CHAPTER 8.4Earth’s Layered Structure

Earth’s interior consists of 3 major layers defined by their chemical composition

Crust Mantle Core

The Earth’s Crust

Thin, rocky outer layer of earth Divided into oceanic and

continental crust

Earth’s Cust

Oceanic Crust 7 km thick Consists of

igneous rocks Density of

rocks=2.7g/cm3 Rocks are much

younger

Continental Crust 8-75 km

thick;average thickness =40km.

Consists of a variety of rocks-mostly granite

Density of rocks=3.0g/cm3

The Mantle 82% of Earth’s volume is found here A solid, rocky shell that extends to a

depth of 2890 km. Periodite is a common rock found in the

uppermost mantle, density=3.4g/cm3 The boundary between the crust and

mantle indicates a change in chemical composition.

The Core

A sphere made mostly of an iron-nickel alloy.

In the center of the core extreme pressures exist producing an average density of 13 g/cm3.

Earth can be divided into layers based on physical properties

The lithosphere The asthenosphere The lower mantle The outer core The inner core

Earth’s layers defined by physical properties

THE LITHOSPHERE THE ASTHENOSPHERE

Earth’s outermost layer made of the crust and upper mantle

Forms a relative cool shell

This layer averages 100km in thickness

Soft and weak layer of Earth

A rigid shell that averages 100km in thickness.

More of Earth’s Layers

LOWER MANTLE INNER AND OUTER CORE

Located 660km down near the base of the mantle.

The rocks here are very hot and can gradually flow

Composed mostly of Fe & Ni alloy.

Outer core is a liquid layer 2260 km thick and produces the magnetic field.

The Inner core has materials that are compressed into a solid state due to extreme pressures.

Discovering Earth’s Layers

Studies of the paths of p and s waves through Earth ‘s layers helped identify boundaries and that the outer core is liquid.

1909-1st evidence of layering within the Earth’s mantle; created the Moho boundary.

1906 another boundary was discovered between the mantle and the outer core.

Discovering Earth’s Composition

Scientists studied seismic data, rock samples from the crust and mantle, meteorites, and high pressure experiments on Earth materials.