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Movements on the Earth’s Surface. Plate tectonics and the Earth’s Plate Boundaries. What is the Earth Made of?. If you could make a journey deep inside the Earth, you would find that it is made of several layers : The crust The mantle The core. The Crust.

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movements on the earth s surface

Movements on the Earth’s Surface

Plate tectonics and the Earth’s Plate Boundaries

what is the earth made of
What is the Earth Made of?
  • If you could make a journey deep inside the Earth, you would find that it is made of several layers:
    • The crust
    • The mantle
    • The core
the crust
The Crust
  • The crust (or lithosphere) is the outer layer of the Earth which is between 7-50km thick
  • It is the thin outer coating of the planet
  • It is not smooth
  • 70% of it is covered by the ocean, so the crust is not just the land that we see
  • It is thickest under the continents and thinnest under the oceans
the mantle
The Mantle
  • The mantle is below the crust and its about 2800km thick
  • The temperatures near the crust are 500°C and at the bottom of the mantle can reach up to 3000°C
  • The bottom of the mantle is solid, but the top rocks move slowly because of convection currents
  • It is the source of our volcanoes and earthquakes
the core
The Core
  • The core is the centre of the Earth
  • It consists of an outer core and an inner core
  • The outer core is mainly metal, not rock; and is between 4000°C to 6000°C
  • The outer core gives the Earth its north and south poles and magnetic field
  • The inner core is almost 10 000°C, but it does not boil because of the weight of the rest of the Earth pushing on it
the moving crust
The Moving Crust
  • The crust is broken into a number of pieces called tectonic plates
  • These plates float on magma at the top of the mantle
  • The speed of movement can be between 1cm and 10cm per year
plate tectonics
Plate Tectonics
  • Plate tectonics is a combination of two theories: continental drift and sea-floor spreading
  • Continental drift is the idea that the continents are continually moving and have significantly changed positions over millions of years
  • The theory of sea floor spreading proposes that the middle of the ocean is spreading apart, moving very slowly in opposite directions
continental drift
Continental Drift
  • For many years people noted the similarities in shape between the coastlines of Africa and South America and that they seemed to fit together like a jigsaw puzzle
  • A German meteorologist named Alfred Wegener put this idea with a range of other evidence into a book outlining a theory we know today as continental drift
  • He proposed that all the continents fitted together into a giant continent known as Pangea
Pangea was a supercontinent that was proposed to have existed 220 million years ago
  • When it started to break up, the continents drifted apart as they moved through the oceanic crust
  • This was backed up with evidence coastlines that fit, similar fossils, rocks and landforms that were created by glaciers
tectonic plate movement
Tectonic Plate Movement
  • We know that it is not the continents themselves that are moving but rather continental and oceanic crust moving
  • These areas are called plate tectonics
  • The movement of these plates explains the existence of continental shelves and deep trenches
  • It also explains earthquakes and volcano distributions
sea floor spreading
Sea Floor Spreading
  • The idea of the sea-floor spreading was suggested by Harry Hess
  • His evidence came from the discovery of the Mid-Atlantic Ridge, a continuous mountain range in the middle of the Atlantic Ocean
  • Hess suggested convection currents deep inside the mantle caused spreading
Hess proposed that new rocky crust was being formed at the ocean ridges and spreading outwards, later called seafloor spreading
  • Hess proposed that the crust was sinking down into the Earth in other places called ocean trenches
  • The process of the crust sinking down is called subduction
magnetic striping
Magnetic Striping
  • When molten rock solidifies, all the magnetite particles of any size line up in the magnetic field pointing in the same direction
  • During WWII, the US navy discovered there were bands of alternating strong and weak magnetism on the sea floor
  • They found the bands were parallel to the mid-ocean ridges
  • These bands were pointing north, then changed to pointing south, showing the Earth’s magnetic field changed every few million years
These patterns of stripes of rocks with alternating magnetism are called magnetic striping
  • The patterns on either side of the ridge were symmetrical – rocks at a particular distance from the ridge on one side always had the same magnetic direction as rocks the same distance away on the other side
convection currents
Convection Currents

