Earth's structure & plate tectonics

Plate TectonicsMr. Kozak

Continental Drift

Earth’s Layers

PlateTectonics Earthquakes

Volcanoes

Alfred Wegener

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Continental Drift

Evidence for

Continental Drift

Continental

Drift

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Alfred Wegen

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•Alfred Wegener was a German scientist who proposed a theory to explain changes in Earth’s surface over time…this theory was called continental drift.

•Wegener had noticed that certain continents like Africa and South America fit together like a puzzle and wondered if other continents did the same thing.

•His continental drift theory proposed that a past supercontinent called Pangaea split apart into pieces which drifted over time into their present location.

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Continental

Drift

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Continental

Drift

A) Continental drift states that Earth started out with one supercontinent called Pangaea.

A)B) Around 200 million years ago Pangaea split into two parts called Laurasia and Gondwanaland.

B)C) Over the next million years both Laurasia and Gondwanaland broke apart into North and South America, Africa, Australia, Eurasia, and Antarctica. These land masses then slowly drifted into their present locations. C)

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Drift

Evidence

• In order to prove his theory of continental drift, Wegener first needed evidence of such drifting.

• Wegener found his evidence in three different forms...

Climate

Fossils Rocks

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Climate

Evidence

• Wegener found his climate evidence in continents such as North America and Antarctica.

• Both of these continents have coal deposits which can only be formed from decaying tropical plants.

• Today neither of these continents lie near the equator where tropical weather occurs.

• This means at one time both North America and Antarctica must have rested at the equator.

• Eventually North American moved north from the equator and Antarctica south.

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Fossil

Evidence

• Wegener found his fossil evidence in continents such as South America, Africa, Australia, India, and Antarctica.

• On these continents are fossils of three extinct reptiles: Lystrosaurus, Cynognathus, and Mesosarus.

• All three of these reptiles are not capable of traveling across ocean.

• Yet all three have fossils that are found on continents that today are separated by vast oceans.

• This suggests that the continents they lived on were once connected.

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Rock

Evidence

• Wegener found his rock evidence on the continents of South America and Africa.

• On these continents are rocks of the same age and type.

• Both continents also have similar rock layers across their borders and mountain ranges that would line up if connected.

• This also suggests that these continents were once connected and later separated.

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Crust

Earth’s

Layers

Mantle

Outer Core

Inner Core

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Crust

• The crust is the very thin layer (3 to 46 miles) of solid rock (think of the skin of an apple) that makes up the outermost part of Earth.

• Within the crust lies most of the natural resources that people use.

• Two types of crust exist: continental (B) and oceanic (A).

• The crust in anywhere from 3 to 46 miles thick. To compare think of the thickness of the skin of an apple.

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Types of

Crust

• Oceanic Crust makes up the ocean floor which is usually 4 or 5 miles thick.

• Continental Crust makes up Earth’s Land.

Continental

Crust

Oceanic Crust

Continental

Crust

Oceanic Crust

• It is made up a lightweight rock called granite which helps make it less dense than oceanic crust. • This is why oceanic crust goes below continental crust in subduction zones.

• It is comprised mostly of basalt which is a denser rock than granite.

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Mantle

• The mantle is the thick layer (1,800 miles) of solid and molten rock that lies beneath the crust.

• This layer of the Earth is divided into the lithosphere (upper mantle) and the asthenosphere (lower mantle).

• The lithosphere is rigid, made up of rocks in the crust that are attached to the upper part of the mantle and is broken up into plates (lithospheric plates) that slowly move and float over the asthenosphere.

• The asthenosphere is made up of rocks that are semimolten or almost melted because of the intense heat and pressure under the lithosphere.

• These rocks bend, compress, stretch and flow giving support and movement to the lithospheric plates.

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Core

• The core is the central part of the Earth that lies beneath the mantle and is believed to be the source of Earth’s magnetic field (twice as dense as the mantle).

