1. Chapter 15 The Atmosphere

2. What is the atmosphere?
The thin layer of gases that surrounds our planet.
Weather is the condition of the atmosphere at a certain place and time.
Our atmosphere makes life possible on our planet.
Provides us with oxygen.
Keeps surface warm so water can exist as a liquid.
Protects the surface from dangerous radiation from the sun.
Protects us from most meteoroids or rocks from space.

3. The Composition of the Atmosphere
Nitrogen makes up 78% of our atmosphere
Oxygen makes up 21%
Argon makes up almost 1%
All other gases have only trace amounts

4. Trace elements/compounds
Carbon dioxide: plants use to produce food. Plants take in CO2 and give off oxygen as a waste product.
Animals take in oxygen to make energy and give off CO2 as a waste product.
Fossil fuels (coal, oil, natural gas) give off CO2 when they are burned. Rising CO2 levels may cause global warming.
The fizz in soda is really CO2 bubbles.
Dry ice is CO2 in the solid state.

5. Ozone Ozone is a molecule of oxygen with 3 oxygen atoms instead of 2.
Often formed when lightning interacts with oxygen in the air or by UV rays in the upper atmosphere.
Forms a layer in the atmosphere that absorbs ultraviolet radiation from the sun. Without this layer life might not be possible on the surface of the planet.

6. Earth’s Early Atmosphere
The Precambrian atmosphere was composed mainly of nitrogen and carbon dioxide, along with some methane and ammonia.
Volcanoes spewed water vapor, carbon monoxide, and even more nitrogen and carbon dioxide into the air. Comets also contributed water vapor, but no free oxygen.
So where did the abundant oxygen that has made life as we know it come from?

8. Precambrian Life
The first life on Earth was cyanobacteria (like single celled blue-green algae).
They used photosynthesis to turn CO2 into the food and energy they needed to survive.
Photosynthesis gives off oxygen as a waste product.
So over the millions of years, oxygen given off by algae built up in the atmosphere, while the amount of CO2 declined.

9. Layers of the Atmosphere

10. Pressure Pressure is a force that acts over a certain area.
Liquids and gases are fluid. Fluid; are any material that is able to flow. Fluids exert pressure because of the motion of their particles.
Pressure will always move from a high pressure to a low pressure area. The pressure will always try to equalize. You see this when you get a hole in your bicycle tire.

11. Air Pressure
Air pressure is the result of the column of air that is above you.
There is so much air above you that at sea level you have 14.7 lbs/in2 pushing on you.
Gravity causes most of the air to be pulled down to the surface.

12. Why are we not crushed by air pressure?
Air pressure is equal in all directions.
So air pushes equally in all sides of us. The forces are balanced!

14. Units of Air Pressure
TV weather stations and aviation use inches of mercury.
Meteorologists (and the NWS) use millibars, an SI unit.

15. Altitude and Density
As the air pressure decreases, the density of the air decreases. The air particles are not squashed together as tightly the higher one goes. This is caused by gravity!
The air at sea level and at 6km has the same 21% oxygen, but at 6km there are fewer molecules, so you take in less oxygen with each breath.

17. Temperature and the Troposphere
Troposphere: temperature at surface is warmed by the earth absorbing energy from the sun.
Convection currents carry the heat upward, so the air cools as it rises.
The air cools by about 6.5°C for every 1-km above the ground.

18. Temperature and the Stratosphere
Ozone absorbs ultraviolet radiation from the sun, causing the temperature to increase.

19. Temperature and the Mesosphere
This layer does not absorb energy from the sun, so it starts to cool again.
Without greenhouse gases, energy pretty much passes straight through!

20. Temperature and the Thermosphere
Solar radiation first hits this layer, so the few particles that are here can gain lots of energy. They move rapidly, so they have a very high temperature.
But the air is so thin here that it takes special instruments to measure the temperature accurately.
So even though it is very hot (over 1000°C), it would feel cold because there are so few particles to transfer heat to you.

21. The Troposphere Lowest (inner) layer weather occurs here
we live in it.
“tropo” means turning or changing conditions
depth varies from 9km above the poles to 16km at the equator
thinnest layer, but contains most of the mass (90%).

22. The Stratosphere “strato” means layer or spreading out
Contains the ozone layer which absorbs energy and causes the temperature to rise
The ozone layer protects the surface from dangerous UV rays

23. The Mesosphere Drop in temperature marks beginning of mesosphere
“Meso” means middle
Most meteors burn up here

24. The Thermosphere Very top layer
Air is very, very thin, about 1/1000th as dense as the air at sea level
“Thermo” means heat
Extends from 80km to space
No definite outer edge
Very hot (over 1000°C), but since air is so thin it would not feel warm at all.
Divided into two parts, the ionosphere and the exosphere

25. The Ionosphere
Energy from sun strips the electrons from the gas molecules creating charged particles called ions.
Radio waves can bounce off of ions, allowing radio waves to travel great distances.
The aurora borealis (Northern Lights) occur here

26. The Exosphere “Exo” means outer Extends for 1000’s of miles
Satellites orbit here
No definite edge
Molecules gradually escape out into space