Sarah MacKenzie
Section 12.1
Evidence for Continental Drift
Study Notes
By the end of section 12.1 you should be able to understand the following:
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Evidence suggests that all the continents were once together, then split and drifted apart by continental drift.
The coasts of the continents seem to fit together like puzzle pieces, and rocks, mountains and fossils that are
now very far apart are very similar, suggesting they were once at the same location.
Climates now are much different on the continents than in the past.
Sea floor spreading is the mechanism that allows continental drift to occur. The continents are attached to
large tectonic plates that slowly move along Earth’s surface.
NOTES
What evidence did Wegener
first observe to support the
idea of continental drift
theory? What name did
Wegener give the original
“supercontinent” that split
apart? What other pieces of
evidence did Wegener also
compare to support his
theory?
1. Jig saw puzzle theory, all the continents used to fit together, coastlines fit together
like a puzzle.
2. Supercontinent:
named the giant land mass Pangaea, from the Greek words pan,
meaning all, and gaea, meaning Earth.
3.
geological structures, fossils, and evidence of ancient glaciers on different continents.
4.
continental drift theory matching shapes of continents, shown in early maps
“appeared tp close to be coincidental”
1.
What evidence did Wegener
find regarding geologic
structures and rocks to
support his theory on
continental drift?
geological structures, fossils, and evidence of ancient glaciers on different continents.
2.
mountain ranges that begin on one continent, end at the coastline, and then appear to
continue on a continent across an ocean.
3.
many similarities between rock structures, such as folds, and the ages of rocks on
continents that are separated by thousands of kilometres of ocean.
4. Wegener reasoned that the world’s major mountain ranges would have
been continuous when the continents were joined as Pangaea
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Sarah MacKenzie
NOTES
What was Mesosaurus, and
why was it important to the
theory on continental drift?
What other fossils did
Wegener study?
1. similar fossils in various parts of the world (matching puzzle pieces)
2.One
fossil that particularly interested him was that of a sharp-toothed, small, freshwater
reptile called Mesosaurus.
3. Found in South America and south western Africa
4. It would have been unlikely for it to swim across 6000km across ocean because it
was so small.
5.
Given that these land animals could not have swum so far, the existence of Pangaea
seemed the best explanation for the fossil findings.
Why were scientists studying
paleoglaciation puzzled by
evidence of ancient glaciers
in Africa and India? What
was another piece of climate
evidence that reveals that
the continents were not
always in their current
positions?
1.
When glaciers advance or retreat, they mark the land with proof of their existence,
leaving behind large, U-shaped valleys, deeply scratched rocks, and various types and
patterns of rock formations.
2.
Ferns do not grow in cold climates, and there was no evidence that, 200 million years
ago, polar climates were milder.
3. wondered how glaciers could have formed in places where temperatures were rarely
known to dip below freezing.
4.Only thing that made sense was Pangaea
How did mapping the
locations of volcanoes and
earthquakes help to support
the continental drift theory?
What is a tectonic plate?
What is the Mid-Atlantic
Ridge?
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1. They plotted volcanoes and earthquakes to find a pattern, the outline of the
tectonic plates also they found the depth of oceans. Supporting the theory, where the
puzzle pieces split.
2.
Earth is broken into large, movable slabs of rock called tectonic plates.
3.
a long mountain range running north to south down the length of the Atlantic Ocean.
This range lay right along the middle of the ocean floor, which earned it
the name Mid-Atlantic Ridge
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Sarah MacKenzie
NOTES
What was discovered about
the age of the rocks found
near the Mid Atlantic Ridge?
How did the thickness of
sediments change the further
away from the ridge
scientists studied?
What is magnetic reversal?
How does magnetic striping,
discovered during the early
studies of paleomagnetism,
help to support the
continental drift theory?
What is the name of the
process that occurs at the
Mid Atlantic Ridge, and which
helps to explain the theory of
continental drift?
What were the nine pieces of
evidence Hess presented to
support the idea of sea floor
spreading?
1. Discovered:
youngest rocks were found closest to the ridge
2.
the layer of ocean sediment—the small particles of silt and organic debris deposited on
the ocean floor—became thicker the farther it was from the ridge
1.
Earth has north and south magnetic poles and a magnetic field but its direction can
completely reverse, a process known as magnetic reversal.
direction of Earth’s magnetic field as it was when the rocks were formed.
Paleomagnetism is the study of the magnetic properties of ancient rocks.
2.
3.
surprising pattern of stripes in the direction that iron-containing minerals pointed on
the sea floor. The pattern, which they named magnetic striping, was repeated on both
sides of the Mid-Atlantic Ridge
1. Earth is like a large bar magnet and has two poles.
2. New ocean floor forms when magma from under Earth’s surface rises, cools, and
hardens at an ocean ridge. New magma pushes older rock away from the ridge.