Practical Exercise

what happens at plate boundaries

What happens at Plate Boundaries

The types of plate movement

transform boundaries
Transform Boundaries
  • One plate can slide past another along a single fault line
  • This is called a transform boundary
  • A fault is a fracture in rock where movement has occurred
The two plates involved can become jammed over a period of time until the pressure builds up and the plate slips
  • The slipping causes earthquakes
  • Example: The San Andreas Fault in California
  • Example: The fault line that runs through New Zealand
converging boundaries
Converging Boundaries
  • At a converging plate boundary, two plates move towards each other
  • There are generally three types of converging plate boundaries, depending on the plates involved
  • Mountain ranges, volcanoes and trenches can all be formed
ocean to continent collision
Ocean to Continent Collision
  • When oceanic crust collides with continental crust, the oceanic landform is pushed downwards into the mantle
  • This is known as a subduction zone
  • It creates a line of mountains and also volcanoes as heat rises through the cracks in the crust
  • An ocean trench will form at the line of plate contact
continent to continent collision
Continent to Continent Collision
  • When two continental plates collide, they have similar densities, so no subduction takes place
  • Instead, the edges of the two plates crumple and fold into high mountain ranges
ocean to ocean collision
Ocean to Ocean Collision
  • When two oceanic plates collide, the older denser crust will subduct below the newer crust, creating a deep ocean trench
  • The subduction also creates a line of undersea volcanoes that may reach above the ocean surface as an island arc
the mariana trench
The Mariana Trench
  • It is the deepest part of the world’s ocean
  • Its current depth is estimated at 10 971m
  • The deepest part of the trench is called Challenger Deep and is a small slot-shaped valley in its floor
  • It forms the boundary between two tectonic plates: the Pacific Plate and the small Marina Plate
diverging boundaries
Diverging Boundaries
  • Diverging boundaries or spreading plat boundaries form different features to converging and transform boundaries
  • These spreading boundaries can occur in the middle of the ocean or in the middle of land
  • When the plates separate, there is a rift between them
  • Magma rises up and cools to form a new crust
plates and currents

Plates and Currents

Teacher Demonstration

mars bar prac

Mars Bar Prac

Plate tectonics

volcanic eruptions
Volcanic Eruptions
  • Volcanoes form where there are weak spots in the Earth’s crust and where extremely hot molten rock called magma has gathered below the weak spots
  • This magma occasionally pushes upwards under great pressure into the volcano
  • When magma reaches the surface it is called lava which changes colour as it cools from white through to orange and red, until it becomes black and becomes a rock.
The eruption can be explosive when the magma:
    • is viscous (flowing very slowly)
    • contains a lot of water and gas
  • The explosion can throw out “volcanic bombs” of rock called scoria
  • Occasionally there can be a pyroclastic flow, where a cloud of ash, rock and gas at about 500°C rushes down the volcano like an avalanche at over 100km/h
The large series of volcanoes encircling the Pacific Oceanare referred to as the Ring of Fire, and notorious for frequent earthquakes and volcanic eruptions. 
  • The Ring of Fire contains over 450 volcanoes and is home to approximately 75% of the world's active volcanoes.
  • Nearly 90% of the world's earthquakes occur along the Ring of Fire; most recently, the devastating quakes in Chile, Japan and New Zealand. 
  • Volcanoes and Earthquakes of note:Christchurch Earthquake, New Zealand

Mount Saint Helens, Washington, USA

Mount Pinatubo, Philippines

Mt. Fuji, Japan

Paricutin Volcano, Mexico

Santiago Earthquake, Chile

Sendai Earthquake, Japan

what causes an earthquake
What causes an Earthquake?
  • An earthquake is the rapid movement of the ground, usually back and forth and up and down in a wave motion
  • It is caused by the rapid release of energy as the tectonic plates move
  • Friction between the plates must be overcome before they can move.
  • When the force is great enough, the plates suddenly move as friction can no longer hold them
  • This sudden movement sends out waves of energy through the rock and the water, which then shake as waves of energy pass through them
detecting earthquakes
Detecting earthquakes
  • Earthquakes are measured using an instrument called a seismometer
  • The trace of a seismometer is called a seismograph
  • The movement of the ground in an earthquake occurs in a shaking back-and-forth motion called a wave.
  • These waves in the Earth caused by the earthquakes are called seismic waves
Primary waves (P waves) are longitudinal waves that travel fast through the Earth
  • Secondary waves (S waves) are transverse waves that travel slightly slower than P-waves through the Earth
  • Surface waves are the slowest waves and cause the most destruction
  • S-waves and P-waves travel deep under the ground and then bend upward to reach the surface of the crust
  • P-waves shake the ground up and down
  • S-waves shake the ground sideways, back and forth
  • They are destructive if the earthquake is near the Earth’s surface
epicentres and foci
Epicentres and Foci
  • Earthquakes happen at particular places under the ground where the Earth slips, usually along a fault
  • The place where the quake starts is called the focus, which may be hundreds of kilometres deep in the Earth
  • The point on the Earth’s surface directly above the focus is called the epicentre
  • Buildings near the epicentre are usually the most heavily damaged
The severity of an earthquake is calculated in several different ways
  • One early method, still used in some cases today, is measured on the Richter scale
  • This scale goes between 1 and 9
  • Each successive number is thirty times more energy released than the previous number
  • An earthquake measuring less than 2.0 is known as a microquake and is rarely detected by people
  • So an earthquake measuring 5.0 is thirty times more energy than one measuring 4.0
the effects of earthquakes
The Effects of Earthquakes
  • Earthquakes can cause damage to buildings on land, and can cause landslides
  • They can also cause destruction in the ocean
  • An earthquake in the ocean can cause a huge wave called a tsunami
  • These waves can be 100m high and cause massive destruction if they collide with the land near where people are living