1. 8.4 Earth’s Layered Structure
Earth’s interior consists of three major layers: the crust, mantle, and core. 3 2 1

2. The Crust
• Thin, rocky outer layer made up of two different types of crust
• Oceanic crust is thin (~7 km)
Continental crust is Thick (~ 8-70 km)

3.  Crust • Continental crust - Upper crust composed of granitic rocks
- Lower crust is more akin to basalt (Old Oceanic Crust)
- Less dense than oceanic crust
- Up to 4 billion years old

4.  Crust • Oceanic crust - Basaltic composition
- More dense than continental crust
- Younger (180 million years or less) than the continental crust
- In this picture Red is young and blue is old

5.  Mantle
• Below crust
• Composition of the uppermost mantle is the igneous rock
Makes up Most of earth’s volume

6.  Core • Below mantle • Sphere with a radius larger than the moon!
• Composed of an iron-nickel alloy
• Very Dense!!! (11 g/cm³)

7. For the purpose of studying plate tectonics, earthquakes, and volcanoes, the Earth is divided into the following layers:
Lithosphere
Asthenosphere
Lower Mantle
Outer Core
Inner Core

8.  Asthenosphere  Lithosphere • Crust and uppermost mantle
• Cool, rigid, solid
 Asthenosphere
• Beneath the lithosphere
• Upper mantle
• Soft, weak layer that is easily deformed
Lithosphere
“floats” on Asthenosphere

9.  Lower Mantle (Mesosphere)
• More rigid layer
• Rocks are very hot and capable of gradual flow.

10.  Outer Core  Inner Core • Liquid Layer
• Convective flow of metallic iron within generates Earth’s magnetic field
 Inner Core
• Sphere of Iron and Nickel (Heavy metals!)
• Behaves like a solid

11. Earth’s Layered Structure

12.  Moho ˇ ´ • Speed of seismic waves increases below 50 km of depth
• Separates crust from mantle

13. Earth’s Interior Showing P and S Wave Paths
How do we know if the core is solid or liquid?