Your turn!
Now open the Ötzi Learning Tool and work through the experimental data to come to your own conclusions about where you think Ötzi lived. Then, reflecting back
on what you have learned in this key idea and taking into consideration your experience with the learning tool, answer the following questions.
Which isotopes were used to locate Ötzi's home? Which of these were stable isotopes and which were radiogenic?
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Using 18O values and Sr/Pb ratios scientists were able to locate the water source and geological area that Ötzi lived in. 18O is a stable isotope and the Sr/Pb ratios came from radiogenic isotopes, which are also stable.
Why do oxygen isotope ratios in water molecules vary and how does this make them useful in these types of forensic analyses?
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Oxygen isotope abundance in water molecules varies based on altitude and distance inland because water molecules with heavier isotopes (2H and 18O) precipitate continuously as an air mass moves inland or to higher elevations. As a consequence, the remaining moisture is progressively depleted in the heavy isotopes. Therefore, water sources at higher altitudes and areas further inland have relatively fewer 18O atoms and more 16O atoms within the water molecules. Comparing the relative amounts of 18O and 16O atoms gives us a ratio that can be used to trace these isotopic variations. This ratio is reflected in Ötzi's body, as the water he drank was deposited in his bones throughout his adult life. Since the mountainous area he lived in has large altitude variations, 18O/16O values varied substantially and were very useful in narrowing down where he lived.
Why do strontium and lead isotope ratios vary and how does this make them useful in these types of forensic analyses?
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Strontium and lead have radiogenic isotopes whose abundance varies based on age. Over time, the radioactive isotopes of these elements decay, and so measuring the amount of decay products (the radiogenic isotopes) can tell us how old they are. Different geological areas have different characteristic ages and therefore different ratios of strontium and lead isotopes. Using the strontium and lead values that were deposited in Ötzi's body while he was alive gives us important clues in narrowing down which geological area he lived in.
When you worked to locate Ötzi's home did you come to an definitive conclusion? Consult the Adapted Paper. How definitive was the conclusion
reached by the original team of scientists? What questions were unanswered?
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The paper suggests many possibilities and assigns a greater likelihood to some. However, it directly states that it is easier to exclude incompatible sites than to make definitive positive assignments, and it does not arrive at a single conclusion. This kind of result is common in scientific work because the nature of experimentation usually makes it easier to find support for a particular hypothesis or to disprove another, rather than to provide definitive proof for one.
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