Introduction to Relative Dating and Index Fossils
Name: ____________________
Relative Dating is the process of ordering rock layers from youngest to oldest. It is called relative dating because the
exact age of the rock remains unknown. All that is being determined is which rock layer is older and which is younger.
Complete each of the parts below to understand the basics of relative dating.
Part 1: Sedimentary Rock Layers
Most often new rock layers form on top of an existing rock layers. If the rock layers are horizontal or straight then the
oldest rock layer is on the bottom and the youngest is on the top. Looking at the picture below, answer the questions to
the right.
1. Write the oldest next to the layer that is the
oldest.
2. Write youngest next to the layer that is the
youngest.
3. Draw an arrow from the where you wrote oldest
pointing to where you wrote youngest.
4. Which type of material made the oldest layer?
_______________________________________
5. Which type of material made the youngest layer?
_______________________________________
6. Circle the layer that is older:
Basalt
or
Limestone
7. Circle the layer that is younger:
Part 2: Fossils in Sedimentary Rock Layers
Mudstone or
Limestone
Rocks layers can contain fossils within them. Look at the rock layers below containing fossils and answer the questions
on the write.
1. What type of fossil is in the oldest layer of rock?
___________________________
2. What type of fossil is in the youngest layer of
rock? ___________________________
3. Circle the fossil that is younger:
Dinosaurs or
Fishes
4. Circle the fossil that is older:
Amphibians
or
Trilobites
Introduction to Relative Dating and Index Fossils
Name: ____________________
Part 3: What is an Index Fossils?
Index fossils are fossils of organisms that lived for a short period of time and are found in many areas of Earth. If they
lived only for a short period of time, they are often found in the same type of rock. Determine which fossils below are
index fossils.
Next to each picture write whether it is an index
fossil or explain why it is not.
_______________________________
___________________________________
__________________________________
___________________________________
Part 4: Find the index fossil.
In each set of pictures there is only one index fossil. Circle the index fossil in the picture below and explain your choice.
Explanation of choice:
____________________________________
____________________________________
____________________________________
____________________________________
Explanation of choice:
____________________________________
____________________________________
____________________________________
____________________________________
Introduction to Relative Dating and Index Fossils
Name: ____________________
Part 5: Using Index Fossils
An index fossil can be used to determine the relative date of a rock. If I know when that fossil lived then the rock
surrounding it must be the same age. We can find that same fossil somewhere else in the world and know the age of
the rock surrounding it. Use the index fossil to determine the answers to the questions below.
1. Which two layers are approximately the same age? How do
you know?
___________________________________________________
___________________________________________________
2. Which layer is the oldest? How do you know?
___________________________________________________
___________________________________________________
3. Which layer is the youngest? How do you know?
___________________________________________________
___________________________________________________
Part 6: Put it all together
1. Determine which rock layers are the same age using the index fossils. Color the layers with the same fossil the
same color.
2. Order the rocks from youngest to oldest. The oldest layer has been numbered 1 for you so the next oldest layer
should be 2 and so forth until you reach the youngest layer. Make sure to put a number next to every layer.
Layers with the same index fossil will have the same number.
3. Write youngest next to youngest fossil and oldest next to the oldest fossil.