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Organic rocks and fossil fuels
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Organic rocks and fossil fuels


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Its really informative and can help you in completing last minute projects.

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  • 1.   Organic or biological sedimentary rocks are formed by living organisms, typically when the remains of living organisms build up and are compacted by sediment. Coal, for example, is made from long-dead vegetation crushed by thick layers of sediment and chemically altered through heat and pressure. Most limestone deposits are made from the shells of microscopic sea organisms. Coral reefs are a beautiful example of organic sedimentary rocks made by creatures that are still living -corals that build their own homes from calcium carbonate. Chemical sedimentary rocks, by contrast, form when conditions favor a chemical reaction or process that causes chemicals dissolved in water to precipitate, creating a layer of sediment. When water in a salty sea or lake evaporates, for example, it may leave behind salt and gypsum deposits. In calcium-rich waters, changes in temperature or acidity may cause calcium carbonate to precipitate. Accumulation of calcium carbonate deposits can lead to the formation of limestone. Sometimes magnesium in water that enters the pores of a limestone rock can replace the calcium in the rock, turning limestone into another chemical sedimentary rock called dolostone.
  • 2. The key difference between organic and chemical sedimentary rocks is  the process that forms them –  and often their texture,  composition and appearance bear mute witness to that process.  Geologists can determine whether a sedimentary rock is organic or chemical by looking at its texture.  Organic sedimentary rocks contain fossilized remains of living creatures, since it is these remains that accumulated to form the rock in the first place.  Chalk deposits, for example, often contain microscopic fossils. Salt deposits formed from evaporation, by contrast, usually contain a mixture of salts, just as you would expect in a rock that formed from the evaporation of a salty lake. 
  • 3. Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years.[1] Fossil fuels contain high percentages of carbon and include coal, petroleum, and natural gas.
  • 4.    There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs – hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon, the basic element in coal and other fossil fuels. The Carboniferous Period occurred from about 360 to 286 million years ago. At the time, the land was covered with swamps filled with huge trees, ferns and other large leafy plants, similar to the picture above. The water and seas were filled with algae – the green stuff that forms on a stagnant pool of water. Algae is actually millions of very small plants. Some deposits of coal can be found during the time of the dinosaurs. For example, thin carbon layers can be found during the late Cretaceous Period (65 million years ago) – the time of Tyrannosaurus Rex. But the main deposits of fossil fuels are from the Carboniferous Period.
  • 5.   This process is called "coalification." During coalification, peat undergoes several changes as a result of bacterial decay, compaction, heat, and time. Peat deposits are quite varied and contain everything from pristine plant parts (roots, bark, spores, etc.) to decayed plants, decay products, and even charcoal if the peat caught fire during accumulation. Peat deposits typically form in a waterlogged environment where plant debris accumulated; peat bogs and peat swamps are examples. In such an environment, the accumulation of plant debris exceeds the rate of bacterial decay of the debris. The bacterial decay rate is reduced because the available oxygen in organic-rich water is completely used up by the decaying process. Anaerobic (without oxygen) decay is much slower than aerobic decay. For the peat to become coal, it must be buried by sediment. Burial compacts the peat and, consequently, much water is squeezed out during the first stages of burial. Continued burial and the addition of heat and time cause the complex hydrocarbon compounds in the peat to break down and alter in a variety of ways. The gaseous alteration products (methane is one) are typically expelled from the deposit, and the deposit becomes more and more carbon-rich as the other elements disperse. The stages of this trend proceed from plant debris through peat, lignite, sub-bituminous coal, bituminous coal, anthracite coal, to graphite (a pure carbon mineral).
  • 6.  Oil and natural gas are formed from the remains of tiny aquatic animals and plants. These organisms, once dead, would have sunk to the bottom of the body of water they were living in, been covered in silt and mud, and then started to decay anaerobic ally. As such, it is reasonable to assume that the bodies of water that these micro-organisms were living in were fairly stagnant, as strong currents in water both improve aeration and prevent the laying down of very thick layers of organic material in the one location.
  • 7. In the graphic on the left, as the diatoms died they fell to the sea floor (1). Here they were buried under sediment and other rock (2). The rock squeezed the diatoms and the energy in their bodies could not escape. The carbon eventually turned into oil under great pressure and heat. As the earth changed and moved and folded, pockets where oil and natural gas can be found were formed (3). Natural gas is lighter than air. Natural gas is mostly made up of a gas called methane. Methane is a simple chemical compound that is made up of carbon and hydrogen atoms. It's chemical formula is CH4 – one atom of carbon along with four atoms hydrogen. This gas is highly flammable.