Study Guide for Drifting Continents
Chapter 3; Lesson 1
Continental Drift: The idea that the continents are always moving very slowly
around the Earth.
Alfred Wegener: The scientist that came up with the idea of continental drift.
His idea was rejected when he was alive because he could not explain HOW it
worked even though he provided evidence that the continents were moving.
Pangea: This was a supercontinent around 300 million years ago. Wegener
named this continent Pangea. Pangea began to break apart and the pieces moved
to form the continents of today.
Fossils: Any trace of an ancient plant or animal that is found in rock.
Evidence that Continental Drift is real:
1] Evidence from Fossils
2] Evidence from Climate
3] Evidence from Apparent Fit
4] Evidence from Land Masses
1] Evidence from Fossils: The fossils of the same type of organism are found in
different land masses separated by oceans. This means that the landmasses were
together at one time, then split and drifted apart.
2] Evidence from Climate: The fossils of ancient organisms that must have lived
in the tropics were found in arctic areas. This shows that the continents must
have moved.
3] Evidence from Apparent Fit: The continents look like they fit together like
the pieces of a puzzle, which shows the continents must have been together at
one time.
4] Evidence from Land Masses: Mountains and rocks on one continent are the
same as the mountains and kinds of rocks in landmasses on the other side of the
ocean. This shows that these landmasses must have been together at one time.
Study Guide for Sea-Floor Spreading
Chapter 3; Lesson 2
Mid Ocean Ridges: Long chains of mountains that rise up out of the seafloor. They are
mostly made of basalt that comes from underwater volcanoes called seamounts.
Sonar: A device that uses sound waves to determine the distance to something. Sonar
was used to discover mountains on the sea-floor.
Sea-Floor Spreading: The process by which new material is added to the seafloor. The
material comes from volcanoes on the mid-ocean ridge.
2 Types of Evidence for Sea-Floor Spreading:
1] Evidence from ocean material such as pillow lava. Pillow lava is lava from
underwater volcanoes that hardens quickly in the water into rounded shapes.
2] Evidence from drilling samples: The samples showed that the farther away
from the mid-ocean ridge, the older the rock is.
Deep Ocean Trenches: Deep underwater canyons near subduction zones. These are the
deepest parts of the ocean.
Subduction Zone: The area in which old material from the mantel is pulled back into
the mantle to be recycled. Older rock is more dense then newer rock, so gravity pulls the
dense rock back into the crust.
FACTS:
 It takes about 200 million years for new material at mid-ocean ridges to reach
subduction zones.
 The size of oceans can change over millions of years.
 The Earth is not getting larger. It always stays the same mass.
 The continents move as the seafloor spreads.
Study Guide for The Theory of Plate Tectonics
Chapter 3; Lesson 3
Tectonic Plates: The many pieces of the lithosphere that has broken up. Cracks separate
the many pieces. These are called Plate Boundaries.
3 Types of Boundaries:
1] Divergent boundaries: Plates are diverging, or moving away from each
other.
2] Convergent Boundaries: Plates come together, or converge at a convergent
boundary.
3] Transform Boundaries: Plates slip past each other. Transform boundaries
cause earthquakes.
Plate Tectonics: The theory that the Earth’s plates are in constant slow motion.
Convection currents in the mantle are the energy source that drives plate tectonics.
Convection Currents: Slow circular motion of molten rock in the Earth’s mantle move
the lithosphere around. Older material is more dense, so gravity pulls the material back
into the mantle through convection currents.
Plate Movement: The plates move very slowly, between 1 and 12 cm per year. The North
American plate is moving about 2.5 cm per year.
Faults: Breaks in the Earth’s crust that form around boundaries.
Rift Valley: This is where pieces of the Earth’s crust diverge on land. This forms a deep
valley in the Earth’s crust.
Convergent Boundaries: When two plates converge, the more dense plate will go
underneath of the less dense plate. Oceanic crust is more dense than continental crust, so
the oceanic crust slips under the continental crust. Oceanic crust can also push up the
continental crust forming mountains. When two pieces of continental crust collide, very
tall mountains are created.
NOTE: The plates are made of the crust and the upper part of the mantle. This is called
the lithosphere. The lithosphere is rigid.