The Earth and its layers

GLGY 209-UofC

How deep is the earth?

6,4000 km deep

What is drilling?

• 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 

What is the different criteria used to discuss earth’s internal layers?

• Chemical composition 

• Mechanical behavior of materials 

  • When a force is applied=how they respond

How many many layers is the earth composed of?

• 3

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

How do we know the layers are there?

• 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 

What are the differnet kinds of earthquake waves?

• 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.  

How are these waves read?

• 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 

What is the crust?

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

• 2 types: continental and oceanic

What is continental crust?

• 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)

What is oceanic crust?

• 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)

What is a hypsometric curve?

• 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)

What is the mantle?

• 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) 

What is the upper mantle composed of?

• 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)

Why is the mantle similar to a pot of water heated from below?

• 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 

What is the core?

• 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 

What is the outer core?

• Liquid iron and nickel 

• Know because of seismic waves 

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

What is the inner core?

• Solid 

• Primarily composed of iron and nickel 

How is earths magnetic field produced?

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

What does the magnetic field do?

• 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

What are compositional layers?

• continental and oceanic crust, mantle and core 

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

What are the mechanical layers?

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

How do the layers act?

• 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  

What is the lithosphere?

• 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

What is the asthenosphere?

• 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)

What is the mesosphere?

• 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