Learning ObjectivesLearning Objectives

• Students will understand the basic structure of the earth

– The solid Earth is composed of a relatively thin crust, a dense metallic core, and a layer called the mantle between the crust and core that is very hot and partially melted. (6-8 ES2E).

– The crust is composed of huge crustal plates on the scale of continents and oceans, which move centimeters per year, pushed by convection in the upper mantle, causing earthquakes, volcanoes, and mountains. (6-8 ES2F).

Looking at the world map, Looking at the world map, what do you notice about the what do you notice about the

shape of the continents?shape of the continents?

Jot down your ideas on your paper…

The thing is…the world didn’t The thing is…the world didn’t always look like this! It used to always look like this! It used to

look like this:look like this:

How is this possible?!?!?How is this possible?!?!?

Geological Changes—3:25

The lithosphere is divided into a number of large and small plates and the plates are floating on the mantle

Plate Tectonics TheoryPlate Tectonics Theory

Lithosphere = the Earth’s crust plus the upper portion of the mantle layer

Earth’s Structure by Brainpop

Plate BoundariesPlate Boundaries

Divergent boundary: Divergent boundary: o Plates are moving away from

each othero Midocean ridges are created

and new ocean floor plates are created

Plate BoundariesPlate Boundaries

Divergent boundary: Divergent boundary:

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

Convergent BoundaryConvergent Boundary: plates are moving toward each other and are colliding (3 types)

• Create subduction zones,

• Trenches• Create near Create near

coast coast volcanoesvolcanoes

When Ocean Plates collide with When Ocean Plates collide with Continental PlatesContinental Plates

• Benioff shear zones (a pattern of earthquakes as an ocean plate grinds down the underneath side of a

continent)

When Ocean Plates collide with When Ocean Plates collide with Continental PlatesContinental Plates

When ocean plates collide with When ocean plates collide with other ocean platesother ocean plates

Island arcs are created (a pattern of volcanic islands created from a subduction zone that is located off the coast)

What About Hawaii?What About Hawaii?

• Do you see any plate boundaries there??

Hawaii

What About Hawaii?What About Hawaii?

• Hawaiian Volcanoes form from HOT HOT SPOTSSPOTS

• (places where (places where the mantle is the mantle is hotter than hotter than others…we’re others…we’re not sure why)not sure why)

• MountainMountain rangesranges are created

• (example: Himalayan Mountains)

When a continental plate collides When a continental plate collides with another continental platewith another continental plate

Himalayan MountainsHimalayan Mountains

Mountains 2:46

Transform Fault BoundaryTransform Fault Boundary

Plates are neither moving toward nor away from each other, they are moving past one another.

Transform Fault BoundaryTransform Fault Boundary

The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas FaultSan Andreas Fault)

San Andreas FaultSan Andreas Fault

NOTE: o Plates are destroyed as fast as

they are created (2 ways)

o Plates may be subducted and melted or may push be pushed upward to form mountains

Why is Earth not getting bigger Why is Earth not getting bigger or smaller?or smaller?

Boundaries Between Tectonic Plates—1:23

How can Oreos model the plate boundaries?How can Oreos model the plate boundaries?

Very carefully, take just the top cookie off the Oreo.

Break the top cookie into 2 equal halves.Replace the cookie halves back on the OreoUsing the cookie, Demonstrate a transformtransform fault boundaryDemonstrate a divergentdivergent plate boundaryDemonstrate a convergentconvergent plate boundary

Learning ObjectivesLearning Objectives

• Students will understand that the surface of Earth changes over millions of years.– Our understanding of Earth history is based on the assumption

that processes we see today are similar to those that occurred in the past. (6-8 ES3A)

– Thousands of layers of sedimentary rock provide evidence that allows us to determine the age of Earth’s changing surface and to estimate the age of fossils found in the rocks. (6-8 ES3B)

– In most locations sedimentary rocks are in horizontal formations with the oldest layers on the bottom. However, in some locations, rock layers are folded, tipped, or even inverted, providing evidence of geologic events in the distant past. (6-8 ES3C)

Seafloor Spreading Theory:

• Ocean floors are moving like broad conveyor belts

• New ocean floor crust is being created at the midocean ridges

Convection currents within the mantle

The up-welling leg of the current creates a divergent boundary which produces midocean ridges

What causes this?What causes this?

Convection CurrentsConvection Currents

Convection Current Demo

The down-welling leg of the current creates one type of convergent boundary that results in trenches and a subduction zone

o Midocean ridges are warmer than surrounding ocean floors

o Active volcanoes on ridges, earthquakes on ridges

o Midocean ridge rocks are younger than surrounding ocean floor rocks

o Midocean ridge volcanoes are younger than volcanoes further away

What evidence do we have to What evidence do we have to support this idea?support this idea?

o Ocean floor sediments are THINNER on the ridges and get THICKERTHICKER as the distance from the ridges increase

o Polar reversal magnetismPolar reversal magnetism proves that the ocean floor is moving away from the ridges

What evidence do we have to What evidence do we have to support this idea?support this idea?

Polar Reversal MagnetismPolar Reversal Magnetism

Magnetic Poles Magnetic Field Reversals—2:54

Atlantic Ocean – 2-3 2-3 cm/year

South Pacific Ocean – 15-1815-18 cm/year

Speed of SpreadingSpeed of Spreading

The Seafloor is Spreading Clip—4:01

How Earth’s Structure Affects Plate Tectonics—5:43

Seafloor SpreadingSeafloor Spreading

Distribution of Volcanoes & EarthquakesDistribution of Volcanoes & Earthquakes

The continents have shifted their position over geologic time…

Continental Drift TheoryContinental Drift Theory

…And at one time all land masses were connected into one piece called Pangaea

Continental Drift Theory 3—2:21

o Pangaea began to split apart 200 million years ago

o DiagramNorth America

Laurasia GreenlandEurasiaEurasia

PangaeaAfricaWest G. S.America

GondwanalandAntarctica

East G. AustraliaIndia

Pangaea—A History of the Continents: 2:23

USGS Plate Motions Clip

o The continents are like packages on the seafloor conveyor belt

ContinentsContinents

o High percentage fit of continents at the 500 fathom level

EvidenceEvidence

o Minerals, fossils, and mountains on now different continents match if the continents were together

EvidenceEvidence

The Mystery of Brachiosaurus (~3 min)

o Glaciation patterns indicate a common ice cap at the South Pole

EvidenceEvidence

o PaleomagnetismPaleomagnetism (magnetism of old rocks) indicate a common pole if the continents were all connected

EvidenceEvidence

Bill Nye’s Great 100: Plate Tectonics 2 –4:22

Plate Tectonics by Brainpop

1) What can be found underneath Earth’s plates?

2) What kind of boundary involves two plates moving toward each other?

3) What process can explain why we see fossils of the same prehistoric animals on DIFFERENT continents?

Pacific Ring of FirePacific Ring of Fire