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1. How old is a rock if the mineral biotite from the rock has 75,000 40K atoms and 25,000 40A atoms? Note: 40K decays to 40Ar with half-life 1300 million years. %3D 2. What if it had instead 125 40K atoms and 875 40Ar atoms? 3. Isotopic analysis of a granitic intrusion indicates that 12.5 % of the original 40K is present. Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is present. 4. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a radiometric age of 300 million years. What can you say about age of the conglomerate based on this data?

1. How old is a rock if the mineral biotite from the rock has 75,000 40K atoms and 25,000 40A atoms? Note: 40K decays to 40Ar with half-life 1300 million years. %3D 2. What if it had instead 125 40K atoms and 875 40Ar atoms? 3. Isotopic analysis of a granitic intrusion indicates that 12.5 % of the original 40K is present. Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is present. 4. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a radiometric age of 300 million years. What can you say about age of the conglomerate based on this data?

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
Problem 1LR
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geology, finding age of rocks

1. How old is a rock if the mineral biotite from the rock has 75,000 40K atoms and 25,000 40Ar atoms? Note: 40K decays to 40Ar with half-life = 1300 million years. 2. What if it had instead 125 40K atoms and 875 40Ar atoms? 3. Isotopic analysis of a granitic intrusion indicates that 12.5 % of the original 40K is present. Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is present. 4. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a radiometric age ric age of 300 million years. What can you say about age of the conglomerate based on this data? 5. Sample of radioactive element with a mass of 200 g, of which 175 g is decayed within 30 days. Calculate the age of this sample. 6. A radioactive parent isotope with 600 atoms. After the decay, 450 daughter atoms were produced. Calculate the age of the rock if you know that the half-life of the parent isotope is 20 million years. 7. If a mineral contains 1.56 % of its parent isotope, how many half-lives have gone?
Transcribed Image Text:1. How old is a rock if the mineral biotite from the rock has 75,000 40K atoms and 25,000 40Ar atoms? Note: 40K decays to 40Ar with half-life = 1300 million years. 2. What if it had instead 125 40K atoms and 875 40Ar atoms? 3. Isotopic analysis of a granitic intrusion indicates that 12.5 % of the original 40K is present. Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is present. 4. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a radiometric age ric age of 300 million years. What can you say about age of the conglomerate based on this data? 5. Sample of radioactive element with a mass of 200 g, of which 175 g is decayed within 30 days. Calculate the age of this sample. 6. A radioactive parent isotope with 600 atoms. After the decay, 450 daughter atoms were produced. Calculate the age of the rock if you know that the half-life of the parent isotope is 20 million years. 7. If a mineral contains 1.56 % of its parent isotope, how many half-lives have gone?
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