The Changing Face of the Planet

Earth’s InteriorInformation gathered about the interior comes from complex instruments and earthquakes

Earthquakes produce shock waves that travel through the Earth

Changes occur in the movement of these seismic waves due to differences in the structure and makeup of the Earth’s interior

Scientist have determined what the interior looks like by monitoring the path and speed of seismic waves

The Earth’s Core The Earth’s core is

subdivided into two layers, an inner and an outer core

Both layers of the Earth’s core are composed of the elements iron and nickel

The Inner CoreInner Core-The solid, innermost layer of the Earth

Temperatures reach 5000° C Radius is about 1300 Km Intense pressure causes the particles of iron and

nickel to remain solid The presence of a solid iron in the core may explain the existence of magnetic fields around the Earth

The Outer Core

Outer Core- Layer of the Earth surroundingthe inner core

Temperatures range from 2200°C to 5000°C About 2250 Km thick High temperatures keep the iron and nickel in the

outer core molten

The Earth’s Mantle

Mantle- The layer of Earth directly above the outer core Extends to a depth of about 2900 Km below the surface Contains about 80% of the volume of the Earth and 68%

of its mass Made mostly of the elements silicon, oxygen, iron, and

magnesium Density increases with depth Temperatures range from 870°C to 2200°C Rock in the mantle can flow like a thick liquid (Has

plasticity)

The Earth’s Crust

The crust is the Earth’s outermost layer Made up of three types of solid rock Thickness of the crust varies with type

Oceanic crust (makes up the ocean floor) is less than 10 Km thick

Continental crust (makes up the landmasses) has an average thickness of about 32 Km

Other Divisions of the Earth’s Interior Mohorovicic discontinuity

(Moho)- Boundary separating the crust from the mantle

Lithosphere- Topmost solid part of the Earth Composed of the crust and part

of the upper mantle Broken into large sections called

plates Asthenosphere-

Layer of Earth directly beneath the lithosphere

Located near the upper edge of the mantle

A hot weak zone, capable of gradual flow

The Earth’s Changing Interior It is believed that the Earth was not originally layered, the

divisions we see today formed slowly over time Shortly after the Earth was formed, the decay of radioactive

elements, along with heat released by colliding particles, produced melting in the planet’s interior

Melting allowed the heavier elements (iron & nickel) to sink toward the center, while lighter, rocky components floated upward

Still occurs today on a smaller scale

Plate Tectonics Theory which links the concepts of Continental

Drift and Sea-floor Spreading to explain how the Earth has evolved over time

Helps to explain the formation, movements, collisions, and destruction of Earth’s outer layers

Helps people understand the geologic past and predict its future

Evidence for Plate Tectonics

Continental Drift

Volcano and Earthquake Belts

Sea-floor Spreading

Paleomagnetism

Continental Drift Proposed in 1912 by

Alfred Wegner States that the continents

were once joined together as a super-continent called Pangaea and have since drifted apart

Evidence for Continental Drift Shape of the continents Similar fossil deposits on

continents thought to have been joined

Rock formations that end at the edges of continents

Glacial deposits Distinctive rock types

Location of the world’s volcano & earthquake belts

Lie along plate boundaries (places where one plate moves relative to another)

Caused by stresses that build up along the boundaries As stresses become too great, fractures form and earthquakes occur Fractures allow magma from the asthenosphere to reach the surface, forming volcanoes Most of the world’s volcanoes are located along the outer edge of the Pacific Plate (the ‘Ring of Fire’)

Sea-floor Spreading Sea-floor spreading- Process in

which old ocean floor is pushed away from a mid-ocean ridge by the formation of new ocean floor

Occurs at divergent boundaries (also called spreading centers) Younger rocks are found closer to the

spreading center The further you go from the spreading

center, the older the rocks become The same pattern of rocks are found

on both sides of the center

Paleomagnetism Paleomagnetism- Study of the

alignment of magnetic particles in ancient rocks

Provides proof for sea-floor spreading and a means of determining how the continents have moved

When magma cools, grains of iron line up with the magnetic pole (like little compasses)

Polarity reversals occur in parallel bands on opposite sides of the mid-ocean ridges

During the past 4 million years, the magnetic poles have reversed themselves 9 times

Theory of Plate Tectonics States that the topmost solid

part of the Earth is divided into rigid plates that move resulting in earthquakes, volcanoes, mountains, and the redistribution of landmasses

Lithospheric plates are made of a thin layer of crust above a thick layer of rigid mantle rock

