Earth’s Structure

• Earth Science is one of the three main

branches of science.

• Geology, (study of rocks), meteorology,

(study of weather), and vulcanology,

(study of volcanoes), are all types of earth

sciences.

• This unit will cover some of the basics of

many branches of earth science.

What does the Earth look like

inside?

What does the Earth look like

inside?

• No one can say with

100% accuracy what

the Earth looks like

under the crust, but

we can make a few

good guesses.

• Scientists use the vibrations

from earthquakes to predict

earth’s structure because

vibrations travel differently

through solids and liquids.

• The earth is

divided into

four main

layers: the

inner core,

outer core,

mantle, and

crust.

Inner Core Facts: • Composed mostly

of iron (Fe) with a

small amount of

nickel (Ni).

• It is about 750-800

miles thick.

• Its temperature is

estimated to be

between 3000 and

10,000 degrees F!!

More inner core facts • Even though the

core is liquid,

extreme pressure

squeezes it so

much that it can't

move around and

acts like a solid.

Outer Core Facts: • The inner core intense

heat forces the outer core to melt into a liquid.

• Composed primarily of Iron, nickel, sulfur, and oxygen.

• It is believed to be between 1400 and 1500 miles thick.

• Temperature is about 7200 - 9000 ºF

The Mantle: Facts • Most of the Earth's

mass is in the mantle.

• It is composed of iron

(Fe), magnesium (Mg),

aluminum (Al), silicon

(Si)/ oxygen (O)

compounds.

• The temperature range

from 2500 – 5400 0 F.

More Mantle

Facts • The mantle is somewhere between a solid and a liquid phase – usually called “plastic”

• Because of this, heat can travel from the lower mantle to the upper mantle by slowly moving convection currents.

• These currents are responsible for the movement of the crust.

The Crust: Facts • The crust is much thinner than any of the other layers.

• The crust can be broken into two parts: continental crust made up of mostly granite and oceanic crust made of basalt.

• The most common mineral in both is quartz SiO2, Minerals containing Al, Ca, K, Na, (such as the Feldspars) are very common.

• Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes.

Crust and Mantle vs. Lithosphere

and Asthenosphere

• Why do we use two names to describe the same

layer of the Earth? Well, this confusion results

from the different ways scientists study the

Earth.

• Lithosphere, asthenosphere, and mesosphere

(we usually don't discuss this last layer)

represent changes in the mechanical properties

of the Earth. Crust and mantle refer to changes

in the chemical composition of the Earth.

What we need to know:

• The lithosphere lower portion of the crust

which is broken up into the continental and

oceanic plates.

• The asthenosphere is the upper portion of

the mantle that is weak and easily

deformed. The convection currents here

cause the plates to move.

Turn Around

The ground is Moving!!

• In the 1960s geologists began to uncover

proof that the continents travel, or drift,

around Earth.

• If you take a good look at a World map,

you can see that the continents "fit into"

one another.

• Today, scientists know that continents are

moving a few centimeters every year.

• Earth has many geologic mysteries that

befuddled scientists.

• One example is the fact the rocks of the exact

same chemical makeup are found on different

continents.

• Another is that there are fossils of fish at the

top of Mt. Everest….and fish rarely climb

mountains.

• Most geologists came up with many ideas as

to why things like these occurred…some

unusual and some crazy.

Almost there!!

History of Plate

Tectonics • The theory was first advanced

by Alfred Wegener.

• It said that Earth's continents

were originally one land mass.

Pieces of the land mass split off

into separate ‘plates’ and

migrated to form the continents.

• This theory is known as the

Continental Drift Theory.

What are plates? • As we said, the crust is

made up of a thin layer

of solid rock.

• This rock is cracked like

a broken egg shell. Each

broken shell is called a

plate.

• There are 13 major

plates and some smaller

ones.

Another View

Wegener’s

Proof:

• The first proof is the most

obvious: The continents look

like puzzle pieces that fit

together.

