Fossils and the Rock Record

1
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 earths
  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 s i l
f o s s i l
c o p r o l i t e
a m b e r
v o l u t i o 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)