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

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Chapter 17 Testing Your Comprehension 1 The Earth’s atmosphere is about 500 km (300 mi) thick, consisting of four layers: the bottommost layer, the troposphere, is only 11 km (7 mi) thick but contains three-quarters of the atmosphere’s mass; the stratosphere extends from 11–50 km (7–31 mi) above sea level and contains most of the atmosphere’s UV-absorbing ozone; the mesosphere is a zone of declining temperatures and extremely low pressures, extending 50–90 km (31–56 mi) above sea level; finally, the thermosphere is the outermost layer of the atmosphere, extending from 90–500 km (56–300 mi) above sea level. In this layer, infrequent molecular collisions allow the atmosphere to become chemically stratified, with lighter hydrogen and helium rising to the top of the layer, and the heavier oxygen and nitrogen sinking toward the bottom. 2 The ozone layer is concentrated 17–30 km (10–19 mi) above sea level in the stratosphere. Stratospheric ozone absorbs UV radiation, which is harmful to life. Tropospheric ozone can contact living organisms, and react chemically with their tissues, causing harmful oxidation to occur. This oxidation can chemically alter a cell’s DNA, leading to mutations and the possibilities of cell death or cancer. 3 Solar energy heats air, causing pressure gradients that drive Earth’s atmospheric circulation. This circulation distributes heat and moisture over Earth’s surface (i.e., determines the main factors of climate). Hadley, Ferrel, and polar cells are convection patterns in the atmosphere, driven by the sun’s energy, that produce predictable bands of precipitation and wind direction over the globe. These factors
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EOC_ch17 - Chapter 17 Testing Your Comprehension 1 The...

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