1. GEOLOGIC HISTORY THE RULES OF THE GAME
© Copyright   M. J. Krech. All rights reserved.

2. Time
What is
time?

3. Time is… Either relative or absolute
Time is: a measured period during which an event, process, or condition exists or continues.

4. One Year =
the time it takes the Earth to complete one orbit around the Sun.

5. Geologic Time Based on the same time units
Generally much greater periods of time
100,000 years
1,000,000 years

6. Dating Techniques
One ways in which geologists look at time: Relative Age

7. Relative Age of a rock…
…is its age compared to the ages of other rocks.
Example:
My niece, Sara, is older than my other niece, Mariam.
What happened first?
What happened next?

8. Absolute Age of a rock… …is the number of years since the rock formed.
Example:
My niece, Sara, is 3 years old and my niece, Mariam, is 3 months old.

9. Relative and Absolute Age

10. Law of Superposition The youngest rocks are on the top.
The oldest rocks are on the bottom.

11. Principle of Superposition
Q#1
Which rocks are older?
Which rocks are younger?
Younger Rocks
Older Rocks

12. Principle of Cross-Cutting
Fault is a break or cut in the rock.
You can't cut something until that something exists, therefore the cut has to be younger.
So faults are younger than the rock it cuts through.
Volcanic vents cutting across
sedimentary rock layers -
Which is youngest?

13. Principle of Cross-Cutting
Q#2
What is younger?
The rocks or the fault line?

14. Intrusions

15. Principle of Inclusions
The inclusion is always younger than the rock layers around and beneath it.

16. Principle of Inclusions
Q#3
Which is older? The rock layer or the rocks included in the layer?

17. Principle of Unconformities
Unconformities are surfaces that represent gaps in the geologic record.

18. Example of Unconformity

19. Principle of Unconformities
missing rock layer = missing time

20. Where is the youngest rock?
Q#4
How do
you
know?

21. Where is the unconformity?
Q#5
How do
you
know?

22. What rock layer is the oldest?
Q#6
How do
you
know?

23. Which is younger? The fault or the rock layers?
Q#7
FAULT
How do
you know?

24. Which is younger? The rock layer or the inclusion?
Q#8
How do
you
know?
inclusion

25. Using Fossils to Date Rocks
Give relative age to a layer of rock
Match layers of rock at other locations
Use index fossils to match rock layers
Index fossils are distributed in different areas & only occur in one area
Ex. pg. 117