3. The magma is molten basalt, a dark rock that is rich in iron. As the basalt cools, it
becomes magnetic.
4. The magnetic minerals in the hardened basalt are like tiny compass needles that
align with Earth’s magnetic field.
5. Earth’s magnetic poles reverse over hundreds of thousands of years.
6. Minerals in the basalt keep the alignment they had when the rock cooled. Therefore,
some portions of hardened rock will have normal polarity, and others will have
reverse polarity.
7. Rocks with magnetic striping, alternating bands of normal and reverse polarity,
surround ocean ridges.
8. The pattern of magnetic striping is the same in rocks on either side of an ocean ridge.
9. Ocean sediments are thicker the farther away they are from a ridge. This is because
the oldest rock is farthest from the ridge and has had the most time to accumulate
sediments.
What is a hot spot?
1.
an area where molten rock rises to Earth’s surface. Like the Hawaiian Islands
What is the name of the
unifying theory of geology?
1.
plate tectonic theory - movement of tectonic plates and helped explain the
transformation of rocks from one type to another in the rock cycle.
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Sarah MacKenzie
Section 12.2
Features of Plate Tectonics
Study Notes
By the end of section 12.2 you should be able to understand the following:


Earth is composed of layers, including the lithosphere (surface) and asthenosphere (just below the surface)

When tectonic plates meet (converge), one plate may slide under the other, or they may crash together and
form mountains.
The asthenosphere is partly molten, and allows the tectonic plates of the lithosphere to “float” on the
convection currents of hot magma.
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When tectonic plates move apart (diverge), rifts (on land) and ridges (under the ocean) widen.
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Volcanoes occur at tectonic plate boundaries or over geologic hot spots.
When tectonic plates move past each other at a transform boundary, pressure may build until an earthquake
releases the pressure.
NOTES
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Sarah MacKenzie
Describe the four main layers 1. The Crust is Earth’s outermost layer. It is made from solid, brittle rock. The
of Earth.
thickness and type of rock varies in different parts of the crust. Continental crust is
made form a lighter type of rock called granite and can be as thick as 70km. Oceanic
crust is made from a dense, dark rock called basalt and can be as thick as 10km.
2.The Mantle is Earth’s thickest layer. About 2900 km thick, it makes up 70percent of
Earth’s volume. It is mostly solid and can be divided into two sections: the upper malt
and the lower mantle. The upper mantle is composed of partly molten rock containing
iron and magnesium. The upper mantle magma flows like thick toothpaste. A transition
zone separates it from the lower mantle, which begins at a depth of about 660 km.
The lower mantle is made of solid, dense material that contains the elements
magnesium and iron.
3. The layer below the mantle is the outer core. Unlike the other layers of Earth, the
outer core is liquid. It is about 2300 km thick and is composed mainly of a mixture of
iron and nickel.
4. The inner core lies at Earth’s centre. A sphere with a radius of about 1200 km, the
inner core is composed mainly of iron and some nickel. Although temperatures at the
core range from 5000oC to 6000oC—four times the melting point of iron—the incredible
pressures at the core keep it solid. Scientists believe that the inner and outer cores rotate
at different speeds and may be responsible for Earth’s magnetic field.
What is the lithosphere, and
how thick is it?
Made up of the crust and the uppermost mantle, tectonic plates form the lithosphere,
which ranges in thickness from 65 to 100 km.
NOTES
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Sarah MacKenzie
What is the asthenosphere,
1. The asthenosphere is the partly molten layer of Earth located beneath the lithosphere.
and where is it located? What 2. Geologists believe that this is because large quantities of radioactive elements such
do scientists think makes the
as uranium occur in some areas.
asthenosphere hot in certain
places, creating a “mantle
convection” current of molten
rock?
What is the name of the two
locations (one in the ocean,
one on land) where magma
rises at spreading centers?
What is “ridge push”? What
are “subduction zones”?
Explain the term “slab pull”.
1. Oceanic Ridge
2. Rift Valley
1. As new material at a ridge or rift pushes older material aside, the tectonic plates
move away from the ridge. This process is called ridge push
Areas of subduction, called subduction zones, typically experience large earthquakes
and volcanic eruptions. Subduction zones themselves are thought to contribute to plate
motion.
2.
3. As
the edge of a tectonic plate subducts deep into the mantle, it pulls the rest of the
plate with it. This process is called slab pull.
Do the Reading Check on page 522
What are the three main types 1. Divergent plate boundaries mark the areas where tectonic plates are spreading
of interaction between tectonic apart (Figures 12.18). Plates that are spreading apart are known as diverging
plates at plate boundaries?
plates.
Briefly explain each term.
plate boundaries occur where tectonic plates collide. Plates
that collide are known as converging plates.
2. Convergent
3. Oceanic-continental plate convergence
When a dense oceanic plate collides with a continental plate, the oceanic plate is
forced to slide beneath the continental plate. A deep underwater valley, called a
trench, forms where the tectonic plates make contact
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Sarah MacKenzie
NOTES
Describe three qualities of
divergent plate boundaries.
