Name Date ______ Per ____ Virtual Lab: Fossil Data

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Name __________________________________________ Date ________ Per ____ Virtual Lab: Fossil Data
Virtual Lab: How can fossil and rock data determine when an organism lived? SC.7.E.6.4, SC.7.E.6.3
http://www.glencoe.com/sites/common_assets/science/virtual_labs/ES12/ES12.html
Background: Fossils are the remains, imprints, or traces of organisms that were once alive. By studying fossils,
scientists can learn where, when, and how those organisms lived.
Fossils are usually found in sedimentary rocks. This is because the intense pressure and heat that creates igneous
and metamorphic rocks often destroy fossils.
Scientists use special fossils called index fossils, to date rocks. Index fossils are fossils from a species that existed
on Earth for relatively short periods of time and were abundant and widespread. Index fossils found in a
sedimentary rock layer can be used to help date the layer.
Another way scientists might determine the age of a rock layer is by using the principle of superposition. This
principle states that in undisturbed layers of rock, the oldest rocks are on the bottom and the youngest rocks are
towards the top. However, layers do not always remain undisturbed. A fault could cause a rock layer to overturn. In
this case, scientists use relative dating to determine the order of events and the relative ages of rocks by looking
at the positions of rocks in a sequence. Relative dating does not indicate the exact age of rock layers. It does
indicate, however, that a layer is younger than the layers below it and older than a fault cutting through it.
Besides using index fossils, superposition, and relative dating, scientists also use a more precise method called
absolute dating, to date rocks. Absolute dating uses the radioactive decay of radioactive isotopes of minerals in
rocks to determine the age of the rock. When a radioactive isotope (parent material) decays, it forms a new
isotope, a daughter product. The half-life of a radioactive element is the time it takes for half of its atoms to decay
into the daughter product. After two half lives, one-fourth of the original isotope’s atoms remain and three-fourths
have turned into the daughter product. After three half-lives, only one-eighth of the original isotope’s atoms remain.
After many more half-lives, a very small amount of the original parent’s isotope remains.
By measuring the amounts of parent and daughter materials in a rock and by knowing the half-life of the parent, a
geologist can calculate the absolute age of the rock. This method is called radiometric dating.
In this Virtual Lab you will confirm or refute the age of a rare fossil and determine when the organism that produced
it was alive. To date the fossil you will use radiometric dating of rock layers and information about index fossils.
Procedure:
1. Begin at one of the three dig sites. Click and drag a nail with a label into each of the four rock layers.
2. Drag the magnifying glass over the rock and sediment layers to look for fossils. Note: A hand is displayed on
the handle of the magnifying glass. As you move the magnifying glass, the layer the hand is on indicates the
rock layer where a fossil may be found. You will need to move the magnifying glass slowly and carefully to find
the fossils. If you go too quickly or don’t search thoroughly you may miss some.
3. When you find fossils, compare them with those shown in the field guide. To access the field guide, click the
laptop computer. Under Menu click field guide. Compare the geologic rock layers shown with those of the dig
site. Click the Next button to research the fossils.
4. Record the names of the fossils and the layers in which you found them in your Table. Return to the dig site.
5. Click and drag the hammer to the layers you want samples from. The samples will be placed in the tray
according to the layers from which they are taken.
6. Click and drag each of the samples to the Utility Truck’s front driver side window.
7. Click the truck window again to send the rock samples to the lab for absolute dating. (the truck will drive away)
8. Click the laptop computer to check your email. Under menu click email to read the results of the absolute
dating tests.
9. Click the Next button and read the graph to determine the age of your rock sample. Find the flashing point on
the graph. Convert the number of half-lives into millions of years. You may use the calculator if necessary. If
you received data for more than one sample, click the Next button again and determine the age of that rock
sample. Record your findings in the Table.
10. To explore a different site click the Reset button until you see a new site number that you have not explored
near the top of the screen.
Name __________________________________________ Date ________ Per ____ Virtual Lab: Fossil Data
Data Table: You may need to hit the refresh button in Internet Explorer several times to get the other dig
sites to work and load properly.
Dig Site 1
Rock/Sediment
Layer
1
Name of Fossils Found
(at least 2 in layers 1 and 3)
Time Period of Fossil Found
Radiometric Dating
Results (layers 2 and 4)
Name of Fossils Found
(at least 2 in layers 1 and 3)
Time Period of Fossil Found
Radiometric Dating
Results (layers 2 and 4)
Name of Fossils Found
(at least 2 in layers 1 and 3)
Time Period of Fossil Found
Radiometric Dating
Results (layers 2 and 4)
2
3
4
Dig Site 2
Rock/Sediment
Layer
1
2
3
4
Dig Site 3
Rock/Sediment
Layer
1
2
3
4
Cenozoic Quarternary = 1.6 MYBP
Mesozoic Jurassic = 208 MYBP
Paleozonic Mississippian = 360 MYBP
Paleozonic Ordovician = 505 MYBP
Cenozoic Tertiary = 64.4 MYBP
Mesozoic Triassic = 245 MYBP
Paleozonic Devonian = 408 MYBP
Paleozonic Cambrian = 544 MYBP
Mesozoic Creaceous = 144MYBP
Paleozonic Permian = 286 MYBP
Paleozonic Silurian = 438 MYBP
Precambrian = 4600 MYBP
Name __________________________________________ Date ________ Per ____ Virtual Lab: Fossil Data
QUESTIONS:
1. What does the principle of superposition state?
2. Does the information you collected from dig sites 1 and 2 support the principle of superposition? Explain.
3. How can you explain the fact that at Dig site 3 there is an older rock layer above a younger rock layer?
4. What steps did you take to date the rock layers? (Summarize your process)
5. What is the difference between relative dating and absolute dating?
6. Why could you use radiometric dating to date the igneous rock layers, but not the sedimentary rock layers?
7.
Give 1 benefit of using this virtual lab model of a geologic dig instead of actually going to a dig site.
8. Give 1 drawback of using this virtual lab model of a geologic dig instead of actually going to a dig site.

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