Lesson 2.1: The Cambrian Explosion
May 8, 2012
1. List the five steps in the process of fossilization.
2. Explain why coal, oil, and natural gas are considered fossil fuels.
3. Look at the pictures of the modern bristle worm and the Canadia fossil. What purpose
would the stalks or small tentacles serve?
4. Look at the modern bristle worm shown in Figure C2.3. Where do you think the fossil
organism named Canadia lived? (free swimming, fixed to the bottom, bottom crawling), and
how can you tell?
5. Was Canadia a predator that hunted small fish, a herbivore that ate algae, or a scavenger
that filtered organic material from mud and water near the sea bottom? How can you tell?
6. Which geological theory are paleontologists applying when they compare fossils with
modern creatures?
Science 20 Unit C Chapter 2 Workbook
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Use the following
picture to answer the
questions that follow. A
more clear version is on
page 333 of your
textbook.
7. Label a trilobite, a
Canadia, and a
Hallucigenia in
Figure C2.9.
8. Layers of microscopic silt and clay particles are often deposited as sediment at the mouths
of rivers or from mud avalanches. These sediments eventually result in shale.
a. Identify the source of the fine silt and clay particles that formed the Burgess Shale.
b. Describe the significance of the silt and clay in the preservation of the Burgess Shale
fossils.
9. Fossils in the Burgess Shale fossils are found in a variety of positions: some upside down,
some vertical. Why are the fossils of the Burgess Shale not arranged in an orderly way,
such as lying on their sides?
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Lesson 2.2: A Billion-Dollar Reef
10. Refer to the “Geological Time Scale” on your formula sheet. How long did the Ordovician
Period last?
11. During the Ordovician Period, it is thought that land plants began to contribute to the levels
of atmospheric oxygen. You will need to recall key ideas from previous science courses to
answer the parts of this question.
a. Describe the process by which plants produce oxygen as a by-product. Include a
chemical equation to aid your description.
b. Some geologists believe it is not accidental that evidence from the fossil record
suggests the first amphibians appeared on land many years after the appearance of the
first land plants. It has been suggested that this time period was necessary to provide
enough oxygen to help produce an atmospheric ozone layer. Explain why an
atmospheric ozone layer would be important to early amphibians.
12. During the 140 million years from the beginning of the Ordovician Period to the end of the
Devonian Period, Alberta was mostly submerged below a warm tropical sea. Explain the
significance of this time period to the creation of Alberta’s petroleum reserves.
13. Characteristics of ocean waters off the coast of the Bahamas are thought to be similar in
many ways to tropical waters that once covered Alberta. Explain why petroleum cannot be
extracted from the bottom of the shallow waters that surround the Bahamas.
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APPLICATION
The speed of a seismic wave depends mostly upon the density of material the wave is
travelling through. In general, the denser the material, the faster the wave travels. The
following table represents typical densities for crude oil—a common form of petroleum—and a
few types of rock.
a. If the seismic wave is capable of travelling through all of these materials, rank the
materials from slowest to fastest.
When the seismic wave encounters a boundary between two layers of rock with different
densities, the sudden change in speed can cause a reflection to occur. It is usually the case
that the larger the speed difference between materials at the boundary, the stronger the
reflection. The reflected part of the seismic wave is redirected toward the surface.
b. Which combination of materials would produce the strongest reflection?
c. Which combination of materials would produce the weakest reflection?
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