A naturally occurring, flammable liquid formed from dead organisms (particularly one-celled plankton) that become buried within sediments at the bottom of the sea. Oil forms after the organic remains have become buried by additional layers of sediment and are subjected to intense heat and pressure, causing chemical changes.

Sedimentary layers are originally deposited flat-lying due to gravity.

Any place where rock is visible or exposed on the surface of the Earth.

A living thing