Unit C: The Changing Earth

Suggested Answers for Investigations and Activities

Chapter 1: The Abyss of Time

Try This Activity: Deep Time, page 295

Analysis

1. The events are concentrated much more in recent times than they are in the distant past.

2. The percentage of Earth’s history taken up by the Precambrian Era is the following:

3. Events on the time line include
  • Planet Earth forms
  • Earth’s crust forms
  • first living cells
  • first photosynthetic organisms

Evaluation

4.

On the time line of Earth’s history, there are three possible reasons why more events seem to have occurred more recently. The first reason is that the record of early events may not be as well preserved as recent events—geological processes may have destroyed or changed the early rocks since their formation. The second reason is that early life may have been too small or simple to leave much fossil evidence. The third (least likely) reason is that less may have happened during Earth’s early history.

Utilizing Technology: Convection, page 300

Analysis

1. The energy source is the heat released from the hot plate under the aquarium.

2. The energy source for Earth’s convection is heat released from nuclear decay occurring in the core.

3. A diagram of the demonstration is on the left, followed by a sketch of Earth’s convection currents.

4.

The hot plate heats water at the bottom of the aquarium. This causes the water molecules to move faster. As they move faster, they get farther apart and occupy more space. Because the water molecules occupy more space, they become less dense than the cooler water above them. Because it is less dense, the hotter water rises. Once it reaches the surface, the water is forced sideways by the hotter water following it. As the water moves sideways, it cools. As it cools, it becomes denser. When the water becomes denser than the surrounding water, it sinks. Once the water reaches the bottom it is drawn toward the heat again, as space is created by rising water. This creates a circular flow called a convection cell.
5. The water moves horizontally along the surface. If something were floating on the surface, it would likely flow along in the same direction as the current.

Investigation: The Early Atmosphere, pages 304 and 305

Analysis

1.

The source of oxygen likely came from cyanobacteria. The cyanobacteria produced oxygen through the process of photosynthesis.
2. a.

This indicates that significant levels of oxygen were not present in the atmosphere prior to 3.8 billion years ago.
b. Starting from 1.8 billion years ago, significant levels of oxygen were consistently present.

c.

During the time of banded iron formations from 1.8 billion years ago to 3.8 billion years ago, significant levels of oxygen were present only at certain times (the red bands). At other times, oxygen was unavailable (the grey bands).

Try This Activity: Take a Wild Guess!, page 306

Answers may vary. You really do not have enough information to make a solid, authoritative identification. But that does not matter. The goal is that you come to appreciate the challenge involved in the interpretation of fossils.

The ammonite fossil is most closely related to the squid. Surprisingly, ammonites are members of the marine group of organisms that include modern squid and octopi—the cephalopods.

Maybe the visual similarity to one of the alternatives—the horn, snake, or snail—led you to think there was a relatedness to the fossil. A lack of familiarity with the fossil record and taxonomy may have contributed to your making an incorrect choice.

Note: Ammonites begin to appear in the fossil record 415 million years ago. Soon after their appearance in the fossil record, a number of different forms were found. This indicated that they quickly diversified into many different species, including some shaped like hairpins. Ammonites disappeared from the fossil record (along with the big dinosaurs) about 65 million years ago.

Utilizing Technology: Pulling It All Together, page 309

Your presentation should answer Steno’s question about fossilized shark teeth.

Shark teeth could have sunk to the bottom of the sea to become part of the sedimentary rock. Later, the sea level could have dropped enough to convert the one-time sea floor into dry land, or the sedimentary rock layers could have been lifted above sea level.

This explanation should be presented as a series of diagrams with captions.

Fossilization of Shark’s Teeth

A shark living in an ancient
ocean sheds its teeth.		 The teeth sink to the bottom of the ocean and are buried in fluid sediment. Over time, the sediment hardens and becomes sedimentary rock.
Over time, more and more layers are deposited and the sea level drops or the layers are lifted to become dry land. Erosion creates an outcropping, exposing part of the layer. The site is excavated to expose the fossils.

Evaluation

1. and 2. As you evaluate your work, this is a good opportunity to read “Self-Assessment Rubric” on page 547 of the textbook.

Investigation: Matching Rock Strata from Different Locations, page 311

Analysis and Interpretation

1. The correct sequence from youngest to oldest spells out the word organism, as shown in the completed handout, “Assembled Stratigraphic Sequence.”

