# College Geology Homework

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Suppose you have a sample of potassium feldspar from a rhyolite and you measure the ratio of atoms of 40Ar to 40K of 0.024 to 1, or for every 10000 atoms of 40K you find 240 atoms of 40Ar. For this problem, consider the decline of 40K from an initial value to the measured value.

a. What is Nt?

b. What is the ratio of atoms of radiogenic 40Ca to radiogenic 40Ar?

c. What is the ratio of atoms of radiogenic 40Ca to 40K

d. What is the current daughter:parent ratio ((40Ca+40Ar)/40K)?

e. For every 10000 atoms of 40K in the sample today, how many atoms of radiogenic 40Ca plus 40Ar are there now?

f. For every 10000 atoms of 40K in the sample today, how many atoms of 40K were there in the sample when it formed? This number is No

g. What is the age of the sample?

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