• The core consists of two parts:1) The outer core: made up of liquid iron and nickel2) The inner core: made up of solid iron and nickel

• These metals at the core are denser (heavier) than rock which is why they lie below the mantle and crust.

• The diameter of the Earth’s core is 4,300 miles and the closer you get to the core the more there is an increase of temperature and pressure caused by the weight of material from the above layers of Earth. Outer Core

Inner Core

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Convection Flow

Plate Boundaries

Plate Tectoni

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Plate Tectonics

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Plate Tectonics

Plate Tectonics:

• The theory that Earth’s surface is made up of separate, rigid plates called tectonic plates that slowly move across the mantle.

Tectonic Plates:• Each plates is curved like the Earth’s surface.• There are 7 large plates and around 12 smaller ones.

• Tectonic plates move along plate boundaries and most plates travel only a few inches each year.

• Plates are broken up into two types: continental and oceanic plates.

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Plate Tectonics

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Convection

Flow

Convection Flow:

• The continuous circular movement of materials as they are heated and cooled.• Most scientists believe that the tectonic plates are moved by the convection flow of rock material in the mantle which lies directly below the plates.• The convection flow in the mantle is very similar to what is seen when water is heated.

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Convection Flow

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Plate Boundarie

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Divergent Plate Boundary

Convergent Plate Boundary

Transform Plate Boundary

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Divergent

Plate

Divergent Plate:

• Plates move away from each other at divergent plate boundaries.

• At these boundaries new crust is formed as magma from the mantle wells up and moves away from the ridge.

• This process of new crust formation is called sea floor spreading.

• Sea floor spreading can be seen at the Atlantic Ocean.

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Convergent

Plate

Convergent Plate:

• Plates move towards each other at convergent plate boundaries.

• At these boundaries usually a more dense plate (oceanic crust) will sink or slide under a less dense plate (continental crust).

• Deep ocean trenches and raised mountains can be formed when oceanic and continental plates converge.

• This process of one plate sinking or sliding under another one is called subduction and occurs and subduction zones.

• Deep ocean trenches are formed when two oceanic plates converge while mountain ranges are formed when two continental plates converge.

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Transform Plate

Transform Plate:

• Plates slide past each other at transform plate boundaries.

• Most of these boundaries occur on the ocean floor but some like the San Andreas Fault occur at Earth’s surface.

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Plate Boundarie

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Volcanoes

Magma

Volcanoes

Eruptions

Types

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Volcanoes

Volcanoes

Volcanoes:

• Volcanoes are vents in the Earth’s crust through which magma, gas, and other materials are forced out.• Most volcanoes occur along plate boundaries where the tectonic plates shift and can be classified as active, intermittent, dormant, or extinct

How are volcanoes created:

• At subduction zones the rocks of one plate are melted into magma.• This melting produces gases that become mixed with the magma that make the magma less dense than the surrounding rock which in turn causes the magma to rise and collect in magma chambers (reservoirs from which volcanoes erupt).• Increasing pressure from above rocks cause the materials in the volcano to erupt or release through vents or fissures (cracks).

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Volcanoes

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Magma

Magma

Magma:

• Magma is molted or melted rock deep below the Earth’s surface.• Is formed in the asthenosphere when heat melts parts of the mantle and lower crust (lithosphere).• The temperature of magma can be from 1,202°F and 2,192°F.

• Magma rises to the Earth’s surface since it is less dense and much hotter than the surrounding rock.• Most often magma is found in magma chambers under Earth’s surface and is released when a volcano erupts.

• Once magma reaches the Earth’s surface it is called lava and from there cools and solidifies over time into igneous rock.

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Magma

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Volcanic

Types

Cinder Cone

Volcano

Shield Volcano

Composite Volcano

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Cinder

Cone

Cinder Cone Volcano:

• Mainly made up of diminutive rock particles and or cinders.• These volcanoes have a tiny cone with steep sides.

• These features are caused by the breaking up lava into tiny fragments after it cools and hardens in the air during an eruption.

• The tiny fragments pile up around the vent forming the steep sides and small vent.

