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CHAPTER
17
The Dynamic Earth
• Earth is composed of layers.
• The three main layers are the crust,
mantle, and core.
• Earth’s outer layer has moved.
• At one time, the continents formed
Pangaea, a single huge landmass.
CHAPTER
17
The Dynamic Earth
• Plates of the outer layer move continuously.
• Plate tectonic theory explains the mechanisms by which tectonic plates move.
• This movement explains Earth’s geological events and features, such as
volcanoes and mountains.
CHAPTER
17
The Dynamic Earth
Activity
• Scientists use both direct and indirect observations/measurements to
solve real-world problems. A direct measurement means you measure
exactly what you mean to measure, while an indirect measurement
measures one thing to get information about something else.
• Try the following:
10 cm
• Indirectly determine the area of one circle if the square is
10 cm by 10 cm.
• Directly determine the area of one circle if you measured
10 cm
2
the radius to be 2.5 cm (Area of a circle = 3.14r ).
• What can you infer about direct and indirect
measurements? Which is better? Is one more accurate?
• Which type of measurement would you use to get information about
• the weight of a car?
• the size of an atom?
• the temperature inside a freezer?
• Find out how scientists use both direct and indirect observations and
measurements to find out about Earth’s structure on pages 494–495.
CHAPTER
17
The Dynamic Earth
Key Ideas
• Earth is composed of layers.
• Earth’s outer layer has moved.
• Plates of the outer layer move continuously.
• This movement explains Earth’s geological features and events.
17.1
Structure of Earth
• Distinct properties define Earth’s three main layers:
crust, mantle, and core.
• The crust is the rigid outer layer that makes up the
continents and sea floors.
• The lithosphere is a region formed by the crust and
the rigid outer layer of the mantle.
• The asthenosphere is the fluid-like layer of mantle
beneath the lithosphere.
• Earth’s centre has two layers:
a liquid outer core and
a solid inner core.
VOCABULARY
crust
mantle
lithosphere
asthenosphere
core
outer core
inner core
seismic wave
17.1
Structure of Earth
• Scientists obtain information about the structure of
Earth through direct and indirect observations.
• Direct observations include analyzing rock directly
from Earth’s interior.
• Indirect observations include measuring gravitational
force differences around the globe to infer the density
of material beneath Earth’s surface.
VOCABULARY
crust
mantle
lithosphere
asthenosphere
core
outer core
inner core
seismic wave
17.2
Evidence of a Dynamic Earth
• The surface of Earth moves constantly.
• The lithosphere is divided into massive tectonic plates
that are pushed and pulled over the asthenosphere.
• Continental drift theory argues that the continents
have moved slowly since Earth formed.
• Fossil and geological evidence support
the continental drift theory.
• At one time, the continents formed
Pangaea, a single huge landmass.
VOCABULARY
tectonic plate
continental drift theory
paleoglaciation
17.3
New Evidence of a Dynamic Earth
• Sea-floor spreading occurs at mid-ocean ridges and
subduction occurs at deep ocean trenches.
VOCABULARY
mid-ocean ridge
sea-floor spreading
ocean trench
• Heat within Earth creates convection currents in the mantle that help
move the plates.
• Radioactive dating of core samples confirmed evidence that the sea
floor is older the further it is from the ridges.
• Magnetic striping patterns in sea floor rock are similar on both sides
of an oceanic ridge, suggesting new ocean floor is being created at
the ridge.
17.4
Theory of Plate Tectonics
• The theory of plate tectonics states that the
lithosphere is divided into 12 large sections (plates)
and about 20 smaller ones.
VOCABULARY
theory of plate
tectonics
divergent boundary
rift valley
convergent boundary
subduction zone
oceanic–oceanic
convergent boundary
oceanic–continental
convergent boundary
continental–continental
convergent boundary
transform boundary
strike–slip fault
17.4
Theory of Plate Tectonics
• Three types of boundaries exist where tectonic
plates meet. These create Earth’s geological
features and events.
• Ridges, rifts, volcanoes and
earthquakes are created at divergent
boundaries, where plates are moving
away from each other.
• Earthquakes and strike-slip faults are
created along transform boundaries,
where plates move past each other in
opposite directions.
• At convergent boundaries (where
plates move toward each other), we
find mountains, trenches, subduction
zones, volcanoes, and earthquakes,
depending on the types of plates
involved.
VOCABULARY
theory of plate
tectonics
divergent boundary
rift valley
convergent boundary
subduction zone
oceanic–oceanic
convergent boundary
oceanic–continental
convergent boundary
continental–continental
convergent boundary
transform boundary
strike–slip fault