Fall 201 T Geol 130S T/TH1-25p the he HW #6-“Absolute Dating” Due Tuesday, Octob
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Fall 201 T Geol 130S T/TH1-25p the he HW #6-“Absolute Dating” Due Tuesday, October 17, 2017 IN CLASS Discussion: Half-life is the time it takes for one half of a given amount of a radioactive substance, the "parent," to decay into its stable product, known as the "daughter." Here's a simplified example. The half-life of uranium (U) is 4.5 bi llion years. If you start with one kilogram of U, and wait for 4.5 billion years, you will end up with a half-kilogram of U, and a half-kilogram of its daughter, lead (Pb). If you waited around another 4.5 billion years, half of the leftover parent, (1/2 kg) would decay into the daughter. This would leave you with ¼ kg of U and ¾ kg of lead, after two half-lives have passed. References: Anthony D. Feig. Cathy Willermet and Sandra Reece. GEOL 1312 (1304) Laboratory Manual Earth Sciences 2. thechive.com highlightskids.com quranandscience.com hanmansfossils.com englishinguiaintermedio.wordpress.com Activity I: Discovering half-life. Each group will get a bag of 100 pennies from your instructor. Start by putting all the pennies on the table face up (heads), and verify that there are 100 pennies. Each face-up penny represents an unstable, radioactive parent" atom. You are starting with 100% unstable, radioactive material. Now place the pennies in the bag, shake it, and dump it out on the table. Separate out the heads and the tails. The heads are still the parent, but the tails represent the stable daughter product Count the number of each, and record these data on the chart on the next page. One half-life of your pennies has passed. How much time (minutes) did it take you to do this? This is how long your "half life" is Now return the HEADS-UP pennies to the bag, shake it thoroughly, and dump it out on the table. Separate the heads from the tails, count the number of each, and record these data on the chart. This is the second half-life Repeat eight more times, for a total of ten. Connect the dots on your graph. What is the shape of the line? 11PageExplanation / Answer
1.
Parent atom of U - 235 = 250
Daughter atom of Pb - 207 =750
total =1000
250/1000= 0.25
percentage =0.25*100
=25%
Half lives corresponds to 25% of parent atoms is "2"
Age = 2*half life
=2*4.5 billion year = 9 billion year.
2.
Parent atom of Rb-87 = 456
Daughter atom of Sr-87 =127
total = 583
456/583= 0.782
percentage =0.782*100
=78.2%
Half lives corresponds to 78.2% of parent atoms is "0.48"
Age = 0.48*half life
=0.48*47 billion year = 22.56 billion year.
3.
Parent atom of C-14 = 973
Daughter atom of N-14 =2713
total =3686
973/3686= 0.2639
percentage =0.2639*100
=26.39%
Half lives corresponds to 26.39% of parent atoms is "1.98"
Age = 1.98*half life
=1.98*5730 year = 11345.4 years.
4.
Parent atom of K-40 =6733
Daughter atom of Ar-40 =10312
total =17045
6733/10312= 0.3950
percentage =0.3950*100
=39.5%
Half lives corresponds to 25% of parent atoms is "1.4"
Age = 1.4*half life
=1.4*1.3 billion year = 1.82 billion year.
5.
Parent atom of C-14 = 2512
Daughter atom of N-14 =143
total =2655
2512/2655= 0.9461
percentage =0.9461*100
=94.61%
Half lives corresponds to 94.61% of parent atoms is "0.07"
Age = 0.07*half life
=0.07*5730 year = 401.1 years.
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