Victory for the ACT Student Text 15e

S CIENCE R EVIEW • 357

In Figure 1, the line for T 0 the x -axis because: F. all radioactive elements decay from parent to daughter isotopes at the same rate. G. the quantities of strontium-87 and •–”‘–‹—Ǧͺ͸ ‡š‹•– ‹ ƒ ϐ‹š‡† ”ƒ–‹‘ throughout the life of the rock. H. the rubidium-87 in the magma does not begin to decay until the rock is thoroughly cooled. J. the Sr-87/Sr-86 ratio was the same throughout the magma when it froze into rock. According to Figure 1, which of the following best describes the composition of the M 5 inclusion sample at T 0 compared with its composition at T 1 ? A. M 5 has more strontium-87 at T 0 than at T 1 . B. M 5 has more strontium-86 at T 0 than at T 1 . C. M5 has more rubidium-87 at T 0 than at T 1 . D. M 5 has less strontium-86 at T 0 than at T 1 . is horizontal to

Experiment 1 Scientists tested the mineral samples in a basalt rock to determine its age. The results are shown in Figure 2. 0.712

60.

0.708

Present Time

Plagioclase

0.704

Pyroxene

Limenite

Olivine

0.700 Sr-87/Sr-86

T

0

0.696

0.05

0.1 0.15 Figure 2 Rb-87/Sr-86

0.2

0.3

0.25

61.

Experiment 2 Scientists tested the mineral samples in a second basalt rock. The results are shown in Figure 3.

0.712

Sample 4

0.708

Sample 3

Present Time

0.704

Sample 2

Sample 1

0.700 Sr-87/Sr-86

T

0

0.696

0.1

0.2

0.3

Figure 3

Rb-87/Sr-86