Journal Question: If your finger nails grow at
about a two inches per year, how long would
it take for them to grow to be a mile? (hints:
12 inches in a foot, 5,280 feet in a mile)
Answer: A nail will grow 1 foot in 6
years. 6 years multiplied by 5,280
feet is how long it will take to grow a
mile…
6 x 5,280 = 31,680 years to grow a
mile
1
CONTINENTAL DRIFT & PANGEA
In 1912, Alfred Wegener proposed
Pangea- long time ago all continents were
one land mass
His evidence:
1. Continent’s fit together like a puzzle
2. rocks and fossils on different
continents matched
Continental Drift –Wegener’s theory of
how continents moved apart
2
1. Crust – solid, rocky outermost surface
2. Upper Mantle – Lithosphere: solid
Asthenosphere: Syrup
3. Lower Mantle – Mesosphere: solid
due to intense pressure
4. Outer core: Hot Liquid metal
5. Inner Core: Hot solid metal – hotter
than surface of sun
3
Theory of Seafloor Spreading
1960s – Seafloor Spreading – theory proposed that new
ocean crust forms at ocean floor as plates are pushed apart,
and causes continental drift.
-Powered by the convection currents of magma in the mantle
4
Seafloor Spreading
Subduction Zone – Area where Lithospheric Plate descents
into Asthenosphere. (think about it: if plates are spreading in
one area, they must be coming together in another)
5
Tectonic Plate Boundaries and Movement
6
JQ: Explain how the Theory of Plate
Tectonics, Continental Drift, and Seafloor
Spreading relate to one another.
7
Evidence for Plate Movement
1. Age of Sea floor crust – The crust near a spreading ridge is
under 200 Million Years old, and gets older as you move
farther away from the ridge (continental crust is 4.6 Billion
years old)
8
Evidence for Plate Movement
2. Magnetic Strips of Rock– The positions of the north pole
switches over thousands of years. Ocean floor rock contains
metal particles that show stripes of sea floor crust that
alternate north and south direction. Layers formed vertically,
not horizontally, like continental crust
9
These are the major plates: North American, South American,
Pacific, Eurasian, African, Nazca, Indo-Australian, and the Antarctic
10
plate.
Evidence for Plate Movement
3. Hot Spots– Areas in Earth’s mantle that are hotter – can
lead to chain of islands; as plate moves over hot spot,
volcanic islands can be formed (ex: Hawaii)
The position of the hot
spot in the mantel doesn’t
change.
11
3Types of Plate Boundaries
Description
Where two
plates move
apart
Where two
plates are
pushed
together
Where two
plates move
past one
another
Example?
Ridges
Trenches
San Andreas
fault line in
Cali
12
71%
Abyssal Plain
Atlantic Ocean
Convection Currents
Hot Spots
Continental Drift
Continental Margin
Continental Rise
Continental Shelf
Continental Slope
Alfred Wegener
Subduction
Guyot
Ice comets & volcanoes
Pangea
Asthenosphere
Lithosphere
Major Ocean Basins
Mantle
Divergent
Near Mid-Ocean Ridges
Oceanic Ridge
Older
Older
On Continents
Pacific Ocean
Recycled
Sea Floor Spreading
Continental Drift
SONAR
Southern Ocean
Thinner
Trench
Hawaiian islands
Volcanoes & Earthquakes
Younger
13
By looking at seismic and volcanic activity around the world,
scientists can identify the plate boundaries.
14
MORE EVIDENCE FOR PLATE TECTONICS
Pattern of reverse & normal polarity in ocean floor rocks
As seafloor cools – the
minerals in the magma
align with the current
magnetic field
Bands of seafloor rock
alternating between
normal and reverse
polarity parallel MORs
and are mirror images
of each other
15
MORE EVIDENCE FOR PLATE MOVEMENT
Oldest continental crust is 4.6 billion years old
Oldest oceanic crust is 200 million years old and gets older away from MOR
Why the difference?
New seafloor is created
at MORs and destroyed
at trenches
16
MORE EVIDENCE FOR PLATE MOVEMENT
HOT SPOTS
Plumes of molten rock
well up from deep within
the mantle and forces its
way up through the
lithosphere to erupt in a
volcano
The plate moves over the
hot spot creating a new
volcanic island
As the plate moves, old
volcanoes are eroded, new
volcanoes form
17
EMPEROR SEAMOUNT CHAIN
18
FOUR TYPES OF PLATE BOUNDARIES
1. Oceanic-Oceanic Boundary - divergent, meaning to
move apart
a. both plates are composed of basalt - the primary type of
ocean floor rock (iron, magnesium and silicon )
b. both plates have the same higher
density rock
c. the result is a spreading center
where new ocean floor is created
ex: Mid-Ocean Ridge (MOR)
This same ridge is 40,000 miles long
and is found in many places in
addition to the middle of the Atlantic
Ocean.
19
2. Continental-Continental Boundary - divergent, meaning to
move apart
a. both plates are granitic - a
type of igneous rock
b. plates have the same lower
density rocks
c. The result is that continent is pulled apart and a rift
valley forms – eventually becoming a new ocean
ex: East Africa Rift Zone
NASA
20
3. Continental-Continental Boundary - convergent, meaning to
come together
a. both plates are granitic - a
type of igneous rock that is the
basis of the rock cycle (silicon
and aluminum)
b. plates have the same lower
density rocks
c. The result is that edges are forced up into mountains.
ex: Himalayas, Atlas Mountains
NASA
21
4. Oceanic-Continental or Oceanic-Oceanic Boundary - a
subduction zone where one plate overrides and the other
is forced down into the mantle (convergent)
a. lighter continental plate or oceanic plate overrides
the denser oceanic plate
b. oceanic plate edge is subducted down into the
asthenosphere and remelted
c. The result is a trench
ex: Peru/Chile Trench
USGS
Chile Trench
22