The Earth and its layers

6,4000 km deep

• way for scientists to probe the Earth's sediments, crust, and upper mantle

• Deepest drill hole– 12 km 

• Marianas trench max 11km- is what we know 

• We have to learn about the interior of the earth through other observation 

• Chemical composition 

• Mechanical behavior of materials 

  • When a force is applied=how they respond

• 3

• Outer: crust, Mantle, Innermost: Core (boiled egg)

• Measured through seismic waves which are measured at stations across the earth

• the speed of these waves increases with density and as you go deeper into the earth the density of rocks increases due to presuure from overlying rocks

• Major change in seismic wave velocities=the density is significantly changing–seismic discontinuity

  • These changes say there are different layers 

• P-wave (body wave), S-wave (surface/shear waves)

  • P-waves travel through compression and decompression

  • P-waves are faster 

• P-waves can travel through solids (rocks and minerals) and fluids (water and magma). S-waves can only travel through solids.  

• Seismic station is where a sensor is 

  • P-wave arrives first and then the s- wave arrives later 

• Speed is determined on the function of the property of the rock  

  • Less dense=slower dense=faster 

  • Affects both waves 

• thick outer shell of rock, referring to less than (<) 1% of the planets radius and volume

• 2 types: continental and oceanic

• Thicker—Avg–25-30 km, but avg can vary (Himalayas-thick crust (80km)) 

•  30% of crust and high elevation

• avg composed of granite (density 2.6-2.7g/cm relative to water)

• Continents are formed at higher elevations because basalt/oceanic crust is floating on the earth's mantle, continental crust floats higher (forms ocean basisn)

• Thinner—Avg 5-7km—Fairly uniform in thickness 

• 70% of the crust and low elevation

• made of basalt (density: 2.9-3g/cm relative to water)

• shows the proportion of the earth's surface at a certain elevation 

  • Distribution of land surface relative to sea level 

  • Continental shelf: edge of a continent that lies under the ocean (submerged)

• Largest and thickest layer 

• 82% of Earth by volume 

• Generally solid rock despite magma, but can behave like a fluid sometimes (over long tome scales, the rock can move) 

• Seismic wave activity increases

  • Show a sharp increase in speed from the base of the crust to the top of the mantle 

• Divisible into 

  • Upper mantle (base to 410 km depth)

  • Transitional mantle (mineralogical changes) 

  • Lower mantle (660-2,900km) 

• ultramafic rock peridotite

  • Peridotite–most common mantle rock 

    • Basalt is volcanic, magma is formed in mantle, and as its moved up it carries fragments of the mantle (Xenolith)

    • Xeno=foreign Lith=Rock, foreign rock 

  • Ultramafic–extremely rich in iron and magnesium (even more dense)

• Below certain depth, mantle convects

• Convection currents occur due to density differences caused by variations in temperature and composition

• As it heats up, the bottom gets hotter and moves up and cold comes down—Convection cell 

• Over long time scales, the mantle can slowly move/flow 

• Over short time scales it behaves as a solid 

• 17% of Earth by volume 

  • Base of mantle to center

• composed of outer and inner core

• Core has a composition similar to iron meteorite 

  • Shooting stars that reach earth and they have a crust, mantle and core 

• Liquid iron and nickel 

• Know because of seismic waves 

• P-wave speed decreases, and s-waves don't travel through 

• Solid 

• Primarily composed of iron and nickel 

• Outer core flows around the solid inner core generates earth's magnetic field (the motion creates the magnetic field)

• shields us from high energy radiation from the sun

  • Also use for navigation 

  •  Interacts with solar waves and protects us 

  • Interaction between high energy particles and magnetic field creates aurora

• continental and oceanic crust, mantle and core 

• Behavior of the layers is different how they respond to force 

The lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core

• The crust and a bit of the upper mantle behave in a rigid way (break rather than flow)

• lithosphere doesn’t take part in convection

• Asthenosphere–convects 

• Lower mantle is also rigid-pressure is too high–Mesosphere

• Outer core convects, inner is solid rock so doesn't convect because of high pressures  

• the outermost physical layer of the earth (crust and upper part of mantle)

  • Diamonds form because its thick and there's high pressure 

• 2 types: oceanic and continental

• It is broken into segments called plates

• from the base of the lithosphere to the transitional mantle

• moves and flows due to convection currents created by heat coming from the earth’s core

• is relatively unbroken (determined this by analyzing seismic waves that pass through the layers)

• the lower mantle, is more rigid due to high pressures and temperatures

• Located at a depth of approximately 410 and 660 km below the earth’s surface

• extreme conditions create a transition zone in the upper mesosphere where minerals continuously change