What is Cretaceous-Tertiary boundary clay, and where did it form? Describe the conditions under which it formed, and what it looks like

Question

What will be an ideal response?

Answer 1

ANSWER: Although the impact site itself is the best source for clues about past impacts, other evidence can be found far from such sites. Fragments and dust sprayed out from a large site can drift around Earth. The enormous impact at the Chicxulub site blew out enough material to deposit a thin, dark layer called Cretaceous-Tertiary boundary (K-T boundary) clay. The dust and elemental-carbon soot layer from fires ignited by the impact fireball 65 million years ago is generally only a centimeter or so thick and chocolate brown to almost black in color. The large amount of soot is related to worldwide fires that burned much of the vegetation on the planet. The clay in this boundary layer contains grains of shocked quartz and other minerals, as well as spherules. The abundance of quartz in the boundary clay strongly suggests that the dinosaur-killing impact occurred in quartz-rich continental rocks, probably in an area rich in granite, gneiss, or sandstone. Also found in the boundary clay of the 65-million-year-old K-T event are anomalous amounts of iridium and other platinum-group elements, an occurrence called the iridium anomaly. The anomalous amounts are tiny, some 0.5 to 10 parts per billion, but those elements are essentially absent in most rocks except for meteorites and dark, dense rocks like peridotite and others derived directly from Earth's mantle.?