• The second proof came from the

rocks themselves. He showed

how the types and layers of

rocks on the west coast of Africa

chemically matched those on the

east coast of South America.

So, how did Wegener finally prove

this theory?

• In addition to the second proof, the chemical composition of coal beds in Europe and North America also matched.

• A third proof was that fossils of the extinct reptile mesosaurus were found on both South America and Africa. A similar fossil connection exists between Africa and Australia.

• A fourth proof also involved fossils – of plants. A fossilized plant is found on South America, Australia, Africa, India, and Antarctica. This indicates that these areas were connected and all had a similar climate.

• Although these arguments are convincing, Wegener lacked a way for moving the continents. This theory was not proved until the discovery of the mid-Atlantic ridge in the 1950’s.

Let’s reverse time for a minute:

• The next slide begins with view of Earth

with continents in their present positions,

2) continents move back in time to reunite

as Pangaea, 3) Pangaea label appears, 4)

Locations of stratigraphic and fossil

evidence that Wegener used to argue in

favor of continental drift is added.

Moving forward….

• Let’s move forward again with this rock

evidence highlighted now.

• The

birth of

North

America

What makes the continents move?

What causes

plates to

move?

• The answer is both simple and complex.

• Simple answer: Convection Currents in the mantle cause the plates above to move.

• The semi-molten rock in the mantle acts like a viscous liquid. It has currents and flows just like any other liquid. When liquids heat up, convection currents form.

• As the magma is heated by the core it rises. This forces the cooler rock at the top to sink. (Convection!!)

• The rock moves like the conveyor belt at a Walmart checkout line. This causes the plates on top of the mantle to move just like your purchases move toward the cashier.

• The plates on top of these currents

being moved along in the direction of

the current.

•

What causes plates to move?

A convection current.

The hot orange/yellow magma rises toward

the surface and the cooler rock in blue

sinks toward the bottom.

Convection currents

• When the continents and plates move, its called

CONTINENTAL DRIFT. (or plate tectonics!)

• Over the billions of years that earth has existed,

the plates have been in constant motion.

• In the past Earth’s continents have looked quite

different from how they look today.

Watch the position of Southern California

from 550 million years ago to the present.

About 240 million years ago, there was only a single Mega-Continent,

called Pangaea.

The earliest types of dinosaurs roamed the earth at this time.

About 160 million years ago, Pangaea split into two parts, Laurasia and

Gondwanaland.

About 140 million years ago, India separated from Gondwanaland and

stated moving northwards.

As we see today, all the continents fit into each other. They have

achieved this state after millions of years of movement.

One possible view of earth 120 million years from

now.

• Another

view

250

million

years

from

now.

Earth at the time that the dinosaurs died

65 million years ago.

Plate Boundaries

• The point at which two plates meet is called a plate boundary.

• There are 3 types: Divergent, Convergent, and Transform.

Divergent boundaries:

• Divergent boundaries form where two plates are spreading apart from each other.

• When the plates move apart, they leave a space between them. This space becomes filled with magma that rises up from the mantle.

• The mid-ocean ridges are areas in which this sea floor spreading takes place.

A divergent boundary

For more on the Mid-oceanic ridge, see

the ‘volcanoes’ portion of this presentation

The Mid-Atlantic Ridge

Convection currents at divergence

zones

• Bridge between continents in Reykjanes peninsula, southwest Iceland across the Alfagja rift valley, the boundary of the Eurasian and North American continental tectonic plates.

Landforms associated with

Divergent Zones • Rift

Valleys

• Mid

Atlantic

Ridge

Convergent boundaries

• When two plates push into each

other the place where they meet

is called a convergent

boundary.

• Convergent Boundaries are

broken into three types: Oceanic-Continental,

Oceanic-Oceanic,

Continental-Continental.

