Essential Environment: The Science behind the Stories (3rd Edition)

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Chapter 9 Testing Your Comprehension 1 It is hypothesized that hunter-gatherers noticed and propagated plants that produced better fruits, eventually learning to save their seeds to plant the next year. This constitutes artificial selection, or the evolution of new crop varieties by selective breeding. Agriculture then encouraged a more sedentary lifestyle, a growing population, and economic specialization. 2 Traditional agriculture is biologically powered, with the work being performed by animal and human effort along with simple tools and machines. This can be done at a subsistence level, in which the farm family raises just enough food for itself, or intensively, in which an excess of food is produced for sale in the market. Industrial agriculture, by comparison, uses fossil fuel combustion to power much of the work on the farm: tilling, sowing, harvesting, irrigation, and fertilizer application. Efficiencies of scale encourage raising crop monocultures. 3 Soil is formed by the weathering of rocks and minerals and by the input of organic material. Physical or mechanical weathering breaks down rocks without changing them chemically. For example, ice wedges can form in small cracks in a rock, breaking it in two. Chemical weathering results from water or other substances chemically interacting with the parent material. Biological weathering occurs when living things are responsible for breaking down the parent material by either physical or chemical
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EOC_ch09 - Chapter 9 Testing Your Comprehension 1 It is...

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