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CS_Ch10_Evolution 2/28/05 2:56 PM Page 647 Activity 5 Mass Extinction and Fossil Records Activity 5 Mass Extinction and Fossil Records GOALS What Do You Think? In this activity you will: Sixty-five million years ago the curtain came down on the age of dinosaurs when a catastrophic event led to their mass extinction. • Investigate fossil data for evidence of mass extinction and adaptive radiation. • Explain the meaning of mass extinction and adaptive radiation. • Describe the meaning of niche in an ecosystem. • What type of disastrous event could have led to the extinction of such a large group of animals? • Did any other life forms become extinct at this time in geological history? Write your answer to these questions in your Active Biology log. Be prepared to discuss your ideas with your small group and other members of your class. For You To Do In this activity, you will investigate fossil data from those “pages” that represent the boundary between the Cretaceous and Tertiary periods (about 65 million years ago). 1. Your teacher will divide the class into groups of three or four students. With the other members of your group, 647 Coordinated Science for the 21st Century CS_Ch10_Evolution 2/28/05 2:56 PM Page 648 A Highway Through the Past Cretaceous and Tertiary periods. Using a technique known as magnetostratigraphy, geologists infer that each meter of this sedimentary sequence represents 0.1 million years of history. The point “0 m” represents the boundary between the Cretaceous and Tertiary systems, 65 Ma (millions of years ago). Paleontologists sampled fossils from the locations shown along the left axis. examine the six brachiopod fossils. Brachiopods are a group of marine animals. Wash your hands after handling the fossils. a) Which species became extinct at the Cretaceous-Tertiary (K-T) boundary? a) What characteristics might paleontologists use to assign these fossils to different species? b) Which species evolved after the K-T boundary? b) What characteristics might paleontologists use to assign these fossils to one group? c) Which species appear to have become extinct and then reappeared later? 2. Now examine Graph A. It plots the ranges of 50 different species of brachiopods across 15 m of sedimentary rock at one location in Denmark. This is one of the few places in the world that contains a continuous record of layers that represent the boundary between the d) What conclusions can you draw from this graph? e) What are the limitations of the data shown in Graph A? (Hint: recall the processes by which fossils are preserved.) Graph A: Range of Different Species of Brachiopods meters 10 9 samples 8 49 50 Tertiary 424344454647 394041 35 3637 38 33 34 2829303132 6 5 4 3 27 2 1 0 Cretaceous Sedimentary Sequence 7 19 20 –1 121314151617 –2 –3 18 24 25 1011 –4 21 22 23 9 –5 1 2 3 4 5 6 7 8 648 Active Biology 26 48 CS_Ch10_Evolution 2/28/05 2:56 PM Page 649 Activity 5 Mass Extinction and Fossil Records Graph B: Number of Families of Marine Organisms through Time 800 Number of Families 600 400 500 400 300 200 Geologic Time (millions of years ago, Ma) 3. Paleontologists have compiled similar data on the ranges of existence of numerous other organisms during the Cretaceous and Tertiary periods. Examine Graph B, which shows a set of data assembled to illustrate the number of families (groups of closely related species) of marine animals through geological time. a) When was the number of families the greatest? b) Has the growth in the number of families been steady? Explain your answer. c) What do the dips in the graph represent? d) What inferences can you draw from this graph? e) What are the limitations of the graph shown in Graph B? 100 Quaternary 1.6 to 0 Ma Tertiary 65 to 1.6 Ma Cretaceous 144 to 65 Ma Jurassic 208 to 144 Ma Triassic 245 to 208 Ma Permian 286 to 245 Ma Carboniferous 360 to 286 Ma Devonian 408 to 360 Ma Silurian 438 to 408 Ma Ordovician 505 to 438 Ma 0 Cambrian 570 to 505 Ma 200 0 4. Now re-examine Graph B. Locate the times of the five greatest decreases in the number of families. Discuss why this might represent mass extinctions. Locate the times of the five greatest increases in the number of families. Discuss why this might represent adaptive radiations. (Adaptive radiation describes the rapid changes in a single or a few species to fill many empty functions in an ecosystem.) a) In your Active Biology log, construct a chart that summarizes your findings. Your chart should have two vertical columns, one labeled “Times of Mass Extinction” and the other labeled “Times of Adaptive Radiation.” Fill in the chart with the estimated date that each event began and the name of the time period (e.g., “beginning of the Devonian period, roughly 410 Ma”). 649 Coordinated Science for the 21st Century CS_Ch10_Evolution 2/28/05 2:56 PM Page 650 A Highway Through the Past 5. Now analyze Graph C, a graph constructed to show the number of families of terrestrial tetrapod families (land animals with four limbs) through geological time. Locate the greatest extinction events and adaptive radiations. Graph C: Number of Families of Terrestrial Tetrapods through Time 200 a) Compare these events to the events listed in your chart for Graph B. Propose a hypothesis to account for the differences and similarities in these two graphs. 