The Earth’s Structure

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2The Earth’s Structure

• series of layers or spheres which differ in density, chemistry (or composition) and physical properties.

2Density

• is the relative heaviness of a substance• Or how heavy something is for its size• defined as the mass per unit volume• usually expressed in g/cm3

• EARTH HAS DENSITY STRATIFICATION

2Evidence of the Earth’s Interior Composition

• Can only drill about 7.5 miles (earth’s radius = 4000 mi)

• Vents, volcanoes, variation in pull of gravity, etc.

• study of the shocks from distant earthquakes

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Seismic Waves reveal that Earth’s Interior Is Layered

If Earth were uniform (homogeneous) throughout

If the density, or rigidity, of Earth increased evenly with depth

If Earth were layered inside

2Compositional Layers

of the Earth

• the Crust– thin outermost layer

• the Mantle – thick middle layer

• the Core– densest inner layer– composed mainly or iron (90%)

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2Continents and Ocean

Basins Differ• Continental crust

– is mainly composed of granite, a light colored, lower density (2.7 gm/cm3) rock

– thicker• Oceanic crust

– is composed of basalt, a dark colored, higher density (2.9 gm/cm3) volcanic rock

– thinner

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Figure 1.17

2Physical Properties of

the Layers

• Not determined only by chemical composition• The behavior of the rock (brittle or plastic) is

determined mainly by temperature and pressure

2Effects of Pressure and

Temperature on Physical State of

Layers• Increasing pressure raises the melting point

of a material.• Increasing temperature provides additional

energy causing material to melt.• Both pressure and temperature increase

toward the center of the Earth, but at different rates.

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2Divisions of the Earth Based Upon Physical

State • the Lithosphere

– cool, rigid outer layer– comprised of continental crust, oceanic crust

and the uppermost cool, rigid portion of the mantle

• the Asthenosphere – hot, slowly flowing layer of the upper mantle

• the Mesosphere (Lower Mantle)– rigid layer, similar chemically to the

asthenosphere but very different physically• the Outer core

– thick liquid layer• the Inner core

– solid layer (due to tremendous pressure)

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What Are the Sources of Internal Heat That

Keep the Asthenosphere Plastic?• Radioactive decay (atoms of elements give

off heat when their nuclei break apart)• Internal heat moves to the surface by

conduction – slow migration of heat through a material by collision of atoms

• And by convection – movement of heat in a fluid as it expands, becomes less dense and rises.

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Fig. 3-11, p. 57

2 Isostatic Adjustment

http://media.pearsoncmg.com/bc/bc_0media_geo/geo_animations/isostatic-adjustment/isostatic-adjustment.html