The Earth

• Folding is the bending of rock layers to form wave like undulations
• Example of fold mountains:

  Himalays

  Alps

  Rockies

  Andes
• Fold mountains are formed by two processes

  1. Where there is a subduction zone
  2. Collisions resulting from two continental plate converging.
• Simple/ Symmetrical fold- Both sides (limb) of the fold is symmetrical. (Equal compression forces)
• Asymmetrical fold- One limb is steeper than the other. One limb is pushed forward by compressional force.
• Over fold- Anticline is pushed forward by compressional forces where both sides (limbs) face the same direction
• Recumbent fold- The fold is almost horizontal
• Overthrust fold- Lies almost horizontal over the lower limb. Can cause fold to fracture.
• Nappe fold- Causing fracture of the fold due to compressional force.
• Sima: This forms the oceanic crust which is beneath all continents. It is dense(Heavy).
• Sial: This forms the continental crust which is above the oceanic crust (floats above the Sima) It is higher.
• Lithosphere: Crust and solid upper mantle(Plate)
• Asthenosphere: This is a part of the upper mantle and semi molten. It lies beneath the lithosphere.
• Why do plates move?

  Convection currents are found in the asthenosphere, these currents are created when molten rock melts, expands and rises upwards and spreads out laterally. Which moves the Lithosphere along with it.
• Continental drift: Alfred Wegener proposed this theory in 1912. He suggested that land masses were once joined together as one supercontinent called Pangaea. Over time they moved apart due to convection currents.
• Continental Drit: the slow movement of continental masses over the surface of the Earth.
• The edge of crustal plate are called plate argins/ boundries.
• Zone of divergence / destruction plate margin moves apart.
• Zone of convergence/ destruction plate margin. Plates move towards eachother.
• What is sea floor spreading?


  When two plates pull apart on the sea floor a gap is created. Hot magma from the asthenosphere rises it gains energy through convection currents and raises through the gaps between the plates. This creates a new lithosphere.
• Transform plate margins plates slide past each other
• A ridge of land is found at a divergent plate. Weakening in the ridge allows magma to escape creating submarine volcanoes.
• Faults are cracks or weaknesses in the rock's layer which leads to displacement of rock on either side of the crack.
• Types of Faults:

  Tensional/Normal fault

  Compressional/ Reserve fault

  Transform/ Ter/ Strike fault.
• Tensional fault- This type of results from blocks of land pulling apart.
• Compressional fault- caused by compressional forces.
• Transform fault - occurs when two tectonic plates move horizontally against one another.
• A rift valley is an elongated deep area/ valley between two block mountains.
• Rift valleys are produced by tectonic movement of the Earth. Rift valleys are the result of tensional forces in areas of divergent plate boundaries.
• Compressional forces on either side of the Rift Valley pushes land upwards creating a block mountain or horst.
• The valley is created when land moves downwards and is called a graben.
• What is an Earthquake?

  An Earthquake is the vibration of the Earth's crust caused by the rapid release of energy in form of seismic waves.
• What is Seismology?

  The study of seismic waves
• Seismic waves are waves that travel through the earth and are caused by earthquakes. They are referred to as primary and secondary waves
• Where does an Earthquake occur?

  At a subduction zone where the lighter plate creates friction over the heavier plate.
• What is the focus?

  The point within the earth which an earthquake's energy originates.
• What is population density?


  This is the number of people living in an area of land expressed as the number of persons per square km.
• What is population distribution?

  This is the way a population is spread or distributed in the available area of space.
• Define Birth Rate

  The number of births per 1,000 population.
• Define Death Rate

  The number of deaths per 1,000 population.