Relative Dating
Relative dating is all about what is older and what is younger. You're showing a relation between dates or times that rocks formed. To do this you'll use the principles found in G8 which are:
Original Horizontality
Superposition
Crosscutting
Inclusions
In the picture we have 3 layers, A, B and C. We have one fault E and one igneous intrusion D. The principle of superposition tells us that the older rock is underneath the younger rock. So C is older than B and B is older than A. The principle of crosscutting tells us the fault or intrusion is younger than the rock it cuts through. E and D both cut through A, B and C. So they're both younger than the layers they cut. We can see that E offset D. This means that D existed first and was later cut by E. So E is younger than D. The order of these rock layers from oldest to youngest is C, B, A, D, E.
Original Horizontality
Superposition
Crosscutting
Inclusions
In the picture we have 3 layers, A, B and C. We have one fault E and one igneous intrusion D. The principle of superposition tells us that the older rock is underneath the younger rock. So C is older than B and B is older than A. The principle of crosscutting tells us the fault or intrusion is younger than the rock it cuts through. E and D both cut through A, B and C. So they're both younger than the layers they cut. We can see that E offset D. This means that D existed first and was later cut by E. So E is younger than D. The order of these rock layers from oldest to youngest is C, B, A, D, E.
This picture shows more rock layers. In this one there are a couple unconformities. This means that layers of rock have been eroded away and we have lost that rock record. Geologists indicate an unconformity with a squiggly line. Can you see the 2 unconformities in the picture? There is one between J and K and the other is between the slanted layers Q-L and H.
Try to figure out the order of these layers from oldest to youngest.
Try to figure out the order of these layers from oldest to youngest.