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The Atmosphere Chapter 15, Section 1 Composition of the Atmosphere • Thinking Questions – What is air made of? – Does it weigh anything? – How do we know anything about it? The Atmosphere • Key Point – The atmosphere is a mixture of gases that surround the Earth. The atmosphere is vital to life on Earth and is constantly changing. Composition of the Atmosphere • The atmosphere is made of gases – Nitrogen = 78% – Oxygen = 21% – 1% = carbon dioxide, argon, water vapor, and other gases Atmospheric Pressure and Temperature • Thinking Question – What causes your ears to pop when you dive into a pool or fly in a plane? • Changes in air pressure – Pressure inside ears must adjust for pressure outside ears Air Pressure • Gas molecules in air move constantly – Always bouncing off other molecules, people, etc – Collisions cause air pressure – Air pressure: force of air molecules crashing into a surface • The more molecules there are, the more air pressure Air Pressure • Thinking Question – Why does air stay around the earth? • Gravity pulls the gas molecules towards the earth – Gravity gives molecules weight – More molecules found closer to the surface Air Pressure • Thinking Question – What is a relationship between gravity and the number of gas molecules present? • • – Is it an inverse or direct relationship? The stronger the force of gravity, the more molecules present. As altitude increases, gravity decreases – Less molecules present – Less molecules = less air pressure Air Temperature • Thinking Question – Would you expect air to become more dense or less dense as you climb a mountain? – Air becomes less dense because there are fewer molecules present. This occurs even though temperatures drop (cooler = more dense) Air Temperature • Air temperature changes with altitude – Cycles between warm and cold – Different gases absorb solar energy differently • Warm = gases absorb solar energy • Cold = gases reflect solar energy • Atmosphere divided into layers – Based on temperature changes Layers of the Atmosphere • Four layers – Troposphere – Stratosphere – Mesosphere – Thermosphere • Thinking question – Which layer names can you interpret? Troposphere • “Tropo” means change • Lowest layer • Most dense – Why? • 90% of atmosphere’s mass • Contains all CO2, H20 vapor, pollution, clouds, and weather Stratosphere • “strato” means layer • Above troposphere • Extremely cold (60 below Celsius) • Temp rises with altitude – Ozone layer absorbs solar energy (UV rays) – Ozone: 3 oxygen atoms bonded together – Ozone layer protects life from radiation Mesosphere • “middle sphere” • Coldest layer of atmosphere • Temp decreases with increased altitude – 93 C below zero • Huge wind storms – Wind speeds of 320 km/hr Thermosphere • “thermo” means heat • Temp increases with altitude • Gases absorb radiation – Temps of 1700 degrees Celsius • However, thermosphere would NOT feel hot – Huh? Heat vs. Temperature • • Heat – Transfer of energy between object – Hot air molecule collides with cold air molecule Temperature – Measure of average energy of molecules – High temp = fast moving molecules Ionosphere • Between mesosphere and thermosphere • Absorbs X rays and gamma rays • Atoms become charged ions • Reflects radio waves • Cause Aurora Borealis and Aurora Australis