1. Describing Earth’s Atmosphere
Chapter 12 Lesson 1

2. Importance of Earth’s atmosphere
The atmosphere is a thin layer of gases surrounding Earth.
It is hundreds of kilometers high but compared to Earth’s size, it is very thin.
The atmosphere contains oxygen, carbon dioxide, and water necessary for life.

3. Importance of Earth’s atmosphere
Earth’s atmosphere acts like insulation on a house.
It helps keep temperatures on Earth within a range in which living organisms can survive.
It helps protect us from the sun’s harmful rays.

4. Importance of earth’s atmosphere
It protects Earth from being hit by meteors.

5. Origins of earth’s atmosphere
Most scientists think that when earth formed it was a ball of molten rock.
As earth slowly cooled, its surface hardened.
Ancient earth’s atmosphere was thought to be water vapor with a little carbon dioxide and nitrogen.

6. Origins of earth’s atmosphere
Water vapor is water in its gaseous form.
The ancient atmosphere didn’t have enough oxygen to support life. As earth cooled and its atmosphere cooled, the water vapor condensed into liquid.
Earth’s organisms could undergo photosynthesis, which changed the atmosphere.

7. Composition of the Atmosphere
Today’s atmosphere is mainly made up of invisible gases, including nitrogen, oxygen, and carbon dioxide.
Some solid and liquid particles, such as ash from volcanic eruptions and water droplets, are also present.
Nitrogen makes up 78% of the atmosphere. 21% oxygen

8. Composition of the atmosphere
The solid particles are pollen, dust, and salt.
The most common liquid particles are water droplets.

9. Layers of the atmosphere
The atmospheric layer closest to earth is the troposphere.
The temperature decreases in this layer as you move away from Earth.

10. Layers of the earth
The atmospheric layer directly above the troposphere is the stratosphere.
This layer has the greatest amount of ozone gas.
The area of stratosphere with a high concentration of ozone is referred to as the ozone layer.

11. Mesosphere and thermosphere
Most of the meteors burn up in these layers instead of striking earth.
The ionosphere is a region within the mesosphere and thermosphere that contains ions. Radio waves can travel long distances by bouncing off earth and the ionosphere.
Auroras occur here. They occur when ions from the sun strike air molecules, causing them to emit vivid colors of light.

12. Exosphere
The exosphere is the atmospheric layers farthest from Earth’s surface.
Gravity pulls the atmosphere towards earth.
Gravity’s pull on air increases its density. At higher altitudes, the air is less dense.
Cooler temperatures in lower layers, warmer temperatures outside bottom layers.