1. Ways to tell the age of a rock
Dating Rocks
Ways to tell the age of a rock

2. 2 Ways to Date Rocks: Relative Dating:
Places events in geologic history in the proper order.
The basis for the geologic time scale
Mainly Sedimentary Rocks
Does not provide a true “age”

3. 2 Ways to Date Rocks: Absolute Dating:
All you need is a tiny sample of material (mineral, bone) no larger than a grain of rice.
Gives us the true “age” of a fossil or rock
Mainly organic tissue or igneous crystals
Measure the amount of unstable isotopes that have “decayed” to figure out age

4. Principles for Relative Dating:
Superposition - The youngest rocks are on the top, oldest at the bottom.

6. Relative Dating Principles
Superposition
Cross-cutting relationships - Geologic features that cut through and across rocks are younger than those rocks.
Mostly Faults and Igneous intrusions

7. Cross-cutting Igneous Rock
Cross Cutting Relationships - Geologic features that cut through and across rocks are younger than those rocks.

9. Relative Dating Principles
Superposition
Cross-cutting relationships
Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.

10. Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.

11. Relative Dating Principles
Superposition
Cross-cutting relationships
Law of Inclusions
Law of Original Horizontality (and Lateral continuity) – layers of sediments are originally deposited horizontally

12. Hikingtripsreport.com

13. Relative Dating Principles
Superposition
Cross-cutting relationships
Law of Inclusions
Law of Original Horizontality (and Lateral continuity)
Law of Unconformities

14. A DISCONFORMITY is a boundary between two layers of non-continuous ages. This boundary is
usually marked
by an erosional
surface and is
often irregular.
M&W4 Fig. 17.8; M&W5 Fig. 17.8

15. An ANGULAR UNCONFORMITY is a disconformity between layers of different angles.
The underlying layers are first tilted, then erosion scours away a new, horizontal surface.
New, horizontal layers form on top

16. An NONCONFORMITY is a disconformity between different rock types, one of them sedimentary.

17. Activity 2: Label the layers from:
A  The Oldest
T  The Youngest

18. Activity 2: Label the layers from:
A  The Oldest
T  The Youngest