Transcript Plate Tectonics

Part I of Plate Tectonics
The origins of plate tectonics
• The idea that the Earth’s surface might be
moving is not new.
• As early as the 17th century scientists
noticed the puzzle fit of many land masses
on Earth.
• In 1912 a German scientist named
Alfred Wegener proposed the
Continental Drift Hypothesis
as a means of explaining this
phenomenon.
What is continental drift?
Hypothesis that proposed that the
continents have moved from one
location to another over time.
At one time, there was a single,
supercontinent, called
Pangaea.
Pangaea
225 MYA (Permian Period)
Continental Drift in Action:
The Break-up of Pangea
25 MY
▪ Formation of Gondwanaland and
Laurasia
Continental Drift in Action:
The Break-up of Pangea
135 mya
70 MY
Breakup of Pangea
Continental Drift in Action:
The Break-up of Pangea
65 MY
Present Day!
Death of Dinosaurs
What evidence did Wegener use to
support his hypothesis of continental
drift?
1. Puzzle fit of Africa & South America
2. Fossil evidence
3. Distinctive mountain and rock
formations
4. Climate change evidence
1. Puzzle fit of Africa & South America
2. Fossil Evidence
2. Fossil remains of Mesosaurus
3. Distinctive rock Formations
Age of rocks are the same on
several continents.
3. Mountain Ranges Correlate
Mountain ranges terminate at same
position across the world.
4. Paleoclimate change evidence
1. Glacial Deposits at Equator
2. Coral Reefs in Antartica
Based on this evidence, do you think that
Wegener’s peers supported his continental
drift theory?
The theory was rejected because it could
not explain HOW the continents had
moved.
The origins of plate
tectonics
• In the 1950’s & 1960’s, discoveries led
other scientists to re-examine Wegener’s
continental drift theory.
• These scientists found that while the
continents did not move the way Wegener
suggested, something was moving . . . . . .
They proposed the theory of plate tectonics!
What is the Plate Tectonic Theory?
The theory that the lithosphere
is made of plates that move on
the asthenosphere and interact
with one another.
Add the following notes to your foldable
The Crust
•
Thinnest Layer-Average
30 km
• Composed of Oxygen
and Silcon based rocks
• Solid
• oceanic crust
– Very dense
• continental crust
– lighter
•
•
•
•
Largest layer of the Earth
–average 2900 km
Composed of silicate
rocks rich in magnesium
and iron.
Molten rock with
convection currents
constantly moving.
Upper mantle and lower
crust make the
ASTHENOSPHERE.
Convection Currents
The middle mantle
"flows" because of
convection currents.
Convection currents
• very hot material at
the deepest part of the
mantle rising,
• then cooling and
sinking again
• repeating this cycle
over and over.
The Outer Core
• Average 2300
km thick
• composed of the
melted metals
of nickel and
iron.
• very hot liquid
The Inner Core
• 1,216 km Thick
• Made of nickel and
iron
• high temperatures and
pressures
• Solid!
Evidence that supports plate
tectonics
1. Seafloor spreading
2. Earth’s Paleomagnetic Record
3. Location of Earthquakes & Volcanic Hotspots
1. Sea Floor Spreading
The process by which new ocean floor is
formed by lava erupting from a crack,
pushing the existing floor outward.
Youngest rock is near the center.
Atlantic Ocean is getting larger.
2. Earth’s Magnet Field
• Metals in Earth’s liquid outer core are always
moving (convection currents)
AND
• Earth is always moving.
When metal moves electric currents are
created this produced a magnetic field.
Paleomagnetic Record
•Lava and sediments contain ironbearing minerals
•When they cool or are deposited on the
iron lines up with the Earth’s magnetic
field.
•If the Earth’s magnetic field switches
then the iron lines up differently.
• This is known as 'paleomagnetism'.
Paleomagnetic Record
• The youngest oceanic crust is at the
ridge crest, and the oldest oceanic
crust is at the continental margins.
• The magnitism moves out on each
side like a mirror.
Youngest
Oldest
Practice Question!
