1. A Trip Through Geologic Time

2. Fossils Fossils are preserved remains or traces of living things.
Most fossils form when living things die and are buried by sediments.
The sediments slowly harden into rock and preserve the shape of the organisms.
Scientists who study fossils are paleontologists.
Fossils

3. Fossils Fossils are usually found in sedimentary rocks.
When an organism dies, its soft parts often decay quickly leaving only the hard parts to fossilize.
Ex. Bones, Shells, Teeth, or Seeds

4. Why Study Fossils?
Scientists study fossils to learn what past life forms were like.
Paleontologists classify organisms in the order in which they lived.
All the information scientists have gathered is called the fossil record.

5. Fossil Record
The fossil record provides evidence about the history of life on Earth.
The fossil record also shows how different groups of organisms have changed over time.
It also provides evidence to support the theory of evolution.

6. A scientific theory is a well-tested concept that explains a wide range of observations.
The fossil record shows that millions of types of organisms have evolved.
However, many others became extinct.
Remember!

7. Finding the Age of Rocks Through Rock Dating

8. D A T I N G R O C K

9. Ages of Rocks
The relative age of a rock is its age compared to other rocks. Use words like: “older or younger”
The absolute age of a rock is the number of years since the rock was formed.
Ex: mya

10. Rock Joke!! What does a rock want to be when it grows up?
A Rock Star!!

11. The Position of Rock Layers
It can be difficult to determine a rocks absolute age. So… scientists use the law of superposition.
According to the law of superposition, in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

12. Rock Joke!!
How do rocks wash their clothes?
The Rock Cycle!!

13. Law of Superposition

14. Practice
Use the glue to place pictures on your side and answer the questions. Write the questions
1. Using the diagram, which
fossil is the youngest? How
do you know?
2. Using the diagram, which
fossil is the oldest? How do
you know?

15. Other Clues to Relative Age
Clues From Igneous Rock
Lava that cools at the surface is called an extrusion. Rock below an extrusion is always older.
Magma that cools beneath the surface is called an intrusion. An intrusion is always younger than the rock layers around an beneath it.

16. Practice
Use the glue to place pictures on your side and determine the relative age of the layers.

17. Which two layers are the same age?
Practice
Which two layers are the same age?

18. Using Fossils to Date Rocks!
Scientists use index fossils to match rock layers.
An index fossil must be widely distributed and represent a type of organism that existed only briefly.
They are useful because they tell the relative ages of the rock layers they are found in.

19. The Trilobite One example of an index fossil is a trilobite.
Trilobites were a group of hard-shelled animals whose bodies had three distinct parts.
They evolved in shallow seas more than 500 million years ago.