Name: ___________________________________________ Regents Earth Science Half Life Regents Review 1. A fossil formed 11,400 years ago. Which percentage of the original amount of carbon14 remains in the fossil? (1) 100% (3) 25% (2) 50% (4) 12.5% Date: ___________ Period: _____ 4. A bar graph of the radioactive decay of carbon-14 is shown below. 2. The table below shows the radioactive decay of carbon-14. Part of the table has been left blank. After 22,800 years, approximately what percentage of the original carbon-14 remains? (1) 15% (3) 6.25% (2) 12.5% (4) 3.125% 3. Radioactive decay of 40K atoms in an igneous rock has resulted in a ratio of 25 percent 40K atoms to 75 percent 40Ar and 40Ca atoms. How many years old is this rock? (1) 0.3x109 y (3) 2.6x109 y (2) 1.3x109 y (4) 3.9x109 y The solid black sections of the bars on the graph represent the percentages of (1) carbon-14 from the original sample that has not decayed (2) uranium-238 from the original sample that has not decayed (3) nitrogen-14 decay product resulting from the radioactive decay (4) lead-206 decay product resulting from the radioactive decay 5. How old is a bone that has 12.5% of the original amount of radioactive carbon-14 remaining? (1) 5,700 years (3) 17,100 years (2) 11,400 years (4) 22,800 year 6. The igneous intrusion contains the radioactive isotope potassium-40, which is used in radioactive dating to determine the age of rocks. State one property of potassium-40 that allows it to be useful in the radioactive dating of rocks. _________________________________________________________________________ Base your answers to questions 7 and 8 on the data table and information below and on your knowledge of Earth science. The data table shows the radioactive decay of carbon-14 and the age of fossil remains, in years (y). Part of the table has been left blank. 7. Identify the decay product when carbon-14 undergoes radioactive disintegration. ____________________________ 8. The carbon-14 in the fossil remains of a mastodont has undergone five half-lives of radioactive decay. Calculate the age of these fossil remains. ________________________ years Base your answers to questions 9 through 12 on the graph below and on your knowledge of Earth science. The graph shows the rate of decay of the radioactive isotope carbon-14 (14C). 9. Complete the flow chart below by filling in the boxes to indicate the percentage of carbon-14 remaining and the time that has passed at the end of each half-life. 10. Identify the decay product formed by the disintegration of carbon-14. ____________________________ 11. Explain why carbon-14 cannot be used to accurately determine the age of organic remains that are 1,000,000 years old. _________________________________________________________________________ _________________________________________________________________________ 12. State the name of the radioactive isotope that has a half-life that is approximately the same as the estimated time of the origin of Earth. ____________________________