Here's the breakdown:
* Organic Matter: Tiny marine creatures die and settle to the ocean floor, along with other organic debris.
* Sedimentation: Layers of sediment accumulate over time, burying the organic matter.
* Heat & Pressure: As more layers build up, the pressure and temperature increase. The organic matter is transformed by heat and pressure, and in the presence of bacteria, into kerogen (a waxy substance).
* Petroleum and Gas Formation: Under even greater heat and pressure, kerogen further transforms into hydrocarbons - the compounds that make up petroleum and natural gas.
* Migration: Petroleum and natural gas, being lighter than water, migrate upward through porous rock formations until they are trapped by impermeable rock layers, forming oil and gas reservoirs.
So, while it takes millions of years and specific geological conditions, the main ingredient for petroleum and natural gas is the organic matter from ancient marine life.
