Plate Tectonics
What a strange trip it’s been…
Earth’s lithosphere is broken into plates (15) that move on the asthenosphere
Some move towards, some away, some slide past one another
Plate tectonics is the theory that describes the formation, movement, and interaction of plates
CONTINENTAL MOVEMENT
Theory developed from observations about the shapes of continents, fossil, and climate evidence
Africa and South America look like they fit together at one point in time
Coincidence!?!?!?
German scientist Alfred Wegener proposed his hypothesis of continental drift He stated that continents move, or drift from one location to another over time
Continents fit together like a puzzle
Fossils of Mesosaurus were found in Africa and South America 270 million years old
Distinctive rock formations lined up on each continent
They must have been together!!!
Broke
up 200 million years ago Wegener knew that they must have been together in the past
His hypothesis didn’t explain HOW the continents moved
He knew the continents moved in the past and are moving in the present, but had no mechanism behind it
Wegener defended it, but did not succeed
In the 1950s and 1960s, studies showed that Wegener’s observations were correct
Continents are embedded in lithospheric plates
As the plates move, they carry the continents with them
The theory explains why earthquakes and volcanoes are likely to occur in particular locations
Explains how new crust is created along the ocean floor at the Mid-Ocean Ridge
Data indicates that Earthquakes and volcanic activity do not occur randomly throughout the world
Instead, they occur primarily in concentrated belts around the world
The belts mark the location of the plate boundaries, or where one plate meets another
RED CIRCLES = EARTHQUAKES AND VOLCANOES
• The continental plate boundaries match up perfectly with earthquake and volcanic http://www.emscepisodes
csem.org/Earthquake/Map/jsmap.php?start _date=2011-07-20&end_date=2011-09-27
Boundaries are places where two plates are pushing toward, pulling away, or sliding past one another
Strain builds up along plate boundaries, then BOOM: Earthquake
Molten rock moves upward to the Earth’s surface causing volcanic activity
Proposed seafloor spreading in the 1960s after Wegener, supporting his hypothesis
The ocean floor is literally spreading out, carrying the continents with it along ridges
Due to convection cells within the mantle
Proved this by magnetic polarity models
Some igneous rocks have magnetic minerals in them In the past, these minerals would line up with wherever the magnetic pole was Shifted between normal and reverse polarity over time
Make a distinct pattern on the ocean floor that Hess observed
Black = normal polarity Grey = reverse polarity Alternating
bands of normal and reverse polarity
Geologists studied the magnetic record on both sides of the mid-ocean ridge
A mid-ocean ridge is a long chain of volcanic mountains on the ocean floor with a deep central valley
When geologists figured out the ages of the rocks on either side of the mid-ocean ridge, they found that:
1.) The rocks at the center of a mid-ocean ridge are the youngest 2.) The rocks furthest from the center of a midocean ridge are the oldest
New rock is formed by hot magma rising up between the spreading plates Oozes up, and piles on both sides of the ridge Convection currents keep it spreading apart away from itself As new rock forms, the older rock spreads away from the center on either side
Red = youngest rock Green = oldest rock
1.) List two pieces of evidence that Wegener used to support his hypothesis of continental drift 2.) True/False: Earthquakes and volcanoes occur along plate boundaries 3.) What happens to the age of the rock at the Mid-Ocean Ridge as it spreads out from the center?
Scientists
classify boundaries between two plates according to plate movement
Three
main types: 1.) Divergent 2.) Convergent 3.) Transform
A boundary between two lithospheric plates that are moving apart
Diverge = spread apart, separate
Divergent boundaries have rift valleys associated with them
Most are on the ocean floor
Best example:
Rift valleys are at the center of the divergent plate boundary
Mid-Ocean Ridge
In Iceland, the mid ocean ridge is exposed
Features
associated:
1.) Volcanos 2.) Earthquakes 3.) Magma 4.) Black smokers 5.) LIFE! LIFE!
A boundary between two plates that are moving toward each other
Convergence = toward, come together
Two classes of convergence: 1.) Subduction 2.) Collision
When
an oceanic plate plunges beneath another plate, it is said to be subducting beneath the overriding plate
The
boundary between is called a subduction boundary
Denser plate subducts or goes under the other
Long, deep sea trenches are at the deepest parts of the ocean floor Example: Marianas trench
Over 9 km deep!!!
Subducted rock melts, rises, and forms volcanoes on the surface of the other plate
Subducted rock melts, rises, and forms volcanoes on the surface of the land
If
two plates are carrying continents, they will collide together creating mountains
Most
famous location: Himalayan Mountains in India CONTINENTAL MOVEMENT
Continental-Continental: mountains Oceanic-Continental: subduction zones, volcanoes along coast, deep trenches Oceanic-Oceanic: subduction zones, volcanic island arcs, deep trenches
ALL ARE CONVERGING TOGETHER WITH DIFFERENT RESULTS
Boundary between two plates that are sliding past each other Located at mid-ocean ridges, and most famously, California at the San Andreas Fault
Pacific plate = Northwest North American plate = Southeast
Shallow Earthquakes Displacement of land
Mantle convection
Magma that rises at the mid-ocean ridge is hot, less dense, and expands
This causes the rock to rise creating a slope
More dense rock slides away from the center, where new crust is created
At a subduction boundary, one plate is denser and heavier than the other As it sinks, it pulls the rest of the plate with it The force that the sinking plate exerts on the rest is called slab pull
Similar to keys in your coat pocket on a table
What are the three types of plate boundaries?
What does subduction mean? Which plate subducts under, more or less dense?
