An investigation into how Newton’s Laws of Motion are applied to the tectonic activity on Earth.

FORCES ON

EARTHUNIT 3.2

Geologists – scientists who study the forces that make and shape the Earth

GEOLOGY

• Destructive – slowly wear

away mountains and every

other feature on Earth

•Constructive – shape the earth by building up mountains and landmasses

Geologists divide the forces that change the Earth into two categories:

SO….HOW DO WE KNOW WHAT’S INSIDE THE EARTH?

• Geologists record seismic waves and study how they travel through the medium of Earth.

• The speed and the path the waves takes reveal how the planet is put together.

• The further “in” you go… temperatureand pressure both increase

• There are three main layers that make up the Earth’s interior:

• Crust

• Mantle

• Core

A JOURNEY TO THE CENTER OF THE EARTH

• The layer of rock that forms Earth’s outer skin

• It consists of about 10 miles of rock

• Continental crust is thicker than oceanic crust

• However, oceanic crust is much denserthan continental crust

THE CRUST

• The mantle extends to a depth of approximately 1,800 miles

• It is made of a thick solid rocky substance

• The uppermost part of the mantle and the crust together form a rigid layer called the lithosphere

• The asthenosphere is super-heated rock(molten)

• The remainder of the mantle is solid

THE MANTLEUpper mantel

Lower mantel

Lithosphere (hard)

Asthenosphere (soft)

Mesosphere

• Consists of two parts

• Outer core – molten iron and nickel metal

• Inner core – solid dense ball of iron and nickel metal

THE CORE

• Heat is transferred through:• Radiation• Conduction• Convection

• Let’s go through what each type of heat is first, before we apply it to the Earth.

CONVECTION CURRENTS AND THE MANTLE

• Radiation – transfer of energy by electromagnetic waves (ex. Sun heating the Earth)

RADIATION

• Conduction –the process by which heat energy is transmitted through collisions between neighboring molecules. Think of a frying pan set over an open camp stove. The fire's heat causes molecules in the pan to vibrate faster, making it hotter.

CONDUCTION

Heat Transfer

• Convection - The transfer of heat energy by movements of a fluid.

• heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.

• The heating and cooling of a fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.

• Convection currents continue as long as heat exists!

CONVECTION

• Heat from the Earth’s core and from the mantle itself cause the convection currents in the mantle

• Convection currents are an unbalanced force that causes heat flow and the movement of material within the earth.

• This moving material results in earthquakes and volcanic eruptions to create mountains and ocean basins.

CONVECTION IN THE MANTLE

• The crust is broken into large pieces, which we call “plates”

TECTONIC PLATES – WHAT ARE THEY?

• Plate movement result in stress within the Earth’s crust which adds energy to rock until the rock either breaks or changes shape

PLATE MOVEMENT

• Plates apply equal and opposite forces on each other. (A push or pull )

• The acceleration of the plate depends on forces acting on the plate and the mass of the plate.

PLATES AND FORCES

http://education.sdsc.edu/optiputer/flash/co

nvection.htm

EFFECTS OF PLATE TECTONICS

*There are several geological processes that occur where plates meet (at the plate edges):

1. Volcanoes tend to erupt at plate margins as a result of a process called subduction

2. Earthquakes occur where plates grind against or over one other

3. Mountain building occurs as one plate is pushed over another

4. Seafloor spreading occurs where two oceanic plates pull apart, makes ocean basins

THE 3 TYPES OF PLATE BOUNDARIES

CONVERGENT BOUNDARIES• Convergent Boundaries are the boundaries between

two plates that are converging, or moving towards each other.

• Earthquakes, island formation, mountain forming, and volcanoes all occur as the result of these plate collisions.

• The type of stress at this boundary is “compression”

• When two plates collide (converge) one plate moves under the other.This process is called “subduction.”

• There are three types of convergent boundaries

“Convergent, means to come together.”

