My Fossil s Older Than Your Fossil

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1 NAME: DATE: PERIOD: My Fossil s Older Than Your Fossil Nicely done! You have completed your first task as a paleontologist. You know how to compare morphology, or the shapes and structures of organisms that have been discovered using fossil evidence. Although there are some evolutionary gaps in the information that you received, you were able to hypothesize the evolution of the Tortugis species. By judging which animals evolved from the others, you have a general idea about which fossils are older. However, there are other ways to find out the age of fossils. Most fossils can be found in sedimentary rocks. One method of determining the age of fossils is by looking at the layer of sedimentary rock, or strata, in which the fossil is found. This is referred to as relative dating. The illustration below shows four rock layers and four fossils. Write the name of the organism next to the rock layer where it probably was found. Assume that these fossils are the oldest of their kind to be found, and they were found in the strata layer, which represents when these organisms first appeared on Earth. You have information about the timeline of Earth and you know the following facts about the fossils. The bone fossil is from the leg of a horse. The shell is a fossil of an early marine invertebrate. The fossilized leaf imprint is from part of a seed fern. The fish fossil is older than the fossilized leaf. 1. Which is the oldest fossil? 2. Where did you place the oldest fossil? Why?

2 PART III: Which Came First? Below is a diagram of the sedimentary rock formations where the Tortugis fossils were discovered. Below the diagram is a list of strata layers and fossil names. Each fossil name appears next to the number of the layer in which it was discovered. Use relative dating to determine the ages of the Tortugis fossils and redraw your evolutionary tree with the information you find. Stratum Fossil Name Number 1 Tortugis ancientis 2 Tortugis scalifiedis 3 Tortugis sliderni, Tortugis tortugis 4 Tortugis proboscis, Tortugis slugenii 5 Tortugis apodsis, Tortugis porkii, Tortugis spinalis 6 Tortugis molluskus, Tortugis predatoris Analysis: 1. Does the method of relative dating tell you the exact age of a fossil? What information does this method help you to find? 2. Explain why areas around rivers or streams or the sides of hills are good places to locate fossils. 3. What is erosion? How would it affect the technique of relative dating? 4. How would disruptions such as earthquakes or volcanic activity affect the technique of relative dating? 3. Why are fossils that are found in ice or in amber more useful for scientists? 4. In which layers were the most complex fossils located? Explain your answer.

3 NAME: DATE: PERIOD: My Fossil s Older Than Your Fossil You are a great paleontologist! So far, you have hypothesized the order in which the Tortugis species evolved by comparing the homologous structures of the fossils, then you used the strata layers to determine which fossil was older than which, but you still don t know exactly how old each fossil really is! To find the absolute age of fossils, scientists often use radiometric dating. This technique involves the use of radioactive elements. Certain elements have unstable nuclei that break down or decay over time. Although the decay of radioactive elements is steady, each element decays at a different rate. When a radioactive element decays, it doesn t disappear, it changes into another element. Scientists have learned the rate at which half of an element decays by measuring the amounts of both elements present at different times. If we know how long it takes for half of a substance to decay, then it will take that long again for half of what is left to decay. So a way of describing how fast a radioactive element decays is to give its half-life, or the length of time it takes for half of any sample to decay. Try this: Element Leydenium has a half-life of 1 week. The graph on the left is a representation of 256g of Leydenium. Each box in the left graph represents one gram of element Leydenium. Follow the steps below to find out how much Leydenium would decay over a 10-week period,. Grams of Leydenium The decay of Leydenium over a 10- week period 1. In the 1 st week, half of the element would decay. To show this on the grid, draw a large X through all of the boxes on the left half of the grid with a red color pencil. How many grams decayed in the first week? 2. In the next week half of the remaining grams of the Leydenium would decay. To show this on the grid, draw a large X through half of the remaining boxes with a different color pencil. How many grams of Leydenium decayed in the second week? The element Leydenium decays into the element Nomoneyium, how much Nomoneyium would there be after 2 weeks? 3. Repeat this process using different color pencils for each of the 10 weeks. 4. Make a line graph on the graph paper on the right that shows the decay of element Leydenium over a 10- week period. Don t forget to label the axes and title.

4 Part IV: How Old Is It? All living things contain the element carbon. Fossils that are less than 50,000 years old are radiometrically dated with Carbon-14. Once an organism dies, the Carbon-14 in their body begins to decay or break apart. The rate of this decay is constant; half of the remaining carbon-14 breaks down every 5,730 years. When Carbon-14 breaks down or decays, it forms Nitrogen-14. Scientists check the amount of radioactive Carbon-14 and the amount of Nitrogen-14 that is present in a fossil. Try This: There are 40 grams of Carbon-14 in an organism that has just died. The half-life of Carbon-14 is 5,730 years. In 5,730 years, there will be grams of Carbon-14 and grams of Nitrogen- 14. Write the ages of the fossils in the blanks at the right. 1. What fraction of the original Carbon-14 would remain after 22,920 years? 2. What fraction of the original Carbon-14 would remain after 28,650 years?

5 Part V: How Old Are They? The following data was collected when paleontologists used the technique of carbon dating to identify the age of the Tortugis fossils that were found. 1. Look at the Carbon-14 and Nitrogen-14 amounts in the second column. 2. In the third column, rank the Organisms from the most ancient (1) to the most recent (11). 3. Make any more necessary changes to your evolutionary tree. Tortugis species Amount of Carbon-14 Present RANK Tortugis ancientis Tortugis apodis Tortugis molluskus Tortugis porkii Tortugis predatoris Tortugis proboscis Tortugis scalifiedis Tortugis slidereni Tortugis slugenii Tortugis spinalis Tortugis tortugis Amount of Nitrogen-14 Amount of Carbon How old must an organism be in order for there to be no Carbon-14 remaining? 2. When is using a radioactive element most useful? 3. Which were the older fossils after Tortugis ancientis? How did you decide that? 4. Which method of dating fossils gives the best information? Support your answer with examples from this activity.