1. Earth’s Atmosphere

2. Atmosphere
The atmosphere is a thin layer of gases that surround the Earth.
The atmosphere protects the Earth by balancing the amount of heat absorbed from the Sun and the amount of heat that escapes back into space.

3. The Past Atmosphere
It is theorized that 4 billion years ago the Earth’s atmosphere contained two deadly gases: methane and ammonia.

4. How did the atmosphere change?
Methane is made up carbon and hydrogen.
Ammonia, is composed of nitrogen and hydrogen.
Sunlight caused chemical reaction among the methane, ammonia and water in the air.
New materials, nitrogen, hydrogen and carbon dioxide, were formed as the methane and ammonia broke down.

5. Ancient Atmosphere The water vapor remained.
Hydrogen, a lightweight gas, escaped into space.
Nitrogen, carbon dioxide and water vapor were left.
Sunlight then broke down the water vapor in the upper atmosphere into hydrogen and oxygen. The hydrogen again escaped.

6. Ozone Layer
The oxygen that was left behind joined together, in sets of three, to form a gas known as ozone.
A layer of ozone gas formed about 30 km above the Earth’s surface.
The ozone layer absorbs harmful ultraviolet radiation from space.

7. Oceans
Before the ozone layer formed, the only living things on Earth were microscopic organisms that lived far below the surface of the oceans.
After the ozone layer formed, certain types of these microorganisms called blue-green bacteria started to appear on or near the water’s surface.

8. Blue-green Bacteria
These bacteria used the energy in sunlight to combine carbon dioxide from the air with water to produce food.
A byproduct of this food-making process was oxygen. This was the first “free oxygen”.

9. Oxygen Unlike ozone, oxygen remains near the surface of the Earth.
This is the oxygen that animals breathe today.
Green plants began to grow on land and take in carbon dioxide and release oxygen in the food-making process.

10. Today’s Atmosphere
600 million years ago the amounts of oxygen and carbon dioxide in the atmosphere began to level off.
Since that time, the composition of the atmosphere has remained fairly constant.

11. Composition of the Atmosphere
Nitrogen gas makes up about 78 percent of the atmosphere.
Oxygen accounts for 21 percent.
The remaining 1 percent is a combination of carbon dioxide, water vapor, argon and trace gases.

12. Solid Particles
Tiny particles of dust, smoke dirt and salt float in the air.
Every time a wave breaks, tiny particles of salt from ocean water are suspended.
Dust in the air comes from the eruption of volcanoes.
Dirt and smoke comes from people as they burn fuels and drive cars.

13. Layers of the Atmosphere
The atmosphere is divided into layers according to the major changes in its temperature. Layers with thinner particles can hold less heat.

14. Air Pressure
The layers of air that surround the Earth are held close to it by the force of gravity.
Because of gravity, the layers of air push down on the Earth’s surface. This is called air pressure.
The upper layers push down on the lower layers so the air pressure near the surface is greater than the air pressure further away.

15. The Troposphere This is the layer closest to the Earth.
Weather occurs in this layer. Life occurs in the troposphere.
The height of the troposphere varies from the Equator to the poles. (17-8 km)
It is highest at the equator.
This layer contains 99% of the water vapor.

16. The Stratosphere
The stratosphere extends from the troposphere to an altitude of about 50 km.
In the lower stratosphere, the temperature is around –60 degrees C.
Here very strong eastward winds called the jet streams reach speeds of 320 km per hour. The jet streams move faster in the winter than in the summer helping storms move across the United States.

17. The Mesosphere
In the mesosphere, 50-90km above the earth, the temperature begins to decrease to –100 degrees C.
The upper region is the coldest. If water vapor is present thin clouds of ice form, noctilucent.
The mesosphere protects the Earth from meteoroids. When they reach the mesosphere, they burn up from the friction of rubbing against the particles of gas.

18. The Thermosphere
The thermosphere begins above the mesosphere at a height of about 90 km.
The air is very thin. The density of the atmosphere and the air pressure are one ten-millionth of what they are at the Earth’s surface.
The temperature is very high in this layer because the rays from the sun are absorbed in this layer.

19. Heat- sphere
Thermosphere means heat-sphere. The temperatures reach 2000 degrees C.because this layer absorbs the ultraviolet radiation from space and convert it into heat.
A thermometer placed in the thermosphere would register below 0 because the particles are so far apart that not enough of them are present to bombard a thermometer.

20. Ionosphere
Within the mesosphere and the thermosphere is a layer of electrically charged particles called the Ionosphere. It allows radio waves to travel around the earth.

21. The Exosphere The upper thermosphere is called the exosphere.
The exosphere extends from 550 km above the surface for thousands of km.The air is very thin.
Artificial satellites orbit in the exosphere.

22. Atmospheric Pressure
Air pressure is caused by Earth’s gravity pulling the air particles toward the Earth.
As you move away from the Earth, air pressure decreases.
Jets that fly in the stratosphere need pressurized cabins for the passengers.

23. Temperature in the Layers
The sun is the source of energy for Earth. As the sun’s light passes through the layers some layers contain gases that absorb the energy.
The troposphere is warmed mainly by heat from the ground.
The air temperature decreases 6.5º every kilometer you climb up.

24. Ozone Layer
Most of the ozone in the atmosphere is found between 16 km and 60 km about the surface of the Earth. Most are between 35 and 60 km.
Ozone molecules absorb much of the het and uv rays from the sun..
Ozone shields the Earth from ultraviolet radiation.

25. CFCs
Chlorofluorocarbons are chemical compounds used in refrigerators, air conditioners and aerosol cans. This enter the atmosphere and break the bond of the three oxygen molecules that from ozone.
One of the chlorine molecules combines with one of the three oxygen atoms, leaving a two atom molecule.
These new atoms do not absorb ultraviolet rays.

26. Hole in the Ozone Layer
The destruction of ozone molecules by CFCs seems to cause a seasonal reduction in ozone over Antarctica called the Ozone hole.
Ozone concentration is lowest in October in this location.

27. Water Cycle
The three steps of the water cycle are evaporation and transpiration, condensation and precipitation.

28. Evaporation
Evaporation occurs when heat from the sun causes water to change from a liquid to a gas.

29. Condensation
If the water vapor or gas is cooled enough it will change back into a liquid.
The process of vapor changing back into a liquid is called condensation.
Clouds form when condensation occurs.
Clouds are made of tiny drops of water that collect to form larger drops.

30. Precipitation
As water drops grow in a cloud, they will become heavy enough to fall to Earth as precipitation.

31. Air Movement
Uneven heating of the earth due to the curved surface of the globe produces winds.
Wind is the movement of air from an area of higher pressure to an area of lower pressure.

32. Uneven Heating of the Earth
Cold dense air from the poles sinks and moves toward the poles.
The hot less dense air near the equator is pushed up and moves back toward the poles.

33. Coriolis Effect
The rotation of the Earth causes moving air and water to appear to turn to the right north of the equator and to the left south of the equator.

34. Global Wind Belts
The Coriolis Effect and differences in solar radiation creates wind patterns on earth, known as Wind Belts.
We live in the prevailing Westerlies where winds move west to east.