1

Weather and the Atmosphere 2

The weather may be hot or cold, wet or dry 3 Vocabulary: weather The condition of the air around us

4 Weather is caused by four factors 1.Temperature 2.Moisture 3.Air pressure 4.Wind

All weather develops in the atmosphere 5 Earth is surrounded by a blanket of air called the atmosphere

6 The atmosphere is a mixture of gases About three-fourths of the atmosphere is nitrogen

7 Almost one-fourth is oxygen The rest of the atmosphere is carbon dioxide and other gases

These gases are important to living things 8 People and other animals use oxygen as they breathe

9 Plants use carbon dioxide to make food

Living things use nitrogen to make proteins 10

The atmosphere is in layers around Earth 11 The layer closest to Earth is the troposphere

12 Vocabulary: troposphere The layer of the atmosphere closest to Earth where nearly all weather occurs

Nearly all weather occurs in this layer 13

14 The next layer up is the stratosphere Vocabulary: stratosphere The layer of the atmosphere that reaches from the troposphere to 30 miles above the Earth

The stratosphere contains an important gas called ozone 15 Ozone keeps most of the sun’s harmful radiation from reaching Earth

Farther out are the mesosphere and thermosphere 16 Vocabulary: mesosphere The layer of the atmosphere beyond the stratosphere

17 Vocabulary: thermosphere The layer of the atmosphere where the air becomes thin and fades into space

The air in the thermosphere becomes thinner and thinner until it fades into space 18