Download Activity 5 Mass Extinction and Fossil Records

CS_Ch10_Evolution
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2:56 PM
Page 647
Activity 5 Mass Extinction and Fossil Records
Activity 5
Mass Extinction and Fossil Records
GOALS
What Do You Think?
In this activity you will:
Sixty-five million years ago the curtain came down on the
age of dinosaurs when a catastrophic event led to their mass
extinction.
• Investigate fossil data for
evidence of mass extinction
and adaptive radiation.
• Explain the meaning of mass
extinction and adaptive
radiation.
• Describe the meaning of
niche in an ecosystem.
• What type of disastrous event could have led to the
extinction of such a large group of animals?
• Did any other life forms become extinct at this time in
geological history?
Write your answer to these questions in your Active Biology
log. Be prepared to discuss your ideas with your small group
and other members of your class.
For You To Do
In this activity, you will investigate fossil data from those
“pages” that represent the boundary between the Cretaceous
and Tertiary periods (about 65 million years ago).
1. Your teacher will divide the class into groups of three or
four students. With the other members of your group,
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Cretaceous and Tertiary periods.
Using a technique known as
magnetostratigraphy, geologists infer
that each meter of this sedimentary
sequence represents 0.1 million years
of history. The point “0 m”
represents the boundary between the
Cretaceous and Tertiary systems,
65 Ma (millions of years ago).
Paleontologists sampled fossils from
the locations shown along the left
axis.
examine the six brachiopod fossils.
Brachiopods are a group of marine
animals.
Wash your
hands after
handling the
fossils.
a) Which species became extinct at
the Cretaceous-Tertiary (K-T)
boundary?
a) What characteristics might
paleontologists use to assign these
fossils to different species?
b) Which species evolved after the
K-T boundary?
b) What characteristics might
paleontologists use to assign these
fossils to one group?
c) Which species appear to have
become extinct and then
reappeared later?
2. Now examine Graph A. It plots the
ranges of 50 different species of
brachiopods across 15 m of
sedimentary rock at one location in
Denmark. This is one of the few
places in the world that contains a
continuous record of layers that
represent the boundary between the
d) What conclusions can you draw
from this graph?
e) What are the limitations of the
data shown in Graph A? (Hint:
recall the processes by which
fossils are preserved.)
Graph A: Range of Different Species of Brachiopods
meters 10
9
samples
8
49 50
Tertiary
424344454647
394041
35 3637 38
33 34
2829303132
6
5
4
3
27
2
1
0
Cretaceous
Sedimentary Sequence
7
19 20
–1
121314151617
–2
–3
18
24 25
1011
–4
21 22 23
9
–5
1 2 3 4 5 6 7 8
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Activity 5 Mass Extinction and Fossil Records
Graph B: Number of Families of Marine Organisms through Time
800
Number of Families
600
400
500
400
300
200
Geologic Time (millions of years ago, Ma)
3. Paleontologists have compiled similar
data on the ranges of existence of
numerous other organisms during the
Cretaceous and Tertiary periods.
Examine Graph B, which shows a set
of data assembled to illustrate the
number of families (groups of closely
related species) of marine animals
through geological time.
a) When was the number of families
the greatest?
b) Has the growth in the number of
families been steady? Explain your
answer.
c) What do the dips in the graph
represent?
d) What inferences can you draw
from this graph?
e) What are the limitations of the
graph shown in Graph B?
100
Quaternary
1.6 to 0 Ma
Tertiary
65 to 1.6 Ma
Cretaceous
144 to 65 Ma
Jurassic
208 to 144 Ma
Triassic
245 to 208 Ma
Permian
286 to 245 Ma
Carboniferous
360 to 286 Ma
Devonian
408 to 360 Ma
Silurian
438 to 408 Ma
Ordovician
505 to 438 Ma
0
Cambrian
570 to 505 Ma
200
0
4. Now re-examine Graph B. Locate the
times of the five greatest decreases in
the number of families. Discuss why
this might represent mass extinctions.
Locate the times of the five greatest
increases in the number of families.
Discuss why this might represent
adaptive radiations. (Adaptive
radiation describes the rapid changes
in a single or a few species to fill many
empty functions in an ecosystem.)
a) In your Active Biology log,
construct a chart that summarizes
your findings. Your chart should
have two vertical columns, one
labeled “Times of Mass
Extinction” and the other labeled
“Times of Adaptive Radiation.”
Fill in the chart with the estimated
date that each event began and the
name of the time period (e.g.,
“beginning of the Devonian period,
roughly 410 Ma”).
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5. Now analyze Graph C, a graph
constructed to show the number of
families of terrestrial tetrapod
families (land animals with four
limbs) through geological time.
Locate the greatest extinction events
and adaptive radiations.
Graph C: Number of Families of
Terrestrial Tetrapods through Time
200
a) Compare these events to the
events listed in your chart for
Graph B. Propose a hypothesis to
account for the differences and
similarities in these two graphs.
400
300
200
100
Geologic Time (millions of years ago, Ma)
Quaternary
1.6 to 0 Ma
Tertiary
65 to 1.6 Ma
Cretaceous
144 to 65 Ma
Jurassic
208 to 144 Ma
Triassic
245 to 208 Ma
Permian
286 to 245 Ma
0
Carboniferous
360 to 286 Ma
100
Devonian
408 to 360 Ma
Number of Families
300
0
6. Consider the pattern of extinction
and adaptive radiation in Graph B
and C.
a) How might adaptive radiation
be related to mass extinctions?
