. Earth is surrounded by an envelope of gases called the _____________.  

• Thermosphere
• Stratosphere
• Troposphere
•  Atmosphere

Clouds form when water vapor ___________ out of the air.    

•  Evaporates
• Condenses
• Precipates
• Disappears

Water forms thin, feathery clouds of ice at the top of the _______________.  

• Thermosphere
• Stratosphere
• Troposphere 
• Atmosphere

Which layer contains the ozone layer.?  

• Mesosphere 
• Thermosphere 
• Troposphere
•  Stratosphere

What is the lower layer of the thermosphere called?  

• Exosphere
•  Ionosphere
• Atmosphere 
• Mesosphere

Which layer do most meteoroids burn up in?   

• Thermosphere
• Exosphere
• Ionsphere
•  Mesosphere

Which of the following is NOT found in dryair? 

• Carbon Dioxide
• Oxygen
•  Vapor Water 
• Nitrogen

 As a hot air balloon rises from 0 kilometers to 6 kilometers above sea level air density _______. 

•  Bursts
• Decreases
•  Increases
• Is the Same

Which of the following is NOT one of the four main layers of Earth’s atmosphere? 

•  Exosphere
• Troposphere
• Thermosphere
•  Mesosphere

In which sphere can the air temperature can reach 1,800º C?     

• Mesosphere
• Troposphere
• Stratosphere
• Thermosphere