Numerous reports suggest an increase in white shark encounters* in the United States in recent years and the public is worried.
*Encounters include sightings and census estimates, as well as physical interactions between humans and sharks.
Fossil shark teeth can inform us about the past.
Click here for NGSS, CCSS (ELA), and California ELD standards.
Prior to this, students were introduced to the anchoring phenomenon of questioning the increased number of white shark encounters in the United States in recent years causing the public to worry.
Since this is positioned at the beginning of the last instructional segment for grade 8, it is expected that earlier in the school year, students learned about the fossil record, documenting the existence, diversity, extinction, and change in life forms throughout Earth’s history. They also learned that the geologic time scale is interpreted from rock strata to organize Earth’s history. This prior learning is recalled as students analyze evidence for white shark evolution and discuss ideas with peers. Students determine that sharks have been on earth a relatively long time and that species changed dramatically after every mass extinction. Species of sharks and the time periods they lived can be observed through fossils. Students mimic the investigation of this by using data to provide evidence for a phenomenon, using “random” sampling to look for patterns in rates of change and numerical relationships. Students come to the conclusion that, although fossil evidence is useful in many circumstances for establishing the existence, diversity, extinction, and change in life throughout time, it is insufficient when attempting to determine past population sizes of white sharks; the data is insufficient, as it relies on too many assumptions. This is the first time students consider assumptions to be a limitation of data, specifically fossil data. Although we can roughly estimate relative size, too many assumptions must be held to have a reliable measure (for example, only a portion of sharks fossilize–teeth, but teeth are constantly being replaced, sharks do not stay in one location, etc). This touches on an important nature of science themes, that the certainty and durability of science findings varies. This lesson is part of a series in the learning sequence that will culminate in students revising an explanation over time, leading to engaging in argument from evidence about the causes of recent increases in the white shark population with the goal of building public understanding and alleviating concerns.
In the next lesson, students analyze how historic fisher logs provide information on changes in white shark populations. They learn how humans have impacted the marine environment through legislation and how this affected the white shark population.
Throughout the lesson, a flag () denotes formative assessment opportunities where you may change instruction in response to students’ level of understanding and making sense of phenomena.
Part I | 25 minutes | Engage |
Part II | 30 minutes | Explore |
Part III | 35 minutes | Explain |
All tubs in the classroom could be identical, but ideally, each tub should represent different locations for the same species, with slightly different ratios. (See Explore Step 4.f.iii for clarification.)
Ask questions about data supported by evidence to determine whether fossil remains from sharks have changed through time and if the fossil record can provide us with reliable information about shark populations in the past.
Ask students to record their questions in their Science Notebook. During a class discussion of questions, chart student questions on the Shark Population Questions Chart for use in the Explore activity.
Work with student ideas about where they think they will find shark fossil teeth. One of the easiest ways for people to access shark fossil teeth is to go to the beach where many wash up at the water’s edge. To help students have a context for this, you can view the following video (show 0.17-2:20) Tips for Finding fossilized shark teeth! At the beach!
Obtain and communicate information to determine whether fossil remains from sharks have changed through time.
8.2.H1: Geologic Time Scale is simply a tool for students to use in order to analyze the relative length of time different species lived and the sequence of events that occurred. You can find 8.2.R1: Geologic Time Scale Key in the Toolbox.
This lesson sequence is designed to be taught at the end of the year after students have learned about the geologic time scale and mass extinctions. If students do not have this prior knowledge, additional instruction may be required. One suggestion when teaching geologic time scale is to construct a classroom-sized geologic time scale model in which adding machine tape is attached to the walls of the room. String with index cards attached is used for labeling. Key events and time intervals, in years, are marked. (A suggested scale is generally 1cm = 1 million years). This provides students with a more accurate perception of the immensity of geologic time and patterns of climate and evolution. If this is already constructed in the room, students can attach special “shark cards” to the existing class geologic time scale as well as track on 8.2.H1: Geologic Time Scale.
For the questions above, students should be relying on evidence in the cards to establish patterns that lead to predictions. For students having difficulty, engage them in a discussion about what this means with all of the cards laid out to help with visually identifying the patterns, and together discuss appropriate predictions given the pattern under discussion.
This sequence uses different descriptors for time. “The Past” is still describing the geologic/evolutionary history of sharks. Ancient sharks precede the Permian (about 290 MYA), with modern sharks in more recent history (origin being “first” and rise as the expansion of diversity). Earliest is used in reference to early shark fossils (the first fossils to have some traits similar to sharks) and white shark fossils to indicate that the fossils are old, but not so old they are considered ancient (geologically speaking). It’s all semantic! If students are confused, have a conversation about the words and ask students to think of a way to clarify the language for their use. Help language learners with selecting appropriate affixes (such as early/earliest).
One suggestion for teaching geologic time with students is to build a scale model of geologic time that can be hung on walls in the classroom. This is often done on adding machine tape (tickets, streamers, or toilet paper will also work); one million years of time can be represented by 1 cm. This could have been done previously in the year, and then used in this lesson. In addition to adding shark evolutionary history to 8.2.H1: Geologic Time Scale, students can add “shark cards” to the classroom scale model.
Use 8.2.R1: Geologic Time Scale Key to guide the discussion.
Geologic time scales are often interpreted as having finite divisions between the time periods. This is not true. For example, mass extinctions are generally viewed as a distinct event occurring between two time periods. In fact, according to many geologists and paleontologists, the Permian Extinction occurred over the course of 15 million years during the late Permian period.
Possible student responses:
If students don’t understand proportions and using patterns to solve math problems, these topics should be reviewed. Below is an example for students who need help specifically on problems in 4.e:
Sampling example: We sampled the water column in nine areas and counted the number of White Sharks over a 5 year period, then calculated the average number of sharks in that water column (n).