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Cinder Cone

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Cinder

Cone

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Shield

Shield Volcano:

• Is made up of layers of lava rocks and is one of the largest volcanoes in the world. • When lava flows out of the vent it spreads out in all directions.• Eventually the lava cools and hardens into rock.• After layers and layers of lava cools, the volcano ends up with broad, gently sloping sides that resemble the shield of an ancient warrior.

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Shield

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Composite

Composite Volcano:• Is made up of layers of ash, cinder, and rocks. • These layers form cones with steep sides that curve inward.• Most composite cones are higher than 9,000 ft.

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Composite

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Eruptions

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Hawaiian

Eruption

Hawaiian Eruptions:

• Are the least violent type of eruption.

• In these eruptions highly liquid lava flows out slowly and builds up shield volcanoes.

• Lava rock is then formed as the lava cools and hardens.

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Strombolian

Eruption

Strombolian Eruptions:• Strombolian eruptions occur frequently and are fairly gentle since pressure is released gradually. • In these eruptions thick magma accumulates in the vent and builds up pressure that is released in the form of cinder fragments that pile up into cinder cones.

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Vulcanian

Eruption

Vulcanian Eruptions:• Vulcanian eruptions typically begin with huge loud explosions followed by tinier ones. • In these eruptions ash, dust, and other volcanic materials are blown into the air.

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Peleean

Eruption

Peelean Eruptions:

• Are the most violent eruptions.

• In these eruptions gases trapped in sticky magma build up tremendous pressure.

• As the pressure is released, tons of ash and rock are thrown into the air as parts of the mountain are blown away.

• Clouds of hot, poisonous gases then rush down the mountain from the vent.

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Earthquakes

Earthquakes

Faults

Seismographs

Earthquake Strength

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Earthquakes

Earthquakes:• An earthquake is a trembling or shaking in the ground caused by the release of energy following plate movement along faults.

Earthquakes

What Causes Earthquakes:• Earthquakes occur when stress within the Earth becomes great enough to overcome the strength of the rocks along the fault.

• This creates movement in the Earth that releases seismic waves that travel through the Earth causing the Earth to move or vibrate.

• Earthquakes produce two types of waves: p-waves and s-waves.

• P-waves travel much faster than s - waves.

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Faults

Faults:• Faults are breaks or cracks in the rocks of the lithosphere along which movements take place.• Fault zones are areas were several faults are interconnected.

•Most fault zones are located along the boundaries between tectonic plates.

Faults

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Faults

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Seismographs

Seismographs:• A seismograph is an instrument that detects, measures, and records the energy of earthquake vibrations at a given location.

• As the ground vibrates a roll of paper in the seismograph vibrates with it.

• A pen with a weight attached to it is suspended above the paper and does not vibrate with the ground, rather it traces the record of the vibrations.

•By using triangulation scientists can determine the focus or point below the Earth’s surface where the quake began.

Seismographs

What Scientists Learn From Seismographs:

•Scientists can also determine the quakes epicenter or the point on the Earth’s surface that is directly above the focus.

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Triangulation

Triangulation:• Scientists use triangulation to locate the epicenter (location on Earth’s surface) of an earthquake. • Triangulation uses information from at least three seismograph stations to find the location.• Circles are drawn around each station which represent how far the earthquake was from the station at all directions.

•Where the circles intersect or meet is where the epicenter of the earthquake is.

Seismographs

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Triangulation

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Focus

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Earthquake

Strength

Earthquake Strength:• The strength of an earthquake is measured in two different ways: magnitude and intensity. • The magnitude of an earthquake is the measure of energy released during and earthquake.• The intensity is the strength of an earthquake that can be felt on the surface.

•Magnitude is measured by the Richter Scale which records the amplitude (distance from the midpoint to the trough or crest of the wave) of the seismic waves.

Earthquake Strength

• The intensity of an earthquake is measured by the Mercalli Scale which tells what people felt and observed when the earthquake occured.

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Richter

Scale

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Mercalli

Scale

Earth's structure & plate tectonics

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