Amass spectrometer was used to measure the 87rb/ 86sr (plot on x axis) and 87sr/ 86sr (plot on y-

axis) isotope ratios in 10 different rock samples from a series of lava flows that appeared, based on their

field relations, to be contemporaneous (i. e., erupted at about the same time). assume that all precautions

were taken to assure high -quality data – including running of duplicate samples – so you can rule out

analytical errors in the analyses. start by plotting the data to obtain an isochron, and then answer the

following questions:

 = 1.42x10-11yr-1;

87 87

86 86

0

87

86

1

ln 1

sr sr

sr sr

t

rb

sr



            −

      = +              

87rb/ 86sr 87sr/ 86sr

0.1935 0.714

0.7008 0.7319

1.1987 0.7455

1.3432 0.750
1.4307 0.7898

6 1.8055 0.7689

7 2.0169 0.7752

8 2.6051 0.7903

9 2.9598 0.8005

10 3.1005 0.8152

1. what is the age of these rocks in ma?

2. if you are asked to exclude some of the samples from your calculations, which sample/s? you

would exclude? after having done that, calculate the new age and the initial ratio!

what is the meaning of this initial ratio?

3. where did the samples plot on your diagram at t=0?