The Dynamic Earth

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The Dynamic Earth
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The Earth
What's inside the Earth?
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Structure of the Earth
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Plate Tectonics
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The World Today
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Science At Work Alfred Wegner

• In 1915 Alfred Wegner proposed a radical theory.
• He suggested that there was once a super
  continent called Pangaea.
• Pangaea then split up to form the continents that
  we know today.
• These then drifted into their current positions

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Pangaea 250 million years ago
Australia
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Pangaea to Now
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Pangaea to Now
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Pangaea to Now
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Evidence - Migration of reptiles
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Evidence - Mountains

• The rock type, composition and formations of
  mountains in eastern North America are similar to
  those of mountains across north-western Europe.

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Evidence Coal

• Coal has been found above the Arctic circle.
• As coal comes from decomposed plants and it is
  far too cold now to support plants, it must have
  once moved from a warmer climate.

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Evidence Magnetic Alignment

• Although the magnetic alignments of ancient rocks
  all point in different directions, they all point
  in the same direction when the continents are
  joined.

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Future Earth?
A
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Future Earth?
A
A
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Questions

• What evidence suggests that the continents were
  once joined?
• Correct these statements to make them true.
• Coal deposits above the Arctic Circle suggest the
  land has floated there from warmer climates
• Continents that do not have glaciers now have
  always been too warm to have them.
• Triassic reptiles could have swum the distances
  required to populate different continents.

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Evidence from below
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World War II - Sonar

• During WW2 the military developed new technology
  called Sonar.
• This technology allowed the military to get
  accurate maps of the ocean floor for their
  submarines.

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Sonar Results

• Sonar revealed some interesting results
• That huge underwater volcanic mountain ranges run
  down the centre of the oceans.
• The ages of the rocks of the ocean floor vary
  from brand new to 200 million years old. (this
  is younger than the rock of the continents).
• The rock of the continents is less dense than the
  ocean floor and seems to float on it.

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Evidence Magnetic Stripes
Ridge

• The seafloor has been widely mapped by
  magnetometers. As the oceanic plates grow the
  magnetic zones form distinct stripes on the map.
  This map is coloured according to the age of the
  rocks
• The stripes show that the youngest rock is next
  to the ridges and the oldest next to the
  trenches.

Red 0 9.7 mya Blue 126.7 180
mya Green 31 - 120 mya
mya Million Years Ago
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Magma and the Ocean
The ocean floor is a conveyor belt dragging new
rock from mid-ocean and in the trenches.
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• All the evidence suggests that the molten rock is
  emerging along the mid-ocean ridges.
• As the molten rock hits the water it cools,
  building new mountains.
• These new mountains push the old ones out of the
  way.
• The ocean floor acts like a conveyer belt,
  carrying everything towards the trenches.

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Floating plates
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Inner Structure of Earth

• The earth is made up of layers we live on the
  crust.
• Next is the Mantle which is approx 2800 km thick.
  

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Keeping the mantle hot

• While the mantle tries to cool the crust helps to
  keep the heat in.
• Patches are also heated by the decay of
  radioactive elements such as Uranium, Thorium and
  Potassium.

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Convection currents

• Just as hot air and liquid rise, so will hot
  liquid rock. Any rock over a hot patch in the
  mantle will rise and cooler rocks will drop.
• This cycle is called a convection current and it
  takes millions of years to complete.

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Convection currents
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Questions

• What causes convection currents?
• How long do convection currents take to cycle
  around the mantle?
• What keeps the mantle from cooling down and
  becoming solid?

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At the Edges
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Tectonic Plates and their Boundaries
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Types of Plate Boundaries

• There are three types of plate boundaries
• A) Divergent Each plate is moving away from the
  other
• B) Convergent Two plates that are moving towards
  each other.
• C) Transform The two plates are sliding past
  each other.

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Example - Spreading

• As plates move apart they create cracks and form
  rift valleys.
• This allows hot magma to rise into the gap.
• This means old rocks are pushed out of the way as
  the magma cools to form new rocks.
• An example of two spreading plates are the
  African plate and the Arabian peninsula.

Fact Some plates have been measured as moving
apart at a rate of 20cm a year!
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Spreading plates Another way of thinking about
it.

• Its like a wound (rift valley).
• A scab (Rock) begins to repair the wound but any
  stress cracks it.
• This allows blood (Magma) to ooze out.
• A new scab then needs to be made.

A Scab
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Science at Work Helgafjell Volcano
The Helgafjell Volcano Iceland

• The Helgafjell Volcano near Iceland is an example
  where volcanic eruptions caused by two spreading
  plates has created an island.

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Example Convergent
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Convergent plates form big mountains

• The Himalayas formed when the plate that carries
  India collided with the Eurasian plate.
• Both plates have similar densities and instead
  of one going under the other they push against
  each other.
• This forms extremely large mountains.

