• Students will learn that the Earth has a history; e.g., rock types are located where they are due to the past history of the Earth; conversely, its history can be derived from the rocks.
• Students will be introduced to the geological time scale: the Earth is ancient; time can be divided into periods based on its fossil content.
• Students will see how sedimentary rocks containing fossils can form.
• Students will see the changes in life through time (e.g., evolution).
• Students will discover that geology is fun by employing an outdoors, hands-on exercise determining the age of a "stratum."
• Students will understand the "Principle of Superposition."

• Pit or lined enclosure containing dry sand about 30 cm deep.
• Cretaceous index fossils (e.g., Exogyra).
• Small fossils to be kept by students (especially shark's teeth).
• Large poster-sized geologic time scale (periods should be labeled with appropriate epithets, e.g., "Time of Trilobites" for Cambrian; "Age of Apatosaurus" for Jurassic, etc.). Typical index fossils should be attached next to each period.
• Series of hand samples on display documenting formation of fossiliferous rock from break down of igneous rocks to sediment to sedimentary rock.
• Series of hand samples on display showing evolution of life through time, from stromatolites through Paleozoic invertebrates to dinosaur bones and human projectile points.
• Tables for hand samples and geologic time scale.
• Cups to put fossils in.
• Trowels to dig up fossils.
• Rake to rebury fossils.

1. The students will engage in the "Fossil Detective Game" by trying to determine the age of the "formation" in the pit, using its enclosed fossils.
2. A short introductory lesson will explain three ideas:
   a) The portion of the rock cycle where sedimentary rocks are formed from the weathering of igneous rocks.
   b) The geologic time scale seen in the layers of rock whose history can be "read" as the pages of a book. The oldest rocks, as the oldest periods on the time scale, are on the bottom.
   c) This history can be read, and thus the age of the rocks determined, because of the changes in life (evolution) through time.
3. The students will be allowed to be "Fossil Detectives" and search for clues as to the age of the "formation." They will dig for fossils that have been previously buried. There are two goals:
   a) Find a large index fossil, then identify it by taking it to the geologic time scale and matching it with the attached fossils. The age of the deposit is then determined. [Whereas any index fossil can be used, it is recommended that Mesozoic fossils be employed; thus, the deposit will be of "The Age of Dinosaurs"]. Assistance from the instructor should be available for younger students.
   b) Find smaller fossils (preferably shark's teeth); at the end of the exercise, the student can be allowed to keep his or her favorite fossil found, thus, retaining a tangible memento to reinforce the lessons learned.

1. Students will discover for themselves that this "formation" was deposited during the Age of the Dinosaurs, and that many other animals (e.g., sharks and Exogyra) lived at that time.
2. A group discussion should follow as to why no dinosaur remains were discovered, if this is a Mesozoic deposit.
3. Further discussion should emphasize why this deposit could not have been Cenozoic or Paleozoic in age, even though sharks are still alive today. Questions regarding fossils likely to be found in underlying older formations, as well as in now eroded overlying younger units, will lead to an understanding of stratigraphic principles. Additional discussions could emphasize the relevance of the dinosaurs' extinction to our current environmental problems, as well as the role of evolution during the immensity of geologic time in forming the fossil record.

Related Activities

• A second, separate dig can be developed to allow the students to search for human artifacts (points, beads, etc.). This will permit discrimination of geology and archeology, and emphasize the differences in time of existence between man and dinosaurs.
• Within the geology dig, crystals of igneous minerals (such as quartz) may also be included. Their discovery can lead to a better understanding of the origin of sedimentary rocks, and the fact that not all igneous material breaks down. The presesence of igneous crystals will, however, permit determination of the source material from which the sediment was derived (igneous, not sedimentary, rocks); this is yet more history to be learned from the deposit.

(This activity is modified from our 1989 Red River Revel "Revel in Geology!" mock-dig, where over 3300 children and their parents participated during its one week duration).

http://www.beloit.edu/~SEPM/Fossil_Explorations/Fossil_Detective.html

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