Convergent #1 Oceanic-Continental &

Oceanic-Oceanic

• When an oceanic plate meets another oceanic

plate or it meets a continental plate, a

subduction zone is formed. Subduction is when

the denser plate, (oceanic plate), gets forced

underneath the less dense plate, (continental

plate).

• The friction caused by the plates moving past

each other causes the rock to melt into magma.

This causes volcanoes to form.

A subduction zone

Landforms found at Subduction Zones #1

Deep Underwater Trenches

• When two oceanic plates meet,

a trench forms where the thicker

plate plunges beneath the

thinner one.

• The great pressure at the

colliding plates causes

earthquakes. These open up

cracks to the hot, molten magma

so it can push through making

volcanoes.

Landforms found at Subduction Zones (2):

Volcanic Island Arcs.

• These volcanoes surround the

Pacific ocean and are known as

the Ring of Fire.

• Examples: the Aleutians in Alaska,

the Kuriles, Japan, and the

Philippines.

• Japan is formed by volcanoes marking the

junction of three plates.

Subduction

zones have

powerful

volcanoes and

usually have

many

earthquakes.

Convergence # 2

Continental Collisions • When two continental plates

converge, they buckle and thicken and usually move upwards.

• Think of two cars in a head-on collision. When they hit, both fronts of the cars are usually crushed upwards.

• When continental plates collide, mountains are made!

The Appalachian Mountains were formed when

Europe collided with the N. American plate.

Mt. Washington, NH.

Landforms associated with

continental collisions:

• Folded Mountains such as the Himalayas

with Mt. Everest

Transform Boundaries

• Transform boundaries form when two plates slide against each other horizontally.

• These areas experience frequent earthquakes when the pressure builds up enough for the plates to move.

Landforms associated with

transform boundaries:

• The San Andreas

Fault in California.

• EARTHQUAKES

ARE NOT

LANDFORMS!

A transform boundary

The San Andreas Fault

These fences

used to be

connected.

They were built

across a fault

line.

Same fence from another point of view.

This road

was built

across a

fault line.

Oops!

A speed bump broken by moving

plates.

Sometimes, the plates move up or down as

they slide past each other.

Mountains made by stretching or

compressing • As a plate is streched due to the movement of divergent and

convergent zones, cracks or faults appear in the surface rock.

• Normal faults are caused by horizontal tension. Part of the crust is uplifted, and part of it moves downward. This happens at the line where the rock is broken, called the fault plane. In an area where there are many faults, mountain ranges can form. These mountains are called fault-block mountains. Fault-block mountains often occur where plates are moving apart. The movement causes the rocks to be stretched. Temperatures are low and the rocks are brittle. Instead of folding, they break into large blocks.

• Tilted blocks are common in the Basin and Range region of the western United States. Level blocks lead to the horst and graben terrain seen in northern Europe. Fault block mountains commonly accompany rifting and are indicators of tensional tectonic forces.

• Block Mountains can also be referred to as a horst. It is a steep-sided mountain, formed where a block of the earth's crust has been squeezed upward between two parallel fault lines. Two types of block mountains are lifted and tilted. Lifted type block mountains have two steep sides exposing both sides scarps. Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp.

• Two examples of fault block mountains that are forming today are the Andes and Sierra Nevada mountain ranges.

Mountains made by stretching or

compressing

• As the plate is stretched, it cracks allowing

portions to slide downward.

A fault visible in the rock

Mixed Boundaries

• Mixed Boundaries

• Mixed plate boundaries tend to occur

where the margins and relative motions of

the two plates involved fail to align neatly.

• In California, the Pacific-North American

boundary is mixed.

Summary of what you need to

know:

• Earth Structure: – 4 parts: Inner core, Outer Core, Mantle, Crust

• Know facts about each layer

• Plate Tectonics: – Wegener and his evidence.

– Convection currents in the mantle are the driving force.

• Plate Boundaries: – 3 boundaries: Convergent, Divergent, Transform

– Facts about each and landforms associated with them.