Usually contain both oceanic and continental crust

Seven major plates, each named after its surface features

Plates move at different speeds and in different directions

Earth’s Tectonic Plates

Plate BoundariesThere are three basic types of plate boundaries

Divergent- moving apart Convergent- moving together Transform fault- sliding past each other

Divergent Boundaries Plates move apart (diverge) Also called spreading

centers or constructive boundaries

New rocks are formed as older rocks are pushed aside (Lithosphere is created)

Examples: Mid-Atlantic Ridge, East Pacific Rise, and the Great Rift Valley in Africa

Convergent Boundaries Occur where two

plates move towards each other

Also called destructive boundaries Lithosphere is

destroyed There are three types

Types of Convergent BoundariesConvergent boundary where two continental plates collide

Forms a single larger continent (India & Asia)

Causes the lithosphere at the boundary to be pushed up, forming a mountain range

Ex.: Himalayas, Urals, & Appalachian Mtns.

Types of Convergent BoundariesConvergent boundary where two oceanic plates collide

One plate subducts (goes under) the other plate Also called a subduction zone Forms a chain of volcanic islands on the overriding plate

and a deep sea trench Ex.: The Mariana Islands and the Mariana Trench are formed where the Pacific Plate subducts under the Philippine Plate

Types of Convergent BoundariesConvergent boundary where an oceanic and a continental plate collides

The oceanic plate subducts under the continental plate Forms a chain of volcanic mountains on the continental

plate and a deep sea trench Ex.: Along the west coast of South America, the Nazca Plate subducts under the South American Plate, forming the Andes Mtns. And the Peru-Chile Trench

Transform Fault Boundaries Also known as strike-slip or sliding boundaries Plates grind together as they try to slip past each other horizontally

causing stress to build up Earthquakes occur when the stress is released Examples:

The San Andreas Fault in California, is a result of the North American Plate and the Pacific Plate trying to slide past each other Transform fault boundaries connect portions of the mid-ocean ridge system that are moving at different rates

Why the Plates Move Convection currents within the asthenosphere are

thought to be the driving force behind plate movement Convection current- the movement of material caused

by differences in temperature Hot magma rises to the surface, pushing the older rocks

aside and driving the plates apart (occurs at divergent boundaries)

Cooler, denser currents sink back into the mantle, pushing the plates together (occurs at convergent boundaries)

Earthquakes Earthquakes- Shaking and trembling that results from the

sudden movement of part of the Earth’s crust The most common cause is faulting

When part of the crust is pushed together or pulled apart Occur when the stress along a fault overcomes the force of

friction and releases stored energy Can also be triggered by volcanic eruptions, collapse of

caverns, and meteor impacts

Where Earthquakes Occur Most earthquakes occur at plate boundaries Focus- Point beneath the Earth’s surface where

the rock breaks and moves Depth of the focus depends on where it occurs Earthquakes at divergent boundaries are shallower than

those that occur at subduction zones Epicenter- Point on the Earth’s surface directly above the focus

Seismic WavesSeismic waves- Shock waves produced

by earthquakes ( 3 types) Primary Waves (P Waves) Secondary Waves (S Waves) Surface Waves (L Waves)

Primary WavesPrimary waves (P waves)- Push–pull seismic waves that can travel through solids, liquids, & gasses Travels from the focus by compressing and expanding the material it passes through Fastest of the earthquake waves

Secondary Waves Secondary waves (S waves)- Side-to-side

moving earthquake waves which can travel through solids but not liquids or gasses Rock particles move at right angles to the direction of the wave Travels through the interior from the focus Slower than P waves, but faster than L waves

Surface WavesSurface waves (L waves)- Up-and-down earthquake waves Move along the Earth’s surface like waves travel

in the ocean Originate at the epicenter Bend and twist the Earth’s surface, causing most of the damage during an earthquake

Locating Earthquakes Seismographs- (Instruments used to detect and measure seismic waves) are used to locate earthquakes Data about each type of seismic wave is taken from the

seismograph and plotted on a time-travel graph The epicenter is located by taking the distances from

three different reporting stations and finding the point where they intersect (also called triangulation)

The depth of the focus is determined by measuring the lag time of the L waves

Measuring an Earthquake Seismographs are used to measure the strength,

or magnitude, of an earthquake Magnitude is determined by measuring the

amplitude (height) of the largest wave recorded by a seismograph

The Richter Scale measures the strength of an earthquake

The Mercalli Intensity Scale measures the damage done to various structures by an earthquake

