Chapter 8 Section 2 Chapter 8 Section 2 Review Page 196Review Page 196

1. What is the difference 1. What is the difference between relative and absolute between relative and absolute age.age.

• Relative age is the age of an Relative age is the age of an object compared to the age of object compared to the age of another object. (This rock layer another object. (This rock layer is younger than this fault.)is younger than this fault.)

• Absolute age is the numerical Absolute age is the numerical age of an object. (This rock layer age of an object. (This rock layer is 125 million years old!)is 125 million years old!)

Relative Age Dating

Absolute Age Dating

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

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

Google Earth.lnk

Rates of erosion and Rates of erosion and depositiondeposition

3. Describe varves, and 3. Describe varves, and describe how and where describe how and where they form.they form.

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

VarvesVarves

4. Explain how 4. Explain how radiometric dating is radiometric dating is used to estimate used to estimate absolute age.absolute age.• By comparing the percentage of a By comparing the percentage of a

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

Radiocarbon Dating: Parent to Daughter

5. Define half-life, and 5. Define half-life, and explain how it helps explain how it helps determine an object’s determine an object’s absolute age.absolute age.

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

66. Suppose you have a shark’s . Suppose you have a shark’s tooth that you suspect is tooth that you suspect is about 15,000 years old. Would about 15,000 years old. Would you use you use 238238U or U or 1414C to date the C to date the tooth? Explain your answer.tooth? Explain your answer.

• You would use radiocarbon (You would use radiocarbon (1414C) dating C) dating because the object is organic and because it because the object is organic and because it is too young to be accurately dated by using is too young to be accurately dated by using 238238U.U.

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