EARTH 20 Lecture Notes - Lecture 2: Memory Stick, Seismometer, Seismic Moment
Internal structure of earth
➔ Earth is layered and dynamic
◆ Composition, density, and physical properties
➔ Crust sits on top of mantle
◆ Moho: boundary between the crust and mantle
◆ Asthenosphere: low viscosity
● Plates move around on it
➔ Crust
◆ Silicate, not metal
◆ Outer layer of Earth
◆ 2x denser than water
➔ Mantle: silicate, not metal
◆ Solid
◆ Iron and magnesium-rich silicates
◆ 4x denser than water
➔ Outer core
◆ Liquid metal
◆ High temperature
◆ Composition similar to inner core
● Mostly iron, some nickel
➔ Inner core
◆ Solid metal
◆ High temperature
◆ Composed of iron and nickel
Lithosphere and Asthenosphere
➔ Lithosphere
◆ Rigid
◆ Made up of plate tectonics
◆ Upper portion of the mantle and crust
◆ Cool, strong, outermost layer of Earth
➔ Asthenosphere
◆ Below lithosphere
◆ Hot, slowly flowing layer of weak rock
◆ Allows the plates of the lithosphere to move around
➔ Boundary between lithosphere and asthenosphere is not defined by a difference
in chemical compositions
◆ Determined by mechanical properties
● Rigidity of material, how material deforms under stress
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The core
➔ Earth is cooling down
◆ cooling of the liquid outer core
➔ The inner core is growing as the outer core cools and solidifies
◆ Growing at the expense of the outer core
➔ Heat is given off as the liquid outer core solidifies and inner core cools
Continents vs ocean basins
➔ Oceanic crust is denser than coastal crust
➔ Continental crust is older than oceanic crust
◆ Oceanic crust is constantly being subducted in subduction zones
◆ Continental crust is less dense so it doesn’t subduct easily
Temperature vs Heat
➔ Temperature: a measure of the warmth or coldness of an object or substance
with reference to some standard value
➔ Heat: form of energy
◆ Amount of heat depends on change in temperature as well as amount and
type of material heated
◆ Heat moves from high temperature to low temperature places
◆ Example: bigger beaker has more heat than a smaller beaker with water
of the same temperature
Three ways to move heat around
➔ Conduction: heat flows through a material from higher temp to lower temp
◆ Hot coffee heats the outside of a cup
➔ Convection: heat is transported by movement of hot material
◆ Circulating hot water which carries heat in a pot of boiling water
◆ Earth’s internal heat
◆ Allows flow of mantle material (solid rock)
◆ Produces magma
➔ Radiation: energy transferred by electromagnetic radiation (light) where heat is
generated from thermal motion of the particles within the matter
◆ The sun
Earthquakes
➔ sudden slip on a fault
➔ Release of elastic energy
➔ Results in group shaking and radiated seismic energy caused by the slip
➔ Seismic waves
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Document Summary
Moho: boundary between the crust and mantle. Upper portion of the mantle and crust. Hot, slowly flowing layer of weak rock. Allows the plates of the lithosphere to move around. Boundary between lithosphere and asthenosphere is not defined by a difference in chemical compositions. Rigidity of material, how material deforms under stress. The inner core is growing as the outer core cools and solidifies. Heat is given off as the liquid outer core solidifies and inner core cools. Growing at the expense of the outer core. Oceanic crust is denser than coastal crust. Continental crust is older than oceanic crust. Oceanic crust is constantly being subducted in subduction zones. Continental crust is less dense so it doesn"t subduct easily. Temperature: a measure of the warmth or coldness of an object or substance. Heat: form of energy with reference to some standard value. Amount of heat depends on change in temperature as well as amount and type of material heated.
