BELLRINGERBELLRINGER

List and explain 3 pieces of evidence that Wegener

used to support the idea of Pangaea.

The Theory of Tectonic The Theory of Tectonic PlatesPlates

Chapter 7 Section 3Chapter 7 Section 3

The Theory of Plate The Theory of Plate TectonicsTectonics

The Earth’s lithosphere (crust and The Earth’s lithosphere (crust and upper mantle) is divided into tectonic upper mantle) is divided into tectonic plates.plates.

These plates move on top of the These plates move on top of the asthenosphere (lower mantle).asthenosphere (lower mantle).

We know that these plates move in We know that these plates move in different ways.different ways.

Tectonic PlatesTectonic Plates

Tectonic Plate BoundariesTectonic Plate Boundaries A boundary is a place where tectonic A boundary is a place where tectonic

plates touch.plates touch.

3 types of tectonic plate boundaries:3 types of tectonic plate boundaries: ConvergentConvergent DivergentDivergent TransformTransform

The numbers on the map represent the rate at which plates are moving in centimeters.

Plate MovementPlate Movement

Convergent Boundary

• When two plates collide, or move toward each other, the boundary is called convergent

• There are 3 types of convergent boundaries, depending on what type of crust comes together.

• Continental-continental• Continental-oceanic• Oceanic-oceanic

Convergent BoundaryConvergent BoundaryContinental-Continental Continental-Continental

The two continental plates The two continental plates come togethercome together Buckle, thicken, and push continental crust Buckle, thicken, and push continental crust

upwardupward

Convergent BoundaryConvergent BoundaryContinental-OceanicContinental-Oceanic

Dense oceanic crust sinks below the continental crust and Dense oceanic crust sinks below the continental crust and sinks into the asthenosphere.sinks into the asthenosphere.

This is a This is a subduction zone.subduction zone. ““Sub” means below (submarine, subway)Sub” means below (submarine, subway) Old ocean crust is pushed below the asthenosphere and Old ocean crust is pushed below the asthenosphere and

gets re-melted and recycled.gets re-melted and recycled.

Convergent BoundaryConvergent BoundaryOceanic-OceanicOceanic-Oceanic

►One oceanic plate sinks below the One oceanic plate sinks below the other.other.

►Another Another subduction zonesubduction zone

Divergent BoundaryDivergent Boundary Two tectonic plates Two tectonic plates move awaymove away from each other. from each other. On the sea floor at the mid ocean ridge this is called On the sea floor at the mid ocean ridge this is called

sea floor spreadingsea floor spreading.. As the plates move apart, magma rises to fill the gaps.As the plates move apart, magma rises to fill the gaps. The magma is cooled and forms new ocean floor.The magma is cooled and forms new ocean floor.

The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.

Divergent BoundaryDivergent Boundary

On-land exposure of the Mid-Atlantic Ridge in Iceland.

Sea Floor Spreading

Transform Boundary

Two tectonic plates move past one another.

Their edges are jagged and irregular.

As they grind together and jerk, they slide past each other creating earthquakes.

3 Possible Causes of Plate Movement

1. Convection: hot rock deep in the Earth rises, cooler rock sinks. This movement of magma causes plates to move

2. Ridge push

3. Slab pull

Tracking Tectonic Plate Movement• Plates move very slowly,

centimeters to inches a year.

• GPS, Global Positioning System, measures the rate of movement.

• Radio signals beam continuously from satellites to the Earth.

• By recording the time it takes for the Ground station to move a given distance, scientists can measure the speed at which plates move.