Fossil Record and Geologic Time Scale

If a sample of a radioactive substance is crushed, the half-life of the substance will

• decrease

• increase

• remain the same

Why are radioactive materials useful for measuring geologic time?

• The disintegration of radioactive materials occurs at a predictable rate.

• The half-lives of most radioactive materials are less than five minutes

• The ratio of decayed products to undecayed materials remains constant in sedimentary rocks.

• Measurable samples of radioactive materials are easily collected from most rock types.

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NGSS.HS-PS1-8

The table gives information about the radioactive decay of carbon-14. [Part of the table has been left blank for student use]. What is the amount of original carbon-14 remaining after 34,200 years?

• 1/8 gram

• 1/16 gram

• 1/32 gram

• 1/64 gram

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NGSS.HS-PS1-8

Which radioactive substance shown on the graph has the longest half-life?

• A

• B

• C

• D

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NGSS.HS-PS1-8

According to the Earth Science Reference Tables, which element is used by Earth scientists for radioactive dating of rocks?

• cobalt-60

• plutonium-244

• potassium-40

• silicon-28

The diagram represents a clock used to time the half-life of a particular radioactive substance. The clock was started at 12:00. The shaded portion on the clock represents the number of hours one-half-life of this radioactive substance took to disintegrate. Which diagram best represents the clock at the end of the next half-life of this radioactive substance?

• 
• 
• 
• 

Tags

NGSS.HS-PS1-8

The diagram represents the radioactive decay of uranium-238. Shaded areas on the diagram represent the amount of

• undecayed radioactive uranium-238 (U238)

• undecayed radioactive rubidium-87 (Rb87)

• stable carbon-14 (C14)

• stable lead-206 (Pb206)

Tags

NGSS.HS-PS1-8

A geologist uses carbon-14 to measure the age of some material found in a sedimentary deposit. If the half life of carbon-14 is 5.7 x 1000 years and the sample shows that only 1/4 of the original carbon-14 is left, the age of the sample is about

• 5,700 years

• 11,400 years

• 17,100 years

• 22,800 years

According to the Reference Tables, which radioactive element would be most useful for determining the age of clothing that is thought to have been worn 2,000 years ago?

• carbon-14

• potassium-40

• uranium-238

• rubidium-87

In order for an organism to be used as an index fossil, the organism must have been geographically widespread and must have

• lived on land

• lived in shallow water

• been preserved by volcanic ash

• existed for a geologically short time