The Richter Scale Used to describe the magnitude or strength of an

earthquake Measures the amount of energy released Each number on the scale indicates an

earthquake that is ten times stronger than the next lower number A magnitude 5.0 earthquake is ten times stronger than a

4.0 quake Major earthquakes have magnitudes of 7.0 or higher

The Mercalli Intensity Scale Measures the intensity of an earthquake Measures the damage done to different

types of structures Identifies what someone might experience

(see, hear, or feel) during the earthquake Scale ranges from I to XII, where I is hardly

felt and XII indicates total destruction

Earthquake Damage The amount of damage mostly depends on the earthquake’s

magnitude and its proximity to populated areas Other factors that determine the amount of destruction

include: Duration of the quake Time at which the earthquake occurs Types of buildings Material on which structures are built Fire caused by broken gas mains Broken waterlines hampering firefighters Tsunamis along coastal areas

Volcanoes Volcano- Place in the

Earth’s surface through which molten rock and other materials reach the surface

Parts of a volcano Crater- Depression at the summit of a volcanic cone Magma chamber- Large reservoir of magma below the Earth’s crust Vent- Opening from which volcanic material is ejected

Volcanism Releases Magma Magma- Melted rock below Earth’s surface Magma forms where temperatures are high

enough to melt rock Asthenosphere Plate boundaries

Magma rises to the surface because it is less dense than the surrounding material

The rate at which magma flows is determined primarily by its silica content

Two Types of Magma Felsic Magma

Also called granitic magma

High silica content Viscous or thick Slow moving Contains a lot of water Creates explosive

volcanic eruptions

Mafic Magma Also called basaltic

magma Low silica content Less viscous or thin Flows easily Contains very little water Produces quiet volcanic

eruptions

Gases in Magma Magma contains dissolved gases that are

released during an eruption Gases are primarily water vapor, carbon

dioxide, and sulfur Magmas containing higher amounts of

dissolved gases produce more explosive eruptions than those with smaller amounts

Temperature of Magma Magma ranges in temperature from about

1000°C to 1200°C The hotter the magma, the easier it flows Hotter magmas trap less gas Hotter magmas are associated with quieter

eruptions

Lava Lava- Magma that reaches the surface

Two types: AA Pahoehoe

How lava differs from magma Composition is slightly different Some gases have escaped New material is often added when the magma comes in

contact with other rock Temperature is lower

Volcanic Eruptions Three factors determine the nature of a

volcanic eruption1. Composition of the magma2. Temperature of the magma3. Amount of dissolved gases

Different types of eruptions form different types of volcanoes

Three Main Types of Volcanoes Shield Volcanoes

Cinder Cones

Composite Volcanoes

Shield Volcanoes Large, gently sloping dome-shaped volcanic

mountains Made from fluid, basaltic lava (mafic magma) Produced by quiet eruptions Formed at “hot spots” Example: Mauna Loa (Hawaiian volcano)

Cinder Cones Small, steep-sided volcanoes Produced by violent, pyroclastic ejections of

material from a central vent Made of cinders and other rock particles (felsic

magma) Usually occur in groups Found along convergent boundaries Example: Paricutin, Mexico

Composite Volcanoes Large, steep-sided, cone-shaped volcanic

mountains Built of alternating layers of rock particles

(pyroclastic material) and fluid lava Produced by very violent eruptions Found along convergent boundaries Example: Mt. St. Helens

Where Volcanic Activity Occurs Divergent boundaries- produces rift zone

eruptions Convergent boundary- creates subduction

zone eruptions At hot spots, in the middle of lithospheric

plates- produces hot spot eruptions

Rift Eruptions Occur along narrow fractures in the crust (usually

along divergent boundaries) Mid-Atlantic Ridge East African Ridge

Magma wells up to fill the gap as the crust splits Eruptions are typically quiet

Magma is basaltic Magma contains little gas

Subduction Boundary Eruptions Occur at convergent boundaries where one

plate is driven below another Magma tends to be thick (viscous) and contain

large amounts of dissolved gas Eruptions are usually explosive Form steep-sided volcanoes (cinder cones or

composite) Most volcanoes occur at subduction boundaries

(the “ring of fire”)

Hot Spots Areas of volcanic activity which occur in the middle of

plates (also called intraplate volcanism) Form volcanoes with broad, gently sloping sides (shield

volcanoes) Magma is thin and flows easily, similar to that of rift

eruptions Produces quiet eruptions Thought to be caused by hot plumes of magma rising from deep within the Earth Example: The Hawaiian Islands