The Theory of Plate Tectonics

C4S5

The cracked eggshell is similar to the cracks in

Earth’s lithosphere

A section of the

Lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust.

Plates

There are cracks in the continents

similar to those on the ocean floor. In the 1960’s scientists proposed that these cracks break the lithosphere into separate sections. The plates fit together along cracks in the lithosphere.

Plates

How Plates Move

Plate Tectonics

The Theory of Plate Tectonics states that pieces of Earth’s lithosphere are in slow constant motion, driven by convection currents in the mantle

What is the Theory of Plate Tectonics?

The Theory of plate tectonics explains the

formation, movement, and Subduction of Earth’s Plates.

What for is great enough to move Earth’s plates?

Geologists think that movement of convection currents in the Earth’s mantle is the major cause of plate motion. Mantle motion is transferred the lithosphere at its boundary with the asthenosphere. The plates are carried along in much the same way ice floats on slow-moving water.

During subduction, gravity pulls one edge of a plate down into the mantle. The rest of the plates also moves. This slow movement is similar to what happens in pot of soup when gravity causes the cooler, denser soup near the surface to sink.

As the plates move, they change Earth’s surface: earthquakes, volcanoes, mountain ranges, and deep-open trenches.

The Theory of Plate Tectonics (continued)

Plate Boundaries

Fault

A break or crack in Earth’s lithosphere along which the rocks move.

San Andreas FaultThe San Andreas Fault runs from Indio, California to the Bay area in

Northern California. It extends 810 miles. This is the fault Californians expect to produce the “BIG ONE”

What are the three types of Plate boundaries?

There are three kinds of plate boundaries: spreading boundaries, colliding

boundaries, and sliding boundaries. A different type of plate movement occurs along

each type of boundary.

Scientists use satellites to measure plate

motion. The plates move ~ 1-24 cm/year in response to movements in the mantle.

The North American and Eurasian plats are moving apart at a rate of 2.5 cm/year. That is about as fast as your finger nails grow. California is moving ~ 1 cm/year.

Plate boundaries (continued)

Spreading Boundaries

A plate boundary where two plates move away from each other.

Spreading boundaries are also known as Divergent Boundaries.

Spreading BoundariesMost spreading boundaries occur along the mid-ocean ridges where sea-

floor spreading occurs.

Rift Valley

When a Valley forms where plates move apart

Colliding Boundaries

A plate boundary where two plates move towards each other.

Another term for colliding Boundary is Convergent Boundary.

When two plates collide, the density of the

plates determine which one comes out on top.

Colliding Boundaries

The 3 types of Colliding Boundaries

1. Two plates made up of oceanic crust meet at a trench (refer to previous slide). The oceanic crust becomes cooler and denser during sea floor spreading.

2. An oceanic plate collides with a continental plate. Subduction occurs as the denser oceanic plate sinks.

3. Two plates carrying continental plates collide, but instead of subduction, it squeezes and a mighty mountain rage is created.

Sliding Boundaries

Is a place where two plates slip past each other, moving in opposite directions. Crust is neither created or destroyed.

Sliding boundaries can also be called transform boundaries.