2. The youngest layer should be placed on the top of the sequence, according to the law of superposition.

3. Relative dating is used in this investigation.

4. The main limitation of relative dating is that you cannot tell the actual age of the fossils or rock layers.

Reporting Your Results

5. The following “Assembled Stratigraphic Sequence” shows the completed fossil record.

6. The fossil record was assembled by overlapping fossils in the record. Graptolite, placoderm, and ammonite are the most suitable index fossils because they are only found during a short amount of geological time.

7. If you were to find a new fossil near one of these index fossils, you would be able to pinpoint its relative age in geological time.

The following is additional information for the fossils used in this investigation.

Sketches of Marine Fossil Organisms (Drawings are not to scale.)

Try This Activity: Hourglass of Time, page 313

Your diagram of the graduated cylinder should indicate the top level of each era according to the following table.

GRADUATED CYLINDER AS GEOLOGICAL TIME SCALE

Era Top Level (mL)
Precambrian 86.9
Paleozoic 94.5
Mesozoic 98.6
Cenozoic 100.0

Try This Activity: Imagine This: Catastrophic Events, page 315

1. Answers will vary. Sample explanations are provided in the second column of the table.

Land Feature Early Catastrophic Explanation
(Answers may vary widely.)		 Current Scientific Explanation
Badland Hoodoos The hoodoos were formed by three enormous floods. The first flood deposited the dark sediment, forming the base of the hoodoos. The second flood formed the lighter sediments in the middle. The heavy caprocks, sitting on top of the hoodoos, compressed the sediments under them—this made the hoodoos more resistant to erosion. A third flood eroded the sedimentary rock surrounding the hoodoos. The dark base is made of red-brown marine shale. It was slowly deposited between 70 and 75 million years ago when this area was submerged by an inland sea. Many marine fossils, such as ammonite, are present. The lighter middle and caprock sections are made of the type of sand and clay that are slowly deposited along the shorelines of deltas and tidal flats. They were deposited millions of years ago when the inland sea had become shallower. Since then, the inland sea has disappeared. The caprocks contain calcite cement to make them more resistant to erosion. They protect the sandstone and clay below them, while wind, rain, and frost erode the surroundings. The hoodoos are considered to be quickly eroding at up to 1 cm per year from some rock faces.
Mount Rundle The sharp, serrated peaks of the mountain suggest a breaking up of the crust due to a violent upheaval during a giant cataclysm. The plate that makes up the crust under the Pacific Ocean began colliding for the second time with the plate that makes up North America about 170 million years ago. This was due to the forces exerted by convection currents in Earth’s mantle. This collision resulted in the very slow compression of the continental crust. Mount Rundle is an example of where the crust snapped and thrust slabs of sedimentary rock up at an angle. Areas such as the Himalayas are still undergoing mountain building. (Their average growth has been measured at just over 6 cm per year.) Erosion by rain and glaciers continues to shape Mount Rundle.
Red Rock Coulee These rocks could be a cluster of meteorites or maybe even the eggs of giant extinct dinosaurs. These formations are called concretions. Each began as a dead organism or an inorganic object that became part of the sediment (around 70 million years ago) at the bottom of the same inland sea that created the hoodoo sediments. Later, ground water flowed past it and deposited hard minerals that slowly accumulated into large spheres. These spheres were resistant to erosion. So, the surrounding rock was eroded to leave the spheres exposed.

Note: Read the current scientific explanations in the third column before completing question 2.

2. The general differences between early catastrophic explanation and current scientific explanation are as follows.

Early Catastrophic Explanation Current Scientific Explanation
These explanations were most often based on naked eye or superficial observations. Logic was used to explain phenomena to avoid disagreements with authoritative works. These explanations often required processes of a type or magnitude not observed in the present and therefore not verifiable. They were often constrained by the presupposition of a young Earth. New evidence was often made to fit into an unchanging doctrine. These explanations require careful measurements, such as present sedimentation rates, crustal plate movement, and radiometric dating. (See Lesson 1.5 for an explanation of radiometric dating.) They employ processes of a type and intensity observed in the present. Laws and theories concerning these processes are constantly tested by experiments and observations. Findings must be verifiable by a global community of researchers. As such, they are subject to change. New evidence often demands that laws and theories be restricted, revised, or reinforced.

Note that the descriptions of early catastrophism were not based on a rigorous application of the scientific method. Modern geology does include catastrophes, but within a uniformitarian framework that requires deep time. The addition of catastrophes to uniformitarian theory is not a revision or restriction, but rather a reinforcement of the theory. This modern blend of ideas will be explored in Lesson 1.4.

