Transcript The Planet Oceanus

The Earth’s Structure
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• series of layers or spheres which
differ in density, chemistry (or
composition) and physical properties.
Density
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• is the relative heaviness of a substance
• defined as the mass per unit volume
• usually expressed in g/cm3
• EARTH HAS DENSITY STRATIFICATION
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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
Earth’s Interior Is Layered
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What evidence supports the idea that Earth has layers?
The behavior of seismic waves generated by earthquakes give
scientists some of the best evidence about the structure of Earth.
(a) If Earth were uniform (homogeneous) throughout, seismic
waves would radiate from the site of an earthquake in straight
lines.
(b) If the density, or rigidity, of Earth increased evenly with
depth, seismic wave velocity would increase with depth, and the
waves would bend smoothly upward toward the surface.
(c) If Earth were layered inside, some seismic waves would be
reflected at the boundaries between layers while others were
bent. Seismic evidence shows that Earth is layered.
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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%)
Figure 1.14
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Figure 1.16
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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
Table 1.1
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Figure 1.17
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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
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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
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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)
Figure 1.14
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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