Inside EarthInside EarthContinental DriftContinental Drift

Sea Floor SpreadingSea Floor SpreadingPlate TectonicsPlate Tectonics

The Earth’s LayersThe Earth’s LayersThe Earth is made of many different and distinct layers. The The Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the hotter, denser and under much greater pressure than the outer layers. outer layers.

Natural forces interact with and affect the earth’s crust, Natural forces interact with and affect the earth’s crust, creating the landforms, or natural features, found on the creating the landforms, or natural features, found on the surface of the earth. surface of the earth.

Before we start to look at the forces that contribute Before we start to look at the forces that contribute to landforms,lets look at the different layers of to landforms,lets look at the different layers of the earth that play a vital role in the formation of the earth that play a vital role in the formation of our continents, mountains, volcanoes, etc.our continents, mountains, volcanoes, etc.

Crust

Mantle

Outer Core

Inner Core

CrustCrust

crust - the rigid, rocky outer surface of the Earth, The The crustcrust is composed of two rocks. The is composed of two rocks. The continental continental crustcrust is mostly is mostly granitegranite. The . The oceanic crustoceanic crust is is basaltbasalt. . Basalt is much denser than the granite. Because of Basalt is much denser than the granite. Because of this the less dense continents ride on the denser this the less dense continents ride on the denser oceanic plates. oceanic plates.

The CrustThe Crust The Earth's The Earth's CrustCrust is like is like the skin of an apple. It is the skin of an apple. It is very thin in comparison to very thin in comparison to the other three layers. the other three layers. The crust is only about 3-The crust is only about 3-5 miles (8 kilometers) 5 miles (8 kilometers) thick under the oceans thick under the oceans ((oceanic crustoceanic crust) and ) and about 25 miles (32 about 25 miles (32 kilometers) thick under kilometers) thick under the continents the continents ((continental crustcontinental crust).).

The The LithosphericLithospheric Plates Plates

The The crustcrust of the Earth of the Earth is broken into many is broken into many pieces called pieces called platesplates. . The plates "float" on The plates "float" on the soft, semi-rigid the soft, semi-rigid asthenosphereasthenosphere..

The LithosphereThe LithosphereThe The crust and the upper layer of the mantlecrust and the upper layer of the mantle

together make up a zone of rigid, brittle rock together make up a zone of rigid, brittle rock called the called the LithosphereLithosphere..

The MantleThe Mantle

The The MantleMantle is the is the largest layer of the Earth. largest layer of the Earth.

The The middle mantlemiddle mantle is is composed of very hot composed of very hot dense rock that flows like dense rock that flows like asphalt under a heavy asphalt under a heavy weight. The movement of weight. The movement of the middle mantle the middle mantle ((asthenosphereasthenosphere) is the ) is the reason that the crustal reason that the crustal plates of the Earth move.plates of the Earth move.

The Mantle CompositionThe Mantle Composition

mantle - a rocky layer located under the crust - it is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium.

Convection CurrentsConvection CurrentsThe middle mantle The middle mantle

"flows" because of "flows" because of convection currents. convection currents. Convection currentsConvection currents are caused by the are caused by the very hot material at very hot material at the deepest part of the deepest part of the mantle rising, then the mantle rising, then cooling and sinking cooling and sinking again --repeating this again --repeating this cycle over and over. cycle over and over.

The Outer CoreThe Outer CoreThe core of the Earth The core of the Earth is like a ball of very is like a ball of very hot metals. hot metals.

The The outer coreouter core is is so hot that the metals so hot that the metals in it are all in the in it are all in the liquid state. The outer liquid state. The outer core is composed of core is composed of the melted metals of the melted metals of nickel and ironnickel and iron..

The Inner CoreThe Inner Core

The The inner coreinner core of the of the Earth has temperatures Earth has temperatures and pressures so great and pressures so great that the metals are that the metals are squeezed together and squeezed together and are not able to move are not able to move about like a liquid, but about like a liquid, but are forced to vibrate in are forced to vibrate in place like a place like a solidsolid. .

DID YOU KNOW?DID YOU KNOW?

Land and WaterLand and WaterPhotographs of the earth taken from space Photographs of the earth taken from space show clearly that it is truly a ”watery show clearly that it is truly a ”watery planet.” planet.” More than 70 percent of the earth’s More than 70 percent of the earth’s surface is covered by water, mainly the surface is covered by water, mainly the salt water of oceans and seas.salt water of oceans and seas.

Continental Drift Continental Drift

and and

Seafloor SpreadingSeafloor Spreading

Continental Drift TheoryContinental Drift TheoryIn the early 1900s a German explorer and scientist In the early 1900s a German explorer and scientist (Alfred Wegener) proposed the continental drift (Alfred Wegener) proposed the continental drift theory. theory. He proposed that there was once a single “super He proposed that there was once a single “super continent” called Pangaea. continent” called Pangaea. He believed that the continent floated on the He believed that the continent floated on the oceanic crust (like an iceberg in the ocean).oceanic crust (like an iceberg in the ocean).Most scientist rejected his theory due to lack of Most scientist rejected his theory due to lack of evidence. evidence.

