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Bellwork 9/21/11

Learn about the differences between cast and mold fossils, the conditions necessary for fossil formation, and the principles of superposition. Explore index fossils and their role in determining relative age. Engage in activities to understand the sequencing of rock layers and the use of fossils in studying Earth's past.

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Bellwork 9/21/11

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  1. 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.

  2. Using Evidence to Study Earth's Past:Ages and Rock Layers Notes September 21, 2011

  3. Superposition Principle of Superposition- a process of reading undisturbed rock layers -oldest rocks in the bottom layer -younger rocks in the top layers .

  4. Undisturbed Rock Layers Disturbed Rock Layers

  5. Relative Age How old something is in comparison to the ages of something else The age of 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!!!

  6. Unconformities Gaps in rock sequences. 3 Major Types Angular – rock layers are tilted, then new rock layers settle horizontally on top

  7. 2.Disconformity – 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

  8. Angular Unconformity Disconformity Nonconformity

  9. It is possible to match up rock layers from different locations!

  10. Index 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.

  11. 3. Surfaces "3, 4 and 5" above are examples of a:________________ 1. Surface "1" above is an example of a:_____________ 2. Surface "2" above is an example 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): ______________________

  12. Superposition 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.

  13. Activity A On 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: • The card with the letters “C” and “T” is on the bottom, or the oldest layer • Look for a card that has either a “T” or “C” written on it for the second layer

  14. 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

  15. 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!

  16. Activity B Flip your eight cards over Arrange the index cards that represent layers of rock and fossils Clues: • The oldest layer has the letter “M” in it • Find a rock layer that has at least one of the fossils you found in the oldest rock layer • Extinction is forever - once an organism disappears from the sequence it cannot reappear later

  17. 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.

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

  19. 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.

  20. Homework • Fossil Review

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