Download Structure of the Earth

2
The Earth’s Structure
2
• series of layers or spheres which
differ in density, chemistry (or
composition) and physical properties.
Density
2
• 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
2
Evidence 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
Seismic Waves
reveal that Earth’s
Interior Is
Layered
If Earth were uniform
(homogeneous) throughout
2
If the density, or
rigidity, of Earth
increased evenly
with depth
If Earth were layered inside
2
Compositional Layers of the
Earth
• the Crust
– thin outermost layer
• the Mantle
– thick middle layer
• the Core
– densest inner layer
– composed mainly or iron (90%)
2
2
2-3
2
Continents 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
2
2
Figure 1.17
2
2
Physical 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
2-1
2
Effects 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.
2-1
2
Divisions 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)
2
2
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.
2
Fig. 3-11, p. 57
2
Isostatic Adjustment
http://media.pearsoncmg.com/bc/bc_0media_geo/g
eo_animations/isostatic-adjustment/isostaticadjustment.html