THE CORRECT NAME for oil is petroleum. The word petroleum comes from two Latin words: petra, meaning "rock," and oleum, meaning "oil." Petroleum is exactly that: oil that comes from rocks.

Ocean beginnings

The majority of the world's petroleum was formed more than a million years ago, during a time when much of the earth's surface was covered by a warm, shallow sea that teemed with life. Millions of plants and animals thrived in this environment, and they reproduced abundantly in the warm, salty water.

As the organisms died, their remains sank to the bottom of the sea. Over the centuries thick layers of organic debris accumulated on the seafloor. Mud mixed with the debris, and sand covered the organic layers. Layer by layer, debris built up on the seafloor. As more debris sank and was added to the top, the bottom...