Table 3. Calculations of Isotopic Ages Chapter 9 Investigation Worksheet: page 2

Question

Table 3. Calculations of Isotopic Ages Chapter 9 Investigation Worksheet: page 2 use these data to calculate the isotopic ages of the granite (G) and dike (D), Calculate the number of half lives that have passed and multiply this by the half life of the measured isotope. Half-Life of | # Parent | # Daughter | Lives that Rock Unit Age lsotope Atoms Atoms Have Passed 500 million years Granite (G) 125 875 40 million years Dike (D) 500 500 Table 4. Sequence of Events Using all the information, number the events in order from oldest to youngest. Order (1 for oldest to 12 for ynungest) Event

Explanation / Answer

For granite (G), total radioactive atoms are 1000 (at the time of formation).

Now, parent atoms are 125. It means (1000-125=875) 875 parent atoms are disintegrated to form 875 daughter atoms.

At present, parent atoms=(125/1000) or 1/8 of parent atoms at the time of formation.

Or, parent atoms suffer 3 half lives .

So, the the half lives that have passed is 3

The age is 3 x 500 million years = 1500 million years.

For Dike, total radioactive atoms are 1000 (at the time of formation).

Now, parent atoms are 500. It means (1000-500=500) 500 parent atoms are disintegrated to form 500 daughter atoms.

At present, parent atoms=(500/1000) or 1/2 of parent atoms at the time of formation.

Or, parent atoms suffer 1 half lives .

So, the the half lives that have passed is 1

The age of Dike (D) is 1 x 40 million years = 40 million years.

Rock unit Half-life of isotope # Parent atoms # Daughter atoms # of half lives that have passed (?) Age (?) Granite (G) 500 125 875 3 half lives passed 1500 million years

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