Determining Absolute Age

How does absolute age differ from relative age?

• only absolute dating indicates which rock is older than another
• only absolute dating finds the age in years
• only relative dating finds the age in years

About how long does it take for one varve to form?

• one year
• ten years
• one month

What does one varve look like?

• a fine summer layer and a coarse winter layer on top
• a coarse summer layer with a fine winter layer below
• a coarse summer layer and a fine winter layer on top

On what process does radiometric dating rely?

• radioactive decay
• counting varves
• sediment accumulation

Suppose you had a sample containing 20 g of a parent isotope. After how many half lives would less than 2 g of the parent isotope remain?

• one
• two
• four

After four half-lives, what fraction of the original parent isotopes remain?

• 1/4
• 1/16
• 1/8

How does the half-life of an isotope affect the accuracy of the radiometric dating method?

• if the rock is too young, there are no isotopes that can give its age accurately
• if the half-life is too long or too short for the rock to have parent and daughter material remaining, the age will not be accurate
• if the rock is too old, its age cannot be determined by any method

Scientists find a rock that they think is about 250 million years old. Which of these dating methods could not be used to date the rock?

• potassium-argon dating
• uranium-lead dating
• radiocarbon dating

What is half-life?

• it refers to the lifespan of a fossil
• the time required for half of a sample of radioactive isotope to form a daughter isotope
• the time required for daughter isotopes to become radioactive

Suppose you have a shark's tooth that you think is about 15,000 years old. Would you use uranium-238 or carbon-14 to date the tooth and why?

• uranium-238 because it is more radioactive
• uranium-238 because it can be used for extremely old fossils
• carbon-14 because it is useful for organic matter less than 70,000 years old