Put in order from oldest to youngest.  Remember to include any erosion, faulting, tilting or folding!

D – oldest – at the bottom – superposition law

A – next to bottom – superposition law

B

Tilt – plate tectonics – Law of Horizontality

E – intrusion – cross-cutting law

Erosion – not horizontal/straight line - Law of Horizontality

C – intrusion – Law of cross-cutting

Erosion – Horizontality

 

DABEC (old to young)

 

E and C are igneous (magma rising)

A, B, D are sedimentary (layers)

 

 

 

 


 

 

 

 

 

 

Put in order from oldest to youngest.  Remember to include any erosion, faulting, tilting or folding!

FEDCBA

Igneous – D

Sedimentary – ABCEF

Top:  erosion

 

 

I, B, F, M, H, R

45’ line = tilt – faulting

If there were no letters, how could you tell B and B were the same age?  Same key/picture/legend.

Sedimentary:  all but H

H:  igneous

 

 

 

The Laws of Geology:  Relative Dating of Rocks (Chapter 16 in text)

 

Key Terms and Laws:

 

Relative Dating:  Determining the age of materials by putting them in a sequence in order of which event took place from most recent to oldest (comparative not exact).

 

 

Law of Superposition

-         The lower layers in any particular cross section of rock are older than the upper layers in that cross section. 

 

-        

 

 

Principle of original horizontality:

- Sedimentary layers are horizontal, or nearly so, when originally deposited. Cross sections that are not horizontal have been deformed by movements of the Earth’s crust (folds, faults, erosion).

 

Principle of crosscutting relations: geologic features, such as faults, and igneous intrusions are younger than the rocks they cut.

 

Principle of faunal succession: groups of fossil plants and animals occur in the geologic record in a definite and determinable order.  

 

If there are fossils embedded in the rock, these fossils (inclusions) are younger than the rock they are embedded in but older than the rock above them.

 

If a fault, fold or erosion occurs, fossils may be used to help “match” up rock layers.

 

 

Faunal succession deals with fossils

 

Principle of inclusion: a rock body that contains inclusions of preexisting rocks is younger that the rocks from which the inclusions came from.

 

 

 

 

Deals with other particles of rocks.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Relative Dating Hints 

 

Hint 1:  The easiest way to do relative age dating is to work from oldest to youngest. Try to find the oldest rock (usually located near the bottom) in the diagram below and work your way up.

 

 

Order (old to young): 

 

 

Hint 2:  Sedimentary rocks:

If rocks are folded, the folding is younger that the youngest rock affected.

If they are folded into a syncline (a U-shaped fold) the youngest rocks are in the core of the fold. The opposite is true for an anticline (a big dome-shaped fold).  Sedimentary rocks that contain fragments of another rock are younger than the rocks that the fragments came from.

� The presence of a line that is not smooth indicates erosion.

 

Order: 

 

 

 

Syncline or Anticline:

 

 

Hint 3:  Igneous Rocks

Igneous rocks are formed by the solidification of a liquid magma; the therefore can intrude into preexisting rocks or be poured out onto the surface of the earth:

If an igneous body crosscuts another rock, the igneous rock is younger than that rock

 

 

 

 


 

Relative Dating Worksheet

 

Put the rocks in relative order.

 

1)

2) 

3) 

 

 

Order: 

 


 

4) 

 

Put the repairs in order from most recent repair to oldest work.  Note:  The picture is from an aerial view.

 

5)  Ancient and modern cross-sections

Look at the two nearly identical diagrams, Figures 7 and 8. The order of events in the archaeological cross section shows that the oldest remains are Roman. After this the medieval remains are more recent and the industrial remains are more recent still. The most recent change of all is the modern bridge support. We know it is the most recent because it has cut through all of the others.

Figure 7: An archaeological cross section      Figure 8: A cross section of a cliff.  Note:  Dolerite dyke is just a type of rock that has formed vertically.

Q 15.   (a) Which rock was the first one formed?

            (b) Which principle (superposition or cross-cutting) helped you to work this out?

 

Q 16.   (a) Which rock was the next one formed?

            (b) Which principle (superposition or cross-cutting) helped you to work this out?

 

Q 17.   (a) Which rock was the next one formed?

            (b) Which principle (superposition or cross-cutting) helped you to work this out?

 

Q 18.   (a) Which rock was the last one formed?

            (b) Which principle (superposition or cross-cutting) helped you to work this out?

 


 

6) 

  Put in order: 

 

 

7) Which rock layers are the same ages?  How do you know?

 

 

b)      Put the layers in order (if they are the same age it doesn’t matter which is first or second but they must be next to each other).

 

 

c)      What might have happened to this strata to cause this? 

a.       Erosion?

b.      Faulting?

 

8) 

 

Label the diagram with anticline and syncline.

 

What causes anticlines and synclines?

 


 

9)  Look at the 3 different locations.  All are near each other.  What has happened in each location so that they are different?  Hint:  use geological key terms …