Lesson ​9
Air and the Atmosphere
Learners connect what they know about air to the bigger picture of Earth's atmosphere, and are introduced to the four systems that make up our planet.

Key Ideas
  • The atmosphere is the layer of air surrounding Earth. There is no air in outer space. Beyond the atmosphere is a complete vacuum.
  • Gravity holds the atmosphere in place because air has weight. Without gravity, air would drift off into space just as an object would.
  • The Moon has much weaker gravity, not strong enough to hold air down. Any gas near the Moon drifts away, which is why astronauts must wear spacesuits there.
  • Earth can be understood as four interconnected systems called spheres: the GEOSPHERE (all solid, rocky material), the HYDROSPHERE (all water), the ATMOSPHERE (the layer of gases), and the BIOSPHERE (all living things).
  • Living things are not made of some special material. They are complex combinations of solids, liquids, and gases, which is exactly why they get their own category.
  • These four spheres constantly interact. Rain connects the atmosphere and hydrosphere. Plants connect the biosphere, geosphere, and atmosphere at once. Nothing in nature works completely on its own.

Vocabulary

  • Atmosphere: The layer of gases surrounding Earth, held in place by gravity because air has weight.
  • Geosphere: All of Earth's solid, rocky material, from the surface crust down to the inner core.
  • Hydrosphere: All the water on Earth, including oceans, lakes, rivers, glaciers, and groundwater.
  • Biosphere: All living things on Earth.
  • Vacuum: A space with no matter in it at all. Outer space beyond the atmosphere is a vacuum.

Discussion Questions
  • Living things are made of combinations of the other three spheres. Does that mean life is just a very organized arrangement of rocks, water, and air?
  • Earth has a moderate atmosphere. Venus has an extremely thick one. Mars has almost none. What might cause those differences?
  • If the four spheres are always interacting, what do you think would happen to the biosphere if the hydrosphere disappeared?

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L9: Air and the Atmosphere by Selene
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