Geologic Time — Unit test Answers

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1
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Which statement describes potassium-argon dating?

A
Potassium-40 decays into argon gas over time.
B
Argon breaks down into other elements and compounds.
C
Potassium-40 becomes stable when trapped in rocks.
D
Argon is unstable and will decay into potassium-40 over time.
2
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From which location does seafloor spreading originate?

A
mid-ocean ridges
B
edges of continents
C
deep-ocean trenches
D
underwater volcanoes
3

Study this image of lithospheric plates.

Question illustration
A
Pacific, Eurasian, and African
B
African, North American, and South American
C
Eurasian, African, and South American
D
North American, Pacific, and African
4

Study this image.

Question illustration
A
Oceanic and continental plates are colliding.
B
Oceanic and continental plates are shifting past each other.
C
Two continental plates are forming a large mountain.
D
Two oceanic plates are creating several island chains.
5

According to the theory of plate tectonics, which is one feature that plates carry?

A
seafloor
B
inner core
C
lower mantle
D
asthenosphere
6

The diagram illustrates radioactive decay.

Question illustration
A
Structure 1 is an unstable atom that turns into structure 2, a new atom.
B
Structure 1 is a stable element that breaks down into structure 2, an unstable element.
C
Structure 1 is a radioactive element that loses particles to create structure 2, released energy.
D
Structure 1 is a radioactive atom that decays into structure 2, half of the original unstable element.
7

Which features form along all types of plate boundaries?

A
faults
B
rift valleys
C
mountains
D
ocean ridges
8

Which is an example of a trace fossil?

A
animal burrow
B
skin of organism
C
preserved bone
D
petrified wood
9

Which method preserves an image of a leaf?

A
The leaf turns into rock over time.
B
Tree sap flows over the leaf and preserves it.
C
Sediment covers the leaf and leaves an imprint on the rock.
D
As the leaf decomposes, carbon from the leaf is left on the rock.
10

Which continents contain folded mountains that match up to form one continuous mountain chain, serving as evidence that they once belonged to one landmass called Pangaea?

A
Antarctica and Africa
B
Africa and North America
C
South America and Africa
D
Eurasia and South America
11

What is the orientation of the magnetic stripes of iron contained in rocks that support the idea of seafloor spreading?

A
east and west
B
north and east
C
south and west
D
north and south
12

The image shows locations of fossils from different geologic periods in Virginia.Which association correctly links the time period with the location of the fossils?

Question illustration
A
Pennsylvanian eastern and western Virginia
Option A
B
Cambrian throughout southern Virginia
Option B
C
Tertiary eastern Virginia
Option C
D
Quaternary eastern and western Virginia
Option D
13

Which characteristic of potassium makes it useful for dating rocks?

A
It has a long half-life.
B
It decays at an unknown rate.
C
It produces lead as it breaks down.
D
It can be used to date all types of rock.
14

Which statement accurately describes a half-life?

A
A rock’s size is determined by half-life.
B
All stable and unstable elements have a half-life.
C
An atom of an element becomes half its original size in a half-life.
D
A half-life is the time required for half of a radioactive element to decay.
15

Which statement describes the law of superposition?

A
Sedimentary rocks were originally in horizontal layers.
B
In horizontal rock layers, each layer is younger than the one below it.
C
Rock layers must be in existence before something can happen to them.
D
Rocks that are not in horizontal layers were shifted by some geologic event.

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