Ch 7-2 Earths Interior

how is the interior structure of Earth determined?

• from geophysics, specifically study of Seismic waves

what are seismic waves?

• mechanical waves that can be produced by artificial sources (explosive, vibrators) or by natural source (earthquakes)

• travel through mediums such as solid, liquid, and gas (causes particles to obsolete and moving the mantle

what does wave speed of seismic waves depend on?

• the density of the material through which they travel

  • can artificially create i.e. explosions

pressure waves (p-waves, primary waves)

• longitudinal and will travel through liquids, solids, and gases

• 1st type of wave to arrive at monitoring station after earthquake

• interior

how do p-waves travel?

• by compressing and expanding material parallel to the direction the wave is travelling

• fast

what are shear waves (s-waves, secondary waves)

• transverse and will only travel through solids, not through liquids or gas

• arrive at monitoring stations after p-wave (slower than p waves)

how do s-waves travel?

• by moving material back and forth perpendicular to wave direction

how can we use the pattern of reflections during earthquakes?

• deduce the interior structure of the Earth

  • travel through interior of Earth

• when liquid → doesn’t transmit to other side of the globe

How do scientists determine the internal structure of Earth?

• By studying how seismic waves from earthquakes travel, reflect, and refract through Earth's interior.

Why are seismic wave reflections useful?

• They reveal the locations and properties of Earth's internal layers.

What is the S-wave shadow zone, and what does it tell us about Earth's interior?

• The S-wave shadow zone is the region on Earth where no S-waves are detected after an earthquake. Because S-waves cannot travel through liquids, this proves that Earth's outer core is liquid.

What is the P-wave shadow zone, and what causes it?

• The P-wave shadow zone is a region where no direct P-waves are detected because they are strongly refracted (bent) when they enter the liquid outer core.

Earths interior

• composed of several layers

  • crust, mantle, core

Earth’s Internal Layer: Crust

• thin, outermost layer, rigid rock

• where we started

how thick is the crust?

• 5-10km (oceanic, dense) to 30-50km thick (continental, less dense)

what is the crust constantly changing from?

• plate tectonics, earthquakes, volcanism

how deep is the deepest hole dug into Earth’s crust?

• ~12.2 km deep

Earth’s Internal layer: Mantle

• largest layer of Earth’s interior

• mostly solid

• ~2900 km thick

what are the 3 sublayers of the mantle?

• upper mantle

• transition zone

• lower mantle

describe the upper mantle

• from crust to ~410 km deep, mostly solid but more malleable regions contribute to tectonic activity

  • lithosphere: very upper portion of mantle and crust

describe the transition zone

• 410-660 km; rocks become much more dense

  • prevents/limits exchange of material from upper and lower mantle

describe the lower mantle

• 660-2900 km deep; hotter and more sense but solid because of intense pressure

  • surface of mantle plumes

    • large volumes of magma that break through crust and form volcanoes

Earth’s internal layer: core

• very hot, very dense, metal rich

• Ni, Fe

• younger than Earth

describe the outer core

• liquid Fe and Ni 4500-5500C; low viscosity, constant violent convection = magnetic field

  • swirling of this liquid metal causes our magnetic field

describe the inner core

• mostly Fe; pressure nearly 3.6 million atm. = solid

  • heart

  • chunk of iron

  • high pressure that solidifies iron

How did Inge Lehmann discover Earth's inner core?

• By studying seismic (earthquake) waves and noticing unexpected P-wave behavior that could only be explained by a solid inner core.

What major contribution did Inge Lehmann make to geology?

• She demonstrated that Earth is composed of a liquid outer core and a solid inner core.

what is the Homogeneous Accretion Theory?

• Earth condensed into its body by solar nebula 4.6 billion years ago

  • uniformed composition and density

  • internal heat of planet increases to melt Fe and Ni

    • more dense than remaining silicate metal

      • sunk to middle of planet

      • lighter silicate metal floated towards surface

      • create Earth’s internal layers