1. What is a fossil?
A fossil is the preserved remains of a once- living organism.

2. What do fossils tell us?
1. help scientists determine the age of the earth
Biodiversity

3. Radiometric dating measures how much certain atoms have decayed in the fossil
A half-life is the amount of time it takes for half of the atom to decay.
Scientists know how long it takes for these atoms to decay.

4. LAW OF SUPERPOSITION
the oldest layer is on the bottom and the youngest is on top- fossils are older in the lower layers

5. What do fossils tell us? 2. give clues about organisms
that lived long ago,
relationships and how
they have changed over time
Biodiversity

6. Homologous structures
Commonalities found in different organisms that show ancestry

7. Behaviors
Nests
Egg laying
Herds
Caring for young
Predation

8. What do fossils tell us?
3. provide evidence about past events (asteroids, volcanoes, ice ages)
Biodiversity

9. What do fossils tell us?
4. show correlations between rock layers from around the world providing evidence of continent movement
Biodiversity

10. What do fossils tell us? 5. provide evidence and
clues for the geological time scale
Biodiversity
Geological Time Scale:
a series of time intervals that divides Earth’s history based on specific events like mass extinctions

11. FIVE MAIN TYPES OF FOSSILS
Petrified
Fossils
Molds and
Casts
Carbon Films 1 2 3
Trace
Fossils
Preserved
Remains 4 5

12. PETRIFIED FOSSILS The word “petrified” means “turning into stone.”
PETRIFIED FOSSIL The Field Museum in Chicago displays a fossil of a T-rex. Below is an alligator.
The word “petrified” means “turning into stone.”

13. Petrified Fossils 1. Sediment 3. Movement 2. Layers 4. Erosion
An animal is buried by sediment
2. Layers
layers accumulate above the animal’s remains. Water seeps into tiny air spaces depositing minerals turning bone into rock.
3. Movement
Movement of tectonic plates pushes the fossil closer to the surface.
4. Erosion
Erosion from rain, rivers, and wind wears expose the fossil

14. MOLDS AND CASTS MOLD FOSSIL
This mold, or imprint, is of an extinct mollusk called an ammonite.
A mold forms when hard parts of an organism are buried in sediment, but dissolve over time, leaving behind a hollow area with the organism’s shape.
A cast forms as the result of a mold.
Water with dissolved minerals and sediment fills the mold’s empty spaces and hardens.
A cast is the opposite of its mold.
CAST FOSSIL This ammonite cast was discovered in the United Kingdom.

15. cast fossil or mold fossil?1 2 3 4

16. CARBON FILMS
When an organism dies and is buried in sediment, the materials that make up the organism break down.
Eventually, only carbon remains.
The thin layer of carbon left behind can show an organism’s delicate parts, like leaves on a plant.

17. TRACE FOSSILS
Trace fossils show the activities of organisms.

18. Some organisms get preserved in or close to their original states.
PRESERVED REMAINS
Some organisms get preserved in or close to their original states.
Tar
Ice
Amber

19. Maybe you will find a fossil?
AND NOW AN ACTIVITY FOR YOU!

20. Spread the cards on the table.
The cards represent rock layers.
The letters represent fossils.
Find the card with TC on it.
This is the oldest layer of rock.
Figure out the order of the rest of the layers.

21. Answer the following questions with your group
1. Which layer is the most recent layer of rock? 2. Which fossil is oldest- X or M? 3. Which fossil is the oldest- B or N? 4. Find a fossil that went extinct? 5. Which fossil lived the longest amount of time? 6. What do we call this idea that we can date fossils based on the layer of rock they are found?

22. Activity 2 Work in the same group as yesterday
Place your cards on the table
Each card is a layer of earth
The oldest layer is “M” (ignore the rest of the letters)
Figure out the order of the rest of the layers.

23. Use your rock layers to answer the following questions.
7. Write the sequence of letters from the youngest layer to the oldest layer 8. Name the fossils found in multiple layers. 9. Name the fossils found in only one layer. 10. What can be said about fossils found in only one layer and fossils found in more than one? 11. What could be said about the environment from these time periods? 12. Which is older- the trilobite or the placoderm?