1. Bellringer
As a group, write what type of fossil each letter represents. You may use your notes!

2. Fossils and Superposition Cornell Notes
Key Terms
Notes
Summary:

3. Most fossils are formed in sedimentary rock.
A fossil is the remaining part of a once-living thing that has been preserved in rock.
Most fossils are formed in sedimentary rock.

4. How do fossils form? Organisms die
Sediments are piled on top of slowly decaying organisms and hardens into sedimentary rock.
Shells and bone take longer to decay.

5. HOT Question
Can fossils form in Igneous and Metamorphic? Why or why not?

6. Fossils and The Law of Superposition

7. How do we know how old a fossil is?
Fossils are clues in the story of Earth’s past!

8. Relative Dating and Index Fossils
Relative dating: Any method of determining whether an event or object is older or younger than other events or objects.
Example: How many students in the class have an older sibling? Younger sibling?
Index fossil: A fossil that is found in the rock layers of only one geologic age and is used to establish the age of the rock layers. Ex Trilobites

9. Index Fossils Squids Dinosaurs Trilobites Cats
1. What is an example of an index fossil?
Squids
Dinosaurs
Trilobites
Cats
2. If you uncovered a Bathyurus Extans, what time period would any fossil found around it be from?
Triassic Period
Ordovician Period
Tertiary Period
Paleozoic Era

10. Determining the ages of rocks using index fossils
When using index fossils for relative dating, scientists study the position of the fossils in the sedimentary rock layers

11. Law of Superposition
Fossils in lower layers of sedimentary rock are older than fossils that are in higher layers of sedimentary rock.

12. Laws of Relative Dating

14. HOT Question!
What is the age of an intrusion igneous rock in relation to the sedimentary rock layers through which it passes?

15. Index Fossils

16. Absolute Age & Radioactive Decay
Absolute dating, using radioactive decay, gives us the actual age of the fossil
Example: How old are your older brother(s) or sister(s)?
Radioactive Decay: When atoms become unstable and breakdown and becomes a different element
The half-life is the amount of time it takes for one-half of the original atoms to decay

17. How Does Carbon Dating Work?

18. How do we know how old a fossil is?
Relative Dating- uses index fossils to date sediment layers
Absolute Dating- (numerical dating) uses radioactive dating

19. What have fossils told us about Mass Extinctions?

20. Analyzing Fossils in Sedimentary Rock Homework
Begin on homework
Due tomorrow!

21. Activity # 1
On your desk, you have 8 large colored index cards with nonsense letters placed on them.
Your task is to determine what the correct sequence of the letters are.
You have two clues:
The card with the letters “C” and “T” is on the bottom, or the oldest layer
Look for a card that has either a “T” or “C” written on it for the second layer

22. M D X O MD N B DXO U A G ON C T NB NBU UA AGC C T
This is one possible way to arrange the cards.
Questions:
What letter is the oldest?
What letter is the youngest?
What letter showed up the most?
Which letters only showed up once?
Which letters could be index fossils?
How did you know which was older: “M” or “X”? MD
DXO ON NB
NBU UA
AGC
C T

23. M D X O N B DXO U A G ON C T NB NBU UA AGC C T
This is one possible way to arrange the cards.
Questions:
What letter is the oldest?
What letter is the youngest?
What letter showed up the most?
Which letters only showed up once?
Which letters could be index fossils?
How did you know which was older: “M” or “X”?
DXO ON NB
NBU UA
AGC
C T

24. Activity # 2 Flip your eight index cards over
Arrange the index cards that represent layers of rock and fossils
Clues:
The oldest layer has the letter “M” in it
Find a rock layer that has at least one of the fossils you found in the oldest rock layer
Extinction is forever - once an organism disappears from the sequence it cannot reappear later

25. This is one possible way to arrange the cards.
Questions:
What fossil is the oldest?
What fossil is the youngest?
What fossil(s) could be used as index fossils?
Which fossil existed in the most time periods?
How can you tell when an organism has become extinct?

27. A N S W E R

28. To think about…
What problems did you run into when trying to arrange the fossils into the correct sequence?
Would this have been more difficult if you did not know which layer was the oldest to start the activity? Why?
Which organism is the most complex of all the fossils and why?

29. Homework
Superposition Worksheet

30. Bell Ringer What does the chart below display?
What could geologist use this for?