Chapter 8: Plate Tectonics
8.1: Earth has several layers
8.2: Continents change position over time
8.3: Plates move apart
8.4: Plates converge or scrape past each other
Review questions
 True or False?
 The rock cycle describes the natural processes that form, change,
break down, and form rocks again
 The most common types of rocks in Earth’s crust are sedimentary
and igneous.
 Heat or pressure can change a rock into another type of rock
 ----- True
 The most common types of rocks in Earth’s crust are igneous and
metamorphic (Sedimentary rock is the most common type only at
Earth’s surface)
 True
8.1 Earth has several layers
 Before, you learned:
 Minerals and rocks are the building blocks of Earth
 Different types of rocks make up Earth’s surface
 Now, you will learn:
 About the different properties of Earth’s layers
 About the plates that make up Earth’s outermost
layers
Earth is made up of materials with
different densities
 Will a denser material sink or float?
 If salt water is added to a container of freshwater, the
salt water will sink to the bottom as it is more dense –
more mass per unit volume (Density = mass/volume)
 Egg Density Experiment
 Chapter Intro Video – (to 9:00; to 20:00)
Earth is made up of materials with
different densities
 4.6 billion years ago, Earth
was a spinning mass or
rocks and dust
 Impacts from comets and
asteroids added to mass
 This plus radioactive decay
and Earth’s gravity
intense heat: melted rock
 Denser materials sank to
the center
 Less dense materials
moved towards the surface
 Layers: core, mantle,
crust
Earth’s layers have different properties
 How do we know???
 Scientists study the energy from
earthquakes or underground explosions
they set off
 Energy travels like ripples through a pond:
moves slower through less dense materials
(ex: liquids) and faster through more dense
materials (ex: solids)
Core, Mantle, Crust
 Core: densest region; metallic
 Inner core: hot, solid metals = extremely hot but intense pressure keeps it
solid
 Outer core: liquid metals = hot but cooler and less pressure than inner core
 Mantle: thickest layer ~2900 km (1700 mi)
 Hot rock less dense than core
 Top: cool and rigid
 Just below: rock is hot and soft – thick paste
 Crust: thin layer of cool rock; surrounds like an egg shell




Continental Crust: all continents and some major islands
Oceanic crust: ocean floors
Thinnest under oceans and thickest under continental mountain ranges
Home to all life on Earth
Core, Mantle, Crust
Litho – “stone” or “rock”
Asthenes – “weak”
 Lithosphere: crust and very top of mantle – solid, most rigid
layer
 Asthenosphere: hotter, softer rock in the upper mantle (just
below the lithosphere) – can flow like hot tar
Less
dense
materials
rise
Denser
materials
sink
The lithosphere is made
up of many plates
 Rather than a continuous shell, the lithosphere is
broken into many large and small slabs of rock:
“tectonic plates”
 Fit together like jigsaw puzzle, or a cracked egg shell –
may be broken but still forms a “crust” around the egg
itself
 Most large plates include both continental crust and
oceanic crust
 Most of the thicker continental crust rises above the ocean,
the rest is underwater
 Looking at a map you are only seeing part of Earth’s crust
The lithosphere is made
up of many plates

Ex: about ½ the
African Plate lies under
water
1) have the continents
always been where they
are today?
2) if not, how did they move
to their present
positions…
Mystery Solved! - Section
1.2