What are the three crustal types of convergent boundaries?
Earth’s lithosphere is broken into plates (15) that move on the asthenosphere
Some move towards, some away, some slide past one another
Plate tectonics is the theory that describes the formation, movement, and interaction of plates
CONTINENTAL MOVEMENT
Theory developed from observations about the shapes of continents, fossil, and climate evidence
Africa and South America look like they fit together at one point in time
Coincidence!?!?!?
German scientist Alfred Wegener proposed his hypothesis of continental drift He stated that continents move, or drift from one location to another over time
Continents fit together like a puzzle
Fossils of Mesosaurus were found in Africa and South America 270 million years old
Distinctive rock formations lined up on each continent
They must have been together!!!
Broke
up 200 million years ago Wegener knew that they must have been together in the past
His hypothesis didn’t explain HOW the continents moved
He knew the continents moved in the past and are moving in the present, but had no mechanism behind it
Wegener defended it, but did not succeed
In the 1950s and 1960s, studies showed that Wegener’s observations were correct
Continents are embedded in lithospheric plates
As the plates move, they carry the continents with them
The theory explains why earthquakes and volcanoes are likely to occur in particular locations
Explains how new crust is created along the ocean floor at the Mid-Ocean Ridge
Data indicates that Earthquakes and volcanic activity do not occur randomly throughout the world
Instead, they occur primarily in concentrated belts around the world
The belts mark the location of the plate boundaries, or where one plate meets another
RED CIRCLES = EARTHQUAKES AND VOLCANOES
• The continental plate boundaries match up perfectly with earthquake and volcanic http://www.emscepisodes
csem.org/Earthquake/Map/jsmap.php?start _date=2011-07-20&end_date=2011-09-27
Boundaries are places where two plates are pushing toward, pulling away, or sliding past one another
Strain builds up along plate boundaries, then BOOM: Earthquake
Molten rock moves upward to the Earth’s surface causing volcanic activity
Proposed seafloor spreading in the 1960s after Wegener, supporting his hypothesis
The ocean floor is literally spreading out, carrying the continents with it along ridges
Due to convection cells within the mantle
Proved this by magnetic polarity models
Some igneous rocks have magnetic minerals in them In the past, these minerals would line up with wherever the magnetic pole was Shifted between normal and reverse polarity over time
Make a distinct pattern on the ocean floor that Hess observed
Black = normal polarity Grey = reverse polarity Alternating
bands of normal and reverse polarity
Geologists studied the magnetic record on both sides of the mid-ocean ridge
A mid-ocean ridge is a long chain of volcanic mountains on the ocean floor with a deep central valley
When geologists figured out the ages of the rocks on either side of the mid-ocean ridge, they found that:
1.) The rocks at the center of a mid-ocean ridge are the youngest 2.) The rocks furthest from the center of a midocean ridge are the oldest
New rock is formed by hot magma rising up between the spreading plates Oozes up, and piles on both sides of the ridge Convection currents keep it spreading apart away from itself As new rock forms, the older rock spreads away from the center on either side
Red = youngest rock Green = oldest rock
1.) List two pieces of evidence that Wegener used to support his hypothesis of continental drift 2.) True/False: Earthquakes and volcanoes occur along plate boundaries 3.) What happens to the age of the rock at the Mid-Ocean Ridge as it spreads out from the center?
Scientists
classify boundaries between two plates according to plate movement
Three
main types: 1.) Divergent 2.) Convergent 3.) Transform
A boundary between two lithospheric plates that are moving apart
Diverge = spread apart, separate
Divergent boundaries have rift valleys associated with them
Most are on the ocean floor
Best example:
Rift valleys are at the center of the divergent plate boundary
Mid-Ocean Ridge
In Iceland, the mid ocean ridge is exposed
Features
associated:
1.) Volcanos 2.) Earthquakes 3.) Magma 4.) Black smokers 5.) LIFE! LIFE!
A boundary between two plates that are moving toward each other
Convergence = toward, come together
Two classes of convergence: 1.) Subduction 2.) Collision
When
an oceanic plate plunges beneath another plate, it is said to be subducting beneath the overriding plate
The
boundary between is called a subduction boundary
Denser plate subducts or goes under the other
Long, deep sea trenches are at the deepest parts of the ocean floor Example: Marianas trench
Over 9 km deep!!!
Subducted rock melts, rises, and forms volcanoes on the surface of the other plate
Subducted rock melts, rises, and forms volcanoes on the surface of the land
If
two plates are carrying continents, they will collide together creating mountains
Most
famous location: Himalayan Mountains in India CONTINENTAL MOVEMENT
Continental-Continental: mountains Oceanic-Continental: subduction zones, volcanoes along coast, deep trenches Oceanic-Oceanic: subduction zones, volcanic island arcs, deep trenches
ALL ARE CONVERGING TOGETHER WITH DIFFERENT RESULTS
Boundary between two plates that are sliding past each other Located at mid-ocean ridges, and most famously, California at the San Andreas Fault
Pacific plate = Northwest North American plate = Southeast
Shallow Earthquakes Displacement of land
Mantle convection
Magma that rises at the mid-ocean ridge is hot, less dense, and expands
This causes the rock to rise creating a slope
More dense rock slides away from the center, where new crust is created
At a subduction boundary, one plate is denser and heavier than the other As it sinks, it pulls the rest of the plate with it The force that the sinking plate exerts on the rest is called slab pull
Similar to keys in your coat pocket on a table
What are the three types of plate boundaries?
What does subduction mean? Which plate subducts under, more or less dense?
What are the three crustal types of convergent boundaries?
