C. The Atmosphere

1. Definition

a. The envelope of gases that surround the earth

b. 78% N, 21% O2, .04% CO2, and very small amounts of other gases

c. The upper limit of it is questionable

d. Consists of 4 layers

2. Layers of the atmosphere

a. Troposphere- lowest layer, up to 18 km

1. Most dense in concentration of gases

2. Where wind and weather occur

b. Stratosphere- second layer, 18-50 km

1. No weather, where planes fly

2. Ozone layer is here O3 not O2

c. Mesosphere- third layer, 50 to 85 km1. Coldest layer- -100 C

d. Thermosphere- outer layer, fades out1. Hottest layer2. Aka the ionosphere b/c sunlight

causes atoms to lose electronsa. Makes ions and they glow

when they touch= Aurora borealis