3. Locations of Earthquakes and
Volcanoes
Earthquakes and volcanoes do not occur
randomly throughout the world.
They occur primarily in concentrated
belts, near plate margins!
3. Locations of Earthquakes and Volcanoes
The crust!
• Crust is divided into two groups.
– Oceanic- underwater, dense crust
– Continental- land, lighter
• Plate boundaries are where lithospheric plates meet.
What happens at the boundary depends on the type
of crust and the direction of the movement.
Plate Boundary Notes
• Add to your table of contents: Plate Boundary
Notes / 2.1.1
• Turn to that page and divide the paper into thirds.
• Use chapter 17.3 to label each section with the
three types of plate boundaries.
• Draw a picture of each (convergent should have at
least two drawings). Make sure they are labeled.
• Leave space to write notes tomorrow.
The major plates of Earth
Divergent (apart) Boundary
• Continental-Continental
– Rift Valley
Divergent boundary of two continental plates.
Creates a rift valley.
Example: East African Rift
Divergent (apart) Boundary
• Continental-Continental
– Rift Valley
• Oceanic-Oceanic
– Mid-Ocean Ridge
Oceanic - Oceanic Divergent boundary
● creates a mid-ocean ridge
● creates new land
Iceland
Mid-Atlantic
Ridge
Convergent (together) Boundary
• Oceanic-Continental
– Volcanic mountain range and trench
– Slab-Pull model
Convergent boundary of an oceanic plate and a
continental plate. Forms a volcanic mountain range
and a trench.
Examples: Cascades or Andes Mts
Convergent (together) Boundary
• Oceanic-Continental
– Volcanic mountain range and trench
– Slab-Pull model
• Oceanic-Oceanic
– Trench and Island Arcs
– Slab-Pull model
Convergent boundary of two oceanic plates. Creates
an island arc and a trench.
Example: Japan
Slab- Pull
.
Convergent (together) Boundary
• Oceanic-Continental
– Volcanic Mountain Range and Trench
– Slab-Pull Model
• Oceanic-Oceanic
– Trench and Island Arcs
– Slab-Pull Model
• Continental-Continental
– Mountain Range
Convergent boundary of two continental plates.
Forms a folded mountain range.
Examples: Himalayas, Alps, Appalachian
• Transform (sliding) Boundary
– Two plates sliding past each other.
– Forms a fault
– Strike-Slip
Example: San Andreas Fault in California
• How fast does all of this happen??????
– SLOWLY
– Approximately 5 centimeters per year
PRACTICE QUESTIONS
1. Places where plates move apart are called
_____________ boundaries.
2. When continental plates diverge a ___________
is formed.
3. When two oceanic plates converge what is
created? _________________
4. The Appalachians formed mainly from
continental plate collisions and therefore are a
__________ mountain range.
5. The force moving the plates is ____________ .
• Tectonic Plate Mapping / 2.1.1
• Answer the Pre-Lab questions #1-5 and 13, 14 on
the back of your map or in your notebook on a
new page. Use a textbook if needed.
• (15 minutes)
• Label the map AS A CLASS to set up for our activity
tomorrow.
• Make sure your name is on your map and turn it in.
Hot Spots / 2.1.1
• Turn to page 486 in the textbook. Read the
section on Hot Spots. Answer the following:
1. What is a hot spot?
2. What US state was formed by a hot spot?
3. Based on the age of the oldest island in the
Hawaiian island chain, approximately how
old is the hot spot that formed Hawaii?
Hot Spots / 2.1.1
• Hot spots are areas of volcanic activity in the
middle of lithospheric plates.
• Lava at hot spots usually flows smoothly over
the surface.
• Hot spots remain in the same location even
though the lithospheric plate above it moves.
• The most famous example of hot spot
volcanism is ____________________.
Hot Spot Activity
• Complete the activity as a class.
• Answer Questions #1-6 on the same page in
your notebook.
Test Remediation
• Test Corrections
– #, Letter, Explanation
– Explanation cannot be rewriting the questions.
Must be definitions, diagrams, examples or
descriptions
• Boundaries diagram
• Seafloor diagram