Utilizing Technology: How Do Rocks Undergo Change?, page 317

Analysis

A sample rock cycle diagram follows.

Investigation: The Fort McMurray Unconformity, page 317

Analysis

1. The missing periods are the Carboniferous, Permian, Triassic, and Jurassic Periods.

2. According to the following calculation, 360–140 = 220 million years are missing.

3. This surface is called an unconformity.

Research

4. Evidence suggests that approximately 360 million years ago, during the Devonian Period, this part of Alberta was at the bottom of an ocean. It was home to marine organisms like Mucrospirifer, a marine brachiopod. It must have been a warm ocean because of the presence of limestone sediments. Sometime during the next 220 million years the sea level either dropped and dried out some of the ocean, or the land was raised, because by 140 million years ago, this area was near a delta where rivers piled sediment into the sea. Organisms like Cyprimeria lived near this coastal delta. As the rivers carried water from the continent to the ocean, they eroded 220 million years of rock strata. This change must have been very gradual, since there is an enormous gap in the geological record. In other areas where sedimentary rock continued to be deposited, there are hundreds of metres of rock containing many index fossils that lived between the time of Mucrospirifer and Cyprimeria.

Investigation: Constructing a Decay Curve, page 320

Part A: Using Arts and Crafts

A completed craft follows.

Analysis

1. The curve is exponential. The rate of decrease starts off very quickly but steadily slows.

2. The curve never reaches 0%. No matter how small the paper gets, it can still be cut in half.

3. Using the graph, the strip has undergone approximately 0.72 half-lives.

Part B: Using Math

A completed table and graph follows.

Time (min) Radioactivity (%)
0 100
1 50
2 25
3 12.5
4 6.25
5 3.125
6 1.5625
7 0.78125
8 0.390625

Interpretation Questions

4. The shapes are similar.

5. A half-life is the amount of time it takes for the radioactive part of a sample to decrease by half.

6. The half-life is a uniform increment of time, just like the seconds, minutes, and hours of a clock.

Chapter 2: A Tropical Alberta

Try This Activity: Interpreting Fossil Evidence, page 329

Analysis

1. a. The objects that were the easiest to identify were those that left a good impression of a complete object, such as an entire toy soldier.

b. The objects most difficult to identify were those that created a poor impression due to air bubbles or due to leaving an impression of an unusual aspect of the object. Alternatively, an object could have been difficult to identify because it was a small, obscure part of a larger object.

c. You could use the criteria mentioned in a. and b. or make up a list of other factors.

d. In some cases, seeing both halves of the impression would have made a difference. This would particularly be the case if the half of the impression presented was an unusual aspect of the object.

2. If the object had consisted of many parts held together with water-soluble glue, then the water in the plaster of Paris may have caused it to come apart in the mould. In this case, the impression would have recorded an object in pieces—this would have been more difficult to interpret than a whole object.

Investigation: Hypothetical Interpretations of Fossil Evidence, pages 332 and 333

Hypothetical Interpretation of Evidence from 1977

1.

Since the fossil evidence collected up to 1977 was so sparse, and since there is no living organism like Hallucigenia, the answer to this question is very speculative. Here are two possible answers from a long list of possibilities.

Possible Answer #1: Each tentacle is a feeding tube with the opening on the end of the tube acting as a tiny mouth. The spiny legs can allow for some locomotion, but their main purpose is to hold the organism rigidly in place as it feeds on organic matter carried along by underwater currents. If Hallucigenia had the proper body position, a stronger current could push the rigid spikes deeper into soft surroundings. When the current weakened, Hallucigenia would have an opportunity to wriggle free and relocate.

Possible Answer #2: This fossil is not the remains of an entire organism but represents a body part of a larger organism. The rigid spikes are not for walking at all but instead are part of an exterior armour. The tentacles are part of the underside of the animal and serve to attach the organism to its underwater landscape. This means that the Hallucigenia fossil is actually a thin sliver of a larger, sea-urchin-like organism.

Hypothetical Interpretation of Evidence from 1992

2.

Since the fossil evidence collected up to 1992 allows a comparison to Onychophora, a related modern animal, interpreting this evidence—though still quite speculative—relies less on imagination than does the response to question 1. Although many responses are possible, here is one that makes the connection to Onychophora.