Evidence of continental driftEvidence of continental drift

Continents fit together like a jigsaw puzzleContinents fit together like a jigsaw puzzleFossils match across oceansFossils match across oceansRock types and mountain ranges match Rock types and mountain ranges match across oceansacross oceansClimate Evidence (Glacial Deposits)Climate Evidence (Glacial Deposits)

““Puzzle Pieces”Puzzle Pieces”

Continents look like Continents look like they could be part of they could be part of a giant jigsaw puzzlea giant jigsaw puzzle

Distribution of FossilsDistribution of Fossils

Plant and animal Plant and animal fossils found on the fossils found on the coastlines of different coastlines of different continents continents

Sequence of RocksSequence of Rocks

Same rock patterns found in South Same rock patterns found in South America, India, Africa, Antarctica and America, India, Africa, Antarctica and AustraliaAustralia

ClimateClimate

Tropical plant remains Tropical plant remains (coal deposits) found (coal deposits) found in Antarcticain AntarcticaGlacial deposits in Glacial deposits in Africa, South Africa, South America, India, and America, India, and Australia during the Australia during the same timesame time

Sea-Floor SpreadingSea-Floor Spreading

Ocean floor moves like a conveyor belt Ocean floor moves like a conveyor belt carrying continents with it. carrying continents with it. New ocean floor forms along cracks in the New ocean floor forms along cracks in the ocean crust as molten material erupts from ocean crust as molten material erupts from the mantle spreading out and pushing the mantle spreading out and pushing older rocks to the sides of the crack. New older rocks to the sides of the crack. New ocean floor is continually added by the ocean floor is continually added by the process of sea-floor spreading. process of sea-floor spreading.

EVIDENCE OF SEA-FLOOR EVIDENCE OF SEA-FLOOR SPREADING……SPREADING……

Sea-Floor SpreadingSea-Floor Spreading1. Evidence from Molten Material – Rocks shaped like pillows (rock pillows) show that molten material has erupted again and again from cracks along the mid-ocean ridge and cooled quickly

Mid-Ocean RidgeMid-Ocean RidgeThe mid-ocean ridge The mid-ocean ridge system is the most system is the most extensive chain of extensive chain of mountains on earth, mountains on earth, but more than 90% of but more than 90% of this mountain range this mountain range lies in the deep lies in the deep ocean. The mid-ocean. The mid-ocean ridge wraps ocean ridge wraps around the globe for around the globe for more than 65,000 km more than 65,000 km like the seam of a like the seam of a baseball. baseball.

Mid-Ocean RidgeMid-Ocean RidgeMid-ocean ridges occur along the kind of plate Mid-ocean ridges occur along the kind of plate boundary where new ocean floor is created as boundary where new ocean floor is created as the plates spread apart. "divergent plate the plates spread apart. "divergent plate boundary." The plates spread apart at rates of 1 boundary." The plates spread apart at rates of 1 cm to 20 cm per year. As oceanic plates move cm to 20 cm per year. As oceanic plates move apart, rock melts and wells up from tens of apart, rock melts and wells up from tens of kilometers deep. Some of the molten rock kilometers deep. Some of the molten rock ascends all the way up to the seafloor, ascends all the way up to the seafloor, producing enormous volcanic eruptions of producing enormous volcanic eruptions of basalt, and building the longest chain of basalt, and building the longest chain of volcanoes in the world! volcanoes in the world!

Sea-Floor SpreadingSea-Floor Spreading2. Evidence from Magnetic Stripes – Rocks that make up the ocean floor lie in a pattern of magnetized stripes which hold a record of the reversals in Earth’s magnetic field

Sea-Floor SpreadingSea-Floor Spreading

Sea-Floor SpreadingSea-Floor Spreading3. Evidence from Drilling Samples – Core samples from the ocean floor show that older rocks are found farther from the ridge; youngest rocks are in the center of the ridge

Sea-Floor SpreadingSea-Floor SpreadingSea-Floor Spreading – Harry Hess in the 1960’s; the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge

Plate TectonicsPlate Tectonics

Most of these changes in the earth’s Most of these changes in the earth’s surface takes place so slowly that they are surface takes place so slowly that they are not immediately noticeable to the human not immediately noticeable to the human eye. eye.

The idea that the earth’s landmasses have The idea that the earth’s landmasses have broken apart, rejoined, and moved to other broken apart, rejoined, and moved to other parts of the globe forms part of the parts of the globe forms part of the – plate tectonic theory.plate tectonic theory.

Plate Tectonic TheoryAlong the mid-ocean ridge the seafloor is pulling apart and the two parts are moving in opposite directions, carrying along the continents and oceans that rest on top of them. These pieces of Earth’s top layer are called tectonic plates. They are moving very slowly, but constantly. (Most plates are moving about as fast as your fingernails are growing -- not very fast!) Currently Earth’s surface layers are divided into nine very large plates and several smaller ones.

