Geoscience Reference
In-Depth Information
S u m m a r y o f K e y C o n C e p t S
1. Four major layers occur in the internal structure
of Earth, including (from lowest to highest): (a) in-
ner core, (b) outer core, (c) lower mantle, (d) upper
mantle (including the asthenosphere, lithosphere,
and crust). These layers are identified on the basis of
their chemical composition and solid or molten char-
acter. Of particular interest is the oceanic and conti-
nental crust. Oceanic crust consists largely of silica
and magnesium ( sima ) and is denser than continen-
tal crust, which is composed of silica and aluminum
( sial ).
sedimentary, or other metamorphic rocks are altered by
intense heat and pressure.
3. The rock cycle describes the ways in which sediments
move from one place to another on Earth over time to
become new kinds of rock, or how they are transformed
to become new kinds of rock. A key concept in this cycle
is that rocks gradually break apart as time goes by. The
liberated rock fragments are then transported to another
place, where they are deposited and gradually lithify to
form new rock.
4. Earth is about 4.6 billion years old. Geologic time refers
to the length of time from the origin of Earth to the pres-
ent and is hierarchically subdivided into (from longest to
shortest time) Eons, Eras, Periods, and Epochs.
2. Three basic kinds of rocks occur on Earth: igneous,
sedimentary, and metamorphic. Igneous rocks form
when magma cools within Earth (forming intrusive igne-
ous rocks) or on the Earth's surface (forming extrusive
igneous rocks). Sedimentary rocks consist of large lay-
ers of formerly loose sediments that slowly compacted
and lithified. Metamorphic rocks form when igneous,
5. Fossil fuels are derived from organic remains that have
been buried within Earth. We use these remains to power
our economy.
C h e C K y o u r u n d e r S t a n d i n g
1. Compare and contrast the four major layers of Earth.
8. Describe the flows that occur within the rock cycle.
Where does the cycle begin? How do igneous rocks
become sedimentary rocks? How do sedimentary
rocks become metamorphic rocks? How do the pro-
cesses of erosion, deposition, and lithification fit within
the rock cycle?
2. Describe the concept of isostatic depression and re-
bound. Why do each of these processes occur, and why
does this concept reflect the relationship between the
crust and asthenosphere?
3. Describe the nature of the Earth's inner core and why it
has the characteristics that it does.
9. How is the geologic timescale configured? Using the
terms Epoch, Era, Period, and Eon, arrange them into
the hierarchy of geologic time.
4. Describe the two types of crust found on Earth. What is
the basic composition of each type of crust?
10. How does the concept of radioactivity fit within the
context of calculating the age of ancient rocks? Why
are the terms radioactive isotope and half-life relevant?
5. What is the difference between intrusive and extrusive
igneous rock? What are some examples of each kind of
rock, and how do you tell the difference between them?
11. Describe how the formation of the Grand Canyon is
related to the geologic timescale and rock cycle.
6. What are the various kinds of sedimentary rock, and why
do they occur? How does the process of lithification fit
into the context of sedimentary rock?
12. How is our economy dependent on organic sedimen-
tary rocks, and why are we vulnerable as far as petro-
leum resources are concerned?
7. What are the two ways that rocks become metamorphic
rocks?
 
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