1. Unit 7 – The Atmosphere and Water

2. Chapter 1, Section 1
Weather and the Atmosphere
Weather - the condition of the Earth’s atmosphere at a particular time and place
Atmosphere - the envelope of gases that surrounds the planet

3. Composition of the Atmosphere
Earth’s atmosphere is made up of:
Nitrogen
Oxygen
Carbon dioxide
Water vapor
Many other gases
Particles of solids and liquids

4. Nitrogen (78% of gas in atmosphere) is the most abundant gas
Each nitrogen molecule is made of two nitrogen atoms (N2)
Oxygen (21% of gas in atmosphere) is the second most abundant gas
Used by plants and animals to release energy from their food
Also used to burn fuels
Most oxygen molecules have two atoms (O2), but ozone has three oxygen atoms (O3)

5. Carbon dioxide (0.04% of gas in atmosphere)
Used by plants to produce food
Given off by plants and animals when they release energy from their food
Given off when fuels are burned
Water vapor
Is water in the form of a gas
Is invisible and varies greatly from place to place and time to time

6. Particles
Made of solid and liquid particles of dust, smoke, salt, and other chemicals
Some can be seen, some cannot
Importance of the Atmosphere
Earth’s atmosphere makes conditions on Earth suitable for living things
Keeps Earth warm
Protects living things from dangerous radiation from the Sun
Prevents Earth’s surface from being hit by most meteoroids

7. Chapter 1, Section 3
Layers of the Atmosphere
Scientists divide the Earth’s atmosphere into four main layers: troposphere, stratosphere, mesosphere, and thermosphere
The troposphere
Inner or lowest layer of Earth’s atmosphere in which Earth’s weather occurs
About 9 to 16 km above Earth’s surface
For every 1 km increase in altitude, the temperature drops 6.5°C; top of troposphere is -60°C
Contains almost all the mass of the atmosphere

8. The stratosphere
Extends from top of troposphere to about 50 km above Earth’s surface
Contains the ozone layer (absorbs energy from the Sun; warming the upper stratosphere)
Protects Earth’s living things from the Sun’s dangerous ultraviolet radiation
The mesosphere
Extends from top of stratosphere to 80 km above Earth’s surface
Protects Earth’s surface from being hit by most meteoroids (chunks of stone or metal from space)
Temperatures in outer mesosphere approach -90° C

9. The thermosphere
Is the outermost layer of the atmosphere
Extends from top of mesosphere outward into space
Air is very thin and hot (up to 1,800° C)
Divided into two layers: ionosphere and exosphere

10. Ionosphere
Is the inner layer of the thermosphere
Begins about 80 km above Earth’s surface and extends to 400 km
Ions here reflect radio waves back to Earth
Aurora borealis occurs here
Exosphere
Is the outer layer of the thermosphere
Begins about 400 km above Earth’s surface
Communication satellites orbit Earth in the exosphere