RAP 3/14 pg. 42

1.How old is the Earth?

2.How do we know?

TOPIC: Geologic History

29.1 Fossils

29.2 Relative Time

29.3 Absolute Time

Paleontology

The study of life that existed in prehistoric times

I. Fossils -Preserved remains or traces of once living organisms

1. Original Remains

-preserved in its entirety

Ex:

Wooly mammoths in ice and soil

Insect in amber

A. Types

2. Replaced remains

-Soft parts replaced by minerals

Ex: Petrified wood

3. Molds and Casts-Mold: hollow depression

(cupcake pan)

-Cast: copy of original fossil

(cupcake)

4. Trace

-indirect evidence of life

Ex: trails

footprints

bite marks

burrows

Trace fossils

And one more example...

coprolite

5. Carbonaceous Remains

-thin carbon film

Ex. Fern print

What do we know about this animal?

Fossil Formation

Fossil formed? Type Why/Why not?

1

4

32

56

7

No not deep enough

Yes Original Remains frozen

No too deep

No too much pressure

Yes replaced remains fused with minerals

Yes mould cast minerals filled in

Yes trace uplifted

Fossil Formation

Burying Bodies

Making Fossils

Who dung it?

RAP 3/15 pg. 42

1. What type of rock do most fossils occur in?

2. What is one method of preserving a fossil?

3. In the picture, which letter represents the mold? Which letter represents the cast?

A B

II. Relative Time- placing events in the sequence in which they occurred

**Does not identify actual **dates

A. Principle of Uniform Processes

1. processes that occurred in past produce same results as today

B. Principle of Superposition

Deposited sediments are compressed into layers, or strata

1. Oldest layer at ; youngest at

bottomtop

Deciphering relative time is like detective work...

Who Dunnit?! Someone took the last cookie in the cookie jar last night.

The last person to leave is the culprit!

Clues: The Butler walks to work The Handyman rides a

bike The Cook rides a

motorcycle The Maid drives a car The Nephew has a

seeing-eye dog

1

3

2

Sequences on pg. 44

1

2

3

4

C. Principle of Cross-Cutting Relationships

1. intrusion is always than rock it intrudesIgneous younger

1

2

3

4

5

Gaps in Relative Time

D. Unconformity

1. indicates where layers of rock are missing

a. Exist because

-Lack of deposition

-Erosion

Example

1. Four characteristics

a. Easily recognizable

b. Abundant

c. Widespread in occurrence

d. Existed only for a brief period

E. Index Fossils

When did I live?

Who’s On First?: Period 6 GroupsLab Table 1Shannon

Jake

Jenny

Lab Table 2Chase

Brice

Lab Table 3Alex

Daniel

Dylan S.

Lab Table 4

Mitchell

Devin

Jordan C.

Kaitlin Bennett

Lab Table 5

Davon

Ashtyn

Trey

Lab Table 6

Josue

Yony

Ben

Luke

With Ms. Renwick

Group 7

Chrissy

Kaitlyn Bishop

Dylan Wimer

Anandhu

Group 8

Zach

Robert

Jordan B.

Put it all together...

Decoding geologic history... And…

RAP 3/19 pg. 42

1. Select the fossil you think would be the best index fossil and explain why.

2. Put the following events in the correct order.

A

D

CB

F. Correlation

1. Matching of rock layers from one area to another

Practice!

unconformity

Section 1 Section 2

Which layers are the same?Of layers E and F, which is oldest?What is the sequence of rock layer from oldest to youngest?An unconformity (buried erosional surface) is represented by the interface between which two layers?

III. Absolute Time

A. Use ACTUAL dates to order events

B. Methods1. Tree rings

2. Varves- layer of sediment representing summer and winter

RAP 3/20 pg. 46

1. What is the difference between relative and absolute time?

2. What type of fossil shows evidence of an organism but not the organism itself?

RAP 3/21 pg. 46**QUIZ ON FOSSILS, Relative and Absolute Time

1. What is the relative age of layer C and D?

2. What two things can cause an unconformity?

3. Which letter to the right represents an unconformity?

3. Radiometric dating

Compares ratio of naturally occurring unstable isotope (parent) and its decay products (daughter)

Pb

Ur

Parent = original element Daughter = the product of the decay

• Example: uranium-238 decays to lead-206

i. Half-life

-Time it takes for half the radioactive atoms to decay

=1 half-life

=2 half-lives

In each half-life, the amount of atoms gets cut in half.

=parent

=daughter

One half-life.

=parent

=daughter

Two half-lives.

=parent

=daughter

Three half-lives.

=parent

=daughter

Four half-lives.

=parent

=daughter

Don’t worry about the last atom. You start with so many trillions that you never really get there. (It will just decay and then they’re all gone.)

=parent

=daughter

About how many students would have had to sit down if we started with twice as many students? What about if we only had half as many in this class? What does that tell you about how the quantity of "radioactive isotopes" affects the number that decay?Can you predict which of you is going to be the first to sit down? Why or why not?

Keys to radioactivity

**Decay at constant rates regardless of time or climate**

**Decay begins as soon as rock crystallizes or organism dies**

**Ratio of amount of radioactive element left to the amount of stable product is used to determine the absolute age**

RAP 3/22 pg. 46

1. What is the definition of a half life?

Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-lives have gone by.

100% parent0% daughter0 half lives

One half-life.

50% parent50% daughter1 half-life

Two half-lives.

25% parent75% daughter2 half-lives

Three half-lives.

12.5% parent87.5% daughter3 half-lives

Four half-lives.

6.25% parent93.75% daughter4 half-lives

Half-lives range from a fraction of a second to billions of years• Protactinium-234 has

half-life of ~1 min

• Uranium-238 has half-life of 4.5 by

Radiocarbon limitations

Only for once living organisms Half-life=5730 years meaning the limit to

dating is about 70,000 years

17190

RAP 3/14 pg. 45

1.

2.

3.

RAP 3/13 pg. 431. What is a half life?

2. You find a piece of wood and use carbon dating to determine the age. The ratio of parent to daughter is 1:1. How many half lives have passed?

3. How do varves help geologists understand the past?

Quiz

Relative Time, Fossils and Absolute Time

Web quest

Let’s get a little more complicated…