Chapter 25: The History of Life on Earth
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Chapter 25: The History of Life on Earth
1. In the last chapter, you were asked about macroevolution. To begin this chapter, give some
examples of macroevolution. Include at least one novel example not in your text.
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2, How old is the planet?
How old is the earliest evidence of life on Earth?
3. The current theory of the origin of life suggests a sequence of four main stages. Summarize
them here.
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2.
3.
4.
.
In the previous chart, the first stage is the synthesis of organic molecules. Consider the early
planet, which was probably thick with water vapor and stinky with methane, ammonia, and
hydrogen sulfide. What gas was missing from this early mix? Why?
.
A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment. What did they suggest was the source of energy for early organic synthesis?
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Chapter 25: The History of Life on Earth
.
In 1953 at the University of Chicago, Stanley Miller and Harold Urey tested the OparinHaldane hypothesis with this apparatus. (It is shown in Chapter 4, Figure 4.2, so you have seen
it before.) Explain the elements of this experiment, using arrows to indicate what occurs in
various parts of the apparatus.
"Atmosphere"
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Water vapor
Electrode
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Cooled "rain"
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7. Wlaat was collected in the sample for chemical analysis? What was concluded from the results
of this experiment?
8. What are proto-cells? What properties of life do they demonstrate?
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9. What did Thomas Cech propose was the first genetic material, DNA or RNA?
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10. What are ribozymes?
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11. Explain the evidence for an early "RNA world."
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12. In what type of rock are fossils found?
13. What do we not know from analyzing rock strata?
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Chapter 25: The History of Life on Earth
14.
Rocks and fossils are dated in several ways. Relatiÿ,e dating uses the order of rock strata to
determine the relative age of fossils. Radiometric dating uses the decay of radioactive isotopes
to determine the age of the rocks or fossils. It is based on the rate of decay, or half-life, of the
isotope. To determine the absolute age of a fossil, radiometric dating is used. Use this figure to
explain the concept of radiometric dating. Label the key elements.
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15. What is the age range for which carbon-14 dating may be used?
16. To date fossils outside the range of carbon-14 dating, researchers use indirect methods of
establishing absolute fossil age. Explain how this can be done using radioisotopes with longer
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17. What are the three groups of tetrapo&'?
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18. Cite three ways of distinguishing mammal fossils from the other two groups of tetrapods.
19. What was the earliest form of life on the planet? How long ago did this life-form first occur?
20. What unique ability was originated with cyanobacteria? How did this alter life on Earth and
lead to a wave of mass extinctions?
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Chapter 25: The History of Life on Earth
21. The first eukaryotes did not appear until approximately 2.1 billion years ago. Using the figure,
label and explain the evolution of eukaryotes by endosymbiosis.
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22. Summarize three lines of evidence that support the model of endosymbiosis.
23.
Use the clock model to note the following events in the life of the planet: origin of Earth,
appearance of prokaryotes, evolution of atmospheric oxygen, occurrence of eukaryotic cells, multicelMarity, and life moves onto land. For each event, also label the number of years ago it occurred.
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Chapter 25: The History of Life on Earth
24.
If you have not studied geology, you will find this concept introduces a fascinating look at
the changes in our planet as explained by continental drift. Define continental drift. How can
continents move?
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On the following figure, complete the time line on the left, then label Pangaea, Gondwana, and
Laurasia. Where was India 65 million years ago?
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See if you can answer each of these short questions:
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a. What is the San Andreas Fault?
b. What caused the uplift of the Himalayas?
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c. How can a fossil freshwater reptile be found in both Brazil and West Africa, areas separated
today by a wide expanse of ocean?
d. Why are no eutherian (placental) mammals indigenous to Australia?
27.
A mass extinction is the loss of large numbers of species in a short period, caused by global
environmental changes. What caused the Permian mass extinction 250 million years ago (mya)?
Summarize the species that were lost.
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Chapter 25: The History of Life on Earth
28.
A second important mass extinction is the Cretaceous mass extinction that happened about
65 mya. Everyone's favorite group, the dinosaurs, was lost, along with more than half of all
marine species. What caused it?
29. What are adaptive radiations?
30. Why did large-scale adaptive radiation occur after each mass extinction?
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31. What two areas of biology are merged in the field of study commonly called evo-devo?
32. What is an evolutionary change in the rate or timing of developmental events?
33.
