Download Chapter 3

Chapter 3 Study Guide
Section 1
continental drift
Pangaea
(supercontinent)
fossil
the hypothesis that the continents slowly move across Earth’s surface
The name of the single landmass that began to break apart 200 million years
ago and gave rise to today’s continents
Preserved remains or traces of an organism that lived in the past
Wegener’s hypothesis was that all the continents were once joined together in one
landmass and have since drifted apart. The idea of the continents moving over Earth’s
surface became known as continental drift.
Alfred Wegener
Evidence from Land Features
 Shapes of continents
looked like a puzzle that
would fit together
 Mountain ranges in
South America and Africa
line up
 Coal fields in Europe and
North America line up
Wegener could not identify the force that moved the continents,
so most geologists of his time rejected the idea.
Evidence from Fossils
Evidence from Climate
 Glossopteris is a plant that lived 250  Fossils of tropical plants have been found
million years ago. Glossopteris fossils
on an island in the Arctic Ocean. These
have been found in Africa, South
plants only could have lived in a warm
America, India, and Antarctica.
climate.
 Fossils of the freshwater reptiles
 Wegener proposes that the island’s
Mesosaurus and Lystrosaurus have
climate changed because it moved toward
been found in Africa and South
the poles (away from the equator).
America, which are now separated
 The plant only could have lived in a
by oceans.
warmer climate, closer to the equator.
Section 2
An
undersea
mountain
chain where new ocean floor is produced
Mid-ocean ridge
A deep valley or canyon along the ocean floor beneath which oceanic crust slowly sinks
Deep-ocean trench
toward the mantle
The process by which molten material adds new oceanic crust to the ocean floor
Sea-floor spreading
The process by which oceanic crust sinks beneath a deep-ocean trench and back into
Subduction
the mantle at a convergent plate boundary
Mid-Ocean Ridges- long chains of mountains rising from the ocean floor
 These ridges are the longest mountain ranges on Earth.
 Scientists mapped mid-ocean ranges using sonar.
 Mid-ocean ridges are found in all of Earth’s oceans.
Sea-floor spreading adds more crust to the ocean floor. At the same time, older strips of rock move
outward from the side of the ridge.



Spreading begins at a mid-ocean ridge, which forms a crack in the oceanic crust
Along the ridge, molten material rises, erupts, cools, and hardens into new rock.
The new crust (rock) pushes older rock outward.
Evidence from Ocean Material
 Rocks shaped like pillows
have been found in the
central valley of mid-ocean
ridges. These rocks can only
form when molten material
cools quickly under water.
Evidence from Magnetic Strips
Evidence from Drilling Samples
 Magnetic minerals in rocks line up in  Older rocks are found as you move
the direction of Earth’s magnetic
away from mid-ocean trenches.
poles. The poles occasionally reverse  The youngest rocks are always at
which results in magnetic stripes on
the center of the trenches.
the ocean floor.
The pattern is the
same on both sides
of the mid-ocean
ridge.
Chapter 3 Study Guide
Section 3
A
section
of
the
lithosphere
that slowly moves over the asthenosphere, carrying pieces of
Plate
the oceanic and continental crust
The theory that pieces of the lithosphere are in constant motion, driven by convection
Plate Tectonics
currents in the mantle
A break in Earth’ crust along which rocks move
Fault
A deep valley that forms where two plates move apart
Rift Valley
Key Idea: Convection currents in the mantle are the forces that cause the plates to move.


During subduction, gravity pulls the denser plate edges downward into the mantle.
This pulls the rest of the plate, causing it to move.
Key Idea: The slow and constant movement of Earth’s plates has changed Earth’s surface.
 the location of continents
Scientists use satellites to
 the shape of oceans
measure
plate movements.
 causes earthquakes, volcanoes, mountain ranges, deep-ocean trenches
Key Idea: Earth’s plates meet at boundaries. At each boundary, plates move in one of three ways.
Divergent Boundary
Convergent Boundary
A plate boundary where two plates move
away from each other
A plate boundary where two plates
move toward each other
A plate boundary where
two plates move past each
other in opposite directions
Transform Boundary

Most occur at mid-ocean ridges
where new crust is added during seafloor spreading

When 2 oceanic plates
converge, the more dense plate
sinks below the less dense
plate.

Where pieces of Earth’s crust diverge
on land, a rift valley occurs.
 Sides of plates are rocky and
jagged, which holds the plates
together
 When forces push them to move,
earthquakes can occur, such as
on the San Andreas fault in
California.

When a dense oceanic plate
converges with a continental
plate, it can push up the
continental plate forming
mountains (Andes Mtns.) and
volcanoes

When 2 continental plates
converge, the collision squeeze
the crust into high mountain
ranges.