Relative Dating

Relative Dating

"What's Up?" Activity

    When discussing rocks and geological time, it is important to be able to identify what exactly was here first. Rocks... of course, but what kinds of rocks were laid first? Because we had previously learned about rocks, this was somewhat easy for us to predict. However, there are certain theories that specify which types of rocks lay in specific places, and what this means for their age.

Based on the "What's Up?" Activity these theories/ideas are:

The Law of Superposition: In a sequence of un-deformed sedimentary rocks, the oldest beds are on the bottom and the youngest are on the top

Principle of Original Horizontality: Sedimentary layers are horizontal, or nearly so when originally deposited. Strata that are not horizontal have been deformed by movements of the Earth’s crust

Principle of Inclusion: A rock body that contains inclusions of preexisting rocks is younger than the rocks from which the inclusions came from

Principle of Faunal Succession: Groups of fossil plants and animals occur in the geologic record in a definite and determinable order. A period of geologic time can be recognized by its respective fossils

Unconformity: A buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. Below are all forms of unconformities

    The assignment that we did in class contained questions about the theories as well as, one of my favorite class activities, identifying which layer of rock came first. They're like puzzles... and are fun for students!

Here is an easier example:

Answer:

Youngest Layer: B

Layer: A

Oldest Layer: C

Here is a more difficult example:

Answer:

Youngest Layer: A

Layer: D

Layer: E

Layer: B

Oldest Layer: C