1. Marks where tectonic plates are spreading apart
2.
3.
Give an example of where
1.
scientists have found a ridge,
and a rift.
2.
What are the various types of
convergent plate boundaries?
Briefly describe each type of
convergent boundary.
1. Oceanic-continental plate convergence
When a dense oceanic plate collides with a continental plate, the oceanic plate is
forced to slide beneath the continental plate. A deep underwater valley, called a
trench, forms where the tectonic plates make contact.
2. Oceanic-oceanic plate convergence
Subduction also occurs where two oceanic plates converge (collide). Cooling will cause
one plate to be denser than the other, and the denser plate will slide deep into the
mantle.
Continental-continental plate convergence
When continental plates collide, subduction does not occur since the plates’ similar
densities prevent either one from being forced into the mantle (Figure 12.19C). As the
massive rocky plates slowly collide, their edges fold and crumple, forming great
mountain ranges.
3.
Which type of convergent
boundary forms trenches?
1. Oceanic-continental
Which type forms volcanic
island arcs? Which type forms
great mountain ranges on the
2. Oceanic-oceanic plate convergence.
continents?
3. Continental-continental
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Sarah MacKenzie
NOTES
What is a transform plate
boundary? Describe a
transform fault.
1. Convection currents in the mantle often cause tectonic plates to slide past each
other. Such regions, which mostly occur near ocean ridges, are known as transform
plate boundaries.
2. A fault that occurs at a transform plate boundary is known as a transform fault.
Do the Reading Check on page 526
Describe why earthquakes
occur. Where do most
earthquakes in the world
occur?
1.
When the plates can no longer resist the stress, there is an earthquake
2. 95 percent occur at tectonic plate boundaries. About 80 percent of earthquakes
occur in a ring bordering the Pacific Ocean.
Where can earthquakes occur 1. Along the Juan de Fuca Plate
in BC, and how often do large
earthquakes occur here?
2. 200- 800 years
What is the difference between 1. The focus (plural foci) is the location
the focus and the epicenter of release begins at the focus.
an earthquake?
2.
inside Earth where an earthquake starts. Energy
The epicenter is the point on Earth’s surface directly above the focus.
Based on their depth of origin,
1.Shallow focus 0-70 km (most damage)
what are the three types of
earthquakes? Which type can
do the most damage to human
inhabitations?
2. Intermediate focus 70 to 300 km
3. Deep focus greater than 300 km
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NOTES
When an earthquake occurs, 1. By studying how seismic waves travel through Earth’s interior, scientists can
energy is released from the
determine much about the composition and thickness of Earth’s layers. Records of
focus. This energy travels as seismic waves also help scientists to describe earthquakes.
seismic waves. What
information can seismologists
learn from these seismic
waves?
What are the three types of
seismic waves? Briefly
describe each type.
Surface waves (L-waves), which roll along Earth’s surface much like ripples in a
pond.
1.
Primary waves (P-waves) travel at about 6 km/s through Earth’s crust. Like sound
waves, P-waves can travel through solids, liquids, and gases. P-waves cause the ground to
compress and stretch like a spring in the direction in which the wave is travelling.
2.
Primary waves (P-waves) travel at about 6 km/s through Earth’s crust. Like sound
waves, P-waves can travel through solids, liquids, and gases. P-waves cause the ground to
compress and stretch like a spring in the direction in which the wave is travelling.
3.
1. Seismometer or a siesmograph
What piece of equipment is
used to measure earthquakes?
What is a seismogram, and
what can seismologists learn
from it?
1.
A seismometer produces a record of ground motion called a seismogram
2.the time
of the earthquake, how long it lasted, and the amount of ground shaking.
NOTES
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Sarah MacKenzie
What is the difference between 1. A magnitude 6 earthquake is 100 times larger than a magnitude 4 earthquake.
a magnitude 4 earthquake and
a magnitude 6 earthquake?
Do the Reading Check on page 531
What are the three types of
volcanoes caused by tectonic
plate movement? Briefly
describe each type.
1. Composite Volcano
large, cone-shaped mountains, belching ash, rocks, and lava. As the magma approaches
the surface, gas gets trapped below, and pressure builds up. Once the pressure is too great
to be contained, there is an explosive volcanic eruption.
2. Shield Volcano
The largest volcanoes on Earth are shield volcanoes. Shield volcanoes do not occur at
plate boundaries but instead form over hot spots. A hot spot occurs where a weak part of
the lithosphere allows magma to break through. The magma that produces shield
volcanoes is much thinner than the magma that forms composite cone volcanoes, and it
traps less gas.
Rift eruptions occur when magma erupts through long cracks in the lithosphere.
Curtain-like fountains of lava erupt at spreading ocean ridges or at rifts in continental
crust
3.
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