Image: Impact layer rock sample This rock sample from New
Zealand shows the layer formed during the end-Mesozoic
extinction event. Over 200 extinction layer sites around the
world have produced elevated levels of the metal iridium.
Iridium is rare in the Earth’s crust but relatively common in
meteorites. - © Australian Museum Sample labels (from top of
sample to bottom): - Recovery zone - Palaeogene rock: contains
fossils of marine life, but not as many as before the end-
Mesozoic event. - Dead zone - Palaeogene rock: contains no
fossils of marine life except for a small amount of plankton. -
Boundary zone - end-Mesozoic rock: contains high levels of
iridium. - Normal zone - Cretaceous rock: contains lots of
fossils of lots of different types of marine life.