1. Journal # 19 The layer of gases that surrounds the earth is called the ___________. Nitrogen makes up about __% of the atmosphere. Oxygen makes up about __% of the atmosphere. Plants produce oxygen through a process called _________. Water can exist as an invisible gas called _____.

3. Atmospheric Pressure Gravity holds the gases of the atmosphere near Earth’s surface. As a result, the air molecules are compressed together and exert force on the Earth’s surface. The pressure exerted on a surface by the atmosphere is called atmospheric pressure Atmospheric pressure is equal in all directions

4. Pressure and Altitude Gravity keeps 99% of the total mass of the atmosphere within 32 km of Earth’s surface. The remaining 1% extends upward for hundreds of kilometers, but gets thinner at higher altitudes. Atmospheric pressure decreases as altitude increase

5. Mountain Climbers At high altitudes, climbers must carry a supply of oxygen to breathe from because the density of the atmosphere there is very low. So, oxygen levels in the air are too low to supply the climber.

6. Pressure and Temperature Atmospheric pressure also changes as a result of differences in temperature and in the amount of water vapor in the air. As temperature increases, atmospheric pressure decreases. Air that has a lot of water vapor is less dense than drier air. As water vapor increases, the pressure decreases.

7. Review What is atmospheric pressure? As altitude increases, pressure ____________. As temperature increases pressure ___________. As water vapor increases, pressure _______. Why do mountain climbers often have oxygen tanks?

8. Today, you will.. Perform a pressure lab, to observe how temperature affects pressure. You will work in groups of 2-3. You must stay within your group. Lab safety. Lab must be completed by the end of the day.