1. Unit 3 Review Please see pages 145-194 in your book for more information *This study guide is just to get you started studying– please look at your notes and book too.*

2. What is uniformitarianism? A principle that geological processes that occurred in the past can be explained by current geologic processes.

3. What is climate? The weather conditions in an area over a long period of time.

4. What is a fossil? The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock.

5. What is a trace fossil? A fossilized structure, such as a footprint or coprolite, that formed in sedimentary rock by animal activity on or within soft sediment.

6. What is an ice core? A long cylinder of ice obtained from drilling through ice caps or ice sheets; used to study past climates.

7. How do organisms become preserved as fossils? Fossils can be trapped in amber or asphalt Buried in rock Become frozen Become petrified

8. What can fossils tell us? Fossils tell scientists about changes to the environment Fossils tell scientist how life forms have changed over time

9. How does sedimentary rock show Earth’s history? The composition of sedimentary rock show the source of the sediment that makes up the rock The texture of the sedimentary rock shows the environment in which the sediment was carried and deposited Features in the rock show what was happening to the sedimentary rock

10. What do Earth’s surface features tell us? How continents move How landforms change over time

11. What other materials tell us about Earth’s climate history? Trees Sea-Floor sediments Ice cores

12. What is relative dating? Any method of determining whether an event or object is older or younger than other events or objects.

13. What is superposition? A principle that states that younger rocks lie above older rocks if the layers have not been disturbed.

14. What is unconformity? A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

15. What is a geologic column? An ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.

16. How are undisturbed rock layers dated? Older layers are on the bottom Younger layers are on the top

17. How are sedimentary rock layers disturbed? Tilting Folding Faults and Intrusions Unconformities

18. How are rock layers ordered? Law of crosscutting relationships states that: “A fault or a body of rock, such as an intrusion, must be younger than any feature or layer of rock that the fault or rock body cuts through.”

19. How are fossils used to determine relative ages of rocks? Fossils can help us determine the relative age of rocks by giving us a reference point for the rocks. Younger fossils= younger rocks Older fossils= older rocks

20. What is absolute dating? Any method of measuring the age of an event or object in years.

21. What is radioactive decay? The process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element.

22. What is half-life? The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope. If you have 6 milligrams of the original isotope in one half-life 3 milligrams of the isotope would be left and 3 milligrams would be the daughter isotope

23. What is radiometric dating? A method of determining the absolute age of an object by comparing the relative percentages of a radioactive parent isotope and a stable daughter isotope.

24. How can the absolute age of rock be determined? Thru absolute dating methods

25. What is the best rock for radiometric dating? Igneous rock

26. What are some radiometric dating methods? Radiocarbon dating Potassium-Argon dating Uranium-Lead dating

27. How is radiometric dating used to determine the age of Earth? Radiometric dating can be done on meteorites to determine the age of the Earth.

28. How are index fossils used? Index fossils are markers for the time that organisms lived on Earth Index fossils can date different layers of Earth