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• Older

B. 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 Mantle

Lithosphere = 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 Earth

Part 1:

http://www.youtube.com/watch?v=kibQWhiymtM

Part 6: 4 min.- mineralogy & seismo.

http://www.youtube.com/watch?v=XYbE5jA0plA

Part 7: Seismic waves

http://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 Quiz

1. 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 Quiz

1. 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