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Earth's Layers
• Standard 8-3.1
Earth’s Layers
• How are the earth’s layers similar to an egg?
• Shell=crust• Egg white=mantle• Yolk=core
Earth Layers Foldable
The Structure of the Earth and Plate Tectonics
The Layers of the Earth
© Copyright 2006. M. J. Krech. All rights reserved.
Structure of the Earth
• The Earth is made up of 3 main layers:– Core– Mantle– Crust
Inner core
Outer core
Mantle
Crust
In which layer is most of the mass of the Earth located?
The Three Layers The Earth is composed of three
different layers. The crust is the layer that you live on, and it is the most widely studied
and understood. The mantle is much hotter and has the ability to flow. The core
(outer core and inner core) are even hotter with pressures so great you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!
The Crust
The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.
The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers.
Outermost layer; thinnest under the ocean, thickest under continents; crust & top of mantle is called the lithosphere .
The Crust/Density
• Least dense layer overall; Oceanic crust (__basalt________) is more dense than continental crust (___granite______)
The Crust• This is where we live!
• The Earth’s crust is made of:
Continental Crust
- thick (10-70km)- (less dense than oceanic crust) - mostly old
Oceanic Crust
- thin (~7 km)- dense (sinks under continental crust)- young
What is one difference between oceanic crust and continental crust?
• the continental crust is composed of granite while the oceanic crust is composed of basalt.
The Crust/Composition
• Solid rock- mostly __Silicon_______ and ___Oxygen_________
• Oceanic crust-basalt;
• Continental curst-granite
• State of Matter: ___Solid___________
Lithosphere
• The layer located between the crust and the upper mantle.
• Composed of tectonic plates or lithospheric plates
• The plates floats on top of the asthenosphere
• State of Matter: Solid
Asthenosphere
• The top portion of the mantle
• Known as the Upper Mantle
• The movement of the mantle (asthenosphere) is the reason that the crustal plates of the Earth move.
The Asthenosphere• Asthenosphere= the fluid like portion of the
mantle that lies just below lithosphere. The lithosphere “floats” on the asthenosphere
Asthenosphere
• State of Matter: Soft Solid
•
The Mantle
The Mantle is the largest and thickest layer of the Earth and is 2900 km thick. The mantle is the middle layer composed of very hot dense rock that flows like asphalt under a heavy weight. The top portion of the mantle is called the asthenosphere. The movement of the mantle (asthenosphere) is the reason that the crustal plates of the Earth move.
Convection Currents
The mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.
The Mantle/Composition
• Hot softened rock; contains __iron___ and __magnesium________
• The mantle is generally considered to exist in a solid state, although high temperatures and pressure can cause some of this solid rock to flow like an extremely thick liquid.
• State of Matter:• ___solid_____________
The Core
• The core of the Earth is like a ball of very hot metals.
• The core consists of 2 parts:
• Inner Core & Outer Core
The Outer Core
The outer core is so hot that the metals in it are all in the liquid state.
Outer Core
• The outer core is so hot that the metals in it are all in the liquid state. It’s the Only Liquid Layer made up of molten metal. This layer creates the Earth’s magnetic field.
The Inner Core
The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid.
Inner Core
• Heaviest material; most dense layer
• Earth’s inner core is incredibly dense, because it is under so much pressure.
The Core/Composition
• Most of the rock in Earth’s outer core is molten, which means that it acts like a hot liquid.
• The core is mostly made up of ___iron_________ and _____nickel___________; outer core- ___is a slow__ flowing liquid, inner core-____solid__________.
• Outer Core State of Matter: ___liquid_________• Inner Core State of Matter: __solid____________
Earth Layers Foldable
Closure
• http://www.harcourtschool.com/activity/science_up_close/606/deploy/interface.html
•
Layers of the Earth
Practice Quiz Question• Can you label the following layers?
Objective
• Complete Falcon Focus
• Present Essential Question
• Video Clip
• Class Discussion
• Note-Taking
• Complete Comparison Chart
Video Clip
• http://www.youtube.com/watch?v=3g5EyKO4L0g
Plate Tectonics
What is Plate Tectonics?
• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
Changes in Landform areas over Geologic Time
• _Convection___Currents within the mantle have broken the layer below the crust into blocks, called plates, which slowly move around, colliding to build mountains or rifting/spliting apart to form new seafloor.
•
• Continents are composed of relatively light blocks that float high on the upper mantle called the __Asthenosphere_____, like gigantic, slow-moving icebergs.
• Seafloor is made of a denser rock called ____basalt______, which presses deeper into the mantle, producing basins that can fill with water.
• Except in the crust, the interior of the Earth _Cannot____ be studied by drilling holes to take samples. Instead, scientists map the interior by watching how ___Seismic____ waves from ___Earthquakes____ are bent, reflected, sped up, or delayed by the various layers.
Plate Tectonics
• The Earth’s crust is divided into 12 major plates which are moved in various directions.
• This plate motion causes them to collide, pull apart, or scrape against each other.
• Each type of interaction causes a characteristic set of Earth structures or “tectonic” features like mountain ranges, volcanoes and rift valleys.
• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
World Plates
Lithospheric Plates or Plate Tectonics
Plates move at very _____slow__________ rates – from about __one_____ to _ten______ centimeters per year;
• At one time in geologic history the _____continents_____ were __joined________ together in one large landmass that was called ___Pangaea_________________.
