A slim, greenish brown band in a layer of clay clearly separates two key geologic eras all over the world, showing abnormally high microscopic concentrations of iridium, a rare dense, brittle element that best resists corrosion and bears a beautiful silvery burnish. It is prevalent in space rocks, like the six-mile wide object that slammed into the Yucatan about 66 million years ago, near the present day Mayan town of Chicxulub and cataclysmically changed life and Earth forever.
Discovered by chance in 1978, the crater emerged while the Mexican state-owned giant Pemex was meticulously mapping and searching the Gulf of Mexico for the best spots to strike oil.