Eventually, 75 million years later—a short, arm-flailing sprint in geological time—the Indian subcontinent ran headlong into the submerged edge of its larger neighbor, Eurasia. The impact zone was 1,500 miles wide. The denser ocean floor north of India, which was primarily made of basalt, dropped into the earth’s mantle and disappeared, literally melting beneath a line of now-extinct volcanoes. The comparatively lighter sedimentary rocks of present-day India and Tibet (limestone, shale, sandstone), formed millions of years earlier on the bottom of the ancient Tethys Sea,† were thrust skyward, having no other place to go. The process, which geologists refer to somewhat blandly nowadays as orogeny, created the youngest and highest-elevation mountains on the planet: the Himalaya (Himā, snow; alāya, abode). Home to the world’s largest subpolar glacial systems and deepest land gorges, the “abode of snow” is also the source of three of the world’s greatest river systems—the Indus, the Ganges, and the Brahmaputra.
