It is surrounded by rays of ejecta that stretch across much of the southern lunar hemisphere, indicating the violence of the impact that formed it.

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This story, though, raises the question of why there is but a single ejecta layer of iridium and shocked quartz in late Cretaceous rocks around the world.

ECONOMIST: Mass extinctions

Extensive dating research at Chicxulub, however, now suggests that the object which created that crater actually struck 300, 000 years earlier than the dinosaur extinction, meaning there really should be two ejecta layers.

ECONOMIST: Mass extinctions

"Apparently, there is a harder, rockier material beneath this veneer of gravel and pebbles, and obviously there's some impact ejecta, " Grotzinger told reporters at NASA's Jet Propulsion Laboratory, where controllers operate the rover.

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Further examination revealed a crater rich in shocked quartz and iridium, minerals that are commonly found at impact sites. (These are also the telltales in distant layers of ejecta that the rock in question has come from an impact.) Most important, the rocks above and below Shiva date it to 65m years ago.

ECONOMIST: Mass extinctions