TYPES OF CONVERGENT BOUNDARIES

Oceanic/oceanic Subduction occurs

Oceanic/continental Oceanic plate sinks

Continental/continental Mountain ranges form

Let’s look at a few examples:

WHAT CAN HAPPEN AT EACH BOUNDARY?

Convergent

boundary of two

oceanic plates.

Creates an island arc and

a trench.

A trench is like a deep

canyon, but in the ocean.

Example: Japan

Mariana Trench

The most famous trench in the world:

Oceanic plate and

a continental plate.

Forms a volcanic

mountain range and

a trench.

Example: Andes Mts

Continental-Continental

Convergent Boundary

The convergent

boundary of the Eurasian

and Indian Plates has

resulted in the formation

of the highest mountain

range in the world – The

Himalayas

This illustration shows

the movement of the

land mass known as

India today. As it moved

on the Indian plate through

time, over millions of years,

it finally collided with the

Eurasian plate forming the

Himalayan Mountains

Mount Everest is the tallest mountain in the

world, at over 29,000 ft. and is part of the

Himalayas. This is a result of the Eurasian

and Indian Plates colliding and it is still

getting higher as these two plates continue

to collide.

DIVERGENT BOUNDARIES

• Divergent Boundaries are the boundaries between two plates that are diverging, or moving away from each other.

• The type of stress is “tension”

“Divergent, means to spread apart.”

When plates are spreading apart from one another there is a lot

of geological activity. Earthquakes and volcanoes occur here.

•In some places like in East Africa, a rift valley can form that is

hundreds of feet deep.

Aerial view of Africa’s Rift Valley

The Mid-Atlantic Ridge is one of the

world’s largest divergent plates,

running North to South in just about

the center of the Atlantic Ocean.

All along this ridge, volcanic activity

takes place and the sea floor is

spreading East and West at a rate of

1.25 cm per year.

Question: So what is happening on the

other side of that same plate?

Divergent Boundary Between the

Eurasian and North American Plate

TRANSFORM FAULT BOUNDARIES

• Transform Boundaries are the boundaries between two plates that are sliding horizontally past one another.

• The types of stress is “shear-stress”

“Transform, means to slide

past one another.”

PLATES MOVE SIDE BY SIDE

• Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.

Earthquakes in Austin

There is a transform-fault boundary where the North American and Pacific

plates are moving past each other.

Example: San Andreas fault in California

Strike Slip Faults

The San Andreas Fault, seen

here, is the result of the Pacific

Plate sliding past the North

American Plate. This is the site

of many of the earthquakes that

occur in the United States

• Plate movement can alter Earth systems and produce changes in Earth’s surface

• Deformation of the crust

• Faults

• Mountain building

• Land subsidence

• Volcanoes

CHANGING EARTH’S SURFACE

• A volcano is a weak spot in the crust where molten, rock-forming magma comes to the surface

• Volcanic activity builds mountains made of lava rock and other volcanic materials

VOLCANOES

• There are more than 600 active volcanoes on land and many more beneath the sea

• Volcanic belts form along the boundaries of Earth’s plates.

• One major volcanic belt is the Ring of Fire

LOCATION OF VOLCANOES

Ring of Fire – very active region of subduction

RING OF FIRE

http://www.volcano.si.edu/players.cfm?pid=2

RECENT EARTHQUAKES AND VOLCANIC ERUPTIONS

• All seismic activity occurs along plate boundaries (except for hotspots)

• Magma rises through the mantle forming an active volcano

• The plate moves over

this spot forming a

chain of islands with

the active volcano

being the one over

the hot spot

WHAT ARE HOT SPOTS?

Hot Spot Volcanoes

HOW IT WORKS

EARTH’S INTERIOR G.O.

• Get a computer and begin working on the web-quest.

• Follow the questions and it will lead you through the online activities.

• This is due –

Wed. March 23 (but you could get it done in class - today!!)

WEB-QUEST!