Download Chapter 17 - Heritage Collegiate

Chapter 17
Earth’s Interior
Notes
(1 class notes + 1 class Xword & review + 1 class test)
Objectives:
1. Use earthquake data to construct a model of the earth's interior. pp.
475-477
2. Describe the 3 major processes that have contributed to the earth’s
internal heat. p. 483
Seismic Waves and the Earth's Interior
Most of our knowledge of the earth's interior comes from the study of
P and S waves. P waves travel faster than S waves so they will take
different times for each to pass through the earth. However, the time it
takes them to travel through the earth also depends on the type of rock
material the waves pass through. Therefore any time difference in the
arrival of P and S waves at a seismic station that could not be
accounted for by the difference in speeds of the waves would indicate
that the rock material in which the waves passed through had
changed.
Seismic waves indicate that the earth has four (4) layers - crust,
mantle, outer core, and inner core (see Figure 17.6 p. 476 text).
1. Crust – the solid, relatively thin outer layer of the earth that
ranges in thickness from 3km at ocean ridges to around 70km in
some continental mountain ranges. It is comprised mostly of low
density elements (recall Table 2.3, p. 44), due to the segregation
of materials when the earth melted.
2. Mantle – the thickest of the four layers. It is solid but has fluidlike properties (think Eatmore Bar) and is composed of both
high density and low density material but is generally denser
and hotter than the crust. The upper part of the mantle
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(asthenosphere) has fluid like properties and is the weakest part
of the mantle. The crust and a thin part of the upper mantle
(lithosphere) tend to act as a single unit and seems to make up
the plates in plate tectonics.
3. Outer Core – the liquid, outer part of the core. It consists of
heavier elements such as iron and nickel which sank towards the
centre of the earth during segregation. Even though it is liquid,
the outer core is denser and hotter than the mantle.
4. Inner Core – the solid, inner part of the core. Like the outer
core, it also consists of heavier elements like iron and nickel but
is hotter and denser.
See video about discovery of core here.
Sample Exam Questions
1. Seismic waves change speed as they pass through the earth. What
does this tell us about the earth's structure?
2. Seismic waves sometimes change speed abruptly in the mantle.
What does this tell us?
Activity: Complete the following table (see pp. 480-483).
Layer
Crust
Mantle
State
Solid with
fluid-like
properties
More dense than
mantle, less dense
than inner core.
Outer Core
Inner Core
Density
Temperature
Least dense  2.7g/cm3 
Solid
Hottest
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Segregation & the Earth’s Internal Heat
Earth melted and allowed segregation to occur because of the heat
within the earth. Three (3) major processes have contributed to the
heat within the earth.
1. Heat from the radioactive decay of isotopes such as uranium,
thorium, and potassium.
2. Heat from the crystallization of iron to form the solid inner core.
3. Heat released from colliding particles when the earth was formed.
This heating, along with gravity and the different densities of the
elements, allowed the elements to separate and create the different
layers than make up the earth.
Do #'s 2-4, 10, 15-16, 18 pp. 488-489 text.
Read Chapter Summary items 1-9 pp. 487-488 text
Read pp. 514-523 for next day.
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