5 Vertebrate History. in Rocks. Vertebrate History in Rocks. Preteach

Transcription

1 Integrating Earth Science 5 Vertebrate History Reading Preview Key Concepts Where are fossils most frequently found? What can scientists learn from studying fossils? Key Terms fossil sedimentary rock paleontologist Target Reading Skill Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask what and how questions for each heading. As you read, write the answers to your questions. Vertebrate History Question How do fossils form? Answer Fossils form by... Fossilized fishes What Can You Tell From an Imprint? 1. Flatten some modeling clay into a thin sheet on a piece of paper. 2. Firmly press two or three small objects into different areas of the clay. The objects might include such things as a key, a feather, a postage stamp, or a flower. Don t let anyone see the objects you are using. 3. Carefully remove the objects from the clay, leaving only the objects imprints. 4. Exchange your imprints with a partner. Try to identify the objects that made the imprints. Think It Over Observing What types of objects made the clearest imprints? If those imprints were fossils, what could you learn about the objects by looking at their fossils? What couldn t you learn? Millions of years ago, in an ancient pond, some fishes died and their bodies settled into the mud on the bottom. Soon heavy rains fell, and more mud washed into the pond, covering the fishes. The soft tissues of the fishes decayed, but their bones remained. After many thousands of years, the mud hardened into rock, and the bones became the fossils shown here. Section 5 Vertebrate History Objectives After completing the lesson, students will be able to B Identify the kind of rock in which fossils are frequently found. B Describe what scientists can learn from studying fossils. Target Reading Skill Asking Questions Explain that changing a head into a question helps students anticipate the ideas, facts, and events they are going to read about. Answers Students questions and answers might include: How do fossils form? (Fossils form from imprints or the remains of organisms.) How are fossils interpreted? (Scientists examine fossil structure and make comparisons to present-day organisms.) Transparency B32 Preteach Build Background Knowledge Identifying Fossils Distribute some fossils. Ask: What do you think made the patterns you see in the rocks? (Students may infer that the patterns are the remains or traces of dead animals or plants that lived long ago.) What can you infer about the organism that made the imprint and where it lived? Does it resemble any living organism that you know? (Answers will vary.) Have students write brief descriptions of the fossils. Skills Focus Observing Materials modeling clay; paper; small objects of various textures and degrees of rigidity Time 15 minutes Tips Each student should use some objects that will make a clear impression, such as coins, and some that will not, such as feathers. Expected Outcome Harder objects, such as a key, will be easiest to identify. Imprints of soft objects with recognizable outlines, such as a leaf, will also be easy to recognize. Think It Over The objects that made the clearest imprints were firm and had distinct borders. If the imprints were fossils, you could learn the size and shape of the object that made them. You could not learn what was inside the object or organism, what it ate, or why it died.

2 Instruct What Are Fossils? Teach Key Concepts Describing Types of Fossils Focus Ask students to describe any fossils or pictures of fossils they have seen. Teach Ask: What chemical process is involved in forming fossils? (Tissues are replaced by minerals.) What is sedimentary rock? (Rock made from layers of sediment) Apply Ask: Why aren t more organisms found as fossils? (Tissues of organisms decay rapidly, so they must be trapped quickly in appropriate conditions to be fossilized.) learning modality: verbal Independent Practice Guided Reading and Study Worksheet: Vertebrate History Student Edition on Audio CD Calculating Sedimentary Rock Depths Materials calculator Time 10 minutes Focus Explain that sedimentary rock is deposited slowly but can eventually be thousands of meters thick. Teach Give an example of a thick sedimentary deposit: Part of the Florida peninsula consists of limestone deposits more than 4,000 meters thick. Ask: Suppose this limestone accumulated at a rate of 1 cm every 50 years. How many years did it take for 4,000 meters of limestone to accumulate? (4,000 m 100 cm/m 50 yr/ cm = 20 million years) Apply Ask: Would dinosaur fossils be in this deposit? (No, dinosaurs became extinct 65 million years ago.) learning modality: logical/mathematical For: Links on fossils Visit: Web Code: scn-0235 Discovering Vertebrate Fossils People have been discovering fossils since ancient times. Here are some especially important fossil discoveries Dinosaur-Bone Illustration Robert Plot, the head of a museum in England, published a book that had an illustration of a huge fossilized thighbone. Plot thought that the bone belonged to a giant human, but it probably was the thighbone of a dinosaur. What Are Fossils? A fossil is the hardened remains or other evidence of a living thing that existed a long time ago. Sometimes a fossil is an imprint in rock, such as an animal s footprint or the outline of a leaf. Other fossils are the remains of bones, shells, skeletons, or other parts of living things. Fossils are made when a chemical process takes place over time, during which an organism s tissues are replaced by hard minerals. Because most living tissues decay rapidly, only a very few organisms are preserved as fossils. Fossils are found most frequently in sedimentary rock. Hardened layers of sediments make up sedimentary rock. Sediments contain particles of clay, sand, mud, or silt Sea Reptile Along the cliffs near Lyme Regis, England, 12-year-old Mary Anning discovered the fossilized remains of the giant sea reptile now called Ichthyosaurus. Mary became one of England s first professional fossil collectors Dinosaur Tooth In a quarry near Lewes, England, Mary Ann Mantell discovered a strange-looking tooth embedded in stone. Her husband Gideon drew the picture of the tooth shown here. The tooth belonged to the dinosaur Iguanodon For: Links on fossils Visit: Web Code: scn-0235 Download a worksheet that will guide students review of Internet resources on fossils.