Hallucigenia was an organism that crawled along the bottom of the sea floor. The tiny openings on the bottom of the tentacles served as gripping devices to help Hallucigenia grip the bottom as it moved along. The function of the spikes along the back served as protection from predators.

Analysis

3. Fossil evidence is never complete. Reconstructing a day in the life of an organism from fossil evidence is like putting together a jigsaw puzzle with many pieces missing. In some cases, paleontologists have most of the pieces to work with, but most of the time the reconstruction is attempted with only snippets of evidence. In the case of Hallucigenia, more evidence is required before a clear picture will emerge.

4. If someone had made a souvenir of the Hallucigenia fossil that led Lars Ramskold to his discovery, then the data from 1977 would be the last word on Hallucigenia, and the picture would be less clear. It is essential that all fossil evidence be treated with great care because there are so few pieces of evidence to begin with, and there is always the possibility that a certain fossil may be the only source of vital information.

5. Lars Ramskold did his initiating and planning while studying similar fossils in China. From this work, he developed the hypothesis that the tentacles were legs and that there should be an additional row of legs hidden in the shale. The procedure performed to confirm this hypothesis was to obtain permission to remove a few chips of shale from one of the rare Hallucigenia fossils. Ramskold recorded his information when he discovered the second row of legs that he had earlier hypothesized. In this case, the analysis and interpretation was quite straightforward: the existence of the second legs supported his hypothesis. Communication and teamwork occurred when he published his work and shared his findings with other people in the scientific community.

Investigation: Charting Patterns in Drill-Core Samples, pages 339 and 340

Sample Diagram

Analysis

1. a. All of these rock layers consist of sedimentary rock.

b. The oldest rock layer is the limestone on the bottom. The youngest layer is the top one consisting of a combination of sandstone, shale, and thin coal. This information is determined by using the law of superposition, which states that in a sequence of rock layers the higher strata are younger than the lower strata.

c. The limestone layer was laid down first as the bed of a sea floor. Ancient sponges and corals formed the reef structure next as the reef is formed on top of the limestone. As rivers flowed into this sea, fine sediment accumulated and eventually covered the limestone and the reef to become the layer of shale. This area likely became the shore of a sea or perhaps an arid desert environment, as shown by the layer of sandstone. The thin coal in the top layer suggests that this area eventually became the home of land plants. Perhaps this region was covered by swamps or forests for a time that followed its period as a shallow sea.

2. The most likely location of a petroleum trap would be in the reef section, under well 3.

3. The rock that makes up the reef formation is porous, so it is possible for petroleum to flow from different formation parts to the point where the well penetrates the ancient reef. A second consideration is that a reef like the one in the diagram has more than 1 km of rock on top of it, so the pressure would be significant. Once the reef was penetrated by drilling, pressure within the formation would naturally force petroleum to the surface.

Utilizing Technology: Seismograph Simulation, page 341

Analysis

1. Geophones would first detect seismic waves from layers close to the surface because these waves do not have as far to travel as the waves from deeper layers.

2.

To lay out a line of geophones the seismic crew must clear away obstacles, such as trees and shrubs, to make room for equipment and vehicles. The track that they cut through these areas can create breaks or gaps in ecosystems. Since the growing season is short in northern ecosystems or high-altitude ecosystems, it may take the vegetation a long time to recover.

The vehicles can disturb or remove the ground cover. This may lead to erosion and excessive run-off. The sedimentation from this run-off can have a significant impact on the ecosystems of streams, lakes, and rivers.

The space created by a cutline in a forested area can have an impact on the interactions between large herbivores—such as the woodland caribou—and wolves.

To offset these potential environmental problems, the petroleum industry has been encouraged to build low-impact seismic lines that cut narrower paths and utilize smaller, less destructive pieces of equipment.

Utilizing Technology: Subduction, page 345

Analysis

1. A. oceanic crust
B. lithosphere
C. asthenosphere
D. epicentre
E. focus
F. continental crust
G. seismic waves
H. fault

2. a. At the point labelled E, the rock that is being pulled into the mantle is subjected to extreme heat and pressure, so it is most likely metamorphic rock.

b. As the oceanic crust is being pulled into the mantle, it is subjected to extreme heat and pressure. This causes the crust material to become metamorphic rock. Once this rock reaches the asthenosphere, it is melted and transforms into igneous rock.

c. The molten rock or magma, described in the answer to question 2.b., forces itself to the surface along fault lines and flows onto the surface as lava from volcanoes.

