Name: Hr:
Earth History Investigation 7 : Fossils and Time
Part One: Index Fossils Fossils provide geologists with important evidence about prehistoric environments. Some fossils also provide evidence for age of rock layers. These fossils are called index fossils. Not all fossils are index fossils. An index fossil must have lived for a relatively short period of time and in many places. An index fossil should be distributed over a wide geographical area to be useful. For example, some of the same index fossils are found in rocks of Devonian age in both the Grand Canyon and the Midwest. If geologists identify an index fossil in a rock layer, they can be pretty sure of the age of the rock layer in which it was found. They know it is about the same age as any other rock layers that contain the same index fossil. A fossil that lived for only a million years or so would be a good index fossil. You would know that any rocks containing that fossil are no more than a million years different in age. Which would make a better index fossil, a fern that has lived on Earth since the Pennsylvanian period, 300 mya, or a trilobite that lived in many areas for only a few million years during the Cambrian period? If musicians were index fossils, which would make a better index fossil, Elvis Presley or Milli Vanili? Lab Sheet – Grand Canyon Fossils p Index Fossil Key – Earth History Resources book Early – the time at the beginning of a geological period. Late – the end of a time period. Lab Sheet – Index-Fossil Identification, Grand Canyon p Labsheet – Bryce Canyon Fossils and Zion National Park Fossils p If you find the same index fossil at both the Grand Canyon and Zion, what does that tell you about the age of the layers in which the fossils are found? Labsheet – Index-Fossil Correlations p Labsheet – Index Fossil Correlation Questions p
Read A Fossil Primer in Earth History Resources book. Labsheet – Thinking about Index Fossils p Part Two – Earth History Sequence Cards What important discovery allowed geologists to add numbers to the relative time scale? Imagine an organism from the past that is now extinct. It did not leave any fossils. How would we know that it ever existed? How do we know what organisms and environments existed in the past? Labsheet – Event Cards A & B p
1. Cut out the cards. You only need one set of cards per pair. 2. Work together to arrange the cards in order. You should use what you know from the
investigations we have done so far and other information that you have notes about from past investigations.
3. Work for a few minutes. Then answer the four questions at the top of the Major Events in Earth history page. P
4. After you have reached an agreement on the order, record them on Major Events in Earth history, p
Where were some of the easiest cards to put in sequence? Which ones were the hardest to sequence? Which cards caused the most disagreement in your pair? What other information would be helpful to you in sequencing the cards?
Journal Writing What surprised you about the correct sequence of event cards? What have you learned from making your time line and sequencing the event on it about the appearance of different life-forms on Earth? Review for Mid-summative Exam Know that the most important use of index fossils to geologists is. Know how to decide what layers are older than others by looking at the fossils in each layer. Know how to use index fossils to decide how old layers of rocks are and what period fossils above and below it came from.
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Limestone
Metamorphic and igneous rocks, no fossils
Sandstone
Shale
Limestone
Limestone
Sandstone, siltstone, shale, dolomite
Shale
Sandstone
Limestone, sandstone
Limestone, sandstoneKaibab
Toroweap
Coconino
Hermit
Supai
Redwall
Temple Butte
Muav
Bright Angel
Tapeats
Vishnu, etc.
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GRAND CANYON FOSSILS
Inv. 7: Fossils and TimeStudent Sheet
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Rock layer Index fossils identified Ages
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INDEX-FOSSIL IDENTIFICATION, GRAND CANYON
Name
Period Date
KaibabFormation
ToroweapFormation
CoconinoSandstone
Hermit Shale
Supai Group
RedwallLimestone
Temple ButteLimestone
MuavLimestone
Bright AngelShale
TapeatsSandstone
Vishnu
Inv. 7: Fossils and TimeStudent Sheet
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Shale
Coal, sandstone
Shale
Sandstone
Shale, sandstone
Sandstone
Shale, sandstone, limestone
Sandstone
Shale, conglomerate
B3
B9
B8
B7B6B5
B4
B2
B1
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BRYCE CANYON FOSSILS
Inv. 7: Fossils and TimeStudent Sheet
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ZION NATIONAL PARK FOSSILS
Inv. 7: Fossils and TimeStudent Sheet
Limestone, sandstone
Shale, limestone
Shale, conglomerate
Sandstone
Shale, sandstone
Shale, sandstone, limestone
Sandstone
Z7
Z6
Z5
Z4
Z3
Z2
Z1
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INDEX-FOSSIL CORRELATIONS
Name
Period Date
L
imes
tone
Met
amor
phic
and
igne
ous
rock
s, n
o fo
ssils
S
ands
tone
S
hale
Lim
esto
ne
Lim
esto
ne
San
dsto
ne, s
iltst
one,
sha
le, d
olom
ite
Sha
le
San
dsto
ne
Lim
esto
ne, s
ands
tone
Lim
esto
ne, s
ands
tone
Kaib
ab
Toro
weap
Cocon
ino
Herm
it
Su
pai
Redw
all
Tem
ple
Butt
e
Muav
Bri
gh
t A
ngel
Tap
eats
Vis
hn
u,
etc
.
Grand Canyon
Inv. 7: Fossils and TimeStudent Sheet
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Cut these rock layers out on the dashed lines and tapethem to the Index-Fossil Correlations sheet to observethe relationship of the rocks in the three national parks.