• The Continental Drift Theory was proposed by Alfred Wegener in 1912.
Continental Drift
Continental DriftContinental Drift – states that the continents have drifted and still are drifting apart.
“Puzzle Pieces”
• Continents look like they could be part of a giant jigsaw puzzle
Changes in Landform areas over Geologic Time
• As the plates continued to __move__ and split___ apart, oceans___ were formed, landmasses____ collided and split apart until the Earth’s landmasses came to be in the positions they are now;
• Evidence of these landmass collisions and splits comes from fossils, landform shape, features, and rock structures, and climate change.
• Landmass changes can occur at hot spots within ______Lithospheric____ plates;
• Earth’s landmasses_ will continue to move and change during the geologic time of the future.
What are tectonic plates made of?
• Plates are made of rigid lithosphere.
The lithosphere is made up of the crust and the upper part of the mantle.
Lithosphere
• The lithosphere includes the crust and part of the upper mantle. Rock in the lithosphere is solid, like the rock above it. “Litho” means rock. The huge rock plates of the lithosphere carry the world’s continents and oceans.
Lithosphere
• As these plates move and collide, mountains are built. Earthquakes are triggered. The lithosphere floats on a layer of soft rock that can flow like taffy; the asthenosphere. Astheno means weak. The rock in the asthenosphere flows slowly like putty or taffy.
What lies beneath the tectonic plates?
• Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
Motion of the Lithospheric Plates
• Plates float on the upper part of the ____mantle_____________.
• ___Convection_____ currents can cause the asthenosphere to flow slowly carrying with it the plates of the lithosphere.
• This movement of plates changes the sizes, shapes, and positions of Earth’s _continents____ and ___oceans_______.
Plate Movement
• “Plates” of lithosphere are moved around by the underlying hot mantle convection cells
Boundaries
• Divergent
• Convergent
• Transform
Three types of plate boundary
Divergent Boundary
• - where two plates are moving __apart____________
• most located along mid-ocean ridge (sea-floor spreading);
• - new crust forms because __magma_____ pushes up and hardens between separating plates.
Divergent Boundary
• the presence of mantle convection cells causing the plates to break apart and also as a source for new molten material.
• Where a divergent boundary forms on a continent it is called a RIFT or CONTINENTAL RIFT, e.g. African Rift Valley.
• Where a divergent boundary forms under the ocean it is called an OCEAN RIDGE.
Divergent Boundary
• In plate tectonics, a divergent boundary is a linear feature that exists between two tectonic plates that are moving away from each other.
• These areas can form in the middle of continents or on the ocean floor.
• As the plates pull apart, hot molten material can rise up this newly formed pathway to the surface - causing volcanic activity.
Direction of Movement/Sketch
Divergent Boundary
Continental
Divergent Boundary
Oceanic
• Spreading ridges– As plates move apart new material is erupted to fill
the gap
Divergent Boundaries/Sketch
Examples: Divergent Boundaries within the Oceanic Crust: Mid-Atlantic Ridge
Courtesy of www.ngdc.noaa.gov
• Iceland has a divergent plate boundary running through its middle
Iceland: An example of continental rifting
Iceland
• Iceland is located right on top of a divergent boundary. In fact, the island exists because of this feature.
• As the North American plates were pulled apart (see map) volcanic activity occurred along the cracks.
• With many eruptions over time the island grew out of the sea!
Example: Divergent Boundaries within the Continental Crust:
East Africa Rift Valley
• There are three styles of convergent plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision
Convergent Boundaries
Convergent Boundary
• where two plates come ___together_____ and __collide____.
• activity depends upon the types of crust that meet;
• more dense oceanic plate slides under less dense continental plate or another oceanic plate – _subduction zone___, some crust is destroyed;
• two continental plates converge, both plates __buckle__________ and ___push up____ into mountain ranges;
Direction of Movement/Sketch
• Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
Convergent Boundary
Continental/Continental
Himalayas
• Called SUBDUCTION
Continent-Oceanic Crust Collision
Convergent Boundary
Continental/Oceanic
Subduction
• Subduction is a way of recycling the oceanic crust. Eventually the subducting slab sinks down into the mantle to be recycled. It is for this reason that the oceanic crust is much younger than the continental crust which is not recycled.
• Oceanic lithosphere subducts underneath the continental lithosphere
• Oceanic lithosphere heats and dehydrates as it subsides
• The melt rises forming volcanism
• E.g. The Andes Mountains, The Cascade Mountains
Subduction
• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
• The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
• The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision
Convergent Boundary
Oceanic/Oceanic
• Where plates slide past each other
Transform Boundaries
Above: View of the San Andreas transform fault
Transform Boundary
• where two plates __slide____________ __past____________ each other
• crust is neither created nor destroyed;
• __Earthquakes________ occur frequently along this type of boundary.
Example
• The San Andreas fault, adjacent to which the US city of San Francisco is built is an example of a transform boundary between the Pacific plate and the North American plate.
• Alpine Fault of New Zealand
San Andreas Fault Zone
…what’s the connection?
Volcanoes and Plate Tectonics…
Volcanism is mostly focused at plate margins
Pacific Ring of Fire
- Subduction - Rifting - Hotspots
Volcanoes are formed by:
Pacific Ring of Fire
Hotspot volcanoes
(Hawaii)
