Chapter 15

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Environmental Science
Carl Mitchell

Chapter 15Fossil Fuels Energy and Impacts 11302011 110100 AM We use a variety of energy sources A great deal of energy emanates from Earths core making geothermal power available for our use Most of our energy however comes from the Sun We can harness energy from the Sun radiation directly in a number of ways y Drive wind patterns and they hydrological circle making possible such forms of energy as wind power and hydroelectric power y Photosynthesis and the growth of plants from which we take wood and other biomass as a fuel source y When plants die and are preserved in sediments under partial conditions they may impart their stored chemical energy to fossil fuels highly combustible substances formed from the remains of organisms from past geologic ages The three fossil fuels we use widely today are oil coal and natural gas Since the Industrial Revolution fossil fuels have replaced biomass as our societys dominant source of energy Besides providing for transportation heating and cooking these fuels are used to generate electricity a secondary form of energy that is easier to transfer over long distances and apply to a variety of uses Fossil fuels are indeed fuels created from fossils Most organisms after death do not end up as part of a coal gas or oil deposit A tree that falls and decays as a rotting log undergoes mostly aerobic decomposition in the presence of air bacteria and other organisms that use oxygen break down plant and animal remains into simpler carbon molecules that are recycled through the ecosystemFossil fuels are produced only when organic material is broken down in an anaerobic environment one that has little or no oxygen Such environments include the bottoms of shallow seas deep lakes and swamps Over millions of years organic matter that accumulates at the bottoms of such water bodies undergoes decomposition forming an oil precursor called kerogen Fossil fuels reserves are unevenly distributed Fossil fuel deposits are localized and unevenly distributed over Earths surface so some regions have substantial reserves for fossil fuels whereas other have very few Developed nations consume more energy than developing nations Even so Canadas per capita energy use is higher This is partly a result of the cold climate and long distances that characterize our nation but careless use patterns are part of the story too Moreover developed and developing nations tend to apportion their energy use differently Because industrialized nations rely more on equipment and technology they use more fossil fuels It takes energy to make energy Net energy expresses the difference between energy returned and energy invested Net EnergyEnergy ReturnedEnergy Invested When comparing energy sources it is useful to use a ratio often denoted as EROI or energy returned on investment EROI ratios are calculated as follows EROIEnergy ReturnedEnergy Invested Higher ratios mean that we receive more energy from each unit of energy that we invest when EROI1 it means that the amount of energy invested is the same as the amount of energy extracted EROI ratios can change over time The ratios decline because we extracted the easier deposits first and now must work harder and harder to extract the remaining amounts Coal is the worlds most abundant fossil fuel The precursor to coal is peat a moist soil composed of compressed organic matteris organic matter generally woody plant material that was Coalcompressed under very high pressure to form a dense carbonrich solid material
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