Chapter 4: Plate Tectonics
Lesson 4.1- Continental Drift
A.
Drifting Continents
1.
People looking at early maps noticed that the edges of the American
continents looked as if they might fit like puzzle pieces
into
and
.
2.
In the early 1900s, Alfred Wegener proposed
the
hypothesis, which states that the
continents move slowly across Earth’s surface.
3.
He thought that a few hundred million
ago, all of the
continents formed one huge landmass he called
.
4.
The landmass eventually started to
, and slowly
the continents drifted to their present locations.
B.
Evidence for Continental Drift
1.
Geographic Fit of the Continents
a.
If the
were removed, the continents
would fit back together.
b.
Some
and
that are now far apart
were previously close together.
2.
Fossil Evidence
a.
Wegener studied the fossils of
, a seed
fern found on five continents.
b.
He didn’t believe the heavy seeds could have
or
so far across the oceans.
3.
Rock Types and Mountain Ranges
a. Particular groups of
on the continents matched.
b.
match across the continental boundaries.
c. The
in eastern North America
are similar to the mountains in Greenland, Great Britain, and
Scandinavia.
4.
Ancient Climate Evidence
a. When sedimentary rocks form, they preserve
about
the climate in which they form.
b. Wegener found rocks formed during the time of Pangaea showing
that the
island of Spitsbergen
had a
climate.
c. Ancient rocks made by
were found across Africa,
India, and Australia.
d. The climates of Pangaea were
the climates
on Earth today.
C.
A Hypothesis Rejected
1.
Wegener proposed that the
drifted by plowing
through the seafloor.
2.
He thought the same
that produced tides had caused
the continents to slowly drift over millions of years.
3.
Most other scientists did not accept Wegener’s hypothesis because
they could not think of any
strong enough to make
continents drift.
Lesson 4.2- Seafloor Spreading
A.
Investigating the Seafloor
1.
2.
was developed for mapping the seafloor using
waves.
Mountain ranges in the middle of the seafloor are
called
.
3.
The closer you move toward a mid-ocean ridge, the
B.
The Seafloor Moves
1.
Harry Hess, an American geologist, suggested a new hypothesis
describing how
the seafloor gets.
were formed.
process by which new
is the
is made at the mid-ocean ridges. (Hot, less-dense
material below Earth’s crust is forced upwards causing seafloor spreading).
a.
Convection brings hot material up from the
b.
toward the surface.
flows out as lava through cracks along the ridge.
c.
Lava
and forms a new seafloor.
d.
The seafloor moves away from the center of the
. (Plates move
apart from each other at the mid-ocean ridge).
2.
The age of the seafloor
3.
Continents drift
C.
Evidence for Spreading
1.
with distance from the mid-ocean ridge.
as the ocean grows.
rock records magnetic polarity
that occurs every
10,000 or more years. (Iron-rich crystals in the basalt provide scientists with evidence
of magnetic polarity reversals). (The magnetic field had reversed itself several times in
the past). (Scientists describe the orientation of the magnetic field today as normal).
a.
Scientists can measure the strength of the magnetic field with an instrument
called a
b.
.
By measuring the distance of a stripe of rock from the mid-ocean ridge and determining its
age, scientists calculated the
4.
of seafloor movement.
The seafloor and attached continents move only
per year. (The speed of
plate movement can be described like the growth of a fingernail).
5.
The boat named the Glomar Challenger
and collected samples from the
seafloor beginning in 1968.
6.
Scientists found that the
rocks were in the center of the mid-ocean
ridge.
Lesson 4.3- Theory of Plate Tectonics
A. Earth’s Plates
1. Earth’s lithosphere is broken into a dozen large, brittle pieces
called
.
2. The theory of
explains how plates
and cause major
geologic features and events on Earth’s surface.
3. The locations of earthquakes and volcanoes indicate the _______________
where the lithospheric plates meet.
a. The edges of the plates run into, move apart, or
past each other.
(Earthquakes can occur when plates slide past one another).
b. Plates also meet at long, deep parts of the seafloor called
.
B. Types of Lithosphere
1. Oceanic lithosphere is much
than the continental lithosphere.
a. Oceanic crust is made up of mainly of the dense igneous rocks of basalt and
gabbro.
b. The oceanic lithosphere is thinnest at the mid-ocean ridge and gets
you move farther from the ridge.
2.
lithosphere is not as thick as the oceanic crust.
(Ocean floor rocks are younger than continental rocks).
C. Plate Movement
as
1.
, which transfer heat energy from inside Earth’s mantle to the
surface, are thought to drive plate movement.
a. (Convection provides the matter and
for plate movement).
b. (Convection current describes the cycle of heating, rising,
, and sinking). c.
(Unlike the water in a pot, convection currents are not the same in all places in the mantle. Also,
convection in Earth’s mantle is much slower than convection in water).
d. Heat
e.
the density of rock.
force pushes heated rock upward.
f. A dense rock plate that sinks back into the mantle is called a
.
g. Hot rock material is brought near the surface and
.
h. Rock then cools at the surface, making new
lithosphere at the ridge.
i. New rock starts to move away from the
.
2. Subduction Forces
a. The force of gravity moves the plate downward and away from the ridge
during
.
b. As oceanic crust cools and becomes denser, it is forced into the mantle because of the force
of
.
D. Measuring Plate Movement
1. The Global Positioning System (
) is a network of satellites used to determine
locations on Earth and measure the direction and
2. Satellite laser ranging (
in plate movement.
) uses pulses of
of plates.
to measure distances