3 How do sediments build up into layers? Have you ever washed a dirty soccer ball and seen sand and mud settle in the sink? If you washed a dozen soccer balls, the sink bottom would be covered with layers of sediments. Sediments build up in many ways. For example, wind can blow a thick layer of sand onto dunes. Sediments can also form when muddy water stands in an area for a long time. Muddy sediment in the water eventually settles to the bottom and builds up. Over a very long time, layers of sediments can be pressed and cemented together to form rock. As sedimentary rock forms, traces of living things that have been trapped in the sediments are sometimes preserved as fossils Bird Bones A worker in a stone quarry in Germany found Archaeopteryx, a feathered, birdlike animal that also had many reptile characteristics. How does sedimentary rock form? 1902 Tyrannosaurus A tip from a local rancher sent Barnum Brown, a fossil hunter, to a barren, rocky area near Jordan, Montana. There Brown found the first relatively complete skeleton of Tyrannosaurus rex. Research and Write If you could interview the person who discovered one of the fossils, what questions would you ask about the fossil and how it was found? Write a list of those questions. Then use reference materials to try to find the answers to some of them Dinosaur Eggs in China Digging beneath the ground, a farmer on Green Dragon Mountain in China uncovered what may be the largest nest of fossil dinosaur eggs ever found. A paleontologist chips carefully to remove one of the eggs from the rock Deinonychus In Montana, paleontologist John Ostrom discovered the remains of a small dinosaur, Deinonychus. This dinosaur was probably a predator that could move rapidly. This fossil led scientists to hypothesize that dinosaurs may have been endotherms. Focus Help students relate these major events in vertebrate paleontology to other events in world history. Teach Have students reproduce the timeline without the descriptive paragraphs, and then add the following major events in world history: The signing of the Declaration of Independence (1776) The end of the Civil War (1865) The end of World War II (1945) The first moon landing (1969) The breakup of the Soviet Union (1991) Extend News of paleontological discoveries is often reported in newspapers. Ask students if they have read of recent discoveries that they might include on the timeline. Suggest discoveries made in China since 1996 of feathered dinosaurs that might represent an intermediate form between dinosaurs and birds. Writing Mode Research Scoring Rubric 4 Includes at least four questions that show an understanding of lesson content; answers are correct, detailed, and complete 3 Includes two or three questions; answers are correct and complete 2 Includes two questions; most answers are correct and complete 1 Includes only one question or answers are incorrect and incomplete Differentiated Instruction Less Proficient Readers Following the Time Line Have students needing a review of the text to write down the dates on the timeline, leaving room for notes. Then have students listen to the Student Edition on Audio CD and record events occurring in each year noted. learning modality: verbal Monitor Progress Writing Have students write paragraphs describing how sedimentary rock is formed. Students can save their paragraphs in their portfolios. Answer Particles of clay, sand, mud, or silt settle from the action of wind or water. The layers are pressed and cemented together over a long time.

