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