1. Fossils and the Rock Record
Chapter 21
Fossils and the Rock Record

2. Geologic History Principles
Law of Uniform Processes
Law of Superposition
Law of Cross-cutting Relationships
Law of Included Fragments

3. Law of Uniform Processes
The processes which are changing the earth’s surface today are the same processes which acted in the past

4. Law of
Superposition
The oldest rock layer is on the bottom of an undisturbed rock column, and each higher layer is younger

5. Law of Cross-cutting Relationships
A fault or intrusion is younger than the rock layers it cuts through

6. Law of Included Fragments
Pieces of one rock found in another rock must be older than the rock in which they are found

7. Tree Rings This tree was approximately how old? About 17 years
How did you determine this age?
By counting the number or light (summer) and dark (winter) rings

8. Geologic Time Scale
Which represents the longest time interval – era, eon, or epoch?
Which of the three eras represents the longest amount of time?
Approximately how old is the earth?
eon
paleozoic
4.6 billion years

9. A B C D E F G X H I J K L Y
Relative Age: List the following rock layer in chronological order starting with the oldest layer.

10. Relative Age
In the previous slide you know rock layer Y is younger than rock layer C because _________________________________.
In the previous slide you know rock layer H is older than rock layer I because _________________________________.
In the previous slide you know rock layer X is younger than rock layers D, E, and F because _________________________________.
Y cuts across C
H is under I
D, E, and F are included in X

11. ____________ Age: By measuring the percentages of parent and daughter isotopes in some rocks or fossils, an age in years of that object can be determined.
Absolute

12. Fossils
Picture C shows what two types of fossils, and how do they form?
Picture D shows what type of fossil?
Picture B shows what type of fossil?
Mold-organism decays
Cast-mold fills with minerals
Trace fossil
Actual remains

13. Chapter 21 Review (clues on next slide)
G a s t r o l i t h n d e x fo s i l f o s i l c o p r l i t e
a m b e r v o l u t i n
p e m n e r a i z a t i n
c a s
m o d

14. Ch 21 Review (continued)

15. Ch 21 Review (continued) ___1.Nonconformity –
___2. Angular Unconformity-
___3.Disconformity- B
sedimentary over nonsedimentary C
sedimentary over tilted sedimentary A
sedimentary over horizontal sedimentary

16. Ch 21 Review (continued) paleozoic ancient life
end marked by many extinctions, including dinosaurs
mesozoic
cenozoic
recent life

17. Ch 21 Review (continued)

18. Ch 21 Review (continued)