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Example - Transform
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San Adreas Fault

• Transform boundaries are formed by plates
  scraping against each other.
• This doesnt make mountains or volcanoes, it
  creates earthquakes.
• The most famous transform boundary is the San
  Andreas Fault.
• This fault lies directly under San Francisco and
  Los Angeles.

Fact Every year the coast of California moves
5cm this is making L.A closer to San Francisco
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Normal and Reverse faults

• Faults are lines of weakness in the earths crust.
  
• Normal faults are caused from movement away from
  each other. The results is the formation of
  cliffs and overhangs.
• In reverse faults movement is towards each other.
  This causes the two surfaces to overlap.

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Questions

• Can you think of an example of a land mass that
• That has broken away from the main mass of
  Australia?
• Outside of Australia?
• Label the boundaries on
• this slide

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What caused such destruction?
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Earthquakes
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Science at work Quake Lakes
May 14th 2006
May 15th 2008
May 19th 2008

• A satellite image shows the Yansai Lake forming
  from a river at Tangjiashan in south-west China's
  Sichuan province. This was the direct result of
  an earthquake that devastated the region on May
  12.

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Richter Scale

• The Richter magnitude scale was developed in 1935
  by Charles F. Richter.
• On this scale an earthquake registering a 6 on
  the Richter scale is 31 times more powerful than
  one registering a 5.

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Richter Scale
Richter Scale Measurement Earthquake effects
3 Felt slightly in areas near the epicentre
4 Felt by most people up to several kilometres from the earthquake. Some objects upset.
5 Strongly Felt. Some damage to weak buildings.
6 Moderately destructive. Some severe damage to weak buildings.
7 Major earthquake. Destruction of many buildings.
8 Very destructive. Total destruction of structures.
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Epicentre and Focus

• The focus is the point at which the earthquake
  starts.
• The epicentre is the point on the surface
  directly above the focus of an earthquake.

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Seismic waves

• Seismic waves can be spilt into two categories
• Body waves which travel through the body of the
  earth. These can be either
• Primary (P)
• Secondary (S)
• Surface waves travel along the surface. These can
  be either
• Rayleigh (R)
• Love (L)

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Body Waves

• P waves are the fastest and are the first to be
  recorded. This is because
• P waves travel through solid and liquid rock.
• While S waves travel only through solid rock,
  being stopped by liquid rock. Therefore they
  travel along the surface.

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Surface Waves

• R waves are rolling waves. They are usually
  quite small (1cm)
• L waves arrive last and travel in an up and down
  motion.
• Together they cause cracks in the surface, which
  then swallow and crush the objects above them.

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Science at Work Boxing Day Tsunami 2004
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How Tsunamis Happen
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How Tsunamis Happen
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Useful animations

• http//news.bbc.co.uk/2/hi/asia-pacific/5194316.st
  m
• http//news.bbc.co.uk/2/hi/science/nature/4126809.
  stm

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Activity Earth Quake Tower

• Your task is to build a tower that will be able
  to survive an earthquake.
• You will have a limited amount of materials to
  use so plan first!
• The best tower team will win a prize.

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Volcanoes
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Volcanoes
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Types of Volcanoes
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Shield Volcanoes
Mauna Loa - Hawaii

• The biggest volcanoes are shield volcanoes.
• They get larger every time they erupt
• However their eruptions are more predictable and
  less explosive.

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Composite Volcanoes
Mt Fuji
Mt St Helens
Mt Vesuvius

• Composite volcanoes are the most dangerous.
• They erupt explosively and violently.
• Examples are Mt Fuji (Japan), Mt St Helens (USA)
  and Mt Vesuvius (Italy).

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Volcanos form islands
Krakatau, Indonesia
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Useful Website

• http//news.bbc.co.uk/2/hi/science/nature/4972366.
  stm

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Mining
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Diavik Mine, Canada
This incredible mine can be found 300km northeast
of Yellowknife in Canada. (It's amazing that it
doesn't fill up with water, being surrounded by
it.) The mine is so huge and the area so remote
that it even has its own airport with a runway
large enough to accommodate a Boeing 737.
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Mirny Diamond Mine, Serbia
This mine is an absolute beast and holds the
title of largest open diamond mine in the world.
It is 525 meters deep with a top diameter of
1200 meters. There's even a no-fly zone above
the hole due to a few helicopters being sucked
in.
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Bingham Canyon Mine, Utah
This is supposedly the largest man-made
excavation on earth. Extraction began in 1863
and still continues today. The pit is constantly
increasing in size. In its current state the
hole is 3/4 mile deep and 2.5 miles wide.
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Kimberley Big Hole - South Africa
Apparently the largest ever hand-dug excavation
in the world, this 1097 meter deep mine yielded
over 3 tonnes of diamonds before being closed in
1914. The amount of earth removed by workers is
estimated to total 22.5 million tons.