The history of tar-pits dates back to millions of years ago. It was not until the 20th century that the excavation of tar-pits first started.
Tar-pits are pools of viscous asphalt. Large amounts of asphalt occur in concentrated form in tar-pits. This is formed by seepage from petroleum deposits when crude oil seeps to the surface through the fissures in the earth’s crust. The light fraction of the oil evaporates, leaving behind the heavy tar (asphalt) in sticky pools. Also known as Bitumen, asphalt is a highly sticky, black and viscous semi solid form of petroleum. It is what is left over after the lighter components of petroleum evaporate away. It is so sticky that it can even trap large animals.
The main application of asphalt or bitumen is for making asphalt concrete for road surfaces. Approximately 85% of the asphalt consumed in the United States is used for such road surfaces.