Lake spillover started Grand Canyon

New geochronology and isotope work on the Bidahochi Formation supports the long‑debated idea that an ancient Arizona lake overflowed and redirected the Colorado River, triggering the main phase of Grand Canyon incision. The finding ties zircon uranium‑lead ages, strontium isotope ratios, and fossil fish assemblages to a specific, time‑bounded event rather than only slow background erosion. — Revising the Grand Canyon’s origin story matters for how the public understands geological change, scientific method, and the timescales over which major landscape features can form.