Bellwork 9/21/11

Have your chart from yesterday out!1.Describe the differences between Cast and

Mold Fossils.2. Would you expect fossils to form in wet or dry

conditions? Explain.3. Would you expect fossils to form in hot or

cold conditions? Explain your answer.

Using Evidence to Study Earth's Past:

Ages and Rock Layers

NotesSeptember 21, 2011

SuperpositionSuperposition.Principle of SuperpositionPrinciple of Superposition- a process of reading

undisturbed rock layers  -oldest rocks in the bottom layer-younger rocks in the top layers

Undisturbed Rock Layers

Disturbed Rock Layers

Relative AgeHow old something is in comparison to

the ages of something elseThe age of sedimentary sedimentary rocks can be determined by examining layer sequences. Relative age doesn’t tell

you ANYTHING about

the age of the rock

layers in actual years!!!

Unconformities Gaps in rock sequences.

1. Angular – rock layers are tilted, then new rock layers settle horizontally on top

3 Major Types3 Major Types

2. DisconformityDisconformity – top rock layer is eroded away, then new rock layers settle on top

3. Nonconformity – metamorphic or igneous rocks are uplifted and eroded, then new rock layers settle on top

Nonconformity

Disconformity

AngularUnconformity

It is possible to match up It is possible to match up rock layers from different rock layers from different

locations!locations!

Index Fossils and Relative AgeIndex Fossils and Relative Age• Index fossils are used to help match rock layers that

are not near each other• They can also be used to tell which layers are older

than others• Remember that index fossils are from organisms that

were widespread and only lived for a short period of time.

1. Surface "1" above is an example of a:_____________ 2. Surface "2" above is an example of a:_____________

3. Surfaces "3, 4 and 5" above are examples of a:________________4. On the left-hand side of the figure above there is an unconformity between the schist and light red unit. This is a(n): ______________________

Superposition ActivitySuperposition Activity• FOLLOW PROCEDURE EXACTLY.

• We will do Set A Procedure together.– Stay with me!!

• You and the person at your table are responsible for completing Set B procedure correctly.

Activity AActivity AOn your desk, you have 8 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

Interpretation Questions:

1) After you have arranged the cards in order, write your sequence of letters (using each letter only once) on a separate piece of paper. Starting with the top card, the letters should be in order from youngest to oldest. 2) How do you know that "X" is older than "M"? 3) Explain why "D" in the rock layer represented by DM is the same age as "M." 4) Explain why "D" in the rock layer represented by OXD is older than "D" in the rock layer represented by DM

Return Set A Cards to correct paperclip (8 cards)!!!

You and the person at your table are responsible for completing Set B

Procedure and answering questions!

Activity BActivity BFlip your eight cards overArrange the index cards that represent layers of rock and fossils 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 layer3. Extinction is forever - once an organism

disappears from the sequence it cannot reappear later

Interpretation Questions:Interpretation Questions:

1) Using the letters printed in the lower left-hand corner of each card, write the sequence of letters from the youngest layer to the oldest layer (i.e., from the top of the vertical stack to the bottom). This will enable your teacher to quickly check whether you have the correct sequence. 2) Which fossil organisms could possibly be used as index fossils? 3) Name three organisms represented that probably could not be used as index fossils and explain why. 4) In what kinds of rocks might you find the fossils from this activity? 5) State the Law of Superposition and explain how this activity illustrates this law.

1. What problems did you run into when trying to arrange the fossils into the correctsequence?2. Would this have been more difficult if you did not know which layer was theoldest to start the activity?3. Which organism is the most complex of all the fossils and why?

Clean-Up and Turn in

• Be sure ALL cards are in the CORRECT bag.• Return appropriate container • Return Procedures to containers. (NICE AND NEAT STACK!)• Be sure your name and partner’s name are on

answer sheet.• Turn answer sheet into shelf.

Homework

• Fossil Review