Homeotic genes are master regulatory genes that determine the location and organization of
body parts. Mutations in a homeotic gene can have a profound effect on morphology. Homeotic
gene mutations can contribute to the potential for evolutionary change. The Hox genes are one
class of homeotic genes. What do they control?
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When a structure that has evolved in one context becomes co-opted for another purpose, this
event is called
. Does exaptation imply that organisms are
anticipating future needs?
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Explain.
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Chapter 26: Phylogeny and the Tree of Life
Name
Period
Chapter 26: Phylogeny and the Tree of Life
1. What is systematics? How is it used to develop phylogenetic trees?
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2. What is taxonomy?
3. Every organism on Earth may be referred to by a unique binomial, or a two-part name. These
are in Latin, or latinized. What is your binomial? What does it mean?
4. What are the two components of every binomial?
.
Taxonomy uses hierarchical categories that nest within each other, like Russian dolls. The following figure shows the categories, each called a taxon. Label each taxonomic category and
then give the one that applies exclusively to this panther to the side of each level.
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Chapter 26: Phylogeny and the Tree of Life
You will notice that the most general category, domain, the one that encompasses the most organisms, is shown at the bottom of the figure. As you move up in the figure, the organisms show greater
and greater degrees of relatedness. You are expected to memorize these taxonomic categories in
order! Most students use a mnemonic device linked to the first letter of each taxon to remember
them. Make up your own, or try ours:
(You may choose to have King Philip come over for something else--whatever you can remember
best!)
6. So, which are more closely related: organisms in the same phylum or those in the same order?
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Here is a phylogenetic tree. Recall that branch points represent common ancestors of the two
lineages beyond the branch or node. Circle the common ancestor of badgers and otters, and
label it as A. Circle the common ancestor of cats and dogs, and label it as B.
Order
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Genus
Species
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Chapter 26: Phylogeny and the Tree of Life
Let's look back at a Study Tip from Chapter 22. This idea is repeated in our current chapter.
Study Tip
omologous structures show evidence of relatedness (whale fin, bat wing).
Aÿmlogous structures are similar solutions to similar problems but do not indicate close related-
ness (bird wing, butterfly wing).
8. Molecular systematics is a valuable tool used today to sort homology from analogy. What is
molecular systematics?
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9. The following figure shows three cladograms. What is a clade? Circle a clade that is not high-
lighted below.
(a) Monophyletic group (clade)
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(b) Paraphyletic group
(c) Polyphyletic group
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B Group I
B
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Group III
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Group II
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10. Why is Group I monophyletic?
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11. Explain why Group II is paraphyletic.
12. What is a polyphyletic group?
171 °
Chapter 26: Phylogeny and the Tree of Life
13. Clades are derived by using shared derived characters. What are these?
14. Explain why, for mammals, hair is a shared derived character, but a backbone is a shared
ancestral character.
Let's summarize some important information from this section. The rate of evolution of DNA sequences varies from one part of the genome to another; therefore, comparing different sequences helps
us to investigate relationships between groups of organisms that diverged a long time ago. For exam-
ple, DNA that codes for ribosomal RNA (rRNA) changes relatively slowly and is useful for investigating relationships between taxa that diverged hundreds of millions of years ago. DNA that codes for
mitochondrial DNA (mtDNA) evolves rapidly and can be used to explore recent evolutionary events.
15. Which method reveals that fungi are more closely related to animals than to green plants?
16. Which method reveals that the Pima of Arizona and Yanomami of Venezuela are descendants
of the same Native Americans that crossed the Bering Land Bridge 13,000 years ago?
17. What are molecular clocks?
18. If we use a molecular clock, approximately when did HIV emerge?
Taxonomy is in flu!! When your authors were in high school, we were taught there were two kingdoms: Plants and Animals. Then in our college courses, we were introduced to five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia. Now biologists have adopted a three-domain system,
which consists of the domains Bacteria, Archaea, and Eukarya. This system arose from the finding
that there are two distinct lineages of prokaryotes.
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Chapter 26: Phylogeny and the Tree of Life
19. On the previous figure, place an arrow at the point showing the common ancestor of all three
domains and label it.
20. What two domains include all prokaryotes?
Explain your
21. Which two domains are most closely related?
reasoning.
22. Which kingdom is made obsolete by the three-domain system? Why?
23. Which kingdom crumbled because it is polyphyletic?
24. Explain the role of horizontal gene transfer in the ring of life hypothesis.
Test Your Understanding Answers
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