Our first introduction to crude oil may have happened only a century and a half ago, but nature has been busily cooking the raw materials for millions of years. Crude oil is, in the simplest terms, the leftover sludge of dead organisms when trapped under heat and pressure. It’s called a fossil fuel for a reason — because it is quite literally dead creatures from eons past!
It’s popularly said that oil is made of dead dinosaurs, but that’s untrue. In fact, the lion’s share of crude oil is made up of microscopic organisms like marine algae and plankton. When these teeny tiny plants and animals die and are not eaten, their bodies drift downward and collect on the seafloor. As they break down, the molecules of oxygen, nitrogen, phosphorus, and other organics get removed, leaving a layer of carbon and hydrogen behind.
If that layer of chemical sludge gets buried beneath sediment and exposed to heat and pressure, then those basic ingredients get transformed into a viscous hydrocarbon mixture known as petroleum or crude oil. The nature of the crude oil depends largely on how deeply the deposit is buried and how much heat and pressure is present, as it has to exist within a sweet spot where the pressure is high enough to create petroleum but not so high that the hydrocarbons are destroyed.
