Earth’s Structure and Composition
•What is geology?•What are the characteristics of Earth’s three layers?
How do we know about Earth’s interior if we can’t see it?
- Interpret seismic (earthquake) waves - Waves travel at different speeds in
different mediums and materials
Geology = The study of the planet Earth’s composition & structure
Seimic waves & E’s interior:http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page01.cfm
2 Forces that Change Earth’s Surface
A. Constructive Forces = Forces that build up mountains etc.
B. Destructive Forces =Forces that slowly wear away any feature
Earth: Cross SectionMajor Layers1. Core (inner and outer)2. Mantle3. Crust
- Why does Earth have layers?Most dense material sinks to center / Light stuff “floats” on top
- Temperature and pressure increase with depth.Temps: Inner core (13 000 F = surface of sun); Mantle (Range fr. 7 000 – 1 600F)
- Each layer varies in physical properties: density, temp., ability to flow (viscosity)
Core Mantle Crust
Iron (85%)
Nickel (11%)
Sulfur (4%)
Density: ~11 g/cm3
Density: ~5 g/cm3
Density: ~3 g/cm3
The Composition of the Earth
CrustTypes of Crust A. Continental• Less dense rocks like
granite• 8 – 40 km thick• OlderB. Oceanic• Dense rocks like
basalt• ~7 km thick• Younger
Composition•Light Rock layer• Thin layer• Made of silicates(Light rocks of silicon & oxygen)
Abundances of Elements in Earth’s
Crust
Silicon & Oxygen compounds = silicates
( ~ 74%)These make
crust light!
“Moho” = boundary b/w crust & upper mantle
Mantle Convection
http://www.see.leeds.ac.uk/structure/dynamicearth/convection/index.htm
The MantleComposition: Hot Heavy
Rock!Made of silicates; but also a lot of
iron & magnesium (heavier)• Temps: 1,600 7,000 F • Pressure increases as you
descend!Not COMPLETELY solid
• Middle part is “plastic”/ taffy like
• Hot rock moves in CONVECTION CURRENTS
3 Divisions of the MantleLithosphere = Upper
mantle + Crust“Plates”, Rigid Slabs
Asthenosphere = Softer, moving hot rock (Convection Currents)
Mesosphere = Stiffer rock near core
How do we know what’s in the mantle?
How do we know what it is made of?
• Scientists infer based on:
• Pushed up rock• Ocean floor/molten
rock• Seismic waves
What is it like?• Like the mineral olivine
• Large amounts of iron and magnesium
Core• Composition: Heavy Metals! • Iron & Nickel(How do we know? Earth’s
magnetic field & seismic waves)• Pressure 3.6 million times that at
surface• Temps: 6 700 C (same as
surface of sun)
2 Layers of Core
• Inner Core– Solid iron and nickel– High pressure keeps
it solid
Outer Core• Liquid iron and nickel• High temp. keeps it liquid• Responsible for Earth’s magnetic field
Visualizations • Earth Science Classzone:• http://www.classzone.com/books/earth_science/terc
/navigation/investigation.cfm• Visuals on plate convection:
http://www.gps.caltech.edu/~gurnis/Movies/movies-more.html
• Mantle Convection: http://www.youtube.com/watch?v=p0dWF_3PYh4&feature=results_main&playnext=1&list=PL8873B6173CE6E948
• Pole Reversal:• http://www.youtube.com/watch?v=x-p49IBuR1Y• Polar Shift• http://www.youtube.com/watch?
v=akBvr_ZUCro&feature=related• Polar Shift 2012: • http://www.youtube.com/watch?
v=23uwKo6vd0Y&feature=related• 2012 mag reversal:• http://www.youtube.com/watch?
v=zOk7_6pcUns
Early Earth & Plate Tectonics:http://www.youtube.com/watch?v=QDqskltCixA&feature=related
Journey to the center of the EarthPart 1:http://www.youtube.com/watch?v=kibQWhiymtMPart 6: 4 min.- mineralogy & seismo.http://www.youtube.com/watch?v=XYbE5jA0plA
Part 7: Seismic waveshttp://www.youtube.com/watch?v=ZP9R20QgDNs&feature=related
Iron (85%)
Nickel (11%)
Sulfur (4%)
Density: ~11 g/cm3
The Core
Label Each Layer.
Be able to describe each layer.
Upper mantle
Self Quiz1. Compare how constructive and destructive
forces affect Earth’s surface.2. List the 3 layers of Earth.3. Which layer has currents of moving rock?4. Which is the most dense layer?5. Which layer is made of light rocks like silicates?6. Which is more dense: Continental or Oceanic
Crust?7. Which layer of the mantle is part of Earth’s
plates?8. Which layer is made of heavy metals?
Answers to Self Quiz1. Constructive forces build new land/crust and
destructive forces destroy crust.2. Crust, Mantle, Core3. The asthenosphere – which is in the mantle4. The core5. The crust5. Oceanic crust is denser (but thinner)6. The upper mantle (and the crust make up the
lithosphere, or plates)7. Core