1. Many different types of landforms
Unit B
Chapter 8
Plate Tectonics
Earth’s Variety
Many different types of landforms
plateau – raised flatland
waterfall
mountain
plain – flatlands with few trees
valley – low land between mountains
ridge – long row towering mountains on
ocean floor
volcano
trench – long narrow cut in ocean floor

2. Earth’s Layers Crust outermost solid layer of Earth-soil & rock
Unit B
Chapter 8
Plate Tectonics
Earth’s Layers
Crust outermost solid layer of Earth-soil & rock
from 5 to 30 kilometers thick
compared to a thin shell
Mantle thick layer below crust – largest part
outer part – solid
inner part – partly melted rock
Core innermost layer
compact/dense
about 5000°C
outer part – liquid
inner part - solid

3. Earth’s Plates Lithosphere crust and solid part of mantle
Unit B
Chapter 8
Plate Tectonics
Earth’s Plates
Lithosphere crust and solid part of mantle
broken into pieces – tectonic plates
12 large plates many smaller ones
Most made of continental and
oceanic crust
Most of U.S. on North Amer. Plate
Plates float atop inner mantle
Earth has a variety of surface features and several layers.

4. Continental drift - theory that continents have drifted
Unit B
Chapter 8
Plate Tectonics
Continental drift - theory that continents have drifted
apart, and continue to do so
Alfred Wegener – 1912 – German
same fossils plants/animals on 2
different continents
matching rock layers
rejected by other scientists

5. Spreading Ocean Bottom
Unit B
Chapter 8
Plate Tectonics
Spreading Ocean Bottom
Mid-Atlantic Ridge – long, deep trenches
and a chain of mountains on floor on
Atlantic Ocean.

6. Sea floor spreading – Magma pushes up,
Unit B
Chapter 8
Plate Tectonics
Sea floor spreading – Magma pushes up,
cools, forms new crust, and moves old
crust aside.
Plates are moving away from each
other, and the ocean floor spreads
apart. Magma rises to fill the gap.

7. Hot liquids weigh less and float above cooler liquids.
Unit B
Chapter 8
Plate Tectonics
Hot liquids weigh less and float above
cooler liquids.
Convection – force that moves Earth’s
plates
Hot, melted rock rises, then cools,
gets heavy and sinks again.
When mantle moves, plates floating on
it also move.

8. Proof of Continental Drift
Unit B
Chapter 8
Plate Tectonics
Proof of Continental Drift
Seafloor spreading
Patterns in magnetism
Evidence of continental drift is found in fit of continents, distribution of fossils, and sea floor spreading.

9. Explaining Earth’s Features
Unit B
Chapter 8
Plate Tectonics
Explaining Earth’s Features
Plate tectonics lithosphere contains 20 moving plates that
float on a layer of partly meted rock.
Scientists measure the movement of
plates using laser beams from space
satellites.
Scientists make predictions about
where the continents will be in 50
million years.

10. Plate boundaries areas where 2 plates meet
Unit B
Chapter 8
Plate Tectonics
Plate boundaries areas where 2 plates meet
Spreading boundary – plates move away
from each other.
Colliding boundary – plates push against
each other.
Fracture boundary – plates slide past
Earth’s plates are constantly moving to give earth its many features.

11. Earthquakes Caused by sudden shifting of rock as
Unit B
Chapter 8
Plate Tectonics
Earthquakes
Caused by sudden shifting of rock as
tectonic plates shift position.
Pressure builds up and when it gets too
strong the rocks suddenly move and an
earthquake occurs.
Focus – underground point where
earthquake occurs
Epicenter – point on Earth’s surface
directly above the focus

12. Energy from an earthquake is released in waves Causes ground to move:
Unit B
Chapter 8
Plate Tectonics
Energy from an earthquake is released in
waves
Causes ground to move:
back and forth
up and down
in a circular motion
As waves spread out they lose energy
Worst damage usually occurs closest to
the epicenter.
Most earthquakes take place near the
edges of plates.

13. Strength measured on a magnitude scale (Richter scale)
Unit B
Chapter 8
Plate Tectonics
Strength measured on a magnitude scale
(Richter scale)
Each increase of 1 represents 31 times
more energy that’s released.
Effects of an earthquake depends on:
size/strength
distance from epicenter
kind of rock in the area
types of buildings
number of people who live there

14. Volcanoes Occurs when magma from mantle comes through crust.
Unit B
Chapter 8
Plate Tectonics
Volcanoes
Occurs when magma from mantle comes
through crust.
Occurs near plate boundaries.
a plate sinks beneath another
sinking crust melts
pressure builds up
magma explodes
lava spreads over surface of earth
Quiet flows are less destructive and
more common.

15. Predicting Seismometers – detect tremors
Unit B
Chapter 8
Plate Tectonics
Predicting
Seismometers – detect tremors
Tiltmeters – detect changes in tilt of
earth
Laser beams – detect movement
between plates
Ways to stay safe
Prepare a safety plan
Get under table/desk
Stay away from falling objects
Move to open area
Most volcanoes and earthquakes occur along plate boundaries.

16. Unit B
Chapter 8
Plate Tectonics