The fossil fuel that powers the modern world economy -- extracted commercially since 1859, the foundation of transportation, agriculture, plastics, and warfare for over a century, and the primary driver of anthropogenic climate change.
Oil is the most consequential substance in modern history that nobody thinks about. It powers every vehicle on the road, every airplane in the sky, every container ship in the ocean. It produces the fertilizers that feed billions of people. It produces the plastics in virtually every manufactured object. And burning it is warming the planet in ways that threaten to make much of it uninhabitable. The modern world was built on oil. Understanding oil means understanding both how that world was built and why sustaining it is the central challenge of the 21st century.