How does Mount Etna help to tell the time? Introduction for Teachers It is very difficult for pupils to grasp the extent of geological time and the rate at which some landforms and landscapes take to form. This activity/exercise is in an attempt to use the real history of the ways in which geologists and physical geographers began to understand time as an accessible approach to grasping tricky concepts and timescales. It simulates how Charles Lyell worked out a secret of the volcano and what it told us about deep time and how to work out how long it takes to form physical landscapes. It allows pupils to use simple numeracy whilst solving a physical geography problem rather than solely relying on description of visual images or sorting/ordering information. The worksheet and approach has been tried with pupils of all abilities in Y9, Y10 & Y11 classes. Most pupils can get something from it, although some can find even the kind of basic arithmetic used in the exercise very difficult and need help and support. A calculator helps (on tablets, ipads or smartphones) and an IWB demonstration of how to do the sums is often appropriate before the exercise is completed. The figures used for the calculations are very rough, and the answer is not necessarily comparable with any real estimate of the age of Etna. The principle(s) of how to begin to work out/estimate the age of something is the important idea and the activity gets pupils thinking about what we might look for, think about and need to work out to discover the age of the Earth s physical features and the rate they change over (geological) time. The activity might be extended to a discussion on how calculations might be useful in determining weathering/erosion rates and might be used for other estimates of the formation of landforms/landscapes - tied in with rates of uplift, age of mountain ranges and plate tectonic processes Teacher Note: Lyell s Conclusions 1. Hardly any difference could be seen between modern animals and those living several million years ago. 2. Even the oldest volcano in Europe could not go back into deep time any appreciable distance. 3. The succession of rocks with fossils of very different animals, as recorded by Smith and Cuvier, must therefore, go back in time many millions of years. 4. Lyell had shown that the Earth must be very old indeed. A significant consequence of Lyell s proof of time. Charles Darwin read Lyell s books (The Principles of Geology) when he was on his famous voyage around the world. When he returned the two became great friends. One significant consequence of Lyell s principles and his proof that the Earth must be very old was that it provided the length of geological time Darwin needed for him to argue and explain how evolution had taken place in his great book The Origin of species. ACKNOWLEDGEMENT This investigation is based on an original exercise by Peter Whitehead of Bluecoat School Walsall, using the work of Wadge, G., Walker, G and Guest, J. (1975) The output of the Etna volcano. Nature 255, pp. 385-387 (May issue).
How does Mount Etna help to tell the time? Instruction sheets Image source: Gitta Dodt via http://scitechdaily.com/italian- volcano- etna- has- its- third- eruption- of- 2012/ About two hundred years ago, the same brilliant discovery was made by two different men in two different places. William Smith (a canal engineer in England) and Georges Cuvier (a biologist in France) had both been looking at layers of rocks (which they called strata ). They recognized that different layers each contained a distinctive set of fossils. They found that the fossils in the topmost strata were of similar types to living creatures and plants but the lower the position of the rock layer in the sequence the more primitive the fossils became. A simple sequence of rock strata that illustrates how fossils can be used to detect the position of a rock layer in the sequence. This meant Smith and Cuvier could establish the sequence of rocks, they could match up rocks of the same age over great distances, and also give a general order of events in the Earth's history (see diagram above). However the question remained - how long was the time involved in the formation of the whole sequence of rocks? This was a very important question - but no- one had an idea of how to answer it accurately.
In 1828 Charles Lyell (a real rock celebrity in the 1800s) set himself the task of trying to get an answer to this puzzle and thought he would do this by applying geological principles and using simple logical arguments. Charles Lyell painted by Alexander Craig in 1840 He decided he needed to find some feature or process of the Earth that changed at a measurable rate and that appeared to have been operating for a very long time. He chose volcanic eruptions, since these happen at regular intervals. Where, he asked himself, was there one place on earth where such eruptions had been happening for a long time? The largest single pile of volcanic material in Europe was Mount Etna on Sicily, so this seemed a good choice. So Lyell set off for Sicily in the south of Italy. Once there, he found that Etna was a volcano 3 km (3000 metres) high and roughly circular in plan, having a radius of about 25 km (see the diagram below). Lyell knew that volcanic eruptions are well- recorded events, because of the effect they have on everyday life, so he put together records of all the eruptions of Etna since Roman times.
Mt Etna : Map showing distribution of lava flows from A.D. 1300 2009 Source: http://boris.vulcanoetna.it/etna_news.html He found that on average there have been 5 eruptions every century in that time. He also found that on average each eruption produced a lava flow 10 km long, 1 km wide and 2 m deep. (Remember that 1 km = 1000 m). We can follow Lyell s method to see how he tried to solve the puzzle of how many years it had taken for all the physical features and rock layers in Earth s history to be formed. From what he knew about Mount Etna, he asked a series of questions. You can be Charles Lyell by working out the answers and reaching conclusions. Drawing of Mount Etna by Charles Lyell, in Principles of Geology Volume 3, 1833
How does Mount Etna help to tell the time? - THE QUESTIONS Question 1. What volume of lava is produced in an average eruption of Etna? Give your answer in cubic kilometers i.e. km 3. Question 2. What volume of lava has been produced by Etna in an average century? Give your answer in km 3. Question 3. What volume of lava has been produced by Etna in the 2000 years since Roman times? Give your answer in km 3. Lyell saw that the whole mountain was made of the products of volcanic eruptions, and assumed that it must have been built up at more or less the same rate since eruptions first began (the principle that the present is the key to the past). Lyell also saw that the total volume of material erupted since Roman times is very small compared with the total volume of the whole volcano. Therefore, the first eruption must have happened long ago. Question4. Using the information in the Introduction, calculate the volume of Etna. Assume the mountain is a simple cone, and use the formula: V = ⅓ π r 2 h where V is the volume of the cone, r the radius and h the height, and take the value of π as 3.20. Show your working. Question 6. Using your answers to Q.3 and Q.4. calculate how long it has taken for Mount Etna to build up to its present size. Next.Charles Lyell needed to fit this result into the rock sequence, the formations and geological time scale; he needed to know during which geological period the eruptions started. He surveyed the whole of the area trying to find the lowest lava flow. He looked for beds of sedimentary rocks below this lowest flow, because he needed to find fossils in these beds, which must be slightly older than the oldest lava of Etna because they are lower in the rock sequence. Lyell eventually found limestones just below the lowest lava. He matched the fossils in the limestone to the geological column (see diagram below) as belonging to the Tertiary period.
Geological column - showing the rock sequence, typical fossils found in particular layers and the names of the geological periods. However Lyll noted that the fossil shells in the limestone were all almost identical with the shells of animals still living in the Mediterranean! Question 7. What can you conclude about the time needed to go down the geological column? Think about what you have discovered and what conclusions you think Lyell reached? Make a list of your conclusions. Remember that Lyell was very logical so your conclusions should be in a sequence that establishes clearly what you have found, with one point leading to the next. Once you have written your conclusions you can compare with Lyell s actual conclusions you can obtain copy from your teacher.