Explain how sedimentary rocks such as sandstone are formed [6 marks].

6 marks indicates that the marker is looking for a factual and concise answer, demonstrating knowledge of at least 6 stages, or facts in order to gain full marks. 6 marks, means approximately 6 minutes to answer the question, so the key to success is to be short and snappy. Sediment which is formed as a result of erosion from land and rock is carried by the sea and rivers. Layers of sediment are deposited on the seabed or riverbed, and build up. Over time, the weight of the layers means that layers below are compressed and compacted under the force of gravity. Under the pressure of the compression, air and water are squeezed out to form solid rock, sometimes shells and the remnants of animals are trapped in the layers, and in the rock can be seen as fossils.