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

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)

 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

 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

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

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

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

 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

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

 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

Earth’s Layered Structure

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

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