WLHS / AP BIO / Monson
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Date
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CHAPTER 25 STUDY QUESTIONS – The History of Life on Earth; Fossil Record
Early Earth:
1) How old is the planet?
How old is the earliest evidence of LIFE on
Earth?
2) The current theory of the origin of life suggests a sequence of four main stages. Summarize them here:
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3) Oparin & Haldane hypothesized that the early atmosphere was a reducing environment. What did they
suggest was the source of energy for early organic synthesis?
4) Label this diagram showing the apparatus
set up by Miller & Urey in their attempt to test
the Oparin-Haldane hypothesis.
(HINT: see figure 4.2 on page 59)
What was collected in the sample cup? What was
Concluded from the results of this experiment?
5) What are protocells? What properties of life do they
demonstrate?
6) What are ribozymes?
7) Explain the evidence for an early “RNA world.”
The Fossil Record:
8) In what type of rock are fossils found?
9) Describe the formation of fossils. Which parts of an organism are most likely to fossilize and how do fossils
provide evidence for evolution?
Key Events in Life’s History:
10) What was the earliest form of life on the planet? How long ago did this life-form first occur?
11) What unique ability was originated with cyanobacteria? How did this alter life on Earth and lead to a wave
of mass extinctions?
12) Label the figure below showing the
evolution of eukaryotes by endosymbiosis.
(see figure 25.9 on p. 517)
13) Summarize three lines of evidence that
support the model of endosymbiosis.
14) Use the clock model below to note the following events
in the life of the planet: (see fig. 25.7, p. 514)
-origin of Earth
-appearance of prokaryotes
-evolution of atmospheric O2
-life moves onto land
-occurrence of eukaryotic cells
-multicellularity
15) 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.
16) A second important mass extinction is the Cretaceous mass extinction that happened about 65 mya.
What is thought to have caused this extinction? Summarize the species that were lost.
17) What are adaptive radiations? Why do large-scale adaptive radiations occur after mass extinctions?
RADIOMETRIC DATING PROBLEMS:
A = Ao x (1/2)t/T
1) Manganese-56 has a half-live of 2.6 hours. Assuming you start with a sample of 10.5 grams of
manganese-56, how much will remain after 16.0 hours?
2) The mass of cobalt-60 in a sample is found to have decreased from 10.0 grams to 2.5 grams in a period of
10.6 years. From this information, calculate the half-life of cobalt-60.
3) A patient is administered 20.0 milligrams of iodine-131. How much iodine-131 will remain in the patient’s
body after 21 days if the half-life for iodine-131 is 8 days?
4) Suppose you have a sample containing 800.0 grams of a radioactive substance. If after one hour only 72.0
grams of the original compound remain, what is the half-life of this isotope?
5) You are an archaeologist and you have discovered the remains of an ancient civilization. In one of the
human bones that you find, you determine that of the original 318.0 grams of carbon-14 present in the bone,
only 92.0 grams remain. Knowing that the half-life of carbon-14 is about 5730 years, what do you determine
is the age of this bone (and thus this civilization)?
7) Living plant material gives off 15.3 disintegrations of C-14 (“clicks,” as detected with a Geiger counter) per
minute per gram of carbon.
a) How old is a fossil that emits about 7.65 disintegrations per minute per gram?
b) How old is a fossil that emits 0.956 disintegrations of C-14 per minute per gram?
8) If the half-life of a particular radioactive isotope is 62 days, and a starting sample contains 58.8 g of this
isotope, what mass of the original isotope would still be present after 550 days?