Iridium is the second-densest element on the periodic table and the most erosion-resistant metal. A layer of iridium in rocks marks the demise of the dinosaurs, according to Allan Blackman from AUT, in ep 40 of Elemental.

Iridium played an important role in a geological whodunnit - the demise of the non-avian dinosaurs.

Iridium is present at high levels in a thin band of rocks that marks the boundary between the Cretaceous and Paleogene geological periods. The theory is that the element came from a large meteor, about 10 kilometre across, the impact of which significantly changed the earth's climate for long enough to kill all the large dinosaurs (although of course avian dinosaurs - birds - survived).

Salts of iridium are very colourful, hence the name iridium, after the Greek messenger to the Gods, Iris, who was also the Goddess of the rainbow.

Iridium is twice as dense as lead and the second densest element (after osmium). It is the most corrosion resistant metal.

It is rare and more valuable than gold, says Professor Allan Blackman from AUT.

Go to this episode on rnz.co.nz for more details