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Guided Reading:
Period:
Earth’s Internal
Start on page 567, §23.2 “Earth’s Internal Layers” and answer Properties
the following questions
Name:
Date:
as you read:
1. In 1909, the Croatian seismologist Andrija Mohorovicic presented the first
convincing evidence that the Earth’s “innards” are __________________.
2. Studying seismographic data from a recent earthquake, he discovered that the
______________ __________ generated by a quake suddenly picked up
______________ at a certain depth below the surface.
3. Knowing that the speeds of the waves depend on the ________________ of the
material they pass through, Mohorovicic concluded that the speed increase he
observed was due to _________________ in the density of the Earth.
4. What does the Mohorovicic discontinuity (“Moho”) separate?
5. The core (of the Earth) is composed mostly of ___________ and _____________.
6. In the ______________ core, the iron and nickel are ______________.
7. Although the inner core is very hot, intense pressure from the weight of the rest of
the ____________ prevents the material of the inner core from ______________.
8. Because less weight is exerted on the ____________ core, the pressure is less
here, with the result that the iron and nickel are _________________.
9. The molten core flows at the low rate of several kilometers per ____________.
10. This flow is evident far outside the Earth’s surface as it generates the
_______________ ______________ that powers the Earth’s ________________
____________.
11. Surrounding the core of the planet is the ______________, a rocky layer some
___________ kilometers thick.
12. Composed of hot, iron-rich silicate rocks, the mantle behaves like ____________,
which means that it responds in a _________________ manner.
13. The upper portion of the mantle, which extends from the ___________ –
__________ boundary down to a depth of about 350 kilometers, has two zones, as
Figure 23.7 shows.
14. The lower part of the upper mantle, called the _________________________, is
especially plastic.
15. Thermal convection currents in the asthenosphere contribute to its gradual
_________. The constant flowing movements in the asthenosphere greatly affect
the _______________ features of our planet.
16. Situated above the asthenosphere is the ________________________. This layer
is about 100 km thick and includes the entire ______________ and the uppermost
portion of the ______________ (Figure 23.7).
17. Unlike the asthenosphere, the lithosphere is relatively ____________ and
_____________ and resists deformation, instead of flowing.
18. The lithosphere is, in a sense, floating on top of the ______________________
like a raft on a pond and is carried along by the motions of the _______________
in the asthenosphere.
19. The motions in the asthenosphere are not uniform, and because of this, as we shall
see later in this chapter, the brittle ____________________ is broken into many
individual pieces called ______________.
20. The movement of the lithospheric plates cause ____________________,
________________ activity, and the deformation of large masses of rock that
create _____________________.
21. The uppermost portion of the lithosphere, the portion on which we live, is the
______________.
22. The density, composition, and thickness of the _____________ vary markedly
from the deep ____________ basins to the lofty ___________________ plateaus.
23. If __________________ crust is so much thicker than _____________ crust, why
are ocean basins underwater and the continents high and dry? The answer is found
in their ________________ differences and _________________ (Chapter 5).
24. Define the principal of isostasy: