It enabled the industrialization of agriculture, led to the discovery of El Nino, helped spawn the modern environmental movement, and lay at the heart of the War of the Pacific. What is it?
Guano, the excrement of South American seabirds.
Guano isn't just any bird poop. (Actually, the word has come to refer to feces of any flying animal, including bats.) Along with mineral nitrates found in the Atacama Desert, the South American seabird variety of guano is the richest source of nitrogen on the planet.