Absolute Age

Why is radioactive decay useful for determining absolute age?

• Radioactive substances decay at a predictable rate.

• All Earth materials contain the same radioactive substances.

• The mass of radioactive isotopes in a material is equal to the age of the material.

• The half-life of a radioactive substance decreases by half after a certain amount of time.

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NGSS.HS-PS1-8

Which is an example of absolute age?

• This trilobite is older than that dinosaur.

• That stromatolite is the absolute oldest fossil I've ever seen.

• Velociraptors lived 71-75 million years ago.

• The oldest sedimentary layer is on the bottom.

A whale bone that originally contained 200 grams of radioactive carbon-14 now contains 25 grams of carbon-14. How many half-lives have passed since this whale was alive?

• 1

• 2

• 3

• 4

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NGSS.HS-PS1-8

Carbon-14 can only be used to determine the age of

• recently living things (thousands of years old).

• recent rocks (thousands of years old).

• very old fossils (millions of years old).

• very old rocks (millions of years old).

What is the approximate age of an igneous rock that contains only one-fourth of its original potassium-40 content due to radioactive decay?

• 1.3 x 10⁹ years

• 3.9 x 10⁹ years

• 2.6 x 10⁹ years

• 5.2 x 10⁹ years

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NGSS.HS-PS1-8

This diagram represents a sample of ⁸⁷Rb. Which diagram represents the correct proportion of ⁸⁷Rb to its decay product, ⁸⁷Sr, after two half-lives?

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NGSS.HS-PS1-8

Which radioactive substance would probably be used in dating the recent remains of a plant found in sedimentary deposits?

• carbon-14

• rubidium-87

• potassium-40

• uranium-238

This graph shows the relationship between mass and time for a radioactive element during radioactive decay. What is the half-life of the element?

• 50 billion years

• 60 billion years

• 350 billion years

• 100 billion years

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NGSS.HS-PS1-8

How old is a rock that contains 6.25% of its original Potassium-40?

• 6.5 x10⁹ years

• 2.6 x10⁹ years

• 3.9 x10⁹ years

• 5.2 x10⁹ years

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NGSS.HS-PS1-4

What fraction of U-238 remains in a rock that is 18 billion years old?

• 1/8

• 1/16

• 1/32

• 1/64

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NGSS.HS-PS1-8