The Alps are displaced seabed. Rocks that accumulated beneath an ocean now stand thousands of meters above Switzerland because converging tectonic plates compressed, buried and raised them, rather than because the sea simply drained away. Height conceals their origins. Within mountain limestone, marine fossils preserve evidence of waters that vanished long before these peaks existed.
Collision did the heavy lifting. Between the approaching European plate and the African plate, including its Adriatic promontory, lay branches of the Tethys Ocean, where shells, carbonate mud and other sediments accumulated and hardened into rock. The ocean floor descended. Through subduction, much of its crust sank into the mantle, while some sediments and crustal fragments were scraped off or caught within the developing mountain belt. Continental crust resisted that descent. As convergence continued, folding and nappe stacking pushed enormous sheets of rock over one another, thickening the crust and carrying former marine deposits into the rising Alps.
Elevation tells only half. The rocks visible today also owe their exposure to rivers and glaciers, which stripped away overlying material while uplift and the crust's response to erosion helped maintain mountain heights. Not everything was sediment. Some Alpine rocks began as oceanic basalt or mantle material, and heat and pressure transformed many buried rocks before they returned toward the surface. Fossils survived in others. The Swiss Alps therefore preserve pieces of several environments, assembled by plate motion rather than lifted as one intact ocean floor. Where a shell rests above the clouds, the missing sea has left its address.
