Earth’s interior

      Comprised of several layers

             Compositional layers

                   Changes in the material

             Mechanical layers

                   Changes in the physical state or properties of the material

      Earth’s Structure

             Core: inner and outer

             Mantle:  mesosphere and asthenosphere

             Crust:  oceanic and continental

 

      Details

             Inner core:  solid  13.5 g/cm3

             Outer core:  liquid 10 g/cm3

             Mesosphere (lower mantle):  solid  5 g/cm3

             Asthenosphere (upper mantle):  plastic 5 g/cm3

             Crust (lithosphere):  solid

                   Oceanic:  iron and magnesium rich  3 g/cm3

                   Continental:  silicon rich  2.7 g/cm3

 

Why do some parts of the earth the same composition but have different physical states

How do we know what the interior of the earth looks like or what it is made of?

 

Seismic waves

      P-waves

             P-waves travel through solid and liquid material

             Longitudinal waves

             Fastest of the two waves

      S-waves

             S-waves travel through solid only

             Transverse waves

             Why can’t s-waves travel through liquid?

 

Wave theory

      Waves will speed up or slow down as they move into material with different

             properties

      Waves will, reflect, refract or be absorbed as they move into material with different

             properties

 

Determined by Snell’s Law

      sin f1/ sin f2=V1 / V2

      Only really pertinent for refracted waves…why?

 

 

 

 

Boundaries discovered based on seismic waves

      Discontinuities

             Boundaries in the earth where seismic wave velocities change or the direction the

                   wave travels changes

      MOHO:

             between crust and mantle

      Gutenberg:

             between the mantle and core

      Lehmann:

             between the inner and outer core

 

Shadow zones help tell us about size and physical state of different parts of earth

 

Other Clues to the interior composition of the earth

      Meteorites

             Irons

             Stones

             Stony irons

      Ophiolites

      Volcanoes and xenoliths

 

Why should we care about what the interior of the earth is like?

      Possible resource

      Help to understand the earth

      Heat production

      Surface features

             Earthquakes

             Volcanoes

 

Plate tectonics

      Unifying theory of Geology

      Says earth’s surface is broken into plates which move around. (more in a bit)

      Relatively new idea (1960’s)

      Started as continental drift

 

1960’s

      Ocean exploration begins

      Found large volcanic mountain ranges in the middle of the oceans

      Magnetic anomaly patterns

      Age of ocean crust

     

Develop theory of Plate Tectonics

      Earth’s surface is broken into a series of plates

      These plates move around on the surface and interact with each other in various ways

             depending on the type of crust

      Movement of plates occurs due to the plastic nature of the asthenosphere and the heat

             generated inside the earth

 

Divergent Plate Boundary

      2 plates moving away from each other

      Occurs primarily in the ocean crust

      Creates the Mid-ocean Ridge system

      Largest mountain range on the surface of the earth

      Volcanic mountains that CREATE the ocean crust

 

Convergent Plate Boundary

      Plates come together

      Different types of plates will interact in different ways

             3 different convergent plate boundaries

                   Continental to oceanic convergence

                         Subduction occurs

                         Ocean plate is forced under continental

                         Volcanoes form on continental plate

                         Cascade Mountains are formed by this process

 

                   Oceanic to oceanic convergence

                         Older oceanic crust subducts

                         Creates Island Arc volcanoes

     

                   Continental to continental

                         Very large mountains form from this process. 

                         EX// Himalayan Mountains are an example

 

Transform Plate Boundaries

      Plates slide by each other

      Often associated with divergent boundaries

 

Hot spots

      Stationary hot plume of material rising from mantle

      Plate rides over plume and creates a volcano

      As plate continues to move, volcano moves off plume and dies

      New volcano is created on top of plume

      Creates a chain of volcanoes

 

Mechanisms

      Slab pull

      Heat convection cells

             Radioactive decay

      Ridge push

 

How do Plate boundaries relate to earthquakes?

 

Important point of plate tectonics

      Main cause of Earthquakes

             Divergent

                   Shallow, often small quakes

             Subduction

                   All depths and magnitudes of quakes

             Cont-Cont Collision

                   Shallow to intermediate quakes, small to large

             Transform boundaries

                   Shallow small to large quakes

 

Shallow < 100 km, inter 100-300 km, deep 300-600 km