1. Ch. 6 Vocabulary

2. 1
Uniformatarianism
idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history

3. 3
Paleontology
study of fossils

4. 4
Relative dating
any method of determining whether an event of object is older or younger than other events or objects

5. 8
Catastrophism
principle that states that geologic changes occur suddenly

6. 17
Geologic column
arrangement of rock layers in which the oldest rocks are at the bottom

7. 7
Unconformity
break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time

8. 10
Isotope
an atom that has the same number of protons as other atoms of the same element but that has a different number of neutrons

9. 22
Extinction
death of every member of a species

10. 5
Superposition
principle that stated younger rocks lie above older rocks if the layers have not been disturbed

11. 2
Radioactive dating
method of determining the age of an object by estimating the relative percentages of a radioactive isotope and a stable isotope

12. 9
Absolute dating
any method of measuring the age of an event or object in years

13. 6
Fossil
remains or physical evidence of an organism preserved by geological processes

14. 15
Mold
mark or cavity made in a sedimentary surface by a shell or other body

15. 12
Half-life
time needed for half a sample of a radioactive substance to undergo radioactive decay

16. 16
Cast
type of fossil that forms when sediments fill in the cavity left by a decomposed organism

17. 21
Epoch
subdivision of geologic period

18. 14
Trace fossil
fossilized mark that is formed in soft sediment by the movement of an animal

19. 19
Geologic time scale
standard method used to divide the Earth’s long natural history into manageable parts

20. 11
Eon
largest division of geologic time

21. 18
Index fossil
fossil that is found in rock layers of only one geologic age and that is used to establish the age of the rock layers

22. 20
Period
unit of geologic time into which era are divided

23. 13
Era
unit of geologic time that includes 2 or more periods