Chapter 21

Fossils and the Rock Record

Geologic History Principles

Law of Uniform Processes Law of Superposition Law of Cross-cutting Relationships Law of Included Fragments

Law of

The processes which are changing the earth’s surface today are the same processes which acted in the past

Uniform Processes

Law of

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

Superposition

Law of

A fault or intrusion is younger than the rock layers it cuts through

Cross-cutting Relationships

Law of

Pieces of one rock found in another rock must be older than the rock in which they are found

Included Fragments

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

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

Relative Age: List the following rock layer in chronological order starting with the oldest layer.

A

B

C

D

E

F

G

X

H

I

J

K

L

Y

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

____________ 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

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

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

Ch 21 Review (continued)

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

Ch 21 Review (continued)

paleozoic ancient life

mesozoicend marked by many extinctions, including dinosaurs

cenozoic recent life

Ch 21 Review (continued)

Ch 21 Review (continued)