This pan of the assignment will allow you to practice your skills at radiometric

Question

This pan of the assignment will allow you to practice your skills at radiometric dating. You will calculate the absolute ages of three different rocks shown in the geologic cross-section below. These rock units are A-a basaltic dike, B-a granite intrusion, and C-a folded metamorphic rock Remember you can also check your age calculations by using relative dating techniques. Use these data to calculate the isotopic ages of the igneous dike (A), granite (B) & metamorphic rode (C). Calculate the number of half lives that have passed and multiply this by the half life of the measured isotope to determine the age then assign a geologic period to that rock from section 9.8 textbook.

Explanation / Answer

Answer:

Half lives are the time which isotopes become half to its daughter from their parent.

For Dike A

Number of half lives passed= 1750/250= 7

Age = 7* 20= 140 million years

140 million years belongs to Cretaceous period

For Granite B

Number of half lives passed= 750/250= 3

Age = 3* 130= 390 million years

390 million years belongs to devonian period.

For Metamorphic rock C

Number of half lives passed= 7500/500= 15

Age = 15*75= 1125million years

1125 million years belongs to middle proterozoic

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