1. How old is a rock if the mineral biotite from the rock has 85,000 40K atoms and 15,000 40Ar atoms? Note: 40K decays to 40Ar with half-life = 1.3 billion years. %3D

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
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1. How old is a rock if the mineral biotite from the rock has 85,000 40K atoms and 15,000 40Ar
atoms? Note: 40K decays to 40Ar with half-life =1.3 billion years.
2. Isotopic analysis of a granitic intrusion indicates that 6.25 % of the original 40K is present.
Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is
present. What is the absolute age of both the granitic intrusion and the dike? What is the
relationship between them?
3. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a
radiometric age of 200 million years. What can you say about age of the conglomerate based
on this data?
4. 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.
5. If a mineral contains 1.56 % of its parent isotope, how many half-lives have gone?
Transcribed Image Text:Questions: 1. How old is a rock if the mineral biotite from the rock has 85,000 40K atoms and 15,000 40Ar atoms? Note: 40K decays to 40Ar with half-life =1.3 billion years. 2. Isotopic analysis of a granitic intrusion indicates that 6.25 % of the original 40K is present. Analysis of a nearby basaltic intrusion indicates that 25 % of the original amount of 40K is present. What is the absolute age of both the granitic intrusion and the dike? What is the relationship between them? 3. Pebbles of an igneous rock are incorporated within a conglomerate. The pebbles yield a radiometric age of 200 million years. What can you say about age of the conglomerate based on this data? 4. 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. 5. If a mineral contains 1.56 % of its parent isotope, how many half-lives have gone?
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