Fossils

The investigation in this example centers on the use of fossils to develop concepts about variation of characteristics in a population, evolution—including indicators of past environments and changes in those environments, the role of climate in biological adaptation, and use of geological data. High-school students generally exhibit interest in fossils and what the fossils indicate about organisms and their habitats. Fossils can be purchased from scientific supply houses, as well as collected locally in some places. In the investigation described here, the students conduct an inquiry to answer an apparently simple question: Do two slightly different fossils represent an evolutionary trend? In doing the activity, students rely on prior knowledge from life science. They use mathematical knowledge and skill. The focus of the discussion is to explain organized data.

[This example highlights some elements of Teaching Standards A, B, D, and E; 9-12 Content Standards A, C, D and the Unifying Concepts and Processes; and Program Standards A and C.]

The investigation begins with a task that students originally perceive as easy—describing the characteristics of two brachiopods to see if change has occurred. The student inquiries begin when the teacher, Mr. D., gives each student two similar but slightly different fossils and asks the students if they think an evolutionary trend can be discerned. The openness and ambiguity of the question results in mixed responses. Mr. D. asks for a justification of each answer and gently challenges the students' responses by posing questions such as: "How do you know? How could you support your answer? What evidence would you need? What if these fossils were from the same rock formation? How do you know that the differences are not normal variations in this species? What if the two fossils were from rock formations deposited 10 millions years apart? Can you tell if evolution has or has not occurred by examining only two samples?"

Mr. D. shows students two trays, each with about 100 carefully selected fossil brachiopods. He asks the students to describe the fossils. After they have had time to examine the fossils, he hears descriptions such as "They look like butterflies," and "They are kind of triangular with a big middle section and ribs." Then he asks if there are any differences between the fossils in the two trays. The students quickly conclude that they cannot really tell any differences based on the general description, so Mr. D. asks how they could tell if the fossil populations were different. From the ensuing discussion, students determine that quantitative description of specific characteristics, such as length, width, and number of ribs are most helpful.

Mr. D. places the students in groups of four and presents them with two trays of brachiopods. They are told to measure, record, and graph some characteristics of the brachiopod populations. The students decide what they want to measure and how to do it. They work for a class period measuring and entering their data on length and width of the brachiopods in the populations in a computer database. When all data are entered, summarized, and graphed, the class results resemble those displayed in the figure.

The students begin examining the graphs showing frequency distribution of the length and width of fossils. As the figure



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