(Hint: consider how life on Earth
might be different if dinosaurs
still existed.)
Making Inferences in Science
Have you ever wondered how scientists know so much about
dinosaurs? No human ever saw a dinosaur eat or run.The huge lizards
disappeared from Earth about 65 million years ago. No fossil evidence of
the human species, Homo sapiens, appears before 500,000 years ago.
The skeletons of dinosaurs have been reconstructed using fossil
records.The skeletons provide indirect evidence of how the dinosaur
might have lived. Evidence from the skull of a dinosaur may indicate
that the dinosaur might have been a meat eater.The premise that this
dinosaur killed other dinosaurs is called an inference. No one ever
saw the dinosaur eating meat, the evidence to support this conclusion
came from examining the skull shape and the structure of the teeth.
Unlike a hypothesis, an inference cannot be tested.
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Activity 5 Mass Extinction and Fossil Records
Mass Extinction and Adaptive Radiation
Extinction is the total disappearance of a species. Extinction means
that not a single organism of the species lives anywhere on Earth.The
fossil record is a virtual graveyard of extinct species. It is strewn with
the fossilized remains of millions of extinct species. David Raup, a
paleontologist at the University of Chicago, notes that “only about one
in a thousand species [that have lived on Earth] is still alive—a truly
lousy survival record: 99.9 percent failure!”
Even more striking, however, is the fossil evidence of mass
extinctions.These are episodes during which large numbers of
species became extinct during short intervals of geological time. In
geological time a few million years or less is a short period! The
extinction of one species often has a domino effect. If one species
vanishes, so do many others.Yet mass extinctions can present new
opportunities to survivors.
Those best able to survive fill empty
niches. (An ecological niche is the function
a species plays in an ecosystem.) Plants and
animals that have the greatest genetic
variation are most often best able to fill
these empty “spaces.” This process is called
adaptive radiation. In this activity, you
investigated evidence of mass extinctions
and adaptive radiations by analyzing data
from the fossil record. Rapid evolution can
also occur when a species moves into a
new area. Natural variation within a species
makes it easier for the species to adapt to
different environments.
Bio Words
extinction: the
permanent
disappearance of a
species from Earth
mass extinction:
the extinction of a
large number of
species during
short intervals of
geological time
niche: the ecological
function of a species;
the set of resources
it consumes and
habitats it occupies
in an ecosystem
adaptive radiation:
the diversification
by natural selection,
over evolutionary
time, of a species or
group of species into
several different
species that are
typically adapted
to different
ecological niches
One remarkable mass extinction event occurred at the boundary
between the Cretaceous and Tertiary periods, roughly 65 million years
ago.This boundary separates the age of the reptiles and the age of the
mammals. Geologists recognized this event over one hundred years
ago when they realized that there was a striking change in the types
of fossils deposited on either side of this boundary.This is where the
language of science may become difficult to follow. However, no
matter how it is said, the concepts are the same.This boundary
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also separates two eras.These two eras
are called the Mesozoic and Cenozoic.
Dinosaurs were prevalent during the
Mesozoic Era and extinct during the
Cenozoic Era.The last segment of the
Mesozoic Era is called the Cretaceous
Period.The first segment of the Cenozoic
Era is called the Tertiary Period.The
abbreviation for the boundary between
the Cretaceous and Tertiary periods is
often referred to as the K-T boundary,
where K is the abbreviation for the
Model of a Brachiosaurus.
German form of the word Cretaceous.
You may also hear of this time referred to
the Mesozoic and Cenozoic boundary. No matter what you call it,
there were dinosaurs before and there are no dinosaurs now, and it
happened about 65 million years ago!
Moreover, at the end of the Cretaceous period virtually all plant and
animal groups were lost from Earth, not just the dinosaurs.Yet, the
beginning of the Tertiary period marks the start of the adaptive
radiation of mammals.
The ultimate cause of the mass extinction at the Cretaceous/Tertiary
boundary is still a debate among scientists. However, more and more
evidence suggests that a meteorite impact caused the mass extinction.
The impact of the meteorite created a chain of devastating
environmental changes for living organisms.
Reflecting on the Activity and the Challenge
In this activity you had an opportunity
to see that life forms that dominated the
Earth many (geological) years ago are
not here now. You also learned that the
evidence to support this fact is found in
fossil records. The new organisms that
evolved to fill the ecological place of the
extinct organisms are also part of fossil
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records. You probably have developed
an even further appreciation of the
importance of fossil records. You may
wish to argue for a delay of
construction of the new highway
whether you represent the
paleontologists or a concerned citizen.
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Activity 5 Mass Extinction and Fossil Records
1. Explain the meaning of adaptive radiation in your own words.
2. What evidence do scientists use to support the idea of mass extinctions?
3. After a mass extinction, which organisms are most likely to survive? Explain your
answer.
4. Explain why the extinction of one species can have a domino effect on an
ecosystem.
Inquiring Further
1. The Cretaceous and Tertiary
boundary event
Research the proposed causes of the
mass extinction during this time period.
Provide at least two explanations.
Which one do you think is more
plausible?
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