400 300 200 100 Geologic Time (millions of years ago, Ma) Quaternary 1.6 to 0 Ma Tertiary 65 to 1.6 Ma Cretaceous 144 to 65 Ma Jurassic 208 to 144 Ma Triassic 245 to 208 Ma Permian 286 to 245 Ma 0 Carboniferous 360 to 286 Ma 100 Devonian 408 to 360 Ma Number of Families 300 0 6. Consider the pattern of extinction and adaptive radiation in Graph B and C. a) How might adaptive radiation be related to mass extinctions? (Hint: consider how life on Earth might be different if dinosaurs still existed.) Making Inferences in Science Have you ever wondered how scientists know so much about dinosaurs? No human ever saw a dinosaur eat or run.The huge lizards disappeared from Earth about 65 million years ago. No fossil evidence of the human species, Homo sapiens, appears before 500,000 years ago. The skeletons of dinosaurs have been reconstructed using fossil records.The skeletons provide indirect evidence of how the dinosaur might have lived. Evidence from the skull of a dinosaur may indicate that the dinosaur might have been a meat eater.The premise that this dinosaur killed other dinosaurs is called an inference. No one ever saw the dinosaur eating meat, the evidence to support this conclusion came from examining the skull shape and the structure of the teeth. Unlike a hypothesis, an inference cannot be tested. 650 Active Biology CS_Ch10_Evolution 2/28/05 2:56 PM Page 651 Activity 5 Mass Extinction and Fossil Records Mass Extinction and Adaptive Radiation Extinction is the total disappearance of a species. Extinction means that not a single organism of the species lives anywhere on Earth.The fossil record is a virtual graveyard of extinct species. It is strewn with the fossilized remains of millions of extinct species. David Raup, a paleontologist at the University of Chicago, notes that “only about one in a thousand species [that have lived on Earth] is still alive—a truly lousy survival record: 99.9 percent failure!” Even more striking, however, is the fossil evidence of mass extinctions.These are episodes during which large numbers of species became extinct during short intervals of geological time. In geological time a few million years or less is a short period! The extinction of one species often has a domino effect. If one species vanishes, so do many others.Yet mass extinctions can present new opportunities to survivors. Those best able to survive fill empty niches. (An ecological niche is the function a species plays in an ecosystem.) Plants and animals that have the greatest genetic variation are most often best able to fill these empty “spaces.” This process is called adaptive radiation. In this activity, you investigated evidence of mass extinctions and adaptive radiations by analyzing data from the fossil record. Rapid evolution can also occur when a species moves into a new area. Natural variation within a species makes it easier for the species to adapt to different environments. Bio Words extinction: the permanent disappearance of a species from Earth mass extinction: the extinction of a large number of species during short intervals of geological time niche: the ecological function of a species; the set of resources it consumes and habitats it occupies in an ecosystem adaptive radiation: the diversification by natural selection, over evolutionary time, of a species or group of species into several different species that are typically adapted to different ecological niches One remarkable mass extinction event occurred at the boundary between the Cretaceous and Tertiary periods, roughly 65 million years ago.This boundary separates the age of the reptiles and the age of the mammals. Geologists recognized this event over one hundred years ago when they realized that there was a striking change in the types of fossils deposited on either side of this boundary.This is where the language of science may become difficult to follow. However, no matter how it is said, the concepts are the same.This boundary 651 Coordinated Science for the 21st Century CS_Ch10_Evolution 2/28/05 2:56 PM Page 652 A Highway Through the Past also separates two eras.These two eras are called the Mesozoic and Cenozoic. Dinosaurs were prevalent during the Mesozoic Era and extinct during the Cenozoic Era.The last segment of the Mesozoic Era is called the Cretaceous Period.The first segment of the Cenozoic Era is called the Tertiary Period.The abbreviation for the boundary between the Cretaceous and Tertiary periods is often referred to as the K-T boundary, where K is the abbreviation for the Model of a Brachiosaurus. German form of the word Cretaceous. You may also hear of this time referred to the Mesozoic and Cenozoic boundary. No matter what you call it, there were dinosaurs before and there are no dinosaurs now, and it happened about 65 million years ago! Moreover, at the end of the Cretaceous period virtually all plant and animal groups were lost from Earth, not just the dinosaurs.Yet, the beginning of the Tertiary period marks the start of the adaptive radiation of mammals. The ultimate cause of the mass extinction at the Cretaceous/Tertiary boundary is still a debate among scientists. However, more and more evidence suggests that a meteorite impact caused the mass extinction. The impact of the meteorite created a chain of devastating environmental changes for living organisms. Reflecting on the Activity and the Challenge In this activity you had an opportunity to see that life forms that dominated the Earth many (geological) years ago are not here now. You also learned that the evidence to support this fact is found in fossil records. The new organisms that evolved to fill the ecological place of the extinct organisms are also part of fossil 652 Active Biology records. You probably have developed an even further appreciation of the importance of fossil records. You may wish to argue for a delay of construction of the new highway whether you represent the paleontologists or a concerned citizen. CS_Ch10_Evolution 2/28/05 2:56 PM Page 653 Activity 5 Mass Extinction and Fossil Records 1. Explain the meaning of adaptive radiation in your own words. 2. What evidence do scientists use to support the idea of mass extinctions? 3. After a mass extinction, which organisms are most likely to survive? Explain your answer. 4. Explain why the extinction of one species can have a domino effect on an ecosystem. Inquiring Further 1. The Cretaceous and Tertiary boundary event Research the proposed causes of the mass extinction during this time period. Provide at least two explanations. Which one do you think is more plausible? 653 Coordinated Science for the 21st Century