Instead of relying on energy-hungry reactors to generate high temperatures and pressure, researchers are looking underground at Earth's natural heat and forces to cook up ammonia for fertilizer. In a proof-of-concept study, researchers generated ammonia by mixing nitrogen-laced water with iron-rich rocks -- without any energy input or CO2 emission. This new recipe may lead to a more sustainable alternative to current methods, theoretically churning out enough ammonia for 2.42 million years.