Download Ch 15 Sec 1 Notes (Earth)

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
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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?
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– 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
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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