coal is produced and consumed annually worldwide.
→(P3) For at least 6,000 years, coal has been used for various purposes, starting with the use of black lignite for carving into ornaments in China. In Britain, coal has been used at least to some extent as a fuel source for over 5,000 years. Today, about half of the coal produced globally comes from China, with most of the rest produced in the United States, India, Australia, and Europe. In total, about 8 billion metric tons (8 trillion kilograms) of coal is produced and consumed annually worldwide.
- Coal, the well-known fuel, is formed as plant material is crushed over many years under deep, growing layers of rock.