Name: LAB: The Geologic Time Scale

Transcription

1 Name: LAB: The Geologic Time Scale INTRODUCTION: It is difficult to comprehend the age of the Earth and the time that various geologic events occurred in the past. A model drawn to scale is often useful in visualizing accurate time spans between events. OBJECTIVE: You will construct a model time scale illustrating some previous geologic/natural events. You will also compare the length of man s existence to the span of geologic time, and to compare the relative lengths of major geologic time periods. MATERIALS: tape; metric ruler; 5 sheets of unlined white computer paper or 4.6 meter length of adding machine tape; scissors; colored pencils (blue, green, yellow, red) and activity sheet. PROCEDURE: 1. If you are using adding machine tape, go to #3. If not, follow these instructions: a. Cut each sheet of unlined paper into four strips ~28cm long by 5 cm wide. b. Each sheet should make four strips of this size. c. When you have cut all four sheets, you will need seventeen strips of paper. 2. Tape the short ends of each strip together to form one long strip which is about 4.6 meters in length. 3. Using a metric ruler, mark and label the following millimeter measurements on the long strip of paper: 1, 50, 65, 100, 200, 225, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, Each millimeter represents one million years on your time line. 4. Draw a green line down the middle of your timeline from 0 mm to 65 mm. Label this time period the Cenozoic Era. Notice that this era lasted 65 million years. 5. Draw a blue line down the middle of your timeline from 65 mm to 251 mm. Label this time period the Mesozoic Era. Notice that this era lasted 186 million years. 6. Draw a yellow line down the middle of your timeline from 251 mm to 542 mm. Label this time period the Paleozoic Era. Notice that this era lasted 291 million years. 7. Draw a red line down the middle of your timeline from 542 mm to 4600 mm. Label this time period the Precambrian Era. Notice that this era lasted 4058 million years (4 billion, 58 million years). 8. Cut out each of the rectangles with the life forms from the Activity Sheet. Tape each rectangle to the correct place on the timeline. Be sure to measure the millimeters using the metric ruler. Remember that each millimeter represents one million years. (Note - Sometime you will have to overlap the rectangles because the event or life form may have appeared at the same or close to the same time.)

2 DISCUSSION QUESTIONS: Answer using data from the timeline constructed and your Earth Science Reference Tables. 1. Which era is the present one? 2. Which era lasted the longest time? 3. In which era did dinosaurs live? 4. In which period did fish first appear? 5. In which period did birds first appear? 6. In which period/epoch did Pangea break up? 7. At the end of which period did Trilobites become extinct? 8. During which period/epoch did humans first appear? 9. Dinosaurs became extinct at the end of which period? 10. On what basis is the geologic time scale developed? CONCLUSION: How does the length of time humans have existed on earth compare with the length of time life has existed on Earth and the age of the Earth? Reading Comprehension: Read the portion of the article on the development of the geologic time scale below and answer the following questions based on the reading. Use complete sentences. The Geologic Time Scale in Historical Perspective What is the origin of the geologic time scale? The first people who needed to understand the geological relationships of different rock units were miners. Mining had been of commercial interest since at least the days of the Romans, but it wasn't until the 1500s and 1600s that these efforts produced an interest in local rock relationships. By noting the relationships of different rock units, Nicolaus Steno in 1669 described two basic geologic principles. The first stated that sedimentary rocks are laid down in a horizontal manner, and the second stated that younger rock units were deposited on top of older rock units. To envision this latter principle think of the layers of paint on a wall. The oldest layer was put on first and is at the bottom, while the newest layer is at the top. An additional concept was introduced by James Hutton in 1795, and later emphasized by Charles Lyell in the early 1800s. This was the idea that natural geologic processes were uniform in frequency and magnitude throughout time, an idea known as the "principle of uniformitarianism".

3 Steno's principles allowed workers in the 1600s and early 1700s to begin to recognize rock successions. However, because rocks were locally described by the color, texture, or even smell, comparisons between rock sequences of different areas were often not possible. Fossils provided the opportunity for workers to correlate between geographically distinct areas. This contribution was possible because fossils are found over wide regions of the earth's crust. For the next major contribution to the geologic time scale we turn to William Smith, a surveyor, canal builder, and amateur geologist from England. In 1815 Smith produced a geologic map of England in which he successfully demonstrated the validity of the principle of faunal succession. This principle simply stated that fossils are found in rocks in a very definite order. This principle led others that followed to use fossils to define increments within a relative time scale. What do the divisions of the geologic time scale signify? The history of the earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are eon, era, period, epoch, age. The Phanerozoic Eon represents the time during which the majority of macroscopic organisms, algal, fungal, plant and animal, lived. When first proposed as a division of geologic time, the beginning of the Phanerozoic (approximately 543 million years ago) was thought to coincide with the beginning of life. In reality, this eon coincides with the appearance of animals that evolved external skeletons, like shells, and the somewhat later animals that formed internal skeletons, such as the bony elements of vertebrates. The time before the Phanerozoic is usually referred to as the Precambrian, and exactly what qualifies as an "eon" or "era" varies somewhat depending on whom you talk to. In any case, the Precambrian is usually divided into the three "eras" shown. The Phanerozoic also consists of three major divisions...the Cenozoic, the Mesozoic, and the Paleozoic Eras. The "zoic" part of the word comes from the root "zoo", which means animal. This is the same root as in the words Zoology and Zoological Park (or Zoo). "Cen" means recent, "Meso" means middle, and "Paleo" means ancient. These divisions reflect major changes in the composition of ancient faunas, each era being recognized by its domination by a particular group of animals. The Cenozoic has sometimes been called the "Age of Mammals", the Mesozoic the "Age of Dinosaurs" and the Paleozoic the "Age of Fishes". This is an overly simplified view, which has some value for the newcomer but can be a bit misleading. For instance, other groups of animals lived during the Mesozoic. In addition to the dinosaurs, animals such as mammals, turtles, crocodiles, frogs, and countless varieties of insects also lived on land. Additionally, there were many kinds of plants living in the past that no longer live today. Ancient floras went through great changes too, and not always at the same times that the animal groups changed. 1. Why would miners have an interest in the order of rock layers? 2. When first making a time-scale, why did scientists first place the Phanerozoic Eon where they did? 3. What determines the divisions between the Cenozoic, Mesozoic, and Paleozoic Eras?

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5 ACTIVITY SHEET Early Land Plant 420 million Late Ammonite 100 million Brontosaurus 150 million Early Fish 500 million Early Pine Tree 240 million Bird 150 million Early Ferns 300 million Woolly Mammoth 1 million Trilobite 500 million Tyrannosaurus Rex 66 million Algae 3000 million Early Angiosperm 80 million Early Human 1 million Modern Humans 0 million Brachiopod 450 million Early Amphibians 350 million Early Horse 50 million Early Reptile 260 million