Millions of years ago, oil shale was formed by deposition of silt and organic debris that are found on sea bottoms and lakebeds. Over extended periods of time, heat and pressure transformed the materials into oil shale in a process similar to the process that forms oil; however, the heat and pressure were not as high.
Oil shale can be mined and processed to generate oil similar to oil pumped from conventional oil wells. The oil substances in oil shale are solid and cannot be pumped directly out of the ground and must first be mined and then heated to a high temperature (a process called retorting); the resultant liquid is then separated and collected.
