Transcript Unit 3 Earth Science Sixth Grade Chapter 6 The Big Idea  Plate tectonics accounts for important features of Earth’s surface and major geologic events.

Unit 3
Earth Science
Sixth Grade
Chapter 6
The Big Idea
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Plate tectonics accounts for
important features of Earth’s surface
and major geologic events.
Earth’s Structure
Section 1
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Key concept--Earth is composed
of several layers.
The continents are
part of the
uppermost layer,
and they move
slowly around
Earth’s surface.
The Layers of Earth
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Compositional Layers
(this should be a
review!)
Crust—made of
silicon, oxygen, &
aluminum
Mantle– thick middle
layer, made of silicon,
oxygen, & magnesium
Core—center of the
Earth, made mostly of
iron.
Continental and Ocean Crust
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2 types of crust on Earth
• Continental
• Oceanic
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Continental crust is thicker
than oceanic crust
Oceanic crust is more dense
and has two times as much
iron, calcium, and magnesium.
Oceanic crust is HEAVIER than
continental crust.
Both types are rocky, and
fractured
The Physical Structure of the Earth
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Lithosphere—divided
into pieces called
tectonic plates
Asthenosphere—very
slow flowing rock that
allows tectonic plates
to move
Mesosphere—even
slower flowing rock
(lower part of the
mantle)
Outer core—liquid iron
& nickel
Inner core—solid iron
& nickel (between
4,000 degrees C and
5,000 degrees C.
Mapping the Earth’s Interior
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How do scientists know what the
Earth is like inside if they have never
drilled down that far?
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Earthquakes!
Earthquakes produce
vibrations called
seismic waves.
Seismic waves travel
THROUGH Earth at
different speeds.
Seismographs
measure the times
earthquakes take to
travel various
distances from an
earthquakes center.
seismograph
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The speed of the seismic wave is
affected by the type of material that
the waves are traveling through.
Continental Drift
Restless Continents
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Alfred Wegener wrote his hypothesis
of continental drift in the early
1900’s
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Continental drift is the idea that a
single large landmass broke up into
smaller landmasses to form the
continents, which then drifted to
their present locations.
Evidence for Continental Drift
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Fossils from the same
plant and animal
species are found on
continents that are far
from each other.
Locations of
mountains and similar
types of rock.
Past patterns of
climatic patterns
found in fossil
evidence on differing
continents
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Evidence for Continental Drift
If the continents were all once
together as Pangaea, it would be
required that the rocks found in a
particular region of one continent
today should closely match in age
and type with those in the adjacent
position on the adjoining continent.
This appears to be the case, and is
most obvious in mountain ranges
that end on one coast line and
continue on a landmass across the
ocean. An example of this is the
Appalachians in northeastern North
America and the mountain ranges in
the British Isles and Scandinavia.
When these landmasses are
reassembled on a map of Pangaea
the mountain chains form a nearly
continuous belt. The rock types, age
and structures all match.
The Breakup of Pangaea
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Wegener called the single
large continent PANGAEA
(Greek for “all earth”)
Existed 245 million years
ago
135 million years ago
Pangaea split into 2
continents: Laurasia and
Gondwana.
As continents drifted they
collided with each other,
which caused landforms
such as mountain ranges,
volcanoes, ocean trenches,
and mid-ocean ridges.
Sea-Floor Spreading
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Scientists did not believe in
Wegener’s theory because of the
strength of rock.
Many years after his death scientists
found new evidence of forces that
moved continents. SEA-FLOOR
SPREADING.
Mid-Ocean Ridges—
A Magnetic Mystery
Mid-Ocean ridges are underwater mountain chains that run
through Earth’s ocean floor.
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Scientists discovered patterns of
magnetism in the sea-floor rocks.
The pattern on one side of the ridge
was a mirror image of the pattern of
the pattern on the other side of the
ridge.
Magnetic Reversals—
Mystery Solved
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As rock forms from
magma, or molten
rock, minerals that
contain iron form.
Some of these
minerals are magnetic
and act like
compasses.
When the molten rock
cools, these tiny
compasses are locked
in position in the rock.
After Earth’s magnetic
field reverses, new
magnetic minerals
align in the opposite
ways
Sea-Floor Spreading
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At a mid-ocean ridge, magma rises
through fractures in the sea floor.
As the magma cools, it forms new
rock.
As this new rock forms, the older
rock gets pulled away from the midocean ridge.
This process is called SEA-FLOOR
SPREADING.
THIS IS HOW CONTINENTS MOVE!!
MOVEMENT OF TECTONIC PLATES IN CALIFORNIA
Summary
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Earth is made up of three layers—the crust, the mantle,
and the core—based on chemical composition. Of these
three layers, the core is made up of the densest materials.
The crust and mantle are made up of materials that are
less dense than the core.
Earth is made up of five layers—the lithosphere,
asthenosphere, mesosphere, outer core, and inner core—
based on physical properties.
Knowledge about the layers of Earth comes from the study
of seismic waves caused by earthquakes.
Wegener hypothesized that continents drift apart from one
another now and that they have drifted in the past.
Magnetic reversals that occur over time are recorded in the
magnetic pattern of the oceanic crust, which provides
evidence of sea-floor spreading and continental drift.
Sea-floor spreading is the process by which new sea floor
forms at mid-ocean ridges.