What is crude oil primarily formed from?

Crude oil is primarily formed from the remains of ancient biomass, particularly tiny marine organisms like plankton that lived millions of years ago. When these organisms died, they settled at the bottom of ancient seas, where they were buried under layers of sediment. Over time, the heat and pressure from the overlying layers transformed this organic material into hydrocarbons, which are the primary components of crude oil.

This process involves both biological and geological changes, where not only the remains of the organisms are involved but also the specific conditions in which they are buried and the timeframe required for their transformation. The other options do not accurately describe the origins of crude oil; for example, dinosaurs did not live long enough for their remains to contribute significantly to oil deposits, while materials like minerals or eroded material from mountains are unrelated to the formation of crude oil. Therefore, the understanding that crude oil originates from ancient biomass, especially plankton, is crucial in grasping the composition and natural history of fossil fuels.