Chapter 17 Unraveling Geologic History
Chapter 17 Unraveling Geologic History
Chapter 17 Unraveling Geologic History
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408 CHAPTER <strong>17</strong>: UNRAVELING GEOLOGIC HISTORY<br />
10. The absolute age of an igneous rock can best be determined by<br />
(1) comparing the amount of decayed and undecayed radioactive isotopes<br />
in the rock.<br />
(2) comparing the sizes of the crystals found in the upper and lower parts<br />
of the rock.<br />
(3) examining the rock’s relative position in a rock outcrop.<br />
(4) examining the environment in which the rock is found.<br />
The diagrams below represent two different geologic cross sections in which an<br />
igneous formation is found in sedimentary rock layers. The layers have not<br />
been overturned.<br />
Key<br />
Cross Section A Cross Section B<br />
Sandstone<br />
Shale<br />
Igneous rock<br />
Contact<br />
Metamorphism<br />
11. Which statement best describes the relative age of each igneous formation<br />
compared to the overlying sandstone bedrock?<br />
(1) In A, the igneous rock is younger than the sandstone, and in B, the igneous<br />
rock is older than the sandstone.<br />
(2) In A, the igneous rock is older than the sandstone, and in B, the igneous<br />
rock is younger than the sandstone.<br />
(3) In both A and B, the igneous rock is younger than the sandstone.<br />
(4) In both A and B, the igneous rock is older than the sandstone.
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