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Geological changes - revision notes

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* Weathering * Rocks * Earth's Structure Tina Doyle Weathering There are 3 main types of weathering: Physical, Chemical and Biological. * Freeze-thaw weathering - this occurs when rain water seeps into cracks in rocks and if the temperature drops below freezing, the water turns to ice and expansion pushes the rocks apart. This keeps happening each time the water thaws and refreezes. Eventually bits of the rock break off. * Acid rain - this is caused by pollution from the burning of fossil fuels being dissolved in it. Limestone is a very alkaline rock so it is quickly attacked by any acid. It also contains a lot of calcium carbonate. This dissolves in cold rain water to make calcium hydrogen carbonate solution. This reaction is shown in the equation below: Calcium carbonate + Carbonic acid Calcium hydrogen carbonate solution As rain water trickles through cracks in the limestone over many years it can dissolves millions of tonnes of rocks to make huge caves. ...read more.


Weathering breaks rocks, erosion wears them away. Rocks Rocks There are 3 main types of rock: Igneous (intrusive & extrusive), Sedimentary and Metamorphic. Name of Rock Type How it's type is made How we recognise the rock by observation Basalt Igneous Formed underground by lava flow dark-coloured (black to medium-grey) Mudstone Sedimentary Formed from mud Often dark grey, splits into layers easily Marble Metamorphic Metamorphosed limestone and chalk Very hard Limestone Sedimentary Composed almost entirely of calcium carbonate Hard, solid rock Granite Igneous Formed underground when magma cools down Hard, coarse and grained Slate Metamorphic Metamorphosed shale Very hard black layered rock Sandstone Sedimentary Made of sand-sized particles Red or yellow Fossils are only found in Sedimentary rocks, because these rocks have been crushed for millions of years, so the fossils can survive. ...read more.


* Volcanoes - these appear in some areas when tectonic plates move apart. Magma rises up to fill the gap and produces new crust made of basalt. Sometimes it comes out with great force, producing volcanoes. Rock Record The rock record, (type, magnetic and fossil) shows the sequence of and evidence for geological changes. Rock layers are also called strata (the plural form of the word stratum), and stratigraphy is the science of strata. Stratigraphy deals with all the characteristics of layered rocks; it includes the study of how these rocks relate to time. Strata, or compacted layers of sediment, deposited in the sedimentary basins of New Zealand provide the raw data from which much of geological history is deduced. Conditions of deposition, the 3-dimensional shape and the distribution of layers of sedimentary rocks are the subject of current research. Much of this work is oriented to exploration for hydrocarbons and other energy resources. ?? ?? ?? ?? ...read more.

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