Investigation: Modelling Seismic Waves with a Spring, page 346

Observations

1. The following is a labelled sketch of a P-wave.
2. The following is a labelled sketch of an S-wave.

3. Answers may vary. Use the following rubric to score your procedure for measuring the speed of a wave.

RUBRIC FOR THE PROCEDURE FOR MEASURING THE SPEED OF A WAVE
Score Scoring Description
Standard of Excellence
(4 marks)		 The procedure addresses the need to make measurements for the variables of distance and time. The procedure for measuring time includes a reasonable attempt to counter the effects of human reaction time with a stopwatch. The procedure includes an explicit reference to the equation for speed.
Acceptable Standard
(2 marks)		 The procedure addresses the need to make measurements for the variables of distance and time. No mention is made of countering the effects of human reaction time caused by using a stopwatch. The procedure implies the use of the equation for speed but does not explicitly state it.

Calculations

4. The speed of a model S-wave when the spring is at its safest maximum stretch is as follows:

Note: More accurate results may be obtained by allowing the pulse to travel several lengths of the spring. This helps to lengthen the time interval and reduce errors.
5. The speed of a model S-wave when the spring is at one-half of its safest maximum stretch is as follows:

Note: This speed value should be slightly less than the value in question 4.

Evaluation

6. a. The speed value depends on the material used and the design of the individual springs. If the springs are all identical and stretched the same amount, then the speed values should be similar. Differences could also be due to difficulties in timing the springs. Human reaction time is such that any attempt to measure an event that lasts less than 2.0 s will result in large errors.

b.

The major area for improvement is measuring the time required for the wave to travel the spring’s length. One approach is to use several timers and average the results. Another possibility is to record the time for the wave to make a round trip—travelling the length of the spring and then back again. This increases the time interval being measured, reducing human timing errors.

A final approach is to completely abandon the use of stopwatches by using a digital video camera. Time is determined by counting the number of frames and then multiplying by the length of time in seconds for each frame.

Utilizing Technology: Earthquake Analysis, page 350

Check for Understanding

1. This is an example of how to find an earthquake’s epicentre.

2. As an S-wave travels through layers of subsurface rock, the energy that it carries becomes more diffuse because it is spread over an ever-increasing volume of rock. A seismic station far away from the epicentre will receive a much smaller portion of the energy transferred by the S-wave than a closer station. Since the amplitude of the S-wave is an indicator of the wave’s energy, it makes sense that a distant station that receives less seismic energy should record an S-wave with a reduced amplitude. In other words, a station that is far away has less energy available to shake the ground and affect the seismograph than does a nearby station.

Analysis

1. and 2. Crustal plates and arrows signifying the motion of the Pacific Plate have been added to the map.

Worldwide Volcanoes, Earthquakes, Crustal Plate Boundaries,
and the Movement of the Pacific Plate

3. The perimeter of the North Pacific Ocean is called the ring of fire because it is surrounded by active volcanoes. The direction of the arrows suggests that the Pacific Ocean is shrinking because it is being subducted below other plates to the north, northwest, and west.

Evaluation

4. The overall pattern should be the same for all students. If you used a source that limited the display to the last year or the last five years, then the process of connecting the dots to find the plate boundaries would have been easier. The time line for the data had to be long enough to provide sufficient data. In most cases, things to change are the key words chosen to insert into the search engine.

Utilizing Technology: Plate Tectonics, page 355

Analysis

1. This diagram illustrates the jigsaw-fit argument for plate tectonics.

2. Canada’s east coast, Iceland, northern Europe, and Africa used to be very close physically due to tectonic plate movements that formed Pangaea. The mountain building that accompanied this collision has parts left that show similar formations in eastern North America and northern Europe.

3. Comparable mesosaurus fossils are found in both South America and Africa. This suggests that these two continents were once connected.

Chapter 3: Changing Climates

Try This Activity: Ice Flows!, page 367

Analysis

1. On the beach there are little sandy areas surrounded by water. There appear to be similar areas in northern Alberta, where land is surrounded by ice that flows, as shown on the topographical map.

2. In Figure C3.1 the islands are there because they started out a little higher than the rest of the beach. When the waves came in, the water flowed around them to erode the sand and make the islands more prominent. The islands in northern Alberta were shaped by repeated periods of glaciation during Alberta’s history. The ice flowed like really slow water around these higher areas to leave a similar erosion pattern to the one left on the beach. This made these islands more prominent. An island surrounded by ice is called a Nunatak, which is an Inuk word meaning “land apart.”

