Which two gases make up most of the atmosphere?

• helium and hydrogen

• nitrogen and oxygen

• carbon dioxide and water vapor

A change in the amount of water vapor in the atmosphere will cause a change in what?

• weather

• temperature

• nitrogen

Name three kinds of solid particles in the air.

A layer of special oxygen molecules high above the Earth is called:

• ozone

• ionosphere

• clouds

The layer of the atmosphere that is closest to the Earth is called:

• the exosphere

• the troposphere

• the stratosphere

Why is the stratosphere warmer than the upper troposphere?