Download Planet Earth Section 1

Planet Earth
Section 1
SECTION 1: EARTH’S INTERIOR AND PLATE TECTONICS
Topics of section:
KEY IDEAS
〉How is Earth’s interior structured?
〉How has the appearance of Earth changed over time?
〉What geologic features are common near tectonic plate
boundaries?
What is Earth’s Interior Like?
Plate Tectonics
Plate Boundaries
Divergent Boundaries
Planet Earth
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A peach can be used as a model for some aspects of
Earth’s structure. Compare the drawing of the cross
section of the peach below with the cross section of
Earth, and answer the following questions.
Copy the diagram of the Earth
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1.
Describe the outer layer of the peach (the skin).
What aspect of Earth’s structure does the outer layer of the peach
represent?
2.
The peach pulp is the next layer.
How would you describe it? What aspect of Earth’s structure does the peach
pulp represent?
3.
The pit is the innermost part of the peach.
What is the pit like? What aspect of Earth’s structure does the peach pit
represent?
Planet Earth
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WHAT IS EARTH’S INTERIOR LIKE?
〉How is Earth’s interior structured?
〉Earth’s interior is made up of several distinct compositional layers.
CRUST: the thin and solid outermost layer of
Earth above the mantle
MANTLE: the layer of rock between Earth’s
crust and core
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VISUAL CONCEPTS: STRUCTURE OF THE EARTH
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WHAT IS EARTH’S INTERIOR LIKE? CONTINUED
Earth’s interior gets warmer with depth.
Earth’s core is nearly as hot as the surface of the
sun.
 Earth’s core is composed mainly of nickel and iron.
 The inner core is thought to be solid and metal.
 The outer core is thought to be made of liquid metal.
CORE: the center part of the Earth below
the mantle
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VISUAL CONCEPT: FORMATION OF EARTH’S CRUST, MANTLE, AND CORE
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WHAT IS EARTH’S INTERIOR LIKE? CONTINUED
Radioactivity contributes to high internal temperatures.
The breakdown of radioactive isotopes
uranium, thorium and potassium give off
energy that contributes to Earth’s high
internal temperatures.
Temperatures in the mantle can reach more
than 1250 °C.
The core may reach temperatures above
5000 °C.
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PLATE TECTONICS
〉QUESTION: How has the appearance of Earth changed over time?
〉ANSWER: Alfred Wegener hypothesized that
all of the continents might have been part of
one landmass in the past before they drifted
apart.
Wegener pieced the continents together like a puzzle
and called the supercontinent they formed Pangaea.
Wegener found nearly identical fossils on widely
separate continents, which supported his idea.
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VISUAL CONCEPT: CONTINENTAL DRIFT (PANGAEA)
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PLATE TECTONICS, CONTINUED
Evidence for Wegener’s ideas came later.
 Wegener’s theory of continental drift
was ignored until structures
discovered on the ocean floor
provided evidence for a mechanism
for the movement of continents.
 Symmetrical bands on either side of
a mid-ocean ridge indicate that the
two sides of the ridge were moving
away from each other and new
ocean floor was rising up between
them.
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Continental drift
was ignored until
symmetrical
bands on either
side of the midocean ridge
showed that they
were moving
away from each
other. New floor
was rising up.
Planet Earth
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EVIDENCE FOR CONTINENTAL DRIFT
Planet Earth
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PLATE TECTONICS, CONTINUED
Alignment of oceanic rocks supports the theory of
moving plates.
 Iron in molten rock aligns itself with Earth’s magnetic field as it
cools.
 The Earth’s magnetic field reverses polarity about every
200,000 years.
 The process is recorded as magnetic bands in rock, based on the
age of the rock.
 Symmetrical bands on either side of the Mid Atlantic Ridge
suggest that the crust was moving away from the ridge.
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PLATE TECTONICS, CONTINUED
Earth has plates that move over the mantle.
 The crust and upper portion of the mantle are divided into about
seven large pieces called tectonic plates.
lithosphere: the solid outer layer of Earth that
consists of the crust and the rigid upper part of
the mantle
plate tectonics: the theory that explains how
large pieces of the lithosphere, called plates,
move and change shape
Planet Earth
TECTONIC PLATES
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Planet Earth
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PLATE TECTONICS, CONTINUED
Scientists do not understand exactly
what makes tectonic plates move.
 One hypothesis suggests that plate movement results
from convection currents in the asthenosphere, the
hot, fluid portion of the mantle.
 Another hypothesis suggests that plate movement
results from the force of gravity acting on the plates.
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PLATE BOUNDARIES
〉What geologic features are common near tectonic plate
boundaries?
〉Volcanoes
〉Earthquakes
〉Mountains
〉Rift Valleys
3 types of Boundaries
Divergent Boundary
Convergent Boundary
(ex. Subduction zone)
Transform Fault Boundary
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MID-OCEANIC RIDGES RESULT FROM
DIVERGENT BOUNDARIES
Boundary-border
between two tectonic
plates
Divergent boundary place where two tectonic
plates are moving apart.
New rock forms here
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MAGMA
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Magma is liquid
rock produced
under Earth’s
surface.
A rift valley is a
narrow valley
that forms
where tectonic
plates separate.
Planet Earth
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PLATE BOUNDARIES, CONTINUED
Plates slide over each other at a convergent
boundary.
 The area where one plate slides over another is called a
subduction zone. Subduction zones produce ocean trenches,
mountains, and volcanoes.
subduction: the process by which one
lithospheric plate moves beneath another
as a result of tectonic forces
Planet Earth
CONVERGENT BOUNDARIES
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Planet Earth
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VISUAL CONCEPT: CONVERGENT BOUNDARY
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VISUAL CONCEPT: SUBDUCTION ZONE
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PLATE BOUNDARIES, CONTINUED
Subduction of ocean crust generates volcanoes.
 Chains of volcanoes form on the upper plate in a subduction
zone.
 These volcanoes can form far inland from their associated
oceanic trench.
Islands may form where two oceanic plates meet.
 Magma rising to the surface may form an island arc.
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PLATE BOUNDARIES, CONTINUED
Colliding tectonic plates create mountains.
 When two plates collide, mountains are formed at the boundary
of the collision.
Transform fault boundaries can crack Earth.
 Causes earthquakes.
FAULT: a break in a body of rock along
which one block slides relative to another