Download Applying Concepts 33. a. Index fossils in each sequence can be

Chapter 1 Review Questions
Knowledge
1. Alberta’s stromatolites are evidence of cyanobacteria, which are photosynthetic organisms
that produced oxygen. Scientists believe that cyanobacteria were one of the first sources of
oxygen for Earth’s early atmosphere.
2. Deep time is the theory that Earth has gone through a very long history (4.5 billion years) of
development and change.
3. The eras are the Precambrian Era, the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era.
4. Diagram C is the most accurate representation of time for each of the combined four eras.
5. Alberta’s oldest rock outcropping exists in the Canadian Shield area of northeastern Alberta.
The one featured in this chapter is the Slave Granite, which forms a series of four famous
rapids in the Slave River. The Slave Granite is two billion years old.
6. Plastic materials are like toothpaste—they are solid but can flow under pressure. This is how
the zones of rock behave within the mantle.
7. The layers within Earth are highlighted.
8. Convection currents in Earth’s mantle push and pull on Earth’s crustal plates.
9. Fossils of coastal organisms, such as stromatolites, have been found along the Rocky
Mountains. Also present are sedimentary rocks, which are indicative of coastal river deltas.
And, finally, the presence of ripple marks, cracks, and salt crystals provide evidence of an
ancient coastline.
10. Earth’s first organisms had to endure very hot temperatures and poisonous gases, such as
hydrogen sulfide.
11. Although each cyanobacterium is very small, a single colony could consist of millions of
individuals. In addition, these organisms were among the dominant life forms on Earth for
two billion years—nearly half of the planet’s total existence.
12. Banded iron formations show that oxygen levels in Earth’s early atmosphere fluctuated.
When oxygen was abundant, red seams of iron were produced. When oxygen was scarce,
grey seams were produced.
13. At the end of the Precambrian Era, Alberta’s coastal reef was home to stromatolites, small
jellyfish, worm-shaped animals, and early plants.
14. An animal dies and sinks to the bottom of a body of water where it is buried by sediments.
Eventually, the organism is under hundreds of metres of sediment that compress the layers
to solid rock. The water is drained or evaporated, or the layers of rock are lifted above the
sea. Erosion exposes the rock layers that contain the fossil. After the fossil has been
discovered, it may be excavated.
15. The law of superposition states that for a sequence of rock layers, any given layer is younger
than the one beneath it.
16. The following table outlines the differences between relative age and absolute age.
Relative Age
This is a determination of which rock layers or
fossils are older or younger. Methods include
Absolute Age
This is a determination of the age of a
rock layer or fossil in the years before
applying the law of superposition and an
understanding of intrusions, as well as using
index fossils in reference to the Geological Time
Scale.
the present. Methods include radioactive
isotope analysis, which uses data from a
mass spectrometer.
17. An index fossil can be used to correlate rock layers in different locations. If the layers contain
the same index fossils, the rock layers are the same age.
18. An ideal index fossil should be easily recognizable, have lived for a relatively short period of
time on Earth, and have a broad geographical distribution.
19. There is no complete stratigraphic sequence of rock layers that shows the whole history of
Earth. It had to be pieced together using sequences from many locations around the world.
Index fossils are used to fit the pieces of the puzzle together. Scientists use the index fossils
to determine that layers from different locations are the same age.
20. Eras are the longest and most general divisions. Eras are made up of periods. Periods are
made up of epochs, which are the shortest and most specific divisions.
21. The theory of uniformitarianism states that the processes of change in operation at the
present—such as erosion by wind, water and ice, volcanism, earthquakes, and rock formation
in the rock cycle—can be used to explain Earth’s history of change.
22. The three major rock types are igneous, sedimentary, and metamorphic.
23. This is one way to describe the rock cycle.
24. The rock cycle is a balanced and sustainable system that could seemingly go around and
around forever. It shows no sign of a beginning or an end.
25. An igneous intrusion must be younger than the rock layers through which it cuts because the
magma invades cracks in pre-existing rock.
26. An unconformity is a gap in the geological record of an area. It occurs when there is a period
of erosion or non-deposition of rock layers.
27. The process of radioactive decay occurs when the nucleus of an unstable atom disintegrates
to become a different element. During the process, energy called radiation is released in the
form of high-speed particles.
28. The radioactive decay curve follows.
29. Radioactive decay makes a good clock for measuring the absolute age of rocks and fossils
because decay occurs in uniform increments of time called half-lives. If you can determine
the percentage of the parent and daughter nuclides in a sample, you can use the decay curve
to determine the absolute age of the sample.
30. The process of radioactive decay occurring in Earth’s core releases a tremendous amount of
energy that is transformed to heat. This provides the thermal energy to melt old rocks and
bring this molten material to the surface as magma.
31. Canada’s oldest rocks are from the Acasta Gneiss in the Northwest Territories. The gneiss
contains tiny crystals called zircons. Uranium radiometric dating was performed on these
crystals to determine their absolute ages.
32. Carbon-14 dating is typically used to determine the absolute ages of organic remains.
Applying Concepts
33. a.
b.
Index fossils in each sequence can be matched in order to assemble a larger sequence.
This combined stratigraphic sequence follows.
c.
34. a.
The bottom layer is the oldest; the top layer is the youngest.
The layers listed from oldest to youngest are E, D, B, and A. This answer is determined
by applying the law of superposition.
b. The rock layers were likely tilted due to a collision between tectonic plates that make up
Earth’s crust.
c. An unconformity has occurred at point C. This is likely due to a long period of erosion of
rock layers.
35. a. The granite, basalt, and lava flow are all igneous rocks.
b. The granite is older because the basalt is an intrusion that has cut through it.
c. The limestones are older because they are beneath the shales, according to the law of
superposition.
d. Point A indicates an unconformity, likely caused by erosion.
e. The sandstones are older than the lava flow because they are beneath the lava flow,
according to the law of superposition.
f. Layers C and B are older than the basalt because the basalt is an intrusion that cuts
through them.
36. To get accurate results, students should use the large decay curve available on the Science
20 Textbook CD.
a. The lava flow:
84% uranium-235 remaining (parent nuclide)
According to the decay curve, 0.25 half-lives have elapsed.
Age = (0.25 half-lives)(7.13 × 108 a/ half-lives)
Age = 1.8 × 108 a (or 180 million years)
b.
The lava flow is 180 million years old.
The granite intrusion:
17% lead-207 (daughter nuclide)
100% - 17% = 83% uranium-235
According to the decay curve, 0.33 half-lives have elapsed.
Age = (0.33 half-lives)(7.13 × 108 a/ half-lives)
Age = 2.4 × 108 a (or 230 million years)
c.
The granite intrusion is 240 million years old.
The volcanic ash layer:
74% uranium-235 remaining (parent nuclide)
According to the decay curve, 0.45 half-lives have elapsed.
Age = (0.45 half-lives) (7.13 × 108 a/ half-lives)
Age = 3.2 × 108 a (or 320 million years)
d.
e.
The volcanic ash layer is 320 million years old.
Fossil A must be between 320 million years old and 180 million years old because it is
located between the lava flow (180 million years old) and the volcanic ash layer (320
million years old).
Fossil B must be between 320 million years old and 240 million years old. It is younger
than the volcanic ash layer (320 million years old) because it is above it. It must be older
than the granite intrusion (230 million years old) because the granite cut through the
layer containing the fossil.
Science 20 © 2006, Alberta Education