Chapter 17 The Dynamic Earth
17.1 Structure of the Earth:
The Earth is composed of layers
Crust – Rigid Outer Layer
That makes up continents and sea
floors
The Lithosphere is the region
formed by the crust and the outer
layer of the Mantle
The Asthenosphere is the fluidlike layer of mantle beneath the
lithosphere (extreme pressure)
•Scientists obtain information about the structure of Earth through __direct__ and
___indirect_________ observations.
Direct observations include analysing rock directly from Earth’s interior.
-
Volcanoes – lava flows
-Rock samples
Indirect observations include measuring gravitational force differences around the globe to infer the
density of material beneath Earth’s surface.
-
Measuring of magnetic fields and gravity
Observations of how earthquake waves travel through the layers (next unit you will learn more on
this!)
Modern Mapping:
-satellite & ariel photos
-GPS
-Infrared and radar images
At one time the continents formed Pangea, A single huge landmass
DO CYU 17.1 p. 496 # 1-11
17.2 Evidence of a Dynamic Earth:
Continental Drift Theory: The surface of the Earth moves constantly- First proposed by Wegner based on the
following evidence:
-
Puzzle fit of continents
Geological coastline matches
Fossil matching
-
Coal deposit matching
Equatorial glacial evidence
Unfortunately his theory was not accepted until when HOW the continents moved was better understood!
DO CYU 17.2 p. 500 #1-7
Sea floor spreading
17.3 New Evidence of a Dynamic Earth:
occurs at mid-ocean ridges
when magma rises from the
mantle and fills in the cracks
left by the sea floor moving
apart
1. Mid-Ocean Ridges & Maps
Mid-oceanic ridges are undersea mountain ranges
The sea floor is cycled back
into earth at ocean trenches
at a divergent boundary
subduction zones
The discover of mid-ocean ridges where the sea floor was spreading, as well as trenches where continents and
oceanic plates met etc. were mapped along with known locations of high volcanic and earthquake history and this
showed the boundaries of the “plates” See Fig 1 p. 501
2. Sea-Floor Spreading
Heat within the Earth creates
convection currents in the mantle
that help move the plates.
Radioactive dating of core samples
confirmed that the sea floor is older
the further it is from the ridge
When basalt cools the iron particles in the rock align with the earths magnetic field (like tiny compass
needles) and since the magnetic poles reverse over earth history, this has created a pattern
Radioactive dating  When they looked at the mid-ocean ridges closer it was discovered that the rock was
youngest at the ridges, and oldest at the trenches where the oceanic plates dip under the continental plates
Magnetic Evidence there is also a pattern of magnetic shifts that can be observed moving away from the
divergent ocean ridges that show that new plate is forming and moving outward from both sides of this boundary. See
Fig 3. P. 503
17.4 Theory of Plate Tectonics:
The theory of plate tectonics states that the lithosphere is divided into 12 large segments and about 20
smaller ones.
The lithosphere is divided into 12 sections called plates plus 20 smaller ones. These tectonic plates “float” on top of the
dense fluid like asthenosphere which creates a push-and-pull on these plates due to large slow moving convection
current within it, causing many different plate boundary phenomena
The point where two plates move away from each other is
called a Divergent Boundary
Rift (land), Ridge (ocean) , and
Volcanoes/Earthquakes are created at this type of
boundary
Plates moving towards each other collide at a Convergent
Boundary
Ocean-ocean islands arc & trench from subduction
Ocean-continent trench from subduction, volcano belt
mountaints, volcanoes, earthquakes
Continent-continent  mountains
Plates move past each other in opposite directions at
Transform Boundary
Earthquakes and strike-slip fault lines are created
along this type of boundary.
, mountaints,
Summary of Plate Movement
Plate Boundary
Convergent
Ocean-Ocean
Description of
Movement
Geological
Formations
Subduction zone
Island Arc Volcanoes
Convergent
Ocean-Continent
Subduction zone
Trench
Volcanoe belt
Mountains
Earthquakes
Convergent
ContinentContinent
Mountain Range
Divergent
Oceans = ridges
Continent = Rifts
Transform
Earhquakes
Faults
Picture
Chapter 18 – Plate Tectonics
18.1 Causes and Effects of Plate
Movement: Shaping the Earth:
Push: out at divergent boundary where
sea floor spreading is occuring
Pull: down at subductions zones
Convection: created when the core
heats the liquid like mantle which then cools as
it rises … and is density dependant
CYU 18.1 p. 521 #1-10 DO Worksheet with new seating partners
18.2: Geological Events:
Volcanoes: - mark cracks in the lithosphere where magma & gas reach the surface
-
Found at:

Mid-Ocean Ridges

Volcanic Belts - Parallel to convergent ocean-continental boundary (on continent)

Volcanic Island Arcs – parallel to convergent oceanic-oceanic boundary

Hot Spots – above a spot of very hot mantle. Often resulting in Volcanic island chains
eg. Hawaii Is.
Earthquakes: - mark locations where transform boundaries form faults
Epicenter – location directly above the focus
Focus – location where the earthquake originated underground
P OR COMPRESSIONAL WAVES – Primary
Travels in the same direction as the wave
Can travel through solids, liquids and gasses
S OR SHEAR WAVES – Secondary (slower)
Travels perpendicular to the wave direction
Can travel through solids only
***P waves travel faster (about 1.7x) than s waves
What do P-waves and S-Waves provide indirect evidence for?
1
Distance to the Epicenter: since the p wave and s wave travel
at different speeds, the time interval between when they reach a
seismograph can be used to determine the distance from the epicents
2 Indirect information about the layers of the earth: tells us the depth,
density and state of the different layers of the earth
(faster)