Key Vocabulary Terms

geologic time - all the time that has passed since the earth formed.
fossil - Trace or remains of an organism preserved in the earth's crust
petrification - replacement of the original parts of a buried organism with minerals.
mold - type of fossil that forms when the shape of a plant or animal is left in a rock.
cast - type of fossil that forms when minerals fill a mold; a model of an organism.

Key Concepts

geologic time is all the time that has passed since the earth formed.
A fossil is the traces or remains of an organism preserved in the earth's crust.
The three ways fossils form are when minerals in groundwater replace the original parts of a buried organism (petrification); when organisms leave an imprint behind in sediment that later becomes rock (and/or when material fills this imprint, creating a cast); and when the actual body of an organism is preserved in ice, frozen soil, tar, or amber.
Petrification occurs when minerals in groundwater replace the original parts of a buried organism.
A cast of an organism forms when a plant or animal becomes buried in sediment that later becomes rock. the organism decays or dissolves. the space left in the rock has the shape of the organism. This is called a mold. Sometimes minerals fill the mold, forming a cast, which is a model of the original plant or animal.

Did you learn these Objectives?

Can you define geologic time?
Are you able to explain what a fossil is?
Can you describe three ways fossils form?

Investigation 14-1 "Making a Model of a Fossil" (Optional, must complete 16 total investigations)

Key Concepts

You will make a model of a mold and a cast using a clay impression model and plaster of paris.

Lesson 2 "The Ages of Rocks and Fossils"

Key Vocabulary Terms

relative dating - method that compares two rock layers to find out which is older.
principle of superposition - in layers of sedimentary rocks, the oldest layer is on the bottom and the youngest layer is on the top if the layers have not been overturned.
Principle of crosscutting relationships - a feature, such as a rock structure or a fault, that cuts across rock layers is younger than the rock layers.
index fossil - fossil that can be used to establish the relative age of the rock in which the fossil occurs.
absolute dating - method that determines the actual age of a rock or fossil.
radioactive element - element that breaks apart, or decays, to form another element.
half-life - length of time it takes for half of the atoms of a radioactive element to decay.

Key Concepts

Relative dating determines which of two rocks is older, while absolute dating determines the actual age of a rock or fossil.
The principle of superposition states that the oldest layer of rock is on the bottom and the youngest layer is on top For example, a fossil found in a deeper layer is older than one found in a higher layer. The principle of crosscutting relationships states that a rock or feature that cuts through another rock must be younger than the rock it cuts. For example, a fault that cuts through rock layers is younger than a rock layers.
Absolute age of a rock can be determined by comparing the amount of a radio active decayed element.
A radioactive element's half-life is the length of time required for half of the atoms of the radioactive element to decay.
Uranium-238 would be used to determine the absolute age of fossils that are more than 50,000 years old.

Did you learn these Objectives?

Can you explain how a rock's relative age is determined?
Are you able to explain how a rock's absolute age is determined?

Investigation 14-2 "Making a Half-Life Model" (Optional, must complete 16 total investigations)

Key Concepts

You will model and graph the decay of a radioactive element using beans and a sheet of paper.

Lesson 3"Eras in the Geologic time Scale"

Key Vocabulary Terms

geologic time scale - outline of the events of the earth's history.
precambrian era - Oldest and longest era of the earth's history; began about 4.6 billion years ago and ended about 540 million years ago.
paleozoic Era - Era marked by great development in sea life; began about 540 million years ago and ended about 245 million years ago.
Mesozoic Era - era characterize by dinosaurs; began about 245 million years ago and ended about 65 million years ago.
Cenozoic Era - era described as the Age of Mammals; began about 65 million years ago and continues today.

Key Concepts

The geologic time scale is an outline of the events of the earth's history.
the Precambrian Era is the oldest and longest era. There was much volcanic activity. simple life forms developed.
Over time many life forms developed, in the Paleozoic - fish, amphibians, reptiles; mesozoic- dinosaurs, mammals, birds; Cenozoic - more mammals, humans.
The Paleozoic went from 540 to 245 million years ago, the Mesozoic went form 254 to 65 million years ago, the cenozoic went from 65 million years ago to the present.
In the Precambrian there was great volcanic activity; in the Paleozoic there was half of North America submerged; In the Mesozoic there was the rise of the sierra Nevada's and Coast Ranges, and in the Cenozoic North America joined to South America.

Did you learn these Objectives?

Can you describe the geologic time scale?
Are you able to summarize events that occurred during each era of geologic time?

Chapter Summary and Review

See pages 354-355.

Chapter 14 Review answers are

1. superposition

2. relative dating

3. fossil

4. mold

5. absolute dating

6. index fossil

7. petrification

8. cast

9. geologic time

10. half-life

11. B

12. D

13. A

14. B

15. A

16. D

17. B

18. A

19. rocks A, B, and C; according to principle of superposition, rocks b and C are younger because they are above rock D; according to the principle of crosscutting relationships, rock A is younger because it cuts through rock D.

20. 2 half-lives; 11,460 years ago.