Chapter 18 Fossils and Geologic Time
Chapter 18 Fossils and Geologic Time
Chapter 18 Fossils and Geologic Time
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
436 CHAPTER <strong>18</strong>: FOSSILS AND GEOLOGIC TIME<br />
In Figure <strong>18</strong>-10, the dashed lines help to illustrate the following.<br />
(1) The mastodont <strong>and</strong> condor, as well as the dinosaur<br />
layers at B are missing from location A. (2) The brachiopod<br />
fossils at A <strong>and</strong> B show that the limestone <strong>and</strong> s<strong>and</strong>stone that<br />
contain them are similar in age. (3) The two bottom layers at<br />
location A seem to be older than any exposed rock at B.<br />
Figure <strong>18</strong>-11 is an exercise in correlation. In using these<br />
diagrams, assume that if a fossil species is not shown in its<br />
ocean or l<strong>and</strong> environment, it did not exist at that time. How<br />
can the following be concluded from this diagram? (1) One<br />
outcrop is a marine environment while the other is terrestrial.<br />
(2) Layer A can be only Cambrian or Ordovician in age.<br />
(3) Outcrop I (only) is overturned. (4) Layers D <strong>and</strong> F must<br />
both be Cretaceous in age.<br />
Catastrophic Events<br />
Figure <strong>18</strong>-10 Application of<br />
correlation principles.<br />
Catastrophic events can create very distinct time markers in<br />
rock layers. A large volcanic eruption can eject great quantities<br />
of ash into the atmosphere. When Mount St. Helens exploded<br />
in 1980, a cubic kilometer of ash <strong>and</strong> rock debris was
Change language