What is the process that forms crude oil and natural gas?

The formation of crude oil and natural gas primarily involves the burial of dead organic material from simple marine organisms, such as plankton, under layers of sediment over millions of years. When these organisms die, their remains accumulate on the ocean floor and are covered by sediment. The heat and pressure from the overlying sediments contribute to the process of diagenesis and subsequently catagenesis, which converts the organic matter into hydrocarbons—essentially crude oil and natural gas.

This transformation occurs through complex chemical reactions and is greatly influenced by the temperature and pressure conditions within the earth's crust. The process is efficient in environments where marine organisms are abundant, as they provide a significant amount of the organic content needed for hydrocarbon generation. In contrast, the burial of oceanic algae and seaweed, while it does play a role in organic matter accumulation, primarily refers to a different type of organic source and does not encompass the main sources for crude oil formation. Similarly, the decomposition of large terrestrial animals and the fossilization of land-based sources generally do not yield significant quantities of hydrocarbons relative to marine sources, which are critical for oil and gas deposits.