The earth and beyond

Introduction to the free On-Line
National Curriculum Science Syllabus Certificate Course
"The Earth And Beyond"


Contents of the Entire Course

Geology, What is it?    
Why Study the Earth?    
Earth Materials and Processes
Principle of Uniformitarianism    
Energy Heat Transfer    
Geothermal Gradient
The Earth -- What is it?    
Internal Structure of the Earth
Surface Features of the Earth    
Plate Tectonics

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University


Geology, What is it?

Geology is the study of the Earth. It includes not only the surface process which have shaped the earth's surface, but the study of the ocean floors, and the interior of the Earth. It is not only the study of the Earth as we see it today, but the history of the Earth as it has evolved to its present condition.

  • Important point:  The Earth has evolved (changed) throughout its history, and will continue to evolve.

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  • The Earth is about 4.6 billion years old, human beings have been around for only the past 2 million years.

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  • Thus, mankind has been witness to only 0.043% of Earth history.

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  • The first multi-celled organisms appeared about 700 million years ago. Thus, organisms have only been witness to about 15% of Earth's history.
  • Thus, for us to have an understanding of the earth upon which we live, we must look at processes and structures that occur today, and interpret what must have happened in the past. One of the major difficulties we have is with the time scale. Try to imagine 1 million years-- That's 50,000 times longer than most of you have lived. It seems like a long time doesn't it? Yet, to geologists, 1 million years is a relatively short period of time. More discussion about time in later lectures. But one thing we have to remember when studying the earth is that things that seem like they take a long time to us, may take only a short time to earth.
     

    Examples:

  •  A river deposits about 1mm of sediment (mud) each year. How thick is the mud after 100 years? -- 10 cm hardly noticeable over your lifetime.

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  • What if the river keeps depositing that same 1 mm/yr  for 10 million years?       Answer 10,000 meters

  •  Things can change drastically!

    Why Study the Earth?


  •  We're part of it. Dust to Dust. Humans have the capability to make rapid changes. All construction from houses to roads to dams are effected by the Earth, and thus require some geologic knowledge. All life depends on the Earth for food and nourishment. The Earth is there everyday of our lives.

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  • Energy and Mineral resources that we depend on for our lifestyle come from the Earth. At present no other source is available.

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  • Geologic Hazards -- Earthquakes, volcanic eruptions, hurricanes / cyclones, landslides, could affect us at any time. A better understanding of the Earth is necessary to prepare for these eventualities.

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  •  Curiosity-- We have a better understanding of things happening around us. Science in general. I'll try to relate geology (and science in general) to our everyday lives.

  • Earth Materials and Processes
     
    The materials that make up the Earth are mainly rocks (including soil, sand, silt, dust) .  Rocks in turn are composed of minerals.  Minerals are composed of atoms,

    Processes range from those that occur rapidly to those that occur slowly


    Heat Transfer

     Heat Moves through material by the following modes:


     
    Geothermal Gradient

    geotherm.gif

    Temperature and pressure increase with depth in the Earth.  Near the surface of the Earth the rate of increase in temperature (called the Geothermal Gradient)  ranges from 15 to 35oC per kilometer.   Temperature at the center of the Earth is about 4500oC


    The Earth -- What is it?

    The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at poles.
     


    Internal Structure of the Earth:


    complayers.gif

    Density, (mass/volume), Temperature, and Pressure increase with depth in the Earth.

    Compositional Layering

      • Continental 10 - 50 km thick
      • Oceanic 8 - 10 km thick

    physproplayers.gif

    Layers of Differing Physical Properties
    Lithosphere - about 100 km thick (deeper beneath continents)

    Asthenosphere  - about 250 km thick to depth of 350 km - solid rock, but  soft and flows easily.

    Mesosphere - about 2500 km thick,  solid rock, but still capable of flowing.

    Outer Core  - 2250 km thick, Fe and Ni,  liquid

    Inner core  - 1230 km radius, Fe and Ni,  solid

    All of the above is known from the way seismic (earthquake waves) pass through the Earth as we will discuss later in the course.


    Surface Features of the Earth

    Oceans cover 71 % of Earth's surface -- average depth 3.7 km.  
    Land covers remaining surface with average of 0.8 km above sea level

    surfacefeatures.gif

    Ocean Basins

    Plate Tectonics
    oceanocean.gif
     

    Convergent Boundaries occur where oceanic lithosphere  is pushed back into the mantle, marked by oceanic trenches and subduction zones.


     
     

    Two types are possible -

    oceancont.gif

    When two plates of oceanic lithosphere converge oceanic lithosphere is subducted beneath oceanic lithosphere.
    When ocean lithosphere runs into a plate with continental lithosphere, the oceanic lithosphere is subducted beneath the continental lithosphere.

     
    transform.gif


    Transform Boundaries occur where two plates slide past one another horizontally.  The San Andreas Fault, in California is a transform fault.
     
     

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    Continental rifting may create a new divergent margin and evolve into an oceanic ridge, such as is occurring in East Africa and between the African Plate and the Arabian Plate.

     
     

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    Continental Collisions: may occur at a convergent boundary when plates of continental lithosphere collide to join two plates together, such as has occurred recently where the Indian Plate has collided with the Eurasian Plate to form the Himalaya Mountains.
     

    Plate tectonics explains why earthquakes occur where they do, why volcanoes occur where they do, how mountain ranges form, as well as many other aspects of the Earth.  It is such an important theory in understanding how the Earth works.

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