Plate Tectonic Notes
Lesson 1—The Continental Drift Hypothesis
A. Pangaea
1. The German scientist
studied whether Earth’s
continents move.
2. Wegener proposed that all continents were once part of a single supercontinent
called
.
a. Over time, Pangaea started breaking apart, and the continents started
to where they are now.
b. The hypothesis that suggests that continents are in constant motion on Earth’s
surface is
.
3. Wegener observed the similarities of coastlines between continents that were
separated by
.
4. The continents that once formed Pangaea have coasts that fit together like pieces
of a(n)
.
B. Evidence That Continents Move
of ancient plants and animals provide evidence for
1.
continental drift.
2. Remains of the same plants and animals are present on different
that are now separated by oceans.
3. Fossils of plants and animals that lived in wet, warm climates are in areas that
now have
climates.
4. Deposits of
in Antarctica are evidence of continental
drift. The fossilized plants in these deposits show that Antarctica was once near
the
.
5. Wegener proposed that certain continents—including South America and
Australia—were closer to the
250 million years ago.
a. Wegener suggested that these continents were covered by a large
sheet.
b. Today, all these continents except one are near the
, where the climate is warm enough to melt ice
sheets.
6.
grooves on continents that currently have warm climates
show that these continents once had cold climates.
7. Wegener observed that there were
and rocks on different
continents that shared common origins.
8. Evidence of continental drift also includes
that have similar or identical chemistry, geologic structure, and age.
on different continents
9. If you pushed North America and Europe together again, their
would look like one long belt with the same rock types.
C. What was missing?
1. Scientists questioned continental drift because it is such a(n)
process. They were unable to
how fast the
continents moved.
2. Wegener could not explain what
causes the continents to move.
3. Additional scientific evidence to prove Wegener’s hypothesis existed on the
between the drifting continents.
4. Evidence to
continental drift was discussed decades after Wegener’s
death.
Lesson 2—Development of a Theory
A. Mapping the Ocean Floor
1. Scientists mapped the depth of the ocean floor using a device called a(n) .
2. In the middle of the oceans are large mountain ranges called .
a. Existence of these
was confirmed through research called echo-
sounder research.
b. These underwater mountain ranges are much
than mountain
ranges on land.
B. Seafloor Spreading
1.
occurs when new oceanic crust forms at a mid-ocean ridge and old
crust moves away from the ridge.
a. Molten rock, or
, rises from the mantle through
cracks in the crust. It erupts as
mid-ocean ridge.
from volcanic vents along the
b. The molten rock cools and becomes
, the rock that forms the
oceanic crust.
c. New oceanic crust forms along a mid-ocean ridge, and
crust moves
away from the ridge.
2. The topography of the
includes the abyssal plain and rugged
mountains.
a. The rugged mountains that make up the mid-ocean ridge can form in different
ways. One way is through large amounts of
erupting from the
center of the ridge, cooling, and building up around the ridge. Another
way is through upward-moving
pushing on the crust above it,
causing it to crack and form jagged, angular mountains on the seafloor.
b. Eventually,
smooth seafloor called the
forms on top of the oldest oceanic crust, making
.
3. Seafloor spreading helps explain continental drift because it shows that continents
move with the oceanic
as it spreads away from mid- ocean ridges.
C. Development of a Theory
1. Evidence to support seafloor spreading first came from studying the
of rocks on the seafloor.
2. Earth’s outer core causes Earth’s
.
a. The direction of Earth’s magnetic field
often.
b. When a magnetic field causes a magnet to point north, the magnetic field
has
.
c. A magnetic field reverses direction during a(n)
.
d. After a magnetic reversal, a magnet points south because Earth’s magnetic field
has
3.
.
form when iron-rich minerals in cooling lava align
with the direction of Earth’s magnetic field.
a. The direction of a magnetic field in minerals can be determined by using a device
called a(n)
.
b. Magnetometers show
magnetic stripes on either side
of a mid-ocean ridge.
c. These stripes alternate normal polarity and
, showing
that each stripe was formed at the mid-ocean ridge and then moved away.
4. Sediment collected from the seafloor show that sediment farther away from a
mid-ocean ridge is
the ridge.
than the sediment that is closer to
Lesson 3—The Theory of Plate Tectonics
A. The Plate Tectonics Theory
1. The theory of
states that Earth’s surface is divided into
large plates of rock. Each plate moves over Earth’s
changes position with respect to other plates.
a. When plates
and
on the seafloor, mid-ocean ridges form.
b. When one plate dives under another plate, earthquakes can result and
can form.
c. Earthquakes can also result when plates
past each
other.
2. Of all Earth’s tectonic plates, the
plate is the largest.
3. The cold, rigid rock layer on the outermost part of Earth is called the
. It consists of crust and the upper part of
the
.
4. Below the lithosphere is the
flows like
, which is so hot that it
.
of lithosphere move because they rest on the flowing
5.
asthenosphere.
B. Plate Boundaries
1. The place where two plates meet is called a(n)
.
2. When two plates move away from each other, a(n)
forms.
a. In the ocean,
are located at divergent plate
boundaries.
b. If divergent plate boundaries separate parts of a continent,
form.
3. When two plates slide by each other, a(n)
forms. This
type of movement causes
.
4. When two plates collide, a(n)
forms.
a. When plates collide, the plate that is denser slides under the less-dense plate
in the process of
.
b. When an oceanic plate slides under a continental plate, a deep ocean
forms. Near the trench, a line of
forms.
c. When two oceanic plates collide, a trench and a(n)
form.
d. When two continental plates collide, neither plate is subducted, and
form.
C. Evidence for Plate Tectonics
1. Scientists now use
to measure how continents move.
2. The theory of plate tectonics explains why earthquakes and
occur in certain locations.
D. Plate Motion
1. Earth’s mantle moves because warmer, less-dense materials rise and cooler, denser materials
.
a. Materials move based on differences in their temperatures and densities in the process of
.
b. Inside Earth,
elements provide some of the thermal energy that
causes convection.
c. Convection currents form in the mantle when thermal energy transfers from the
to the mantle.
forces interact to cause tectonic plate motion.
2.
a. Convection currents in the mantle produce a force that causes motion called
.
b. Plates are pushed away from each other at mid-ocean ridges by the force of
.
c. When a plate sinks below another plate, it pulls on the rest of the plate, exerting a force called
.
E. A Theory in Progress
1. Plate tectonics is the unifying theory of
2. Plate tectonics theory is still being
how Earth’s tectonic plates move.
.
as scientists learn more about