Raising mountains for a habitable Earth

Abstract The formation of mountain belts (orogens) raises rocks above sea level and makes them available for chemical weathering, altering the composition of the atmosphere and oceans, which in turn control habitability. The typical elevation of mountain belts through time depends on their crustal thickness, which depends on crustal strength and tectonic style, which both changed during secular cooling of Earth's interior. Here we show that the thickness of orogenic crust has increased, in two pulses, around 2.2 and 0.8 billion years ago, adding c. 30 km to the orogenic crust each time. To this end, we used pressure estimates from metamorphic rocks that tectonically or magmatically rose up from the base of orogenic belts. We postulate that these changes resulted from geological responses to subduction and collision processes in a cooling Earth. The two orogenic growth spurts correspond to coeval major increases in terrigenous element and nutrient fluxes, changes in biological sulfur metabolism, and oxygenation, which can be explained by the enhanced weathering of taller mountains. This suggests first-order mechanistic links between secular geodynamic change, changes in Earth system state and habitability, which shaped the conditions for the evolution of complex life.