Chapter 3 - Chapter 3: Earths Modern Atmosphere Study Guide...

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Chapter 3: Earth’s Modern Atmosphere Study Guide Air: is a simple mixture of gases that is naturally odorless, colorless, tasteless, and formless, blended so thoroughly that it behaves as if it were a single gas. the principal substance in the modern atmosphere. Exosphere : Means “outer sphere”, Has rarefied atmosphere and is nearly a vacuum Contains scarce lightweight hydrogen and helium atoms, is weakly bound by gravity, and is as far as 32,000 km (20,000 mi) from Earth When referring to the atmosphere, think of it in layers, then break it down into three components: composition , temperature , and function . Table 3.1 Air pressure : Is weight (force over a unit area) of the atmosphere on us. The atmosphere exerts an average force of approximately 1kg/cm 2 at sea level. Over half the total mass of the atmosphere is compressed below 5500 m, 75% occurs below 10,700 m, and 90% is below 16,000 m. All but 0.1% of the atmosphere exists below an altitude of 50 km. The heterosphere : The outer atmosphere in terms of composition Begins at about 80 km altitude and extends outward to the exosphere and interplanetary space transition Has less than .001% of the atmosphere’s mass The gases are not evenly mixed Hydrogen and helium are at the margins of outer space and oxygen and nitrogen are dominant in lower heterosphere. The homosphere : Below the heterosphere, in terms of composition , Extends from an altitude of 80 km to Earth’s surface Atmospheric density rapidly changes in the homosphere and the blend of gases is nearly uniform throughout The air of the homosphere is a vast reservoir of relatively inert nitrogen , a key element of life, lies within nitrogen-fixing bacteria and is 78% of the atmosphere; oxygen forms about one-fifth of the atmosphere and forms compounds that compose about half of Earth’s crust and makes up 20.9% of the homosphere; the gas argon constitutes for less than 1% of the homosphere, is unusable in life processes, and is residue from the radioactive decay of potassium-40; carbon dioxide is important for maintaining global temperatures at only .039% of the atmosphere. Table 3.2**
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Chapter 3 - Chapter 3: Earths Modern Atmosphere Study Guide...

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