Crude oil is formed from the remains of what type of ancient biomass?

Crude oil is formed primarily from the remains of microscopic organisms, particularly plankton, that lived in ancient seas. Over millions of years, the remains of these organisms were buried under layers of sediment and subjected to heat and pressure, leading to the formation of oil.

Plankton, which includes both phytoplankton (plant-like) and zooplankton (animal-like), plays a significant role in this process because their remains can accumulate in oceanic environments where sedimentation occurs. The conditions of burial and the chemical changes over time transform these organic materials into hydrocarbons found in crude oil.

While other organisms like plants, forests, and even larger animals like dinosaurs may contribute to the overall fossil fuel supply (in the case of some natural gas or coal), it is the plankton that are most directly responsible for the majority of crude oil reserves. This makes the connection between plankton and crude oil formation critical to understanding the origins of this vital energy resource.