Earth experienced a major mass extinction 65 million years ago, at the Cretaceous-Tertiary ("K-T") boundary.  The most famous victims of this event were the dinosaurs, but many other groups of organisms also disappeared.  The cause of the K-T extinction has long been a major mystery in geology.


Starting in the late 1970s, abundant evidence has been accumulated indicating that the dinosaurs & company were wiped out by the effects and aftermath of a gigantic impact event.  An approximately 6-mile large object ("bolide") hit what is now Mexico's Yucatan Peninsula to form the Chicxulub Crater.  Enormous quantities of debris were kicked up into the atmosphere.  This material settled out all over Earth to form the K-T boundary clay.


The K-T boundary clay sample shown below is from southeastern Spain.  It's a thin, poorly lithified claystone with a 2-3 mm thick yellowish/orangish-brown, oxidized, ferruginous layer at the base.  The orangish stuff is the "fallout layer".  Geologists have determined it is relatively enriched in Ir, Co, Cr, and Ni.  These elements are all derived from the original bolide.  The fallout layer also has altered microtektite spherules.


K-T boundary clay (Maastrichtian Stage-Danian Stage boundary, 65 m.y.) from the upper Quipar-Jorquera Formation along the Agost-Castalla Road, 1-2 km north of the village of Agost, Alicante Province, southeastern Spain.  Specimen is 21 mm thick.




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