3. Studying a process at work in the present—the flow of water on a beach—can be used to understand processes in the past, including the flow of ice sheets across Alberta during periods of glaciation.

4. The rock likely came from somewhere in Alberta’s Rocky Mountains. Some geologists think it originated from northwest of Jasper.

5. Answers will vary. The following account is one possible scenario.
Big Rock fell as part of a rock slide off a mountain near Jasper. It landed on a glacier. The ice flow then carried it northeast until it collided with the continental glacier moving southeast. Big Rock continued in that direction until it was hundreds of metres above its present location near Okotoks. The continental glacier stopped advancing and melted. At that point, Big Rock was deposited in its present location.

Investigation: A Record in Deep-Ocean Sediments, pages 372 and 373

Part A: Oxygen Isotopes in Shells

Analysis

1. As the average deep-ocean temperature increases, the ratio of oxygen-18 to oxygen-16 decreases.

2. The slope calculation:

The slope of the best-fit line is –0.33 ppm/°C. Note that answers may vary slightly from this value.
3. The answer to question 2 includes a negative slope value. This means that as the variable on the horizontal axis is increasing, the variable on the vertical axis is decreasing.

Part B: Oxygen Isotopes in Ocean Sediments

Analysis

4. The following table includes the temperature data. Note that answers may vary slightly from these values.

Time
(106 a Before Present)		 Oxygen-18: Oxygen-16
Ratio (ppm)		 Average Deep-Ocean
Temperature (°C)
50 1.0 9.3
45 1.1 9.0
40 1.9 6.4
35 1.7 7.1
30 2.2 5.4
25 2.3 5.1
20 2.4 4.8
15 2.0 6.1
10 3.3 1.9
5 3.2 2.3

5. This graph answers question 5.

Conclusions

6. There is an overall cooling trend.

7. There are several fluctuations in the rate of cooling. There are even three time intervals where the temperature is increasing. Each of these increases appears to last about five million years.

8. Because there are five million years between data points, this graph probably leaves out many fluctuations. As students will see later in Chapter 3, the average deep-ocean temperature has risen and fallen many times in just the last several hundred thousand years. More measurements—and therefore more data points—are required to show the true fluctuating nature of Earth’s past climate.

Utilizing Technology: Antarctica: A Flying Tour of the Frozen Continent, page 377

Analysis

1. RADARSAT has a polar orbit. This means that it traces out a path on Earth’s surface that takes it from the North Pole to the equator, to the South Pole, back up to the equator on the opposite side of Earth, and then back to the North Pole again. When it’s not over Canada’s northern seaways, RADARSAT can be re-assigned to other tasks, such as gathering data while it flies over Antarctica.

2. a. Canada is a country with a small population spread over a huge land mass. In these circumstances, telecommunication is very important; the best way to perform this task is with satellite technology. Canada also has a vast amount of coastline. The monitoring of this coastline is best done from space. This allows Canada to keep track of ice flows that could damage ships or offshore oil rigs.

b. The most up-to-date information about the latest initiatives of the Canadian Space Agency can be obtained from its website.

Investigation: A Record in the Ice, page 378

Conclusion

1. Advantages and disadvantages of using a spreadsheet follow.

Advantages Disadvantages
  • A spreadsheet is much less time-consuming than creating a graph by hand, once you’ve figured out how to work the technology.

  • Speed allows you to include many more data points in your analysis, which leads to more detailed results. (Note: Comparing the graph in this investigation to the “Average Deep-Ocean Temperature Versus Time” graph from Lesson 3.1 illustrates this point.)

  • More accurate graphing allows you to make subtle distinctions when interpreting graphs (as students will see in Lesson 3.3 when the data are revisited).
  • A spreadsheet removes you from the tactile and rigorous nature of doing the graph yourself. Simply typing in an equation and filling in a column doesn’t provide practice in doing calculations.

  • With smaller data sets, sketching the graph yourself is good practice.

2. The relationship between time and average temperature fluctuates greatly. However, it does show two particularly warm periods, including the present day. These warmer periods are actually called interglacial periods, which means between glaciations.

3. Note that the graph produced by the Microsoft® Excel software has zero on the far left and 160 000 years before the present on the far right. The following graph is more correct because it shows time progressing from 160 000 years ago forward to the present. A dashed line shows the current temperature.