4 Interpretation of Fossils Teach Key Concepts Examining the Fossil Record Focus Tell students that scientists learn about how organisms change over time and how they are related to one another by studying fossils. Teach Direct students to Figure 27. Ask: Are mammals more closely related to fishes or to amphibians? (Amphibians) Which groups of vertebrates arose from reptiles? (Mammals and birds) Apply Ask: What vertebrate fossils would be found in sediments 350 million years old but not in sediments 450 million years old? (Remains of amphibians) learning modality: visual Transparency B33 Understanding Sedimentary Rock Formation Materials plastic jar with lid, marbles, pea gravel, sand, powdered clay Time 10 minutes Focus Help students understand how sedimentary rock forms and traps fossils. Teach Students will simulate the effect of moving water on different sizes of rocks. Have students half-fill the jar with the pebbles, gravel, sand, and clay, which represent different-sized rocks. Have them then fill the jar, fasten its lid securely, and shake it until the solid contents are suspended. Then they should quickly set the jar down and record the order in which the materials settle to the bottom. (Pebbles first, then the gravel, then the sand, then much later, the clay) Apply Ask: What is the relationship between the size of the rock and the length of time it takes to settle? (The larger the rock, the faster it settles.) learning modality: kinesthetic FIGURE 26 Layers of Fossils Fossils most often form in layers of sedimentary rock. Interpreting Diagrams Which rock layer probably contains the oldest fossils? Differentiated Instruction Gifted and Talented L3 Identifying Fossil Ages Challenge students to use library and Internet resources to investigate the actual processes that go into determining the ages of fossils, either by interpreting layers of sedimentary rock or carrying out radioactive dating. Students investigating fossil dating through examining sedimentary rock layers should Interpretation of Fossils What information can scientists learn from fossils? Paleontologists (pay lee un TAHL uh jists), the scientists who study extinct organisms, examine fossil structure and make comparisons to present-day organisms. By studying fossils, paleontologists can infer how animals changed over time. One important piece of information that paleontologists can learn from a fossil is its approximate age. A Fossil s Age One method for estimating a fossil s age takes advantage of the process in which sediments form. Think about sediments settling out of water the lowest layers are deposited first, and newer sediments settle on top of the older layers. Therefore, fossils in higher layers of rock are often younger than fossils in lower layers. However, rock layers can become tilted or even turned upside down by events such as earthquakes. So, a fossil s position in rock is not always a good indication of its age. Scientists usually rely on other methods to help determine a fossil s age. For example, fossils and the rocks in which they are found contain some radioactive chemical elements. These radioactive elements decay, or change into other chemical elements, over a known period of time. The more there is of the decayed form of the element, the older the fossil. Using Fossils Paleontologists have used fossils to determine a likely pattern of how vertebrates changed over time. You can see in Figure 27 that this pattern of vertebrate evolution looks something like a branching tree. Fossils show that the first vertebrates to live on Earth were fishes. Fishes first appeared on Earth about 530 million years ago. Amphibians, which appeared on Earth about 380 million years ago, are descended from fishes. Then, about 320 million years ago, amphibians gave rise to reptiles. Both mammals and birds, which you will learn about in Chapter 4, are descended from reptiles. Based on the age of the oldest mammal fossils, mammals first lived on Earth about 220 million years ago. Birds were the latest group of vertebrates to arise. Their oldest fossils show that birds first appeared on Earth 150 million years ago. What is a paleontologist? prepare a visual display of the types and ages of fossils that could be found in rock layers in their area. Students exploring the details of radioactive dating should choose an example of a famous fossil whose age has been determined this way such as an important dinosaur find and provide a display presenting the steps involved in the technique. learning modality: visual

5 FIGURE 27 The pattern of vertebrate evolution is branching. Based on fossils, the first vertebrates, the jawless fishes, arose about 530 million years ago. Interpreting Diagrams Which is the latest group of vertebrates that appeared on Earth? First vertebrates Present 5 Section 5 Assessment Pattern of Vertebrate Evolution Millions of Years Ago Target Reading Skill Asking Questions Use your graphic organizer to answer the questions below. Reviewing Key Concepts 1. a. Identifying Where are fossils most often found? b. Describing What are some types of fossils? c. Inferring How might a small fish that dies in a muddy pool become a fossil? 2. a. Reviewing What can be learned from studying fossils? b. Summarizing How does the measurement of radioactive elements help scientists calculate a fossil s age? c. Interpreting Diagrams Look at Figure 27. About how much time passed between the first appearance of vertebrates and the time birds appeared? Mammals Birds Reptiles Amphibians Bony Fishes Cartilaginous Fishes Jawless Fishes Sedimentary Newspaper? If your family keeps newspapers in a stack, check the dates of the newspapers in the stack with a family member. Are the newspapers in any kind of order? If the oldest ones are on the bottom and the newest are on the top, you can relate this to the way in which sediments are laid down. Ask family members to imagine that two fossils were trapped in different newspapers. Explain which fossil would probably be older. Monitor Progress Answers Figure 26 The lowest layer should contain the oldest fossils because it was deposited before the other layers. Figure 27 Birds A person who studies extinct organisms, examines fossil structure, and makes comparisons to present-day organisms. Assess Reviewing Key Concepts 1. a. Sedimentary rock. b. Some fossils are imprints, such as a footprint, and some are remains of parts of living things. c. The fish is covered with mud and is buried. Over many thousands of years, the tissues are replaced with minerals. 2. a. How organisms change over time b. Scientists measure the ratio of decayed chemical element to non-decayed chemical element to find out a fossil s age. c. 380 million years Reteach On the board draw a rough sketch of layers of sedimentary rock. Have students use the information in Figure 27 to place vertebrate fossils in their correct order. Performance Assessment Organizing Information Have students draw flowcharts that show the stages in the making of a fossil. Students can save their flowcharts in their portfolos. Section Summary: Vertebrate History Review and Reinforce: Vertebrate History Enrich: Vertebrate History Sedimentary Newspaper? Ask: What could you conclude if the newspapers in the top layer were older than those in the bottom layer? (Something must have disturbed the stack.) How is this similar to what can happen to rock layers? (Rock layers can be disturbed by natural events so that their original order is altered.) learning modality: verbal