Crude oil is formed from the remains of dead sea plants and creatures that became buried in the sediments of the sea floor millions of years ago. Ancient humans used crude oil that they found as 'pitch'. This gathered as pools where oil bearing rocks were exposed at the surface of the Earth. They used this thick and gooey substance for waterproofing their huts and perhaps even on the planks they used to make their boats. Come the modern era things changed. After the discovery was made of how to drill for it, crude oil become one of the most useful resources that we take from the Earth's... Show more

Crude oil is formed from the remains of dead sea plants and creatures that became buried in the sediments of the sea floor millions of years ago. Ancient humans used crude oil that they found as 'pitch'. This gathered as pools where oil bearing rocks were exposed at the surface of the Earth. They used this thick and gooey substance for waterproofing their huts and perhaps even on the planks they used to make their boats. Come the modern era things changed. After the discovery was made of how to drill for it, crude oil become one of the most useful resources that we take from the Earth's crust.

Various methods of processing are required before any use can be made of crude oil. Oil straight from the ground is a complex mixture of many thousands of chemical compounds which, when separated, can be used in many ways - as fuels, for making plastics, for making medicines, and much more besides. The pitch used by early humans was processed by natural means - the volatile chemicals evaporated into the air leaving the less volatile chemicals behind as pitch. We still use pitch for making waterproof building materials like roofing felt and for gluing together small stones to make road surfaces.

Mixtures of liquids can be separated by distillation. This works only if the liquids have different boiling points. The chemicals in crude oil have a wide range of boiling points so the process of fractional distillation (or fractioning) is used. This process allows complex mixtures of liquids to be separated because of their different boiling points. To obtain even more useful products from the 'fractions' of oil, some of the chemicals are 'cracked'. Cracking involves using heat and a catalyst, or steam and very high temperatures, to break longer molecules into shorter ones that are more reactive and can be used as polymers.

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