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Assignment #3: Investigating Geologic Time and Fossils
Directions: Read the Introduction to answer the questions that follow. Then complete the step-by-step activity that follows.
Part I Introduction
Fossils are preserved remains of past life or trace evidence of such life in the Earth’s crust. Rapid burial is a primary factor in
fossilization. Marine plants and animals are fossilized more frequently than land organisms because they undergo rapid burial more
readily. One of a number of processes may lead to fossilization. These processes may be as simple as freezing of an animal or as
complex as minerals filling voids in the bone or the shell of an organism.
For identification, geologists will study and examine the structure and the smallest parts of the fossil. In addition they will also
evaluate the geologic environment that the fossil came from (land, shallow sea, lake, etc.) by looking at the types of rocks the fossil
was found in and the other fossils in the area. Geologists often use this saying: “The present is the key to the past”.
Part II Questions:
1. What are fossils? ___________________________________________________________________________________________
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2. Identify two ways organisms are fossilized. ______________________________________________________________________
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3. What do you think the phrase “The present is the key to the past” means to geologists? __________________________________
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Directions: Read the following paragraphs and then answer the questions using the diagram given.
Part III Fossils: A record of Earth’s Past
Scientists have divided the history of our Earth into intervals of time. The longest, called eons, are divided into shorter intervals of
time called eras, which are divided into periods, which are divided into epochs. Each of these intervals is characterized by different
life forms or geologic events. This history in stone is based on layers of rock which hold fossils that show the type of life that was
abundant during the era. Scientists have given each of these layers a name. The age of dinosaurs and the beginning of human
history have been shown by fossils found in rock layers. The Earth’s age has been calculated to be about 4.6 billion years. Although
long compared to our lifetime, humans and their ancestors have been around for only a relatively short time: less than five million
years!
The layers on the diagram represent a cross-section of rock strata with fossils in them. The pictures are not drawn to scale – for
example, the dinosaur footprints would be much larger than the fish fossils. Also, fossils in real rock aren’t usually positioned as they
are in the pictures. Instead, most would be lying flat-parallel to the surface of the ground. Deeper layers of rock contain the oldest
fossil record, while the top layer contains the most recent fossil record.
Part IV Answer the following questions using the diagram provided.
1. What type of habitat was layer 1 a part of when it was laid down?
A. Forest
B. Fresh water marsh
C. Desert
D. Beach on Lake Michigan
E. Saltwater pond or ocean
2. True or False? Layers 6, 8 and 10 were probably located near a volcano or some other area where molten rock was rising.
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3. Do you think the animal whose fossil jaw is in layer 12 was a plant eater or meat eater? Explain your answer._________________
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4. When layer 9 was forming, the area could have been a swamp. Do you agree? Why or why not? What about this environment
would allow the footprint to be fossilized? Explain your answer.________________________________________________________
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5. Examine layers 1-5 and describe the type of habitat you think existed at that time. Justify your answer. _____________________
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Fossils: A Record of Earth’s Past