PLATE TECTONICSChapter 7 – Inside the Restless

Earth

Section 1 – Inside the Earth

The Earth is made of 3 layers with based on what

each layer is made of (COMPOSITION):

1. Crust – the outermost layer of the Earth. Ranges from 5 to 100 km thick. (The thinnest layer) Less than 1% of the Earth’s mass.

* Continental crust – composition similar to granite. Average thickness is 30 km.

* Oceanic crust – composition similar to basalt. It is generally between 5 and 8 km thick.

2. Mantle – the layer of the Earth between the crust and the core. Extremely thick and contains most of the Earth’s mass. Approximately 2,900 km thick.

3. Core – extends from the bottom of the mantle to the center of the Earth. Approximately 33% of the Earth’s mass. Made mostly of iron with small amounts of nickel and some sulfur and oxygen.

The Earth is divided into 5 based on their

physical properties (MECHANICAL):

1. Lithosphere – the outermost, rigid layer of the Earth. Made of the crust and the rigid upper part of the mantle. Divided into tectonic plates.

2. Asthenosphere – the soft layer of the mantle on which pieces of the lithosphere move. Made of solid rock that flows very slowly.

3. Mesosphere – strong, lower part of the mantle. Extends down to the core.

4. Outer Core – the liquid layer of the Earth’s core that lies beneath the mantle and surrounds the inner core.

5. Inner Core – The solid, dense center of our planet. Extends to the center of the Earth, about 6,378 km beneath the surface.

These layers can be described by what they

are made of (COMPOSITION) and how the

act (PHYSICAL):

Composition: Physical:

Granite Rigid

Basalt Strong

Iron Liquid

Nickel Solid

Sulfur Soft

Oxygen

Tectonic plates are pieces of the lithosphere

that move around on top of the asthenosphere.

Tectonic plates are different sizes and may

contain oceanic crust, continental crust or a

combination of both. Each piece fits together

like a giant jigsaw puzzle.

Plate boundaries are areas where plates come

into contact with each other.

Section 2 – Restless Continents

Continental Drift is the theory that continents

can drift apart from one another and have done

so in the past. This was first described by Alfred

Wegener in the early 1900’s.

This theory explained why fossils of

the same plant and animal species

are found on both side of the Atlantic

Ocean. It also explained why some

of the continents seemed to fit together

like a jigsaw puzzle.

Plates move because of the convection currents in the mantle.

Mid-Ocean ridges are

underwater mountain chains.

Along these mountains, you will

find sea-floor spreading.

During this process new oceanic

lithosphere is created as magma

rises toward the surface.

Section 3 – The Theory of Plate Tectonics

Plate tectonics is the theory that the Earth’s

lithosphere is divided into tectonic plates that

move around on top of the asthenosphere.

A boundary is a place where tectonic plates

touch.

There are 3 types of boundaries and they are

labeled by how the boundaries meet.

1. Convergent Boundaries – two tectonic plates collide. (Usually creates mountains.)

2. Divergent Boundaries – two tectonic plates separate. (New sea-floor is created.)

3. Transform Boundaries – two tectonic plates slide past each other horizontally. ( An example is the San Andreas Fault.)

• http://www.wwnorton.com/college/geo/animations/basic_plate_boundaries.htm

At convergent boundaries,

subduction zones are

created when one plate

subducts (or goes

underneath) another plate.

These create ocean

trenches, volcanoes and

earthquakes.

• http://www.wwnorton.com/college/geo/animations/the_process_of_subduction.htm

Scientists use satellites and global

positioning to track the movement of the

Earth’s plates. Tectonic movement is so

slow it is measured in centimeters per year.

Section 4 – Deforming the Earth’s Crust

Stress is the amount of force per unit area

on a given object. Stress applied to rock will

cause it to change.

Deformation – process by which the shape

of a rock changes because of stress. Rocks

reach their elastic limit and break.

• Compression – type of stress that occurs when an object is squeezed. (Two tectonic plates colliding.

• Tension – stress that occurs when forces act to stretch an object. (Divergent boundaries.)

Folding is the bending of rock layers

because of the stress in the Earth’s crust.

Scientists assume that all rock layers started out

as horizontal layers. The folds in rock layers

shows that deformation has taken place.

There are 2 most common types of folding;

synclines and anticlines.

1. Anticlines – upward-arching folds in rock.

2. Synclines – down-ward, troughlike folds in rock.

The surface along which

rocks break and slide past

each other is called a fault.

The foot wall is sitting down

and the hanging wall is

“hanging” or resting on the

foot wall.

1. Normal fault – the hanging wall moves down relative to the footwall.

2. Reverse fault – the hanging wall moves up relative to the footwall.

3. Strike-slip fault – opposing forces cause rock

The movement of tectonic plates can create mountains.

1. Folded mountains – form when rock layers are squeezed together and pushed upward.

2. Fault-Block Mountains – form when tension causes large blocks of the Earth’s crust to drop down relative to other blocks.

3. Volcanic mountains – magma that rises to the surface, cools and forms mountains. May be on the surface or under the water.

There are 2 types of

vertical movement of the

Earth’s crust; uplift and

subsidence.

Uplift – the rising of

regions or Earth’s crust to

higher elevations.

Subsidence – the sinking

of regions of Earth’s crust

to lower elevations.

Subsidence can also occur when the

lithosphere becomes stretched in rift zones.

A rift zone is a set of deep cracks that forms

when 2 tectonic plates are pulled away

from each other.