Tar is a derivative of a variety of organic material, commonly consisting of small animals and plants, decomposed by high temperatures and limited exposure to oxygen. This process is referred to as destructive distillation.
Over time, layers of accumulated organic material compressed into what are known as petroleum-rich rocks. Only certain types of porous rocks, including shale, limestone and sandstone, possess tar deposits. The La Brea Tar Pits, located in Los Angeles, are among some of the most famous tar seepage pits in the world. Tar is a mixture of hydrocarbons and free carbons and features a distinctive black color and thick, sticky texture.
Wood tar has a long history dating back to ancient Greece, where it was used as a water repellent for roofs, boats and ships. Pine-derived tar played a considerable role in the development of the Northern European economies, with the largest demand source being the Royal Navy. Demand for pine-tar sealed ships decreased with the advent of iron and steel vessels. In the modern era, tar is commonly used as a color additive to foods, candy and alcohol. It is also used as an anti-dandruff agent in shampoos and is a common component of many types of cosmetics.