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1. GEOLOGICAL TIME: DATING
PAGES 56-63 of the Oxford book

2. •
> Relative: Placing events in a sequence based
on their positions in the geologic
record.
> Absolute: Placing a specific number of years
on an event or rock sample.
• Two ways to relate time in geology:
> Relative
> Absolute
Important concepts

4. 4
Tools used to determine
• Using radiometric
dating
• Principle of
superposition
• Principle of cross-
cutting
• Principle of lateral
continuity
• Principle of faunal
succession
Absolute Age Relative Age

5. RELATIVE DATING

6. Relative Dating
Principle of Superposition
In undisturbed strata, the layer on the bottom is
oldest, those above are younger.

7. GRAND CANYON- LAW OF SUPERPOSITION

8. Relative Dating
Principle of Cross - Cutting
An event that crosses several layers of rocks must be
younger than the rocks it affects, and older than the
rocks it does not.
Types of events: folds, faults, magmatic intrusions (dykes), inclusions (one
rock type included in another rock type), erosion….

10. ACTIVITY: Which stratum is older?

11. ACTIVITY: Geological cross section

12. ACTIVITY

13. ACTIVITY: Order the strata and events

14. Relative Dating
Principle of Faunal/Floral Succession
Each period in the history of the Earth can be
associated with a group of characteristic fossils.

15. 15
FOSSIL
Naturally occurring preserved remains or
impressions of living things
Relative Dating
Principle of Faunal/Floral Succession

16. 16
Guide Fossils
• Index Fossils—the ones used to date sedimentary
strata
• Their characteristics are:
– Fossils from creatures that existed for a geologically
short period of time
– Fossils from creatures that had a wide geographic
distribution

17. Location A Location B Location C
Rock layer 1 W W W Z
Rock layer 2 W Z Y Z
Rock layer 3 W X X X Z
ACTIVITY
Which letter would make a good guide fossil?

18. Relative Dating
Principle of Lateral Continuity
• Strata are deposited
in a basin and are
continuous from end
to end
• Any breaks are due to
erosion or
deformation after
deposition

19. Rocks with the same fossils can be correlated as the same
age, even if the rocks occur in widely separated locations
or are of a different rock type.
CORRELATION

20. 1. Which layers are the same?
2. Which layer is older E or F?
3. What is correct sequence of rock layers from oldest to youngest?
4. What has happened between C and B?
ACTIVITY

21. ACTIVITY - HW

22. ABSOLUTE DATING
(Apart)