Geology 131

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					Geology 131
Miss Yafah Hoosain
• Geology 131/132

• 3 Lectures per week

• 1 Tutorial per week

• 1 Practical per week (Friday 14:00-17:20)
     Continuous Assessment
• Tests/assignments : 25%

• Practicals:        20%

• Tutorials          5%

• Main Test:         50%
     Continuous Assessment
• Note:
  A minimum of 40% Course work mark
  required to qualify for examinations.
       Outline of Practicals
• Week 1 - 3
Minerals and Properties

• Week 4
Igneous Rocks
      Outline of Properties
• Week 5
Sedimentary Rocks

• Week 6
Metamorphic Rocks
• A practical test will be given every 2 to 3
  weeks during Practical times
• All exercises should be handed in after the
  practical session.
• Remember, Practicals count 20% of your
  final course work mark
Course Readers
           Geology Staff
• Head of Dept: Prof A Thomas
• Deputy H.O.D : Mr ACT Scheepers
• Lecturers:
Prof Jan van Bever Donker (Dean,
  Science Faculty)
Prof C Okujeni
Prof P Carey
Prof N Jovanovic
Mr Domoney
• Secretary: Mrs Bronwen Honigwachs
            Main Content
• The Earth in the Universe

• Structure of the Earth, Plate Tectonics,
  Isostacy, Earth Quakes, Paleomagnetism

• The Rock cycle, Geologic Time
           Main Outcome
• Understand the basic concepts of Earth
     Geology 131

Introduction to Geology
              Course Outline
•   Introduction to Geology
•   The Earth in the Universe
•   The Structure of the Earth
•   Plate Tectonics
•   Rock Cycle
•   Geologic Time
     Introduction to Geology
• What is Geology?

• Why study Geology?
        Earth in the Universe
• Introduction

• Formation of the Earth
  - Big Bang Theory
  - Nebula Hypothesis

• The Solar System
        Structure of the Earth
• What is the Earth made of?

• Structure of Earth’s Layers

• Interior of the Earth
              Plate Tectonics
•   Introduction to Plate Tectonics
•   Isostacy
•   Paleomagnetism
•   Earth Quakes
•   Volcanoes
            Rock Cycle
• Igneous Rocks

• Metamorphic Rocks

• Sedimentary Rocks
            Geologic Time
• Introduction

• Geologic Time Scale
      Lecture 1

Introduction to Geology
     Introduction to Geology
• What is Geology?
     Basic Terms and Definitions
• Earth Science:
  Collective term referring to all sciences
  that attempts to understand Earth and
  other planets/objects in space. This
  includes Geology, Meteorology,
  Oceanography and Astronomy.
• Geology:

 -Focuses on the description of Earth’s
  composition, behaviour and history.

 -Consists of many sub-disciplines such as
  Mineralogy, Geochemistry, Petrology,
  Environmental Geology, etc.

 -Divided into Physical and Historical Geology
          Physical Geology
• Studies the composition of the Earth

• Understanding of processes that occur
  above and below the earth’s surface

• Internal processes: Earth quakes

• External processes: Landforms
          Historical Geology
• Origin of the Earth

• Development through 4.6 Billion years of

• Sequence of physical and biological
  changes throughout geologic time
         Earth in the Universe
• Universe:

  -Whole cosmic system of matter and
   energy of which Earth is a part

  -Main constituents are the galaxies, within which
   are stars and stellar groupings and nebulae

  -Earth's Sun is one star among the billions of
   stars in the Milky Way Galaxy
• The universe is governed by four
  fundamental forces:

   strong force
   weak force
   electromagnetic force
   gravitation
         Origin of the Universe
    Numerous theories have been proposed
    for the origin and structure of the universe:

   big bang
   cosmology
   expanding universe
   steady-state theory
               Assignment 1
• Explain the following theories describing the
  origin on the Earth/Universe:

 Big Bang Theory
 Nebula Hypothesis

• Assignment should be 2 pages only + 1 page for
• Due Date: 12/02/2007
• A star is a massive, luminous ball of
• Stars group together to form galaxies, and
  they dominate the visible universe.
• The nearest star is the Sun, which is the
  source of most of the energy on Earth,
• A star shines because nuclear fusion in its
  core releases energy which moves
  through the star's interior and then
  radiates into outer space.
• A star is composed primarily of hydrogen
  and some helium as well as heavier trace
• Without stars, life on Earth and most
  atomic elements would not exist.
• Large aggregation of stars, gas, and dust,
  typically containing billions of stars

