Looking+at+Sedimentation

= Looking at Sedimentation = People have always been interested in how the Earth was made, and how the Earth changes through time. Scientists look at how rocks are made, and how they change, and the processes which affect the way the Earth looks and how its systems work. Sedimentation is proces by which small particles of rock are deposited in water and how this then leads to the formation of new rocks. Scientists want to know how this happens, and o understand how new rocksare formed. Scientists have been studying this for a long time, and the study still continues today. In 1669, Nicolaus Steno looked at sediment settling in water. He saw that the sediment settled in horizontal bands, called layers, and that layers could form on top of each other. This meant that the layers on the bottom would be older than the layers on the top. He used his observations to explain what would happen in an ideal system - what would happen if sedimentation happened with nothing to disturb it while it was happening, and if nothing disturbed it afterwards. In reality, sediements are usually disturbedat some point, during or after deposition. Natural processes like earthquakes can affect them, and humans can affect them too, by digging and building, for example. All these processes affect how the Earth looks, and scientists try to understand them, too. Much later, in 1815, William Smith published a geological atlas of England and Scotland, in which he recorded all the different types of rock in those countries. He also noticed that the fossil in sedimentary rock could be used to say how old different rocks were. He could also look at the fossils in rocks and see if they were the same n different places. Where he found the same fossils in rocks from different places, he knew that the rocks were the same age. This is called biostratigraphy. //Activity// This activity lets you recreate some of Steno's and Smith's findings. The activity is in two parts. 1. Describing how sedimentary rock is formed in water. Using a large tank, sediment is poured into water. At this point, observations can be made about how the sediment behaves – how it falls, that it fits the container, any observations about different grain sizes. Learners can then feedback any answers in small groups and as a whole group, so that observations can be shared. In this way, everyone has the same information, and learners are able to get insights from other learners that they may not have seen themselves. Following this, another, different coloured sand is added to the tank. Learners should now make observations about this layer. Many learners may consider that only the same observations will apply; however, they could consider the differences between the two layers. Asking, at this point, which layer is older – which one settled first? This process should make it clear that 'obvious' statements are not necessarily obvious and needed to be thought about. It also allows a discussion of empirical observation as a basis for hypothesis forming. 2. From the previous activity, you can move forward in time. William Smith had a fascinating life and career. He described the geology of England and Scotland (4), and laid down the principles for using fossils to tell how old different layers are. Fossils can also be used to match up layers all over the country, and even all over the world. A way to investigate this further is to use excavation of sediment and matching up layers based on the fossils found there. This can be modelled using margarine tubs prepared with different coloured layers of sand with different shells or fossils in it. Learners excavate the sediment in the tubs, numbering the layers from the top, recording what they find in each layer. They are then given a key of the shells or fossils with an age range for each type. From this they can put together a chronology of their margarine tub. If the tubs have different (but consistent) layering, learners can compare the records, and find equivalent layers. This leads into the work of geologists, what they do and why they'd want to. This introduces key figures and key principles, without neglecting the required content for the National Curriculum. It also allows the teacher to emphasise how Smith's work followed on from Steno's.