FINDING THE CRATER

Asteroid impact—different types of evidence 10 km wide asteroid Massive crater Where is it?

Evidence in 65 MYO rocks Rock boundary between Cretaceous and Tertirary periods (K-T boundary) Time of asteroid impact

K-T boundary is rich in iridium Iridium is rare in the Earth’s crust, however, abundant in comets and asteroids K-T asteroid was vaporized on impact Fine particles of iridium traveled high into the atmosphere Distributed all over the Earth

Deposits of the K-T boundary hold clues… Deposits worldwide contain pieces of melted or crushed rocks blasted from impact site ejecta

Ejecta – spherules and tektites On impact, asteroid left some of surrounding rock in Earth’s crust melted is it was ejected from impact site Melted rock particles particles fell back on planet and cooled, formed into glass-like objects (sperules and tektites)

Spherules in K-T sites worldwide Spherules—glassy spheres (0.1 mm—2 mm) Found close and far from impact site

Tektites Tektites—closer to impact site Nickel-rich spinels 2-3 cm in size More irregular shapes Nickel-rich spinels Fusion/oxidation of asteroid impact Found in K-T sites throughout world

Shocked quartz High pressure of asteroid impact Quartz grains to shatter/fracture