7. Law of Superposition

EQ: How do fossils provide a record of Earth’s geologic history?

Learning Target: I can analyze how rock layers and fossils provide evidence of Earth’s history.

Learning Task: Task: I will practice using Law of

Superposition to determine the relative age of rocks layers. I will identify index fossils within

rock layers.

Warm-up: Tuesday 4/8/14

1. How are molds and cast fossils alike?

2. How are mold and cast fossils different?

Intro to Stratigraphy

Stratigraphy is a branch of geology which studies rock layers and layering

A key idea in Stratigraphy is the Law of Superposition: the idea that lower rock layers are older than the upper rock layers

Which layer would be the oldest?

A B C

A

B

C

Which rock layer would be the youngest?

A B C

A

B

C

Intrusion and extrusion

Clues From Igneous RockLava that cools at the surface is called an extrusion. Rock below an extrusion is always older.Magma that cools beneath the surface is called an intrusion. An intrusion is always younger than the rock layers around an beneath it.

4th Quarter Table of Contents 1

Title Assignment #

Ice Cores 2Ice Core Webquest 3Fossil Notes 4Getting into the Fossil Record 5Fossil Vocab 6Fossils over Time (Molds vs Casts) 7Law of Superposition Vocab

8Who’s on First? (Wkst)

9

Law of Superposition VOCAB 8

Law of superposition – the idea that rocks and fossils found in lower layers are older than the rocks and fossils found in the top layers

relative dating – a method of dating rocks which can’t give us an actual age, but can tell us whether a rock layer is older or younger than another

strata – a certain rock layer unconformity - gaps in rock layers and/or the fossil record

intrusion - a rock layer that forms when magma hardens beneath Earth’s surface

extrusion - a rock layer that forms when lava flows onto Earth’s surface and hardens

radiometric dating – using radioactive elements found naturally in substances in order to determine how old they are.

absolute age – the actual age of a rock or fossil

Who’s on First?

Today you will start an assignment to help you learn how to determine the relative age of rocks and fossils.

You need a partner, and each person needs their own paper.

You will share a set of cards. You must finish with the pink cards to get

the green cards!

Fossils 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 FossilsWhat 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

EX: GUM, ANE, TZR, RID, MAN, DOG, BYS, NEB

START WITH TZR

Set A – Pink Cards

On your desk, you have 8 pink 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 layer

2. Look for a card that has either a “T” or “C” written on it for the second layer

MDXONBUAGCT TC

CGA

AU

UBNBN

ONOXD

DM

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”?

Set B – Green CardsObtain some Green Fossil CardsClues:

1. The oldest layer is labeled SET B2. Find a rock layer that has at least

one of the fossils you found in the oldest rock layer. This rock layer will be younger because of the presence of new fossils.

3. Extinction is forever! Once an organism disappears from the sequence it cannot reappear later

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?

Extension:

If you finish, you can complete the Skills Lab in our book on page 330, and answer Questions 1-9.

Turn this in on Google DRIVE of paper.

EXIT