Fossils and Geologic Time - Study Guide
Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true.
False
1. Fossils usually occur in metamorphic rock. ____sedimentary_________________________________
True
2. Footprints and trails are examples of trace fossils. ________________________________
False
3. Generally, only the soft parts of organisms become fossils. ____hard_____________________
False
4. The law of superposition helps geologists determine the absolute age of a rock layer.
______________relative__________________________
True
5. At the beginning of the Paleozoic Era, a great number of different types of organisms evolved in an event
called the Cambrian Explosion. _________________________
False
6. Rock layers are always younger than the faults that cut across them. _____older___________________
False
7. Geologists divide Earth's long history into smaller units that make up the fossil record.
___geologic_____ _____time____________ ____scale______________
True
8. On the geologic time scale, the Mesozoic Era is divided into the Triassic, Jurassic and Cretaceous periods.
______________________________________________
True
9. The era before the Mesozoic Era is the Paleozoic Era. ___________________________________
True 10. Life on Earth first appeared during Precambrian Time. ______________________________
Completion
Complete each sentence or statement.
11. Paleontologists are scientists who study ______fossils__________________________________.
12. Scientists know how groups of animals changed over time by studying information contained in the
_____fossil records_________________________________________________.
13. A _____cast________________________________ fossil forms when dissolved minerals replace the
remains of an organism and then harden to form rock.
14. An index fossil can help geologist tell the __relative__________ age of a rock layer.
15. Organisms, such as dinosaurs, that no longer exist and will never again live on Earth are said to be
___extinct____________________________________________________.
16. A rock layer's ____relative__________________ age is its age compared to the ages of other rock layers.
17. Certain trilobites are used as _______index____________________ fossils because they lived in many
different areas but for only a brief time.
18. __Uniformatarianism__________________ is a geological theory. It states that current geologic processes,
occurring at the same rates observed today, in the same manner, account for all of Earth's geological features.
19. In the fossil record, older rocks contain fossils of ______simpler_____________________ organisms.
20. __Core___________samples are obtained by drilling with special drills into a substance, like the ocean floor.
21. Geologists use radioactive dating to determine the ___absolute_________________________ age of a rock or
fossil.
22. __Paleontology______________________________________ is the study of fossils.
23. Geologic time begins with the long span of time called __Precambrian_______________ Time.
24. On the geologic time scale, periods are divided into ___epochs___________________________.
25. The present day is part of the ______Cenozoic_____________________________________ Era.
26. The principle that states that layers of rock are formed in horizontal layers is called original
__horizontality____________________________________.
27. Some scientists believe that the Mesozoic Era ended due to a major impact from a
________meteorite________________________________________ into Earth’s surface.
28. The mass extinction at the end of the Paleozoic Era may have occurred because Earth's ___continents___
________________ moved together into one large landmass, changing Earth's climate.
29. During the Paleozoic Era, __reptiles__________ evolved from amphibians to live on land.
30. The extinction of the dinosaurs gave warm-blooded vertebrates called
___mammals____________________________________ a chance to become abundant.
31. A. Which sedimentary rock layer is older, A or B? B is older because it is deeper (Law of Superposition)
B. Which layer is younger, C or G? G is younger because it cut through layer C