Chapter 8 Section 2 Review Page 196

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Chapter 8 Section 2 Review Page 196
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1. What is the difference between relative and
absolute age.

• Relative age is the age of an object compared to
  the age of another object. (This rock layer is
  younger than this fault.)
• Absolute age is the numerical age of an object.
  (This rock layer is 125 million years old!)

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Relative Age Dating
Absolute Age Dating
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2. Explain why calculations of absolute
age based on rates of erosion and deposition can
be inaccurate.

• The rate at which sediment is deposited or eroded
  away can vary from year to year due to many
  factors.

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Rates of erosion and deposition
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3. Describe varves, and describe how and where
they form.

• Varves are layers of sediment made of one layer
  of sand covered by one layer of silt. They are
  deposited at the bottom of glacial lakes and
  represent one year of deposition.

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Varves
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4. Explain how radiometric dating is used to
estimate absolute age.

• By comparing the percentage of a radioactive
  (parent) isotope to a stable (daughter) isotope
  in a sample of rock, and based on the known rate
  of decay of the parent, scientists can calculate
  the length of time since the rock formed.

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Radiocarbon Dating Parent to Daughter
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5. Define half-life, and explain how it helps
determine an objects absolute age.

• Half-life is the amount of time that one half of
  a sample of a radioactive isotope takes to break
  down by radioactive decay to form a daughter
  substance.

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6. Suppose you have a sharks tooth that you
suspect is about 15,000 years old. Would you use
238U or 14C to date the tooth? Explain your
answer.

• You would use radiocarbon (14C) dating because
  the object is organic and because it is too young
  to be accurately dated by using 238U.

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The End