In many parts of the world, there is a rock layer rich in the metal iridium. Iridium is very rare on Earth, but it is relatively common in meteorites and other debris that comes from outer space. All occurrences of this iridium layer are from the same geologic epoch, at the very end of the Cretaceous. Most of the fossils in rock layers below the iridium layer, including dinosaur fossils, do not appear in layers above the iridium layer.
Based on this evidence from the rock and fossil record,
A.
meteoroids and other space debris did not impact the Earth at the end of the Cretaceous.
B.
an asteroid impact likely caused a mass extinction at the end of the Cretaceous.
C.
meteorites and other space debris no longer contain the metal iridium.