Fossils and Fossils and The Law of SuperpositionThe Law of Superposition

Liz LaRosa 5th Grade Science http://www.middleschoolscience.com 2009

This PPT was created with the information from the FOSREC Activity “Who’s on First?” and “Fossil Inferences” by UEN.

Fossils and SuperpositionFossils and SuperpositionWhat is a fossil?

The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock

What is a superposition?Younger rocks lie above older

rocks if the layers have not been disturbed

Relative Dating and Index Relative Dating and Index FossilsFossilsWhat is relative dating?

◦Any method of determining whether an event or object is older or younger than other events or objects.

What is an index fossil?◦A fossil that is found in the rock layers

of only one geologic age and is used to establish the age of the rock layers.

◦ Is found in rock layers around the world, ex Trilobites

Activity # 1Activity # 1

On your desk, you have 8 large colored index cards with nonsense letters placed on them.

Your task is to determine what the correct sequence of the letters are.

You have two clues:1. The card with the letters “C” and “T”

is on the bottom, or the oldest layer2. Look for a card that has either a “T”

or “C” written on it for the second layer

You have two clues:You have two clues:The card with the letters The card with the letters ““CC”” and and ““TT ”” is on is on the bottom, or the oldest layerthe bottom, or the oldest layerLook for a card that has either a Look for a card that has either a ““TT ”” or or ““CC”” written on it for the second layer written on it for the second layer

Questions when you finish:

1.What letter is the oldest?2.What letter is the youngest?3.What letter showed up the most?4.Which letters only showed up once?5.Which letters could be index fossils?6.How did you know which was older: “M” or “X”?

C T

AGC

UA

NBUNB

ONDXO

MD

This is one possible way to arrange the cards. Questions:

1.What letter is the oldest?2.What letter is the youngest?3.What letter showed up the most?4.Which letters only showed up once?5.Which letters could be index fossils?6.How did you know which was older: “M” or “X”?

Activity # 2Activity # 2Flip your eight index cards overArrange the index cards that represent

layers of rock and fossils. Each card represents one layer of rock.

Clues:1. The oldest layer has the letter “M” in it2. Find a rock layer that has at least one of

the fossils you found in the oldest rock layer

3. Extinction is forever - once an organism disappears from the sequence it cannot reappear later

Teacher Note: I replaced the letters with nonsense letters b/c spelling the word “organism” was too easy for my 5th graders

To think about…To think about…What problems did you run into

when trying to arrange the fossils into the correct sequence?

Would this have been more difficult if you did not know which layer was the oldest to start the activity?

Which organism is the most complex of all the fossils and why?

Fossils of an organism can be found within multiple “layers” or periods in history if it lived for a long period of time.

If a fossil that was only found in one layer, however, it would be considered an index fossil because it only lived for a short time.

Rock layers can be helpful in figuring out what order geologic events took place.

We will be looking at cross sections and using the Law of Superposition to figure out the correct order of layers from youngest to oldest.

Law of Superposition: Oldest sedimentary rock layers will be on the bottom, youngest on top.

Principle of Original Horizontality: When layers of sedimentary rock are first made, they are layered horizontally.

Rock Layers Can Rock Layers Can Change!Change!

Rock layers can fold underground. Can you still figure out the order from oldest to youngest?

Intrusions of igneous rock can cut through different layers, like A. The intrusion is always younger than the layers it cuts through (even if it comes from the bottom!).

A fault or crack could form in the middle of rock layers (B). If this happens, the fault is always younger than the layers it cuts through.

Task: Put the layers in order Task: Put the layers in order from oldest to youngest.from oldest to youngest.Hints:Start at oldest first – look at the

bottom layersIgneous intrusions are younger than

the layers they cut throughFault lines are younger than the

layers they cut throughIf igneous and metamorphic are

side by side, metamorphic was there first