4. There were two cold periods. The most recent one was between the two warm spikes, and the other one occurred more than 140 000 years ago.

5. a. The most recent major cooling trend began around 125 000 years ago.
b. The last glaciation reached its maximum about 20 000 years ago.
c. The temperature finally returned to near-current values approximately 10 000 years ago.

6. The return of Earth’s average temperature to present-day levels marks the end of the chilly Pleistocene Epoch and the start of the Holocene Epoch.

7. It’s a tough call! Answers may vary but must be supported. Possible answers include the following:

A: This is difficult to support. The temperature seems to fluctuate widely over long periods of Earth’s history.

B: There seems to be a pattern of warm spikes and long glaciations. If the temperature is going to follow the pattern of the last spike, Earth is in for another ice age.

C: Based on the graph, this is difficult to support. You may choose this based on your knowledge of current global warming predictions.

Note: Over the very long term, choice C seems most supported if you examine deep-ocean sediment data going back further in time.

8. Data sharing is very important. It allows the international community to analyze its findings in an effort to reach consensus regarding conclusions and future projections. In the case of climatology, it is particularly important as researchers around the world require raw data to develop new numerical methods. Researchers also need computer models to simulate climate and to make future predictions. Scientific consensus is vital if scientific evidence is to influence political decisions regarding societal activities—such as the consumption of fossil fuels by both industries and consumers—that may artificially affect climate.

Investigation: Fresh Water, pages 380 and 381

Questions

The answers from questions 1 to 8 illustrate how a student living in the Edmonton area might respond.

1. Edmonton’s drinking water comes from the North Saskatchewan River.

2. The North Saskatchewan River is fed by meltwater from the Saskatchewan Glacier, which flows out from the Columbia Icefield. Students could include a picture of the glacier and/or a map of the river.

3. The entire Columbia Icefield and the many glaciers it feeds have been shrinking over the past few decades. Students can see this for themselves by visiting the Athabasca Glacier—fed by the Icefields—and looking at signs that show how far the toe of the glacier reached in past years.

4. There is overwhelming evidence that the Greenland Ice Sheet and the Antarctic Ice Sheet are shrinking, as well as most mountain glaciers. Reams of evidence can be found from the Canadian Geological Survey, the United States Geological Survey, NASA, and many more research organizations.

5. Scientists use satellite images, historical photographs, and maps to chart changes in glacial size.

6. Many scientists predict Earth’s climate will continue to get warmer due to human-induced global warming—also called the enhanced greenhouse effect. This is believed to be caused by human emissions of greenhouse gases, such as carbon dioxide and methane. These gases trap energy from the Sun in Earth’s atmosphere and have a global-warming effect. It is important to note that global warming is not caused by holes in the ozone layer!

7. If the Saskatchewan Glacier and the Columbia Icefield were to melt quickly, there would be extreme flooding. Once the water had drained, Edmonton would be plagued by water shortages because glaciers help to supply a constant source of year-round fresh water.

8. If Earth’s glaciers were to melt, there would be a dramatic rise in the global sea level. Over the past 100 years of warming, the sea level has risen 15 to 20 cm. The International Panel on Climate Change predicts a rise of another 50 cm by 2010. If the entire Greenland Ice Sheet were to melt, it would add 7 m to the sea level. The melting of glaciers would return the fresh water stored in glaciers back to the salty ocean. This would result in a shortage of drinking water. Also, coastal areas would face severe flooding.

Investigation: Return to Vostok, page 387

Analyzing Data

1. The two variables are correlated. They both jump sharply at about 145 000 years, both peak at approximately 134 000 years, and both jump sharply at about 18 000 years.

Conclusion

2. This does not show carbon dioxide as a conclusive cause of fluctuations but rather as a correlation.

3. It is highly unlikely that people could have had an effect on global carbon-dioxide levels until the Industrial Revolution, due to the low consumption of fossil fuels and a smaller global population.

Utilizing Technology: The North Atlantic Conveyor, page 389

Analysis

1. Near the end of the applet, the North Atlantic Conveyor is shown to be slowing down. It is pushed further south due to the melting of the Greenland Ice Sheet.

2. This event is paradoxical because the event that could trigger the melting of the Greenland Ice Sheet is global warming. However, the effect of slowing down the North Atlantic Conveyor and pushing it further south would be the cooling of northern Europe and eastern North America.

Science 20 © 2006, Alberta Education