• Held together by the gravitational
  attraction between its constituent parts,
  while its rotational motion prevents it from
  collapsing on itself
• Gravitation binds individual stars into
  galaxies and also acts to hold clusters of
  galaxies together
• Many large galaxies have smaller
  galaxies, called satellite galaxies, in close
• The galaxies nearest the Milky Way form a
  cluster called the Local Group
             Local Group
• The Local Group includes:

Andromeda Galaxy, which is similar to the
 Milky Way
Magellanic Clouds, which are satellite
 galaxies of the Milky Way
           Milky Way Galaxy
• Large disk-shaped aggregation of stars,
  gas, and dust in which the solar system is
• Large spiral galaxy, typically disk-
  shaped, with greater concentration of
  stars near the centre

• 100,000 light years in diameter

• 10,000 light years in thick

• What are light years?
               Light Years
• Unit of measurement of astronomical
• The distance light travels in 1 sidereal year
  (time required for one complete revolution
  of the earth about the sun)
• Light travels at a speed of 300,000 km /
  sec, so this distance is equal to 9.46 x
              Light years
• One light-year is equivalent to 9.461 ×
  10^12 km
• The star nearest to our sun, Alpha
  Centauri, is more than four light years
• Alpha Centauri and Proxima Centauri, the
  stars nearest our solar system, are about
  4.3 light-years distant
           Milky Way Galaxy
• Contains four major structural subdivisions:
 the nucleus
 the bulge
 the disk,
 and the halo
• The Sun is located in the disk about half way
  between the center and the outer edge of the
  disk of stars
                Solar System
• Sun and the bodies moving in orbit around it

• Most massive body in the solar system is the
  Sun, a typical single star that is itself in orbit
  about the center of the Milky Way Galaxy

• Other bodies in the solar system—the terrestrial
  planets, outer planets, asteroids, and comets—
  revolve on orbits about the Sun
          Terrestrial Planets
• Mercury, Venus, Earth, Mars
• Closest to the sun
• Composed primarily of silicate rock
  (mantles) and iron (cores)
• Earth is the largest terrestrial planet,
  Mercury is the smallest
   Jovian Planets (Gas Giants)
• Jupiter, Saturn
• composed primarily of hydrogen and
  helium gas, like the Sun, but with rock and
  ices, such as frozen water, methane, and
  ammonia, concentrated in their cores
            Ice Giant Planets
• Uranus, Neptune
• have rock and ice cores surrounded by
  envelopes with smaller amounts of
  hydrogen and helium
• Discovered in 1930

• Now classified as Dwarf planet (Body, other than
  a natural satellite (moon), that orbits the Sun and
  is smaller than the planet Mercury yet large
  enough for its own gravity to have rounded its

• Diameter less than half that of Earth
• Thought to be made of frozen gases with a
  significant fraction of rocky material
• Started to form, along with the other planets,
  from material rotating around the young Sun
  about 4 thousand million years ago (4000 Ma
  years or 4 Ga)
• Solid material came together in a process called
  planetary accretion
• During the this process, small solid objects are
  drawn together by gravity, producing a larger
• Estimated age of the Earth is 4.6 Ga
Lecture 2
• Without the Sun there would be no Solar

• The Sun does not just provide the energy
  required for life, but also provides the
  gravitational force to hold the planets in
  their orbits

• The Sun orbits the centre of our galaxy
• The Sun's orbital period is about 240
  million years
• The Sun rotates with an average period of
  27 days.
• The rotation period varies with latitude -
  equatorial regions have a rotational period
  of 25 days, whereas polar regions are
  slower and take 34 days to complete one
 Physical properties of the Sun
• most massive body in the Solar System,
  containing 98% of the mass of the Solar

