At Earth’s surface, a complex suite of chemical, biological, and physical processes combines to produce soil from bedrock and sediments within the zone that extends from the outer limits of vegetation to the lower limits of groundwater. This weathering engine transforms primary minerals, provides nutrients to nourish ecosystems and human society, mediates the transport of toxic components within the biosphere, creates water flow paths that shape and weaken bedrock, and contributes to the evolution of landscapes at all temporal and spatial scales. At the longest time scales, the weathering engine sequesters CO2, thereby influencing the global carbon cycle, long-term climate change, and weathering rates.