1. Chapter 8

2.  itarianism  A principle that geologic processes that occurred in the past can be explained by current geologic processes.  Volcanism and Erosion Uniform p.185

3.  Relative Age  The age of an object in relation to the age of other objects p.186

4.   The law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed. Law of Superposition p.187

5.   A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. Un ities p.189 conform

6.  Absolute Age  The numeric age of an object or event, often stated in years before the present.  Using a process like “radiometric dating” or “carbon dating”

7.  Rates of Deposition  In general, about 30 cm of sedimentary rock are deposited over a period of 1,000 years.  However, a flood can deposit many meters of sediment in just one day.

8.  Radiometric Dating  A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) and a stable (daughter) isotope.  Half-Life: the time required for half of a sample of a radioactive isotope to break down.

9.  Carbon -14 Dating  Plants absorb Carbon during Photosynthesis  Scientists compare the carbon isotopes 12 C and 14 C (radioactive)  This can be used to determine the ages of wood, bones, shells and other organic remains that are less than 7,000 years old.

10.  Paleontology  The scientific study of fossils.

11.  Trace Fossils  Fossilized evidence of past movement of an animal such as tracks, footprints, borings and borrows.

12.  Index Fossils  A fossil that is used to establish the age of rock layers because it is:  Distinct – features different from other fossils  Abundant – occurs in fairly large numbers  Widespread – present in scattered rocks  Existed only for a short span of geologic time