Victory for the ACT Student Text 15e

358 • S CIENCE

64. Which of the following provides the best explanation for why the Sample 2 data point in Experiment 2 does not align with the other three sample data points on the isochron in Figure 3? F. At some point after the initial formation of the rock, it melted, uniformly mixed with other molten magma with a higher rubidium-87 concentration, and then refroze. G. At some point before the initial formation of the rock, it partially froze, melted, and then refroze with rubidium-87 to strontium-86 ratios unchanged. H. Sample 2 was collected from a different rock than Samples 1, 3, and 4. J. Each of the four samples was collected from a different rock. 65. The graph below shows isochrones of mineral inclusion samples taken from four different rocks today. Based on the graph, which of the rocks is the oldest?

62. Based on the results of Experiment 1, what was the approximate Rb-87/Sr-86 ratio in the olivine inclusion sample at the time the rock froze from magma? F. 0.03 G. 0.06 H. 0.07 J. 0.13 63. Š‡ ‰”ƒ’Š „‡Ž‘™ ‹• ƒ •‹’Ž‹ϐ‹‡† ’Ž‘– ‘ˆ the rubidium-strontium system for the rock studied in Experiment 1. Which of the dimensions labeled on the graph represents the decline in the amount of rubidium-87 in the limonite inclusion sample over time? d

b

0.704

0.703

Limenite

0.702

a

c

0.701

0.700

Sr-87/Sr-86

0.699

Rock 1

0 0.02 0.04 0.06 0.08 0.10 0.12 0.14

Rock 2

Rb-87/Sr-86

Present Time

Rock 3

A. a B. b C. c D. d

Rock 4

Sr-87/Sr-86

T

0

Rb-87/Sr-86

A. Rock 1 B. Rock 2 C. Rock 3 D. Rock 4