In the sediment layers of one of Earth's most forbidding landscapes, a single fossilized tooth has quietly rewritten the biography of the Atacama Desert. Discovered in Chile's Bahía Inglesa Formation and dated to 8.8 million years ago, the tooth of Cardiatherium — an ancestor of the modern capybara — speaks to a time when wetlands and palms flourished where only stone and dust now remain. The find reminds us that the planet's most extreme places were not always so, and that understanding how they became what they are may be essential to understanding what our own world is becoming.