Millions of years ago, dense forest and animal got buried under the soil due to natural process like floods, earthquakes and thunder storms. When they got buried deep in the soil, they were exposed to very high pressure and temperature. Under these conditions, these slowly got converted into coal. This process of formation of coal vegetation is called carbonization. 

About 300 Millions Years Ago.The Earth has dense forest In low lying wet land areas.Due to natural process like earthquake,flood,tsunami etc these forest got buried under the soil as more soil deposited over them they compressed.Under High Temperature and High Pressure.They Become Dead VegetationThe process of conversion of dead Vegetation into coal is termed as carbonisation.This Lead to formation of caol
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Millions of years ago various creatures roamed the surface of this earth. Some of these creatures have become extinct, while there are some which still exist today. So where did all these creatures go when they became extinct? Some of them made their way to the ocean after their dead and sunk thousands of feet below to finally settle on the seabed. Both plants and animals settled on the seabed after their death. In the due course of time, they decomposed and combined together with the silt and the sand that make up the seabed. This decomposition process brought up certain chemical changes in the organic compound with the help of bacteria that are found in the seabed which resulted in large quantities of hydrogen and carbon compounds being left behind. Due to the dearth of oxygen in the seabed, the decomposition process was however not complete and with the passage of time more and more silt and sand came to be deposited on the top of this semi-decomposed matter. Due to many geological formations, there was a rise of intense heat and pressure due to which this matter was able to decompose properly and thus was formed what is today known as crude oil or the rawest form of petroleum. Since not, all the places of the seabed are subjected to the same decomposition pattern and geological formations and changes, so no formation of petroleum takes place only in certain places around the world.
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