Chapter 8 Section 1 Review
1. So they can understand the age and history
of Earth.
2. It’s like what happened in the past is just
like what is happening now man.
3. According to the law, a rock layer is always
younger than the rock layer below it if the
layers are undisturbed.
4. An unconformity is a break in the rock
record; a nonconformity is a kind of
unconformity in which metamorphic or
igneous rock layers are overlain by
sedimentary rock layers.
5. In an angular unconformity, tilted rock
layers are overlain by horizontal rock layer.
In a disconformity, the rock layers above
and below the unconformity are parallel.
6. The law of crosscutting relationships helps
scientists understand that a body of rock or
fault is always younger than any other body
of rock that it cuts through.
Chapter 8 Section 2 Review
1. Relative age is the age of an object in
relation to the age of other objects.
Absolute age is the numeric age of an
object.
2. The rate at which sediment is deposited or
eroded can vary.
3. Varves are layers of sediment that consist
of one layer of sand covered by one layer
of silt, that are deposited at the bottom of
glacial lakes, and that represent one year of
deposition.
4. By comparing the relative percentages of a
radioactive (parent) isotope and a stable
(daughter) isotope in a sample of rock,
based on the known rate of decay of the
parent, scientists can calculate the length of
time since the rock formed.
5. Half life is the time one half of a sample of
a radioactive isotope takes to break down
by radioactive decay to form a daughter
substance.
6. Chose any 3 radiometric dating methods in
Table 1 on page 19 in your books.
Chapter 8 Section 3 Review
1. An Entire organism may be preserved as a
fossil if it is mummified, trapped in amber
or in tar seeps, frozen, or petrified.
2. Four types of fossils that can be used to
provide indirect evidence of organisms are
imprints, molds and casts, corprolites, and
gastroliths.
3. When scientists know the time interval
during which a specific organism lived,
they can use the presence of those fossils to
date sedimentary rock layers that contain
those fossils.
4. Mummification occurs in very dry regions,
where bacteria cannot decay the body.
Thus, much of it remains unchanged.
Petrification occurs in areas where mineral
solutions replace the buried organic
materials with new materials, such as silica
and calcite.
5. Index fossils are fossils of distinct
organisms that lived during short spans of
geologic time. Any rocks that contain
index fossils can be given an absolute age.
Chapter 8 Review
1. An example of uniformitarianism would be
volcanoes erupt the same today as they
have in the past.
2. Varves are like tree rings in that varves are
laid down each year.
3. Radiometric dating compares the relative
percentages of a radioactive (parent)
isotope and a stable (daughter) isotope.
4. A half life is the time it takes half the mass
of a given amount of radioactive isotope to
decay into its daughter isotopes.
5. Relative age is the age of an object in
relation to the age of other objects.
Absolute age is the numeric age of an
object.
6. According to the law of superposition, a
rock layer is always younger than the rock
layer below it if the layers are undisturbed.
The law of crosscutting relationships helps
scientists understand that a body of rock or
fault is always younger than any other body
of rock that it cuts through.
7. A trace fossil is a fossilized mark that
formed in sedimentary rock by the
movement of an animal on or within soft
sediment. Index fossils are fossils of
distinct organisms that lived during short
spans of geologic time. Any rocks that
contain index fossils can be given an
absolute age.
8. b
9. b
10.c
11.d
12.c
13.b
14.a
15.He noticed geologic changes occurring on
his farm and assumed that same forces had
changed Earth’s surface in the past.
16.The law of superposition helps scientists
determine rocks’ relative ages because
older rocks are at the bottom of undisturbed
strata and younger rocks are at the top.
17.All are breaks in the geologic record. A
nonconformity is the boundary between
new sedimentary rock on top of uplifted
and eroded igneous or metamorphic rock.
An angular unconformity occurs when
horizontal rock layers are tilted and eroded.
The layers below the unconformity are not
parallel to rock layers above the
unconformity. A disconformity is an
unconformity in which the layers below the
unconformity are parallel to the layers
above the unconformity.
18.Scientists know the half life (rate of decay)
of radioactive isotopes. By comparing the
relative percentages of a radioactive
(parent) isotope in a rock and a stable
(daughter) isotope they can calculate the
time at which the rock formed.
19.Three other methods of estimating absolute
age are using rates of erosion, using rates
of deposition, and counting varves.
20.Organisms can be preserved by
mummification, or drying; by being
trapped in tree sap, which hardens into
amber; by being trapped and preserved in a
tar seep; by freezing in ice or soil; or by
petrification, a process in which minerals in
groundwater replace original organic
material and solidify into rock.
21.An index fossil must occur in rocks spread
over a wide area; it must have features that
distinguish it clearly from other fossils; it
must have existed during a relatively short
geologic time span; and it must occur in
large numbers.
25.If the fossil was rare and could not be
found easily in rock in different areas, it would
not make a good index fossil.
28.
29.
30.
33.The intrusion is younger because it cuts
through the fault.
34.Angular unconformity; The layers below
the unconformity are folded and are tilted
where they are cut by the unconformity.
35.Layer x is older, because layer Y is on top
of it.