interpret archaeological strata using the law of superposition; apply cross-dating to determine the age of other artifacts.

Transcription

1 Grade 8: Standardized Task Competency Goal 5: The learner will conduct investigations and utilize appropriate technologies and information systems to build an understanding of evidence of evolution in organisms and landforms. 2.3 Stratigraphy and cross-dating Provided by Research Laboratories of Archaeology Objectives In their study of stratigraphy, students will use an activity sheet to: interpret archaeological strata using the law of superposition; apply cross-dating to determine the age of other artifacts. Materials Five books of any size; Site Near Roanoke Rapids and Cross-Dating activity sheets for each student. Vocabulary Cross-dating: the principle that a diagnostic artifact dated at one archaeological site will be of the same approximate age when found elsewhere. Diagnostic artifact: an item that is indicative of a particular time and/or cultural group; a computer would be a diagnostic artifact of our time and culture. Spatial: concerned with space. Strata: layers (the plural of stratum); in archaeology, this term usually refers to layers of earth. Stratigraphy: the layering of deposits in an archaeological site. Cultural evidence and natural sediments become buried over time. The layer on the bottom is the oldest; the layer on top is the youngest. Stratum: layer (the singular of strata); in archaeology, this term usually refers to a layer of earth or human-generated debris. Temporal: concerned with time. Background Natural materials such as rocks, soil, and traces of plants and animals settle on the earth s surface and over time can accumulate in layers. Each layer, or stratum, may be distinguished by its physical characteristics: color, texture, and structure. Similarly, materials of human origin are also deposited onto the earth s surface. In archaeological sites, natural and humangenerated materials occur together in layers. These layers, called strata, form a record of past events that archaeologists analyze and interpret. The materials deposited first are the oldest and are always found at the bottom of a given stratigraphic section. The most recently deposited materials are the youngest and are always

2 at the top. This concept is known as the Law of Superposition. It always applies except when some type of disturbance has occurred. Strata in archaeological sites provide archaeologists with temporal and spatial information. All of the artifacts in a given stratum will be of approximately the same age, while those in strata above or below will be younger or older respectively. Cross-dating can indirectly establish a date for artifacts and sites. Artifacts such as stone points and pottery were made in distinctive styles through time. A modern analogy is automobiles: one would not mistake the style of a car made in the 1920s with one made in If an arrow point was found in association with a hearth that was radiocarbon dated to be 500 years old, it is assumed that the arrow point is the same age. When that style of arrow point is found at another site, the archaeologist would assign the site and the arrow point an age of approximately 500 years. Often cross-dating is the only method archaeologists have to determine the age of sites. Archaeological sites in North Carolina often contain evidence of repeated occupations. Usually these occupations occurred on exactly the same surface, which results in a mixing of artifacts from different periods. Yet archaeologists also find stratified sites, in which each occupation is associated with a distinct stratum. Stratified sites contain artifacts and other evidence that can show culture change over time and have the potential to give clues about the relationship one group of people had to those who came before or after them. In North Carolina, information from just four stratified sites--three in the Uwharrie Mountains and one near Roanoke Rapids allowed archaeologist Joffre Coe to construct a chronology of different Native American cultures spanning the time from 10,000 years ago until Colonial times. Because of their great information potential, and their rarity, archaeologists regard stratified sites as particularly important. When an archaeological site is vandalized or artifacts are removed, knowledge about past cultures is lost forever. Damage to stratigraphy by unauthorized digging destroys the information that could be obtained under controlled scientific excavation. The removal of diagnostic artifacts from a site by vandals often removes all possibility of determining the site s age. Setting the stage Stack five books on a table. Tell the students that the books were placed in their positions one at a time. Ask them which book was placed in position first. Which one was placed last? This illustrates the Law of Superposition. Now have the students imagine how thick the dust would be on a table if no one dusted it for 100 years. Each book represents a layer of sediment built up in a similar fashion for hundreds or even thousands of years. Procedure 1. Using the Site Near Roanoke Rapids activity sheet as a guide, draw a layer near the bottom of the blackboard. Show how artifacts and other traces of past life are deposited as people live on top of the layer. Then a new layer of sediments is deposited on top of that, by natural processes or by another group of people leaving different types of evidence. This happens several times until the stratigraphy is built up to present-day levels. 2. The artifacts on the Site Near Roanoke Rapids activity sheet have been dated based on the age of the stratum in which they are found. If you found similar artifacts elsewhere, would you know approximately how old they are? Yes. This concept is known as cross-dating. An artifact type that has been dated in one place can be assumed to have the same date when found elsewhere.

