Essential and guiding questions:
Interpretation Questions:
Procedure Set (1) A:
- 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.
- How do you know that "X" is older than "M"?
- Explain why "D" in the rock layer represented by DM is the same age as "M."
- Explain why "D" in the rock layer represented by OXD is older than "D" in the rock layer represented by DM.
Procedure Set (1) B:
- 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.
- Which fossil organisms could possibly be used as index fossils?
- Name three organisms represented that probably could not be used as index fossils and explain why.
- In what kinds of rocks might you find the fossils from this activity?
- State the Law of Superposition and explain how this activity illustrates this law.
Procedure Set (2) A:
- 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. The correct sequence of letters for the cards in Set A from youngest to oldest rock strata is MDXONBUAGCT. Please note that none of the letters in this sequence may be reversed and still be correct. The sequence must be exactly in the order as written. It is not uncommon to have students reverse the M and D for example and begin the sequence with DM because that is the way they are printed on the card. It is good at this time to remind them that these letters represent fossils in a rock layer and that one fossil next to another within a rock layer implies no particular sequencing; they both are approximately the same age as that particular rock layer. The following question may help clarify this point.
- How do you know that "X" is older than "M"? "X" is older than "M" because it appears in an older rock strata (i.e., the card beneath the "DM" card). "M" is not present in the card below it in the stack and is, therefore, younger.
- Explain why "D" in the rock layer represented by DM is the same age as "M." Since fossils D and M died and were deposited in the same rock layer, they both are the same age as the rock layer.
- Explain why "D" in the rock layer represented by OXD is older than "D" in the rock layer represented by DM. Using the Law of Superposition, the rock layer OXD is beneath rock layer DM and, therefore, is older. The fossils within rock layer OXD (i.e., fossils O, X, and D) are older than the fossils in the layer above it (i.e., D and M in rock layer DM). Therefore, D in the rock layer OXD is older than D in the rock layer DM.
Procedure Set (2) B:
- 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.
- Which fossil organisms could possibly be used as index fossils? The graptolite, placoderm, ammonite, ichthyosaur, and shark's tooth could possibly be used as index fossils since they are found in only one layer. Technically, however, given only this set of strata, one cannot say that the shark's tooth and ichthyosaur could be used as index fossils because we do not know if they continue in younger rock layers above this set of strata.
- Name three organisms represented that probably could not be used as index fossils and explain why. The brachiopod, crinoid, eurypterid, foraminifera, gastropod, horn coral, pelecypod, and trilobite could probably not be used as index fossils since they overlap more than one stratum.
- In what kinds of rocks might you find the fossils from this activity? Marine sedimentary rocks such as limestone, shale, and sandstone might contain fossils similar to those depicted in this activity.
- State the Law of Superposition and explain how this activity illustrates this law. In a "normal" horizontal sequence of rocks, the oldest rock layers will be on the bottom with successively younger rocks on top. This activity illustrates this law because when the cards are placed in the correct order, the vertical stack shows the oldest fossils in a rock layer in the bottom of the stack and the youngest fossils in rock stratum on the top.