We then sampled the upper sediment and found x number of modern teeth. There is a proportional relationship between the number of teeth and the number of sharks.
We can use this same relationship to estimate the number of extinct sharks by sampling the lower sediment and finding the number of fossilized teeth (y) and setting up a proportion.
In both of the Chesapeake Bay scenarios stated above, the proportional relationship is 4% for number of teeth to number of sharks.
For example: 5 modern teeth are found in a sample and 100 sharks in the water column. In the deeper level, 15 fossil teeth are found. Estimate the number of extinct sharks in the water column.
As an extension for students at a higher math level or for those wanting to explore, ask them to scale this up even further to estimate the number of extinct sharks there were in any ocean region.
This sampling exercise allows students to see that the use of modern teeth is a way to estimate a modern population size as a proxy for predicting ancient population size. Since we cannot go back in time to count how many individual sharks there were in an ancient population, we can use the ratio of modern teeth to modern observed sharks to predict ancient population based on number of fossil shark teeth found. (A proxy is a preserved characteristic that can be a stand-in for direct measurement, and is important in science. For example, an ice core is a proxy for past temperature; the oxygen isotopes found in ice cores can give us a measure of temperature the year the snow fell even though we cannot directly measure the temperature that year.)
When placing the manipulatives modeling modern and fossilized shark teeth in the tubs of sand, stir them around to randomize their placement in the sand. The amount of modern and fossilized teeth you put into each tub is determined by you, based on the scenario you provide (like the Chesapeake Bay scenario), being clear about the number of sharks sighted as this sets the ratio that is needed for predicting the estimated ancient shark population.
This is written for students to “discover” the ratio and use it to determine the ancient shark population. In order to do that, students will need to know the modern shark population and work with the data in their table to figure it out. If you prefer, you could instead provide the ratio (similar to the one given in the Chesapeake Bay scenario) and have students just use that to determine the populations for both modern and ancient shark populations.
Students should generate their own data table, but a sample, such as the one below, can be provided for those that need guidance. (Consider simply making the table accessible to students who want/need to see it so they can build it in their Science Notebook, rather than printing the table.)
To differentiate the questions for students, all students should work with questions i, ii, v due to their general nature. Questions iii and vii are looking for relationships and, therefore, require application of general knowledge. For students that would like/need to dive deeper into the material and tackle something more challenging, suggest that they think about and discuss iv and vi as they require more application of knowledge to a system and a greater understanding of mathematical concepts to apply an understanding of what relative means.
Some possible assumptions that students could come up with include the following:
This portion of the lesson reveals an important nature of science connection for students as they attempt to make sense of the phenomenon. Science assumes that objects and events in natural systems occur in consistent patterns that are understandable through measurement and observation. That being said, shark tooth fossil data is inadequate for estimating population size because too many assumptions must hold true. Many times, problems in science (such as, what was the ancient shark population) can’t be solved by experiment and you are limited by what you have access to. Have a brief discussion with students to see what their thoughts are. If students reveal in the discussion that they aren’t understanding this important point, adjust instruction. Asking questions such as, “What exactly did you observe? What were you looking for? Why were you looking for this? What is limiting your explanation? What is making you unsure? What would need to be different for you to be confident in the data? ” may help, as well as providing an example from an experience students may have in their own lives. (An example could be to ask students to consider a time they were given a wrapped present. How could they know what was inside without opening it? Think of similar ways they might gather data and what assumptions they would need to make to decide.)
Analyze and interpret data to find patterns of shark diversity extinction, and changes in life forms on a geological time scale.
Prompt students to consider what they have learned in this lesson. (Students may use the charts generated and their Science Notebook.) Ask them to discuss with their group and then record how they are making sense of the following in their Science Notebook. Before students begin work, inform students that you will be peeking into their Science Notebook to give “sticky note feedback.”
Examples of sample student responses:
When students are finished, take time to read Science Notebook responses and leave sticky note feedback. Return Science Notebooks to students and ask them to review the feedback and, if helpful, to discuss questions they may have with their group. After discussing any questions, ask students to consider the feedback and refine their work. Ask students to identify their revisions in some way so that you can check on their progress.
When students are finished, take time to read Science Notebook responses and leave sticky note feedback. Return Science Notebooks to students and ask them to review the feedback and, if helpful, to discuss questions they may have with their group. After discussing any questions, ask students to consider the feedback and refine their work. Ask students to identify their revisions in some way so that you can check on their progress.
For more information on this, see: Tyler, B., & DiRanna, K. (2018). Next Generation Science Standards in practice: Tools and processes used by the California NGSS Early Implementers. San Francisco, CA: WestEd. Retrieved from http://www.k12alliance.org/docs/NGSS-In-Practice-Report_FINAL.pdf.
The Engage activity connects students’ past learning and experiences about the geologic time scale to the present lesson. Most students own or have seen shark teeth and that experience can be recalled as they begin the lesson. By writing about the topic in their Science Notebook BEFORE discussing, second language learners and low language students can gain confidence and organize their thoughts before speaking in front of a group. Also, sharing ideas in small groups throughout the rest of the lesson lowers the affective filter of low language students. To support students learning English, allow conversations and notebook work to happen in the language that the student is most comfortable expressing understanding, and then encourage expression using simple English phrases (or more complex for students with increasing proficiency). Having students work in teacher-selected partnerships or groups allows the teacher to match students in a way that they are being supported. Allow advanced or motivated students to have the opportunity to explore additional questions that arise.
Amy’s Traveling Shoes. (2014, July 31). Tips for Finding fossilized shark teeth! At the beach! [Video]. YouTube.
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