3 3. Give the Cross-Dating activity sheet to the students. Ask the students to imagine that the site near Roanoke Rapids is ten miles away from their town. Tell them that the artifacts shown on the Cross-Dating activity sheet were found in a plowed field close to their town. Have the students determine the approximate age of the artifacts based on the information from the Site Near Roanoke Rapids activity sheet. 4. Ask the students if they would be able to study the stratigraphy of a site if the strata had already been mixed up by illegal digging. If someone took an arrow point, what kind of information would he or she have removed from the site?

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5 Cross-Dating Activity Sheet Answers: 1. AD BC 3. After AD after AD AD

6 Battle of the Beaks Author: Judy Scotchmoor Overview: In this lesson, students learn about adaptive advantage, based on beak function, by simulating birds competing for various foods. Lesson Concepts: Inherited structures provide adaptive advantage in a competitive environment. Grade Span: 6 8 Materials: (for 28 students) 7 scissors 7 plastic spoons 7 tweezers 7 large binder clips 4-5 boxes of large paper clips 200 large rubber bands 4-5 boxes of toothpicks 2 cups of macaroni 28 plastic cups (best if clear) 28 Recording Sheets Graph paper Grid for recording results (see below) Advance Preparation: Gather materials and prepare the grid. Time: Two hours Grouping: Whole class Teacher Background: In any habitat, food is limited and the types of foods available may vary. Animals that are better adapted to take advantage of available foods will fare better than those who are less well adapted, and thus live to pass on their genes to the next generation. While this concept seems rather obvious, it is essential that each student fully grasp its significance. Understanding the idea of adaptive advantage opens the door to understanding populations in ecosystems as well as the process of evolution. Vocabulary: population, selection, advantage

7 Procedure: First hour 1. Have students select either a spoon, tweezer, binder clip or pair of scissors, and a plastic cup and then sit quietly in a large circle. 2. Explain to them that they are now birds. They are very hungry birds. They can only eat with the implement they have selected and they can only use that implement for eating. The cup represents their stomach. It must remain upright at all times. They must hold their beak in one hand and their stomach in the other. They can only place food in their stomachs with their beaks. 3. Explain to them that certain food items will be placed in the feeding area (middle of the circle but spread out evenly towards the students/birds). When you say go they are to collect as much food and place it in their stomachs as possible until you say stop. 4. Take one of the food items (paper clip beetles) and distribute the clips within the feeding area. Say go and allow birds to feed for 1 2 minutes or until all of the food is gone. [NOTE: Depending upon your students you may need to caution about behavior. Even adults doing this activity become a bit more aggressive as the activity proceeds, but obviously safety is foremost. If some students are not responsible enough for this, have them be observers and take notes on the birds behaviors.] 5. Once you have said stop have students empty their stomachs and count the contents. Hand each a Recording Sheet to fill in. Have them return all food items. 6. Repeat this activity using each of the other food items (toothpick twigs, rubber band worms, macaroni munchies). By the end of the activity, each of the students should have completed his/her row for the beak type and filled in the total amount of food. 7. Pause for a class discussion: a) What did you notice about your feeding abilities? b) Did everyone with your type of beak have the same success rate with the same foods? Why or why not? c) What did you notice about your behavior and the behavior of others? 8. Examine the data: Tally up the class totals for each of the beak types in a grid on the board. Have the students create bar graphs that represent the class total for each of the beak and food types. This can be started in class and continued for homework. Second hour 9. When all of the graphs have been completed, have students pick up their beaks and stomachs once again and return to their circle. Explain that obviously most habitats have more than one kind of food available. Ask: What will your strategy be if all of the food types are available? 10. Spread out all of the materials into the feeding circle. Allow about 4 minutes for feeding. Gather the data and have students help to sort out the food items once again for clean up. 11. Again continue with the class discussion. What were your strategies? How was this different from the previous eating experiences? 12. Assess student understanding by posing this question. Have students record their answers with the graphs/tables: What would happen if all the bird types we have been working with flew to an island where no birds had been before and the only food type available was macaroni munchies. Which bird beak type would be mot likely to be successful? Explain your answer.

8 Recording Sheet Name: Date: First Hour Data: Scissors Paper Clips Macaroni Rubber Bands Toothpicks Spoons Tweezers Binder Clips Second Hour Data: Scissors Paper Clips Macaroni Rubber Bands Toothpicks Spoons Tweezers Binder Clips Bar Graph: Complete on back of page!

9 Scoring Guide: Score & Description Complete Student response includes correctly completed graph and explains that only one bird type will survive the island because of its ability to dine on Macaroni. Partial Student response includes the correct graph only with no correct written responses. OR Student response omits the graph, but correctly answers how one bird type will survive the island because of its ability to dine on macaroni. Unsatisfactory/Incorrect Student response does not include correct graph or correct answer to island question.