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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 19. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. How many species of flowering plants are found on the continent of Antarctica?
  2. What is macroevolution?
  3. How long did it take for the ancestors of the whale to make the transition from life on land to life in water?
  4. What role did the increase in oxygen concentration in the atmosphere play in the evolutionary history of life?
  5. During what geologic time period did most of the major living animal phyla appear in the fossil record?
  6. During what geologic time period did the supercontinent Pangaea begin to break up?
  7. Approximately how many species are presently listed as endangered or threatened with extinction?
  8. According to the fossil record, from which group of organisms did the mammals evolve?

A Guide to the Reading

When exploring the content in Chapter 19 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Carbon Dating

Radioisotopes, radioactive forms of chemical elements, occur naturally in the environment.  These unstable substances undergo the process of radioactive decay, transforming into a more stable version of the element.  The decay of the radioisotope is accompanied by the release of radioactive energy which we can measure as radioactivity.  The key to understanding how this process can be used to determine the age of fossils is realizing that not only do these compounds exist naturally, but the process of decay occurs naturally as well.  One radioactive substance which is used to date fossils is carbon-14.  Recall from chapter 4 that the element carbon typically has an atomic weight of 12.  Carbon-14, in contrast, has an atomic weight of 14 due to the presence of additional neutrons which make the nucleus unstable.  When carbon-14 undergoes decay, the additional neutrons are released, yielding a stable carbon atom with an atomic weight of 12.  The release of neutrons during the decay process is measured as radioactivity.  The time it takes for ½ the amount of carbon-14 (e.g. 5 out of every 10 atoms) in a sample to decay to carbon-12 is 5,730 years.  Therefore, by knowing that all fossils originated with roughly the same percentage of carbon-14 present and by measuring the amount of carbon-14 that remains in a fossil, scientists are able to estimate the age of the fossil with relative accuracy. 

For more information on this concept, be sure to focus on:

  • Section 19.1, The Fossil Record: A Guide to the Past
  • Figure 19.1, Fossils through the Ages

Continental Drift

While it may seem impossible, the continents that are present on our planet are in constant motion.  The movement of the continents that occurs over time is called “continental drift” and results from the sliding of “plates” that float on the surface of the earth’s liquid core.  This is how large land masses, such as the Pangaea super-continent that existed over 200 million years ago, have broken apart resulting in the continents as we know them today. Recall from chapter 18 that the geographic isolation of species that occurs when land masses separate in this fashion can contribute to speciation as populations become reproductively isolated and have reduced gene flow.

For more information on this concept, be sure to focus on:

  • Section 19.3, The Effects of Continental Drift
  • Figure 19.7, Movement of the Continents over Time

Adaptive Radiation

Adaptive radiation refers to the process that occurs when a group of organisms “expands” to inhabit new habitats and ecological roles.  Adaptive radiation often occurs after various groups of organisms go extinct, removing ecological competition for resources.  With reduced competition or predation, surviving organisms are more free to expand to take advantage of the resources available in an ecosystem.  In other cases, adaptive radiation may occur after an organism has acquired an adaptation that allows it to survive or reproduce more efficiently within an ecosystem.  Adaptive radiations can occur on a small or a large scale, depending upon the supporting ecosystem. 

For more information on this concept, be sure to focus on:

  • Section 19.5, Adaptive Radiations: Increases in the Diversity of Life

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Total Number of Species on Earth

  • Interlude A – How Many Species Are There on Earth?

Oxygen and Metabolism

  • Chapter 7 – Section 7.2, Using Energy from the Controlled Burning of Food

Natural Selection

  • Chapter 16 – in Section 16.2, Natural selection and genetic drift are important aspects of evolution

Fossil Record

  • Chapter 16 – in Section 16.4, Evolution is strongly supported by the fossil record

Adaptive Radiation of Galapagos Finches

  • Chapter 16 – in Section 16.4, The formation of new species can be produced experimentally and observed in nature

Speciation and Geographic Isolation

  • Chapter 18 – in Section 18.4, Speciation often results from geographic isolation


  • Interlude D – The Impact of People on Evolution

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