Shale
Coal, sandstone
Shale
Sandstone
Shale, sandstone
Sandstone
Shale, sandstone, limestone
Sandstone
Shale, conglomerate
B3
B9
B8
B7B6B5
B4
B2
B1
Bry
ce C
an
yon
Zio
n N
ati
onal P
ark
Inv. 7: Fossils and TimeStudent Sheet
Limestone, sandstone
Shale, limestone
Shale, conglomerate
Sandstone
Shale, sandstone
Shale, sandstone, limestone
Sandstone
Z7
Z6
Z5
Z4
Z3
Z2
Z1
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Answer these questions after you have identified and correlated the rock layers at the three parks.
1. Which rock layers contained the same index fossils at Zion and the Grand Canyon?
2. Which rock layers contained the same index fossils at Zion and Bryce?
3. Which rock layers contained the same index fossils at Grand Canyon and Bryce?
4. Is rock layer B3 at Bryce older or younger than Supai Group at the Grand Canyon? How do youknow?
5. Is rock layer B2 at Bryce older or younger than rock layer Z1 at Zion? How do you know?
6. What do you think the environment was like at the time layer B9 was being deposited at Bryce?
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INDEX-FOSSIL CORRELATION QUESTIONS
Name
Period Date
Inv. 7: Fossils and TimeStudent Sheet
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1. What big ideas did the following people contribute to the study of fossils? How didtheir ideas help people better understand fossils and what they mean?
a. James Hutton
b. Lamarck
c. William Smith
2. Fossils have been called the index to Earth history. What does that mean?
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THINKING ABOUT INDEX FOSSILS
Name
Period Date
3. Smith noticed that wherever he found his index fossils, fossil a was always in the toplayer, fossil b was in the layer under a, and fossil c was in the layer under b. One timehe found a rock column with fossil a in the top layer and fossil c in the layer directlyunder layer a. There was no layer with fossil b. What might this mean? How wouldyou find out for sure? Draw a picture to help you think about this.
Inv. 7: Fossils and TimeStudent Sheet
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4. Suppose you found a rock column with fossil c in the top layer, with fossil b in the nextlayer, and fossil a in the lowest layer. What might this mean? How would you find outfor sure?
5. This illustration shows what might be a typical column of rocks exposed in a canyon onthe Colorado Plateau. Using potassium-argon dating, geologists have calculated an ageof 200 million years for rock A, a granite. Rock F, the volcano, has been given an age of225,000 years.
a. How can you use this information to estimate the age of rock layers B, C, D, and E?
b. Which is younger, the volcano or the basalt dike leading up to it?
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— — — — — — — — — — — — — — — — — — — — — — — — — — – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –— — — — — — — — — — — — — — — — — — — — — — — — — — – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –— — — — — — — — — — — — — — — — — — — — — — — — — — – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –— — — — — — — — — — — — — — — — — — — — — — — — — — – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
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B
C
D
E
F
Schist and granite
Sandstone
Limestone
Shale
Volcano
Sandstone
Canyon
Basa
lt di
ke
Inv. 7: Fossils and TimeStudent Sheet
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Archaeopteryx(early bird)
Forests of coal plants
First crocodiles Recorded written history
First mammals First sharks
First bony fishes Protozoa (single-celled,microscopic animals)
Pangaea, the supercontinent,begins to divide
Dinosaur extinction
Water appeared onEarth’s surface
Neanderthal man(1400 cc brain)
Grass
First flowering plants
Trilobites
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EVENT CARDS A
Inv. 7: Fossils and TimeStudent Sheet
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Pangaea, the supercontinent,forms
Jellyfish appear
First reptiles Great Extinction
First land animals Earliest life (bacteria-like)
Tyrannosaurus rex First amphibians First vascular land plants(plants with roots and stems)
Earth formed First vertebrates (jawlessfish with skeletons made of
cartilage)
Modernhorse
First dinosaurs
Bees
First insects
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EVENT CARDS B
Inv. 7: Fossils and TimeStudent Sheet
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Consider the following pairs of events. Which do you think occurred first in each pair?Explain why you think so.
• Dinosaurs appear; dinosaurs become extinct.
• Jellyfish appear; protozoa (single-celled animals) appear.
• Bees appear; flowering plants appear.
• Trilobites appear; fish with backbones appear.
Take turns arranging the event cards in the order they might have occurred. Explain toyour partner why you are putting them in that order. Reach an agreement about the orderand record the sequence here.
1. ______________________________ 16. ________________________________________ 2. ______________________________ 17. ________________________________________ 3. ______________________________ 18. ________________________________________ 4. ______________________________ 19. ________________________________________ 5. ______________________________ 20. ________________________________________ 6. ______________________________ 21. ________________________________________ 7. ______________________________ 22. ________________________________________ 8. ______________________________ 23. ________________________________________ 9. ______________________________ 24. ________________________________________10. ______________________________ 25. ________________________________________11. ______________________________ 26. ________________________________________12. ______________________________ 27. ________________________________________13. ______________________________ 28. ________________________________________14. _______________________________ 29. ________________________________________15. _______________________________ 30. ________________________________________
After you have recorded your sequence, place the cards on your time lines where you thinkthey should go.
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MAJOR EVENTS IN EARTH HISTORY
Name
Period Date
Inv. 7: Fossils and TimeStudent Sheet