s8pe-41302-ca
10/28/05
12:37 PM
MAZER
Page 422
Layers
How do the layers inside of planets form?
In this model, the materials you use represent different rocks and metals that
make up the solid planets.
SKILL FOCUS
Using models
(8.4.e)
PROCEDURE
1
Put pieces of gelatin into the container until it is about one-quarter full.
2 Mix in a spoonful each of sand and wax. Use the spoon to break the gelatin
into small pieces as you mix. Remove the spoon.
3 Place the container in a bowl of hot tap water (about 70°C) and observe
what happens as the gelatin melts.
WHAT DO YOU THINK?
• What happened to each of the materials when the gelatin melted?
MATERIALS
•
•
•
•
•
•
container
spoon
firm gelatin
sand
wax pieces
bowl of hot
tap water
TIME
40 minutes
• How do the results resemble the core, mantle,
and crust of Earth and other planets?
CHALLENGE How might you improve
this model?
Atmospheres
Atmospheres on terrestrial planets mainly formed from gases that
poured out of volcanoes. If a planet’s gravity is strong enough, it pulls
the gases in and keeps them near the surface. If a planet’s gravity is
too weak, the gases expand into outer space and are lost.
Venus, Earth, and Mars each had gravity strong enough to hold
heavy gases such as carbon dioxide. However, the lightest gases—
hydrogen and helium—escaped into outer space. The atmospheres
of Venus and Mars are mostly carbon dioxide.
An atmosphere can move energy from warmer places to cooler
places. This movement of heat energy makes temperatures more
uniform between a planet’s day side and its night side and between
its equator and its poles. An atmosphere can also make a planet’s
whole surface warmer by slowing the loss of energy from the surface.
After Earth formed, its atmosphere of carbon dioxide kept the
surface warm enough for water to be liquid. Oceans covered most of
Earth’s surface. The oceans changed the gases of the atmosphere, and
living organisms caused even more changes. Earth’s atmosphere is
now mostly nitrogen with some oxygen.
check your reading
422 Unit 4: Space Science
Why is the solid Earth surrounded by gases?
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