According to the theory of plate tectonics, the According to the theory of plate tectonics, the earth’s outer shell is not one solid piece of earth’s outer shell is not one solid piece of rock. Instead the earth’s crust is broken into rock. Instead the earth’s crust is broken into a number of moving plates. The plates vary a number of moving plates. The plates vary in size and thickness.in size and thickness.

These plates are not anchored in place but These plates are not anchored in place but slide over a hot and bendable layer of the slide over a hot and bendable layer of the mantle.mantle.

As mentioned earlier, those tectonic plates are As mentioned earlier, those tectonic plates are always moving. always moving.

– pulling away from each other (Divergent)pulling away from each other (Divergent)– crashing head-on (Convergent)crashing head-on (Convergent)– or sliding past each other. (Transform)or sliding past each other. (Transform)

Divergent BoundariesDivergent Boundaries

Boundary between two plates Boundary between two plates that are moving apart or that are moving apart or riftingrifting

RIFTINGRIFTING causes causes SEAFLOOR SEAFLOOR SPREADINGSPREADING

They’re Pulling Apart!They’re Pulling Apart!

When plates pull away from When plates pull away from one another they form a one another they form a diverging plate boundary, or diverging plate boundary, or spreading zone.spreading zone.

Thingvellir, the spreading zone in Iceland between the North American (left side) and Eurasian (right side) tectonic plates. January 2003.

Features of Divergent Features of Divergent BoundariesBoundaries

Mid-ocean ridgesMid-ocean ridgesrift valleysrift valleysfissure volcanoesfissure volcanoes

Convergent BoundariesConvergent Boundaries

Boundaries between two Boundaries between two plates that are plates that are collidingcolliding

There are 3 types…There are 3 types…

Ocean to Continent Ocean to Continent Ocean plateOcean plate colliding with a less colliding with a less dense dense continental continental plateplateSubduction ZoneSubduction Zone: : where the more where the more dense plate slides dense plate slides under the less under the less dense platedense plateVOLCANOESVOLCANOES occur at occur at subduction subduction zoneszones

Continental/Oceanic Continental/Oceanic Crush Crush

Subduction – Process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle; allows part of the ocean floor to sink back into the mantle

Subduction zoneSubduction zoneDeep-Ocean Trench – Occurs at subduction zones. Deep underwater canyons form where oceanic crust bends downward

Subduction ZoneSubduction Zone

Andes Mountains, Andes Mountains, South AmericaSouth America

Ocean to OceanOcean to Ocean

Ocean plateOcean plate colliding with colliding with another another ocean plateocean plateThe more dense plate slides The more dense plate slides under the less dense plate under the less dense plate creating a creating a subduction zone subduction zone called a called a TRENCHTRENCH

When both are oceanic plates, one slides When both are oceanic plates, one slides under the other. Often an island group under the other. Often an island group forms at this boundary. forms at this boundary.

Converging... They crash!And they’re both ocean plates!

Aleutian Islands, AlaskaAleutian Islands, Alaska

Continent to ContinentContinent to ContinentA A continental platecontinental plate colliding with another colliding with another continental platecontinental plateHave Collision Zones:Have Collision Zones:The plates push The plates push against each other, against each other, creating mountain creating mountain ranges. ranges.

They Crash and are both They Crash and are both continental platescontinental plates!!

Earth’s highest mountain range, the Himalayas, was formed millions Earth’s highest mountain range, the Himalayas, was formed millions of years ago when the Indo-Australian Plate crashed into the of years ago when the Indo-Australian Plate crashed into the Eurasian Plate. Even today, the Indo-Australian Plate continues to Eurasian Plate. Even today, the Indo-Australian Plate continues to push against the Eurasian Plate at a rate of about 5 cm a year!push against the Eurasian Plate at a rate of about 5 cm a year!

Transform Fault BoundariesTransform Fault Boundaries

Boundary between two plates Boundary between two plates that are that are slidingsliding past each other past each otherEARTHQUAKES EARTHQUAKES along along faultsfaults

San Andreas Fault, CASan Andreas Fault, CAFor example: Here, the San Andreas Fault lies on the boundary between two tectonic plates, the north American Plate and the Pacific Plate. The two plates are sliding past each other at a rate of 5 to 6 centimeters each year. This fault frequently plagues California wit hearthquakes. These areas are likely to These areas are likely to have a rift valley, have a rift valley, earthquake, and volcanic earthquake, and volcanic action.action.

All graphics were taken from Google Images, enchanted All graphics were taken from Google Images, enchanted learning, boom zone, and other educational sites.learning, boom zone, and other educational sites.All written information was taken from Prentice Hall, All written information was taken from Prentice Hall, World Geography, PBS.org, and other educational World Geography, PBS.org, and other educational websites.websites.A good website for a deeper understanding is A good website for a deeper understanding is www.observe.arc.nasa.gov/Animations of sea-floor spreading at the mid-oceanic riftsImage: http://www2.nature.nps.gov/geology/usgsnps/animate/pltecan.html