• more than 330,000 times more massive
  than the Earth

• diameter of 1,391,900km
 Physical Properties of the Sun
• The Sun is layered and can be divided into
  three regions:
Radiative zone
Convective zone
• The "surface" of the Sun that we see is the
  photosphere, above which lies the
  chromosphere and the outlying corona.
• The Moon orbits the Earth at a distance of
• Greatest distance between the Earth and
  Moon is 405,503km
• The Moon rotates once on its axis in
  27.3216 days - this is the same as its
  orbital period and therefore the Moon
  always keeps the same face presented to
• Moon does not orbit the centre of the

• Earth and Moon orbit about the common
  centre of mass, or barycentre (located
  about 4,670km from the Earth's centre, in
  the Earth's mantle)
• Over a long period of time, tidal friction
  within the Earth-Moon system has caused
  the Moon's rotation rate to slow down
• Earth's rotation has also slowed - we used
  to have a day of less than 22 hours about
  360 million years ago
• Growth rings in fossil coral indicate that
  the tidal period used to be different
• The slowing down of the Earth-Moon
  system, which is still occurring, results in
  the Moon slowly moving away from Earth
  at a rate of about 4cm per year

• The length of our day simultaneously
  increases by 0.002 seconds per century
• The Moon's orbit will continue to expand,
  until the length of an Earth day is the same
  as a lunar month
• This will occur when our day is 47 days
  long, and the Earth-Moon system has
  achieved a stable synchronization
            Doppler Effect
• Red Shift
  If source of the wave (light) is moving
  away - light appears redder
• Blue Shift
  If the source of the wave (light) is
  approaching – light waves shift towards
            Doppler Effect
• Shows whether Earth and another
  celestial body are approaching or leaving
  one another
• Amount of shift allows us to calculate the
  rate at which the relative movement
• Therefore, Large shifts indicate Higher
  velocities, whereas Small shifts indicate
  Lower velocities
• Meteoroids are small rocks in orbit around
  the Sun. Far smaller than asteroids, they
  make their presence known to us when
  they enter Earth's atmosphere and burn up

• As the meteoroid burns when it comes into
  contact with our atmosphere, it creates a
  bright trail across the sky - at this point it is
  called a meteor
• Commonly called a “shooting star”

• If a meteor hits the surface of the earth it is
  termed a meteorite

• Most meteors never reach the surface of
  the earth as it is vapourized when it comes
  into contact with the earth’s atmosphere
      Meteorite Classification
• Classified according to composition into 3

Irons (mostly Fe with 5-20% Ni)
Stony (Silicate minerals with other
Stony-irons (combination of the two)
• Stony meteorites are more common
• More iron meteorites are found
• Iron can withstand the impact better than
  the stony meteorite
• Stony meteorites are more easily
• Meteorite dating indicates that our solar
  system may be older that 4.6 Ga
              Meteorite craters
• A few large meteorites have produced craters on the
  earth’s surface

• Eg: Barringer Crater in Arizona
 1.2 kilometers wide and 200 meters deep
 Formed about 49,000 years ago by the impact of a 50
  meter nickel/iron meteorite

• Many of the 200 known impact sites around the world
  are in the oldest, stable continental rocks, or cratons,
  dating back more than 500 million years
Barringer Crater in Arizona
• Asteroids are rocky bodies in space

• Most asteroids lie between the orbits of
  Mars and Jupiter

• Smaller than planets, the largest is about
  1000km in diameter, but most are
  approximately 1km in diameter
• Suspected to be fragments of broken up planet
  that may have been between Mars and Jupiter,
  though it has very little mass compared to earth

• Some have orbits and travel close to the sun

• A few large asteroids regularly pass close to the
  Earth and its moon
• Asteroids have a variety of chemical
  compositions that match meteorites found on

• It is because asteroids have not suffered erosion
  and other destructive processes, that they
  represent a snapshot of the early Solar System

• Therefore a knowledge of asteroid geology is an
  important tool in understanding the formation of
  the Solar System
• Usually comets are very small bodies in
  space consisting of frozen gases and
  grains of dust and rock

• When comets approach the inner Solar
  System and become subjected to the
  Sun's heat, they develop a “tail” millions of
  kilometers long
• Comets have very elliptical orbits
• They come very close to the Sun, and
  then travel to the outer Solar System
• Short-period comets have periods of less
  than 200 years
• Long-period comets can take up to a
  million